View Full Version : Building a precision AR-15: Questions about barrel, bolt, twist, etc...
So I'm gearing up to build my second AR-15. This one will be specifically for precision target shooting and the occasional varmint hunt. So weight is really not a factor.
I'm going to have a Bartlein barrel made for this build so it will be customized to my specifications. It'll have a quality high powdered scope, PRS stock, etc... I will be handloading its food.
I have a few questions about this build before I put in my order.
1. What would be the perfect length, profile, and twist? I was thinking something heavy, 20", 1/7 twist, rifle length gas system.
2. Is a custom chamber possible? I was going to ask the builder to spec the chamber to where mag length rounds won't have so much jump to reach the lands.
3. Is there such a thing as a match bolt/carrier assembly? The barrel maker was telling me to send him the bolt I want to use and he'll match it to the barrel.
4. What are some tricks I can apply to smooth things out? I plan to use Lapua brass and match bullets. I wanna try to not beat the brass up as much as a combat AR does. I've read about trimming the ejector spring and employing certain types of buffers.
That's pretty much what I'm curious about. If you have any additional information that would help this build, please post it.
Obscenejesster
01-05-14, 21:51
I'd personally just do a SPR build and call it a day. I don't think the velocity gain from 18" to 20" is enough.
You could go either 1/8 or 1/7 but you will find more precision oriented barrels in 1/8 which is what I'd personally go with.
I never really cared enough about matched bolts. To tell you the truth, I can't shoot good enough to benefit from them and personally, I don't even know if they do improve accuracy.
Sent with a Gen 2 Nexus 7
The difference between in velocity between 18 & 20 isn't much different than the difference between 16 & 18. But the difference between 16 & 20 when shooting long ranges is enough to make it worth going with the 20. The 18 doesn't give enough of an advantage in velocity to make it worth choosing over a 16 inch barrel and not handy enough to choose it over a 20.
Properly matching bolt to barrel does improve shot to shot consistency and is worth it for a varminter.
A heavy profile is no guarantee of accuracy. A quality lightweight barrel will be more accurate than a so-so heavy barrel. It may be after a certain point, a heavy barrel could be a detriment to accuracy. Check out the two threads about upper flex in the sticky section of the Technical Discussion forum.
The 223 Wylde chamber is known for accuracy yet has a longer leade to accomodate 5.56 loads. You'll have to experiment for yourself to see if using a shorter leade will help your accuracy.
Tighter twists are needed to stabilize longer bullets. Longer bullets are usually, but not always, heavier. Best thing to do is figure out what style & weight range you want to shoot with. If you're going to be shooting boatailed bullets up to roughly 55 grains, you might be best served with a 1:9. Barrels with 1:8 or 1:7 twist tend to work well with boatailed bullets running about 70 - 80 grains. A longer barrel will be more forgiving stabilizing longer bullets because muzzle velocity is increased.
I built a varminter with a 20 inch Lothar-Walther barrel with a 223 Wylde chamber and 1:8 twist. It prefers boatailed bullets between 70 & 80 grains. It has a HBar profile and unloaded the rifle weighs 10.75 lbs. A bull barrel would have added more weight than I want to carry.
Varminter is the top rifle in the photo below
http://i115.photobucket.com/albums/n289/SgtSongDog/Liberty/DSC_0001_zpsc8532be9.jpg
I'm reconsidering my idea to go with a custom barrel. WOA and Raniers seem to make some fine barrels that are exactly what I'm looking for.
I don't need the ability to shoot 5.56 in this particular rifle. Would I be better served to just go with a 223 REM barrel or does the 223 Wylde have other benefits other than being able to fire both cartridges?
Obscenejesster
01-06-14, 10:08
I'm reconsidering my idea to go with a custom barrel. WOA and Raniers seem to make some fine barrels that are exactly what I'm looking for.
I don't need the ability to shoot 5.56 in this particular rifle. Would I be better served to just go with a 223 REM barrel or does the 223 Wylde have other benefits other than being able to fire both cartridges?
Yea, Rainier and WOA make some good barrels. If you aren't going to shoot 556 then you can just go with a 223 chamber.
Sent from my SGH-T999 using Tapatalk
JBecker 72
01-06-14, 10:22
I too am looking at building a precision rifle right now. In my searches I came across http://highcalibersales.com/ for SPR builds. They sell the same barrels used on the SOCOM SPR rifles, and from what I've read they work very well. The chamber and twist were chosen to work with the MK262 77gr OTM ammo. I'm gonna be buying one of these barrels for my build.
Just throwing an idea out there for you.
Yea, Rainier and WOA make some good barrels. If you aren't going to shoot 556 then you can just go with a 223 chamber.
Sent from my SGH-T999 using Tapatalk
Gotta chime in here - going with a 223 Remington chamber in an AR is ridiculous. Practically speaking, a 223 Remington chamber and more precisely, the throat is for all intents and puposes useless in an AR - much less a precision AR. The throat on a 223 Rem was designed to digest light bullets - 40-50 gr type. It uses an extremely short freebore and has a leade angle of nearly three times a 556 anything. If you want to build an AR with a 1/12 or 1/14 twist and shoot 50gr FBHP - then by all means go with a .223 Rem. If you want precision, with better bullets at distances that are actually meaningful- then use any one of a myriad of custom 556 chambers.
If you want specifics - let my know and I'll pull my chamber prints on a 1/2 dozen different 556 & 223 Rem reamers that I own.
The 223 Wylde isn't in nearly any way a 223 Rem. Bill Wylde started the development of that chamber by using the 223 Rem as the base - it is completely different than a 223 Rem. The Wylde actually has a longer throat than a 556 NATO and is known for it's ability to digest a wide range of bullets - accurately and reliably. There are many others too....
From another post in a different thread – I had submitted the following and it is appropriate here:
“there is a plethora of 223 / 556 reamers that have been "re-engineered". 556 Trophy - specifically dimensioned for shooting mag length 69/77gr match ammo for across the course (200-600yds) matches.
Another is the 556 Target - specific to optimal length match ammo utilizing 80gr Sierra's.
Still another is the 556 LR - set up for the 90gr VLD's for 1000yd use.
All share the tightest free bore that can safely / reliably run ~ .2240-.2242". The first two use 1 deg 30 min leads while the LR uses a 1 deg 10 min lead (matched to the VLD design secant type ogive.)
The Wylde chamber is a great chamber - it is a do it all type and one can expect very good accuracy with a huge range of bullets. Bill Wylde was a pioneer in the development of the 223 as a viable competition / long range cartridge. His chamber generally runs a little loose in the neck - even more so than a 556 NATO. Numbers wise the neck dia at the mouth are .254 for a 223 Rem & the 556 NATO. The Wylde runs .2558". The neck dia at the shoulder is .255 for both the Rem & NATO, while Wylde's runs .2568"
The Wylde has a tight free bore just like the Remy.
One very big difference is the free bore lengths - the Remy run .025", the NATO is .0566 and Wyldes is .0619 - longer that the 556 NATO - and one of the reasons it handles pressure as well as 80gr projectiles.
There are many other minor differences as well - specifically in case body diameters. Unfortunately, some companies still chamber in 223 Rem. I have Rem 700 SPS in 223 and it has a SAAMI spec 223 Rem chamber - it is SHORT!! I only shoot 50-52gr pills out of it and it is very sensitive to seating depth."
I'll also add, that if a prospective builer of a precision AR plans on using a custom / match grade bbl, then by all means get a match chamber to compliment the barrels inherent accuracy.
opsoff1,
Thank you for the very detailed response. You explained the differences between the 3 chambers very well and I appreciate you typing all that out.
I've pretty much sworn off going the custom route. With that said, do you have any recommendations? Specifically brand, length, gas system, twist...
I'm not going to shoot 90g bullets, so those can be discounted for this rifle. The plan right now is to stick with 69-80g match bullets (primarily 75's and 77's), handloaded to magazine length, and shooting them out to around 500 yards. Maybe a little further. I don't have the ability to shoot 1K where I'm currently stationed.
opsoff1,
Thank you for the very detailed response. You explained the differences between the 3 chambers very well and I appreciate you typing all that out.
I've pretty much sworn off going the custom route. With that said, do you have any recommendations? Specifically brand, length, gas system, twist...
I'm not going to shoot 90g bullets, so those can be discounted for this rifle. The plan right now is to stick with 69-80g match bullets (primarily 75's and 77's), handloaded to magazine length, and shooting them out to around 500 yards. Maybe a little further. I don't have the ability to shoot 1K where I'm currently stationed.
SW,
There are a number of bbl makers that offer basically drop in match grade bbls. Unfortunately it usually comes down to what are you willing to pay and how much accuracy you want - the old adage relating to cars is appropriate here - "speed cost money - how fast fast do you want to go?" Same same - accuracy cost money - how accurate do you want to be?
With that being said - Holliger at White Oak Precision (part of WOA) uses Shilen, Kreiger & Pac Nor bbls. Frank White at Compass Lake uses Douglas & Krieger that I know of. There are plenty of others - each one can be had with a match grade chamber precut. There are mfr's that offer fully finished match grade bbls w/ HS'd bolt - I would strongly urge you to consider this route - different bbls will require you to part with different height stacks of dead presidents ($$$) but - you get what you pay for.
I have a rack of AR's where each one is purpose built - they all wear various bbls - I have primary & backup NM rifles that have Kreigers (cut rifled), Douglas (button rifled) and Pac Nor (button rifled). A DMR with a Badger (broach cut), and a long range rifle with a Noveske / PacNor. I've used others and wouldn't go back to them. Perfect example is Wilson - shot great but was effectively shot out in 1800 rds. I get 5-6-7000rds out of a Krieger - so in the end - the Kreigers are actually cheaper. Another aspect is consistency - I can work up a load for a Krieger bbl and use that same load on the next bbl and the next and the next. Other lesser bbls have to have the load tweaked at every replacement. I shot a Rocky mountion bbl on a NM course gun back in 05 - best shooting bbl I have every had - literally a laser. Next one shot minute of barn door. Stopped using them. I thing some of the best bargains out there are the Douglas bbls. I've used them on bolt guns and gas guns, AR's, M14's, M1's and customs autoloaders as well - they all shot great. Never had a bad one.
If you are looking for precision at ranges out to and in excess of 500yds - then I would absolutely go with a 20" bbl. It's free velocity. It also allows easier handloading by using heavier bullets and slower powders.
Twist? 1 in 7.5 or 7.7 to be safe - or a straight 1 in 7. A 1 in 8 is USUALLY fine - however in button barrels - the buttons tend to slip a bit and you end up with a twist that is a bit slower than advertised. A 1 in 8 is on the hairy edge of stabilizing an 80 gr bullet.
An 8 twist will shoot 77's all day long and they are great at 500 and shoot pretty dam good at 600 as well.
But again caveat emptor - a drop in Kreiger with matching bolt (read head spaced to the bbl) fully chambered / finished is north of $500. They shoot and they last -
Also - going with a 20" bbl will equate to using a rifle length system.
Using heavier bullets and slower powders will change the gas system - the AR does operate fairly well with a relative wide variety of bullet weights and powder burn rates, but when you egt on the outer fringe - goofy things start to happen.
Some of the bigger / better bbls guys out there:
Obermeyers are cut (Krieger started mfr bbls working for Boots)
Hart - button (push) (VERY VERY good button bbls - big in BR)
Schneider - button (pull) Tubb uses them
PacNor - button (very good and consistent - offer odd land arrangements)
Shilen - button (push) (huge in short range BR)
Lilja - button (big in 6mmBR & considered among the best in 22RF)
Broughton - button (pulled)
Brux - cut (big in F Class 6.5mm & 7mm)
Bartlein - cut
Border - Cut (Obermeyer style - mfr in Scotland)
Kostyshyn - button (big in 30BR)
Lawton - cut & pull button (big in LR BR)
Spencer - button (very big in 1000yd big bore BR)
There are more - but IMHO, I'd stay away from any chrome plated bbl. Go with a stainless bbl. Use a 1/7 - 1/7.7 twist, 20" and get a match grade chamber cut by the mfr or smith.
PM me if you need more info.
Edited to add: As far as 1K shooting with an AR - WHOLE different ball game - purpose built and highly specialized - so don't even equate that to anything else even remotely connected to any other AR type precision shooting.
Again, huge thank you for taking the time to be so exponentially helpful!!! You're a gentleman and a scholar.
Being a military man, my cammies weren't tailored with deep pockets. So going super-huge on a barrel is pretty much off the table. I've been scouring the interwebs looking for AR barrels from WOA, Shilen, Ranier, Bartlein, Kreiger, and a few others. I'm not coming up with a whole lot. WOA and Raniers seems to have some options but they're all backordered.
I did find a Shilen barrel/bolt set that looks promising, but it has a 1/8 twist. If it had a 1/7 twist I would be posting this reply to tell you I had bought it.
http://www.midwayusa.com/product/156629/shilen-drop-in-match-barrel-with-bolt-ar-15-223-remington-wylde-service-rifle-hbar-contour-1-in-8-twist-20-stainless-steel
Again, huge thank you for taking the time to be so exponentially helpful!!! You're a gentleman and a scholar.
Being a military man, my cammies weren't tailored with deep pockets. So going super-huge on a barrel is pretty much off the table. I've been scouring the interwebs looking for AR barrels from WOA, Shilen, Ranier, Bartlein, Kreiger, and a few others. I'm not coming up with a whole lot. WOA and Raniers seems to have some options but they're all backordered.
I did find a Shilen barrel/bolt set that looks promising, but it has a 1/8 twist. If it had a 1/7 twist I would be posting this reply to tell you I had bought it.
http://www.midwayusa.com/product/156629/shilen-drop-in-match-barrel-with-bolt-ar-15-223-remington-wylde-service-rifle-hbar-contour-1-in-8-twist-20-stainless-steel
Retired Army here - 28yrs. Thanks for your service.
Try Frank White at Compass Lake Engineering (CLE) - look for one of his stainless Douglas premiums with a bolt. I think he gets right around 400 for the bbl & bolt fully finished.
If it's back ordered - order one - it appears you are getting into high power rifle (NRA/CMP) (I may have missread that from another post - if so disregard) and this is a great initial bbl. They shoot well, they last and Frank stands behind his work. There are three things make all the difference on a NM AR - barrel, sights & trigger - THAT is where you need to spend you hard earned dough. Don't chase the snake oil BS. Sights are relatively inexpensive - get them pinned and get a 1/2 x 1/2. Triggers - buy what you can afford - Giessle is creme del la creme - older 1st Gen Armalites are good (adjustable) Krieger Milazzo 2 stage triggers were the best until the Giessles. Unfortunately I think Charlie Milazzo doesn't make them anymore - all he does is sue everyone that copies his design KAC - great but way over priced. All the rest of your cash - put it in a good bbl. You'll never regret it.
Retired Army here - 28yrs. Thanks for your service.
Try Frank White at Compass Lake Engineering (CLE) - look for one of his stainless Douglas premiums with a bolt. I think he gets right around 400 for the bbl & bolt fully finished.
If it's back ordered - order one - it appears you are getting into high power rifle (NRA/CMP) (I may have missread that from another post - if so disregard) and this is a great initial bbl. They shoot well, they last and Frank stands behind his work. There are three things make all the difference on a NM AR - barrel, sights & trigger - THAT is where you need to spend you hard earned dough. Don't chase the snake oil BS. Sights are relatively inexpensive - get them pinned and get a 1/2 x 1/2. Triggers - buy what you can afford - Giessle is creme del la creme - older 1st Gen Armalites are good (adjustable) Krieger Milazzo 2 stage triggers were the best until the Giessles. Unfortunately I think Charlie Milazzo doesn't make them anymore - all he does is sue everyone that copies his design KAC - great but way over priced. All the rest of your cash - put it in a good bbl. You'll never regret it.
U.S. Marine for 15 years now. LOVE IT!
I'll look into the CLE combo you mentioned. That price range sounds good to me, as I'm willing to go up to about $600. I'm not getting into any competitions. I'm just an expensive hobby kind of guy. I'm going to scope this rifle with some good glass. I have a Geissele in my other AR-15 and this one will most definitely receive the Geissele treatment as well. To me they're the only game in town when it comes to AR triggers.
Good stuff - try your hand at the HP stuff - it's intoxicating. If you use a flat top, you can get (and it's legal in competition) a carry handle w/ a competition tuned rear sight - it'll get you out to 600yds. Pop the handle off and you can scope it pretty quick.
I used to shoot at the Interservice Championships at Quantico every summer - that was some seriously riflery - off for 3 days then to the Nationals for 3 weeks - at the end of it all I didn't want to look at a rifle, never mind shoot one...LOL
If you're at Quantico - look up the Quantico Shooting Club (http://www.quanticoshootingclub.com/) GREAT bunch of folks and you get a ton of assistance / help.
Also - forgot to add from before - Free float tube or forend - a CMP legal under the hand guard version or a tactical version is imperitive - nothing touching the bbl.
1/7 is geared more for 16"barrels. I would go 1/9 with a 20" inch personally.
Good stuff - try your hand at the HP stuff - it's intoxicating. If you use a flat top, you can get (and it's legal in competition) a carry handle w/ a competition tuned rear sight - it'll get you out to 600yds. Pop the handle off and you can scope it pretty quick.
I used to shoot at the Interservice Championships at Quantico every summer - that was some seriously riflery - off for 3 days then to the Nationals for 3 weeks - at the end of it all I didn't want to look at a rifle, never mind shoot one...LOL
If you're at Quantico - look up the Quantico Shooting Club (http://www.quanticoshootingclub.com/) GREAT bunch of folks and you get a ton of assistance / help.
Also - forgot to add from before - Free float tube or forend - a CMP legal under the hand guard version or a tactical version is imperitive - nothing touching the bbl.
Sounds like fun. I'll have to check it out. I've been stationed at Quantico before but I'm currently stationed down in Petersburg at Fort Lee. We teach the Small Arms Repair Course here.
I was planning to go with a 15" Troy VTAC Alpha Rail so it can match my other AR. It mounts to the barrel nut and doesn't touch anything else. I really like that rail.
BTW, I sent you a PM.
superstratjunky
01-06-14, 18:10
Give Black Hole Weaponry a look. Not trying to step on any toes, just making a suggestion. They will make you anything you specify at a reasonable cost. Carl is good people, he just ran into some bad situations before he moved to Oregon. I think he's on to something with the 3 grove poly. All his 5.56/.223 chamberings are in fact 5.56. Give them an honest look.
http://www.google.com/url?q=http://www.blackholeweaponry.com/&sa=U&ei=nUXLUuSnN6HIsASkxIC4DQ&ved=0CB0QFjAA&sig2=gqDKpDeH6ce3hfK3cBfpGA&usg=AFQjCNGY9T5iVEyBw2efpO7iAFZd2jvYKg
1/7 is geared more for 16"barrels. I would go 1/9 with a 20" inch personally.
Umm....whaaaat?
A 1/9 will limit you to 69gr stuff - max and a 69grainer at 500 or 600yds will be like throwing wiffleballs in a wind storm. Barrel length has VERY little to do with stabilizing bullets - it does help but in very small and in a different way - longer bbls will give you more velocity which aids stabilization. A bullet that is on the edge of stabilization can be helped "a bit" by velocity.
A 1/7 isn't geared towards any 16 inch bbl in any way shape or form.
I don't mean to be rude but where does this bovine scathology come from??
A 1/9 will limit you to 69gr stuff
In general you're right, of course, opsoff1, but there are bullet options above 69 grains that "appear" able to be stabilized in a 1/9 twist barrel.
On a cursory look only, it appears the Miller stability breaks at around less than 1" in length projectile for stability in the 1/9 twist barrel and there are valid options above 69 grains one could use with that twist. Of course, not all are going to work and they are on the fringe of being acceptable, but they do fall within the acceptable range.
For example, a .990" 77gr bullet shows a Miller stability of 1.44 which is deemed stable, although admittedly on the edge.
Am I missing something? I've not shot anything above 69 grains yet as my distance shooting options are limited.
Edit: To be clear, I'm not just talking about "fictional" bullets. The Sierra 77 gr Matchkings are .994 and appear to be judged stable if you believe the Miller formula. I suppose experience might be different from theory. Not trying to argue with you, hoping you have some experience that says different. :)
BrigandTwoFour
01-06-14, 19:19
Opsoff1 posted some very good info, and I don't see a need to rehash it.
My personal inclination for your purposes would be a 20" barrel. Just last week I ready a study on the relationship between velocity, gas pressure, and sound pressure with regards to barrel length. 18" - 20" was the sweet spot, with 20" producing the best velocity (the tests went up to 24").
Here's the study: http://www.dtic.mil/ndia/2010armament/WednesdayCumberlandPhilipDater.pdf
I'd go for a 20" 1/8 or 1/7 twist from manufacturer of choice. Mount it in a Vltor MUR or quality billet upper. Get good glass and call it a day.
In general you're right, of course, opsoff1, but there are bullet options above 69 grains that "appear" able to be stabilized in a 1/9 twist barrel.
On a cursory look only, it appears the Miller stability breaks at around less than 1" in length projectile for stability in the 1/9 twist barrel and there are valid options above 69 grains one could use with that twist. Of course, not all are going to work and they are on the fringe of being acceptable, but they do fall within the acceptable range.
For example, a .990" 77gr bullet shows a Miller stability of 1.44 which is deemed stable, although admittedly on the edge.
Am I missing something? I've not shot anything above 69 grains yet as my distance shooting options are limited.
Edit: To be clear, I'm not just talking about "fictional" bullets. The Sierra 77 gr Matchkings are .994 and appear to be judged stable if you believe the Miller formula. I suppose experience might be different from theory. Not trying to argue with you, hoping you have some experience that says different. :)
Sierra's doppler radar would disagree with you
Sierra's doppler radar would disagree with you
Say what?
In general you're right, of course, opsoff1, but there are bullet options above 69 grains that "appear" able to be stabilized in a 1/9 twist barrel.
On a cursory look only, it appears the Miller stability breaks at around less than 1" in length projectile for stability in the 1/9 twist barrel and there are valid options above 69 grains one could use with that twist. Of course, not all are going to work and they are on the fringe of being acceptable, but they do fall within the acceptable range.
For example, a .990" 77gr bullet shows a Miller stability of 1.44 which is deemed stable, although admittedly on the edge.
Am I missing something? I've not shot anything above 69 grains yet as my distance shooting options are limited.
Edit: To be clear, I'm not just talking about "fictional" bullets. The Sierra 77 gr Matchkings are .994 and appear to be judged stable if you believe the Miller formula. I suppose experience might be different from theory. Not trying to argue with you, hoping you have some experience that says different. :)
Sure do - and there's a joke about engineers and therories that comes to mind, but I can't remember the whole thing. LOL, no arguing at all! Healthy exchange of ideas!! Anyway - I've shot bullets from 50gr FBHP all the way up to 90gr VLD experimentals in twists from 1/14 all the way to 1/6.5. Cut rifled, pull button, push button, broach cut, hammer forged, 4 groove, 3 groove, 6 groove and 8 groove bbls.
In my experience - as far as a 1/9 - I have never, ever got anything above a 69 to shoot in that twist - ever. Especially a 75 (HPBT or AMAX) or 77's. An 8 twist is HIGHLY marginal with 80's - it is right on the hairy edge. I've seen a lot of theoretical formulas - but as they say - proof is on the target.
I can give you a lot more on this later - but given any situation - I'd always opt for a tighter twist.
Just ordered my barrel. I went with opsoff1's recommendation and got a CLE Douglas. Should have it in a couple weeks!
Say what?
Sierra uses a dopler radar to measure the ballistic coeffecient of bullets in flight. They found that the more stable a bullet, the better it's BC. In testing the 69 gr Matchking HPBT, they found the bullet had the best BC with a 1:7 twist. Slower twists resulted in a lower BC due to precession. Precession is basically nose wobble. Sierra determined that the slower the twist, the less stable the bullet, the greater the precession, resulting in greater drag.
Real life shooting shows that shooting longer 22 caliber bullets in a 1:9 twist doesn't work well if the shooter is chasing after accuracy, regardless of Miller Stability
Sierra uses a dopler radar to measure the ballistic coeffecient of bullets in flight. They found that the more stable a bullet, the better it's BC. In testing the 69 gr Matchking HPBT, they found the bullet had the best BC with a 1:7 twist. Slower twists resulted in a lower BC due to precession. Precession is basically nose wobble. Sierra determined that the slower the twist, the less stable the bullet, the greater the precession, resulting in greater drag.
Real life shooting shows that shooting longer 22 caliber bullets in a 1:9 twist doesn't work well if the shooter is chasing after accuracy, regardless of Miller Stability
Sound info. Agreed, bullets that are longer than normal (think VLD style), generally do better with a Faster Twist.
Sierra uses a dopler radar to measure the ballistic coeffecient of bullets in flight. They found that the more stable a bullet, the better it's BC. In testing the 69 gr Matchking HPBT, they found the bullet had the best BC with a 1:7 twist. Slower twists resulted in a lower BC due to precession. Precession is basically nose wobble. Sierra determined that the slower the twist, the less stable the bullet, the greater the precession, resulting in greater drag.
Real life shooting shows that shooting longer 22 caliber bullets in a 1:9 twist doesn't work well if the shooter is chasing after accuracy, regardless of Miller Stability
AS I wrote last night, I'd add more today and MistWolf provided a great segue to this addendum;
HKGuns provided some interesting info derived from the Miller Stability Calculations - but there is always a story behind the story
.
On the surface - the handy dandy calculator is easy and provides a ESWAG (Educated Scientific Wild Ass Guess) at the stability of a projectile in a specific twist.
This gives a lot of us a warm and fuzzy feeling that engineers / ballisticians get when something works as hoped. In the grander scheme of things however, we as trigger pullers and reloaders are really relagated to the bottom of the food chain in firearms/ammo/bullet design/testing, basically "knuckle draggers" (and I'd gladly stand in that celebrated line.) :cool: The point is, that warm feeling we get after plugging in all the numbers and see that our Earschplittinloudenboomer 5 twist barrel will (should) stabilize our 507 gr FBHP bullets may actually be poop - when we get to the range and can't hit the barn from inside it - the "plan" turned out to be a guess in a dress.
In order to really get warm and cozy with these theories, there are several data points and "ya, well, but" issues that need to be considered.
1. The calculations and formulas are based on a "proposed" semi-imperical formula - semi imperical being based on observation & experiment. He based much of the calculations on correlating experimental Army projectile data. There is also a hefty amount of mathmatical theory here as well.
2. This proposed formula is based on a set of standard conditions - some of which are exceedingly important and WILL effect the outcome: A velocity of 2800fps AND standardized atmospheric conditions, namely 59deg F, 78% Humidity, 29.53 inche of Mercury and at sea level. All your inputs correct off of these numbers.
3. APROXIMATE corrections are provided for velocity and temperature.
4. Specific bullet types - boattails, hollow points and bronze bullets are lighter in relation to length ~ they are less stable and need tighter twists.
5. The calculations utilize a constant to determine "density" in relation to weight. However, this number is specific ONLY to bullets at 2800fps @ 59deg F., 78% Humidity, 29.53 inches of Mercury and at sea level.
6. Assumptions are universal that a stated twist on a barrel is exactly that - not so. It is a well known fact that button barrels (and other mfring methods as well) can slip and provide slower than advertised twists. None of that is addressed in the calculations.
7. The is also an inherent presumption that we have gyroscopically stable bullets to begin with - meaning there are no manufacturing anomalies - jacket thickness is exactly the same 360 deg, there is no core shift, meplats are identical etc - we all know this is pie in the sky stuff. Just doesn't happen - it the reason we knuckle dragger accuracy nuts sort our bullets... <guilty> None of that is addressed in the calculations.
When calculations are run for low temps - the safety margin for stability jumps up to 2.0 as minimum due to cold air's density.
Those of you who's eyes have not glazed over should sit up and pay attention to this part. The plug & play calculation is based on a VERY rudimentary correction of muzzle velocity based on a constant of 2800fps. Your velocity input "mildly" corrects the stability value.
So - the question then becomes - What is a safe twist for bullets fired in non standard conditions? Like Quantico in August ~ 95deg & 95% humidity.
If one were to actually run the calculations or just plug in your known data - you'd get a number that may be something like 1.46 and he color codes the number - I believe red is unstable, yellow is marginal and green is stable. In theory and supported by semi-impirical data (derived from the Army Research Lab) stability factors above 1.0 are deemed acceptable - Miller has pushed the threshold up a bit to incorporate a safety margin. His acceptable range is 1.3 to 2.0 The Army however considers 1.5 to 2.0 as acceptable. This extra margin is factored in to account for gyroscopic instability (say that 10x fast) - basically lower quality bullets AKA GI Ball. Add to this the issues from #7 above as well as #6 and we can fast forward to the range as we stand in front of our 600 yd target and look at perfectly shaped holes made by bullets going sideways - it's really kinda cool - as long as they are on paper (preferably yours)
So - in the end, it is important to remember that Miller formula is a proposed rule based on Standard Conditions - it does not take into account projectile anomalies, actual barrel twist deviations and wildly different atmospheric conditions. And again - proof is on the target.
I've never been able to get a 75 or a 77gr .224" bullet to stabilize in any 9 twist bbl - ever.
Hope this helps.
ETA - I ran the Miller calculations on a 90gr JLK VLD in .223 (using my known load data) - plugged in conditions that would aproximate a day on the range in the summer and it showed me that it would stabilize in a 1/7.5 twist bbl. Which is not even close. A true cut rifled 1/7 ....maybe... but a 1/6.5 definitely, which is what I use (3 groove) Its an MOA gun with irons at 1K.
Sound info. Agreed, bullets that are longer than normal (think VLD style), generally do better with a Faster Twist.
Bear in mind that "over spinning" a bullet generally has no ill effects. The rare occasions when over spinning rears it's ugly head is using light bullets/thin jackets in really fast twist bbls and at hyper velocities - I have shot some 40 gr'ers out of a 8.5 twist 28" bbl (22-250) and they literally came apart - poof!! little grey puffs of smoke a 10-20 yds from the muzzle...gone, nothing on target.
Also consider the implications of velocity and twist.
We have all seen a spinning top on a table top - the faster you spin it the more stable it becomes - same same (to a degree) with bullets. BUT! Introduce any anomaly (put a piece of tape on one side and see what happens) and it won't spin right or for long. Same with a bullet that has jacket / core issues.
A bullet in flight looses velocity far quicker that it's spinning slows down. Because of this a bullet actually becomes more stable the farther it goes, further underscoring the use of appropriate twist rates.
Ballistic coefficient is really a comparrison of a bullet to a "theoretical perfect bullet" i.e. one that carries a BC of 1.0. Higher BC bullets don't loose velocity as quickly as a low BC bullet. As MistWolf added, wobble - aka precession hurts stability / BC and obviously accuracy. Another anomaly occurs as well, known as nutation - this is when the bullet rotates (spins) on an axis that is not centered in the core. Both of these issues CAN occur when bullets have insipient flaws AND are over spun - one huge reason why hard core Bench Rest shooters generally opt for the slowest twist possible that will stabilize their bullets - they do not want to introduce any other issue that will open a group.
guitarist1993
01-07-14, 14:36
Just ordered my barrel. I went with opsoff1's recommendation and got a CLE Douglas. Should have it in a couple weeks!
Excellent choice. I've been incredibly impressed with the accuracy I'm getting from my CLE recon. What length did you decide on?
I'd just get one of WOA's varmint uppers and go shoot!
Sierra uses a dopler radar to measure the ballistic coeffecient of bullets in flight. They found that the more stable a bullet, the better it's BC. In testing the 69 gr Matchking HPBT, they found the bullet had the best BC with a 1:7 twist. Slower twists resulted in a lower BC due to precession. Precession is basically nose wobble. Sierra determined that the slower the twist, the less stable the bullet, the greater the precession, resulting in greater drag.
Real life shooting shows that shooting longer 22 caliber bullets in a 1:9 twist doesn't work well if the shooter is chasing after accuracy, regardless of Miller Stability
Gotcha. Thanks for the clarification.
ETA: Opsoff, again amazing information! Thanks.
I'm admittedly not a long distance shooter. I am looking to build a new varmint upper, however. I may need or see moa at 1k, but the information in this thread is priceless. Thank you, guys, for explaining the theories, as well as first hand knowledge.
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Check out Centurion Arms. Monty may have a Douglas/CLE barrel already in stock.
https://www.centurionarms.net/
FWIW, I have a Centurion MK12 upper that will shoot 3/8" five shot groups all day long at 100 yards.
Very cool thread, thanks to all for contributing! I have learned quite a bit from it.
As a laboratory employee, I know that theory often does not allow for perfect predictions of real world performance.
Very cool thread, thanks to all for contributing! I have learned quite a bit from it.
As a laboratory employee, I know that theory often does not allow for perfect predictions of real world performance.
Amen to that - a classic (and disasterous) "oops" was the US nuke test at Bikini Atoll in 1954. The Castle Bravo detonation was supposed to be a 5 or 6 mega ton yield. The <ahem> experts miscalculated and the actual blast was almost 3 times what they expected - 15 mega tons. It resulted in the the worst accidental radiological contamination ever by the US. It was the first fusion (hydrogen) bomb ever detonated. When it went off, it formed a fireball over 4 miles wide and was seen 250 miles away. The blast left a crater 1-1/4 miles wide and 250 ft deep. Ten minutes after the blast, the mushroom cloud was 25 miles high and 62 miles wide. It contaminated over 7000 square miles of the Pacific.....that was a serious "Oh shit" moment for the engineers...
My bet is they went right back to work crunching numbers, after they cleaned their shorts.
Excellent choice. I've been incredibly impressed with the accuracy I'm getting from my CLE recon. What length did you decide on?
20". Heavy contour with CLE's match chamber. I got a matched bolt and gas block with it too.
Check out Centurion Arms. Monty may have a Douglas/CLE barrel already in stock.
https://www.centurionarms.net/
FWIW, I have a Centurion MK12 upper that will shoot 3/8" five shot groups all day long at 100 yards.
Already ordered the CLE. I should have it in two weeks.
Amen to that - a classic (and disasterous) "oops" was the US nuke test at Bikini Atoll in 1954. The Castle Bravo detonation was supposed to be a 5 or 6 mega ton yield. The <ahem> experts miscalculated and the actual blast was almost 3 times what they expected - 15 mega tons. It resulted in the the worst accidental radiological contamination ever by the US. It was the first fusion (hydrogen) bomb ever detonated. When it went off, it formed a fireball over 4 miles wide and was seen 250 miles away. The blast left a crater 1-1/4 miles wide and 250 ft deep. Ten minutes after the blast, the mushroom cloud was 25 miles high and 62 miles wide. It contaminated over 7000 square miles of the Pacific.....that was a serious "Oh shit" moment for the engineers...
My bet is they went right back to work crunching numbers, after they cleaned their shorts.
Castle Bravo was actually the second ever thermonuclear shot, but the first "dry" one.
From Wikipedia:
Ivy Mike was the codename given to the first test of a full-scale thermonuclear device, in which part of the explosive yield comes from nuclear fusion. It was detonated on November 1, 1952 by the United States on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy. The device was the first full test of the Teller-Ulam design, a staged fusion bomb, and was the first successful test of a hydrogen bomb.
Due to its physical size and fusion fuel type (cryogenic liquid deuterium), the Mike device was not suitable for use as a weapon; it was intended as an extremely conservative experiment to validate the concepts used for multi-megaton detonations. A simplified and lightened bomb version (the EC-16) was prepared, and scheduled to be tested in operation Castle Yankee, as a backup in case the non-cryogenic "Shrimp" fusion device (tested in Castle Bravo) failed to work; that test was cancelled when the Bravo device was tested successfully, making the cryogenic designs obsolete.
The reason the the engineers/physicists said "WTF!!!" at the Bravo shot:
It was expected that lithium-6 isotope would absorb a neutron from the fissioning plutonium and emit an alpha particle and tritium in the process, of which the latter would then fuse with the deuterium and increase the yield in a predicted manner. Lithium-6 obeyed this assumption.
When the lithium-7 isotope is bombarded with energetic neutrons, it captures a neutron then decays yielding an alpha particle, a tritium nucleus, and the captured neutron. This means more tritium was produced than expected, and the extra tritium is fused with deuterium. In addition to tritium formation the extra neutron released from lithium-7 decay produced a larger neutron flux. This caused more fissioning of the uranium tamper and increased yield.
This resultant extra fuel (both lithium-6 and lithium-7) contributed greatly to the fusion reactions and neutron production and in this manner greatly increased the device's explosive output. The test used lithium with a high percentage of lithium-7 only because lithium-6 was then scarce and expensive; the later Castle Union test used almost pure lithium-6. Had more lithium-6 been available, the usability of the common lithium-7 might not have been discovered.
And now, back to our regularly scheduled program...
I can see that this thread is going to compel me to spend money.
I work with a guy who was a USAF technician during a bunch of the Bikini and Eniwetok tests - Retired now in his 80's, and man o' man does he have stories about that stuff. He said they lost virtually every piece of test instrumentation /sensors - most of which was literally vaporized when it went off. He is out on sick leave a lot - skin issues...go figure.
I have a vested interest in these "fireworks" as my dad, also USAF, helped develop the "bottle rockets" that went along with them. One of his launches:
http://m.youtube.com/watch?v=mrnfRfawtI0
[QUOTE=Tzed250;1829738]I have a vested interest in these "fireworks" as my dad, also USAF, helped develop the "bottle rockets" that went along with them. One of his launches:
Chilling stuff - I remember doing the "Drills" when I was a kid in Florida in the early 60's...under the desk and cover your head...
Back on topic, if you had to choose a barrel to shoot NRA HP match rifle with an AR platform what would it be ?
Back on topic, if you had to choose a barrel to shoot NRA HP match rifle with an AR platform what would it be ?
Personally, I've probably shot 20 different bbls manufacturers in AR type platforms over 18-20years of NRA HP shooting.
Some were stunning in their accuracy - real "hummers". Others were boringly mundane and some where tomato stakes.
In order to pick a barrel - part of the process is to consider consistency; i.e. when I shoot it out can I get another one that will perform to the same standard? I also want bbls that are pre-contoured and unchambered. Kriegers for example are contoured 1st, THEN rifled. Button bbls like PacNor are rifled first, then contoured / stress relieved. First and foremost is accuracy - any of the big names will produce
With that said, here is what I would choose.
Krieger SS 1/7.7
PacNor SS 1/7
Douglas Premium Air Gauged SS 1/7
Any of these will run you $300 - $450 easy... you get what you pay for.
Most accurate bbl I ever shot was a Rocky Mountain SS 1/7 - a laser, but the next one wasn't even close to the same level, never tried another.
All of these were service rifle configuration - you said match rifle, so you have a bit more fexibility - specifically length. I would use a 24" bbl and move the gas port forward by at least 2", maybe even 3 or 4". I'd also use a medium contour. I've done match rifle bbls for friends - 24" Kriegers that weighed a ton - serious front end heavy - go medium and if you want use a bloop tube to gain sight radius.
Thanks for the insight. I'm pretty sure I would go with a bloop tube as I dislike a front heavy rifle. I need the sight radius though as my presby has started to opia...;)
Thanks for the insight. I'm pretty sure I would go with a bloop tube as I dislike a front heavy rifle. I need the sight radius though as my presby has started to opia...;)
Bear in mind, with a match rifle, if you go with a lighter contour, you can always add weight to the forend to get the balance and dampening effects you desire. A bloop tube willl add years to your eyeballs as well. My presbyopia kicked in 10 years ago and it has gotten steadily worse.
TheAxeShooter
01-10-14, 10:50
opsoff1, just out of curiosity, do you have any experience with lothar walther AR barrels?
travellightfreezeatnight
01-10-14, 12:56
Just ordered my barrel. I went with opsoff1's recommendation and got a CLE Douglas. Should have it in a couple weeks!
SWT
Looking at these also, do you know what they mean by standard profile? Pictures would be helpful, as I could not find any on there sight.
opsoff1, just out of curiosity, do you have any experience with lothar walther AR barrels?
I shot a couple a few years ago. Maybe 2002 time frame (??) They were good - as in decent. They are button rifled and IIRC they use their own proprietary steel. Both the ones I shot were SS. My understanding is they fall more into "production" barrels. Bear in mind that folks really need to try hard to get bad accuracy from an AR - theres a lot of inherent accuracy built into the design. Other may have more up to date info - but I think (again IIRC) that they are a big OEM suppliers. I do know guys that shot them XC and they liked them. They are very affordable. Always remember - you get what you pay for.
SWT
Looking at these also, do you know what they mean by standard profile? Pictures would be helpful, as I could not find any on there sight.
Standard HBAR profile.
travellightfreezeatnight
01-10-14, 15:53
Standard HBAR profile.
awesome, thank you, that has much more meaning than "standard" Profile and is something I can relate to.
Great Job in explaining bullet stability by the way. I have read Brian Litz's book and it always helps to have things explaned in different ways. Another good read for anybody interested is The Bullet's Flight From Powder To Target: The Internal And External Ballistics Of Small Arms (1909) It is truly interesting what they were able to figure out over a century ago without the aid of computers and the electronics we take for granted today.
semper fi
awesome, thank you, that has much more meaning than "standard" Profile and is something I can relate to.
Great Job in explaining bullet stability by the way. I have read Brian Litz's book and it always helps to have things explaned in different ways. Another good read for anybody interested is The Bullet's Flight From Powder To Target: The Internal And External Ballistics Of Small Arms (1909) It is truly interesting what they were able to figure out over a century ago without the aid of computers and the electronics we take for granted today.
semper fi
You are correct - great book. F.W. Mann, actually Dr. Mann. I used to live 4 houses down from his original house,where along with Harry Pope (legendary barrel maker / schutzen rifle shooter from NY) they built an indoor 200 yd range. The range is gone now, but the remnants / framing of it where there for a long time. The original house was torn down last year and the family built a new one right next to it. I actually was able to recover a bunch of wood from the old range and the house when they demo'd it and built a shooting box, reloading press mounts and some other small items - i.e. cartridge boxes. It's my connection to history.
Years back, the ODCM (now CMP) had for sale, original Mann test barrel / recvrs (1903's) They were short heavy bull bbls. I kick myself for not buying one...
My most accurate gun I own is a Rem700 5R 1/9 and it shoots 77g SMK's and 80's half MOA all day long. Its a 20inch gun.
I had a 18 WOA 1/8 Wylde that shot lights out in a heavy SPR config. Shot great.
I changed it to a 16 Bergara wylde 1/8 , Markm stacked 5 each 77's in a very small ragged hole. These Begaras are new to the market but very impressive.
We lobbed 77SMk's out to a 1K last saturday and I probably was 60% hit rate. That Begara aint bad. None where tumbling because the misses where wind close misses.
This is a great thread! I'm in a similar s(h)ituation. After a house, kids, etc. I no longer have the budget for the uber cool toys. So, I was thinking instead of a .308 bolt gun (rifle + new stock+bedding+match ammo+everything else = $$$$$$), I would look into a precision AR upper. I already have a couple cases of match ammo, a bunch of lowers, etc. so I thought an AR might be best. Anywhoo...how are the complete uppers from Stag (3G) and RRA (R3)? At one time when I shot service rifle I had a White Oak upper built by John Holiger, and holy crap, that thing could shoot. Now, the one thing is I don't want a "varmint" type upper. I have no need for a 24" bull barrel. I'm more drawn to the recce/spr length and weight.
Would one of the "prefab" Stag or RRA shoot well? Would I be better off getting a barrel separately from Nordic/White Oak/Black Hole and having one built? Is a billet upper really superior, or ultimately, just cooler looking? Is there any special voodoo that goes into putting together a precision AR upper that's any different from a "traditional" one? I like the notion/cost of the BCM 410 uppers, but is the 5.56 chamber instead of the Wylde chamber a concern?
Also, I don't have access to anything over 200 yards.
Which do y'all think would offer the most accuracy for the $$?
Obscenejesster
02-15-14, 15:14
This is a great thread! I'm in a similar s(h)ituation. After a house, kids, etc. I no longer have the budget for the uber cool toys. So, I was thinking instead of a .308 bolt gun (rifle + new stock+bedding+match ammo+everything else = $$$$$$), I would look into a precision AR upper. I already have a couple cases of match ammo, a bunch of lowers, etc. so I thought an AR might be best. Anywhoo...how are the complete uppers from Stag (3G) and RRA (R3)? At one time when I shot service rifle I had a White Oak upper built by John Holiger, and holy crap, that thing could shoot. Now, the one thing is I don't want a "varmint" type upper. I have no need for a 24" bull barrel. I'm more drawn to the recce/spr length and weight.
Would one of the "prefab" Stag or RRA shoot well? Would I be better off getting a barrel separately from Nordic/White Oak/Black Hole and having one built? Is a billet upper really superior, or ultimately, just cooler looking? Is there any special voodoo that goes into putting together a precision AR upper that's any different from a "traditional" one? I like the notion/cost of the BCM 410 uppers, but is the 5.56 chamber instead of the Wylde chamber a concern?
Also, I don't have access to anything over 200 yards.
Which do y'all think would offer the most accuracy for the $$?
As long as you do your part, you'd be better off getting a barrel from one of the companies you listed. The 5.56 chamber on the BCM is of no concern to me because the barrel can already out shoot me. If it had a Wyld Chamber, your groups might be a millimeter better. What I'm trying to say is that unless you're shooting competition at 500 yards, you will not notice a difference.
I wouldn't worry about a Billet upper so much. Sink your money into the barrel, optics and trigger as they make up the most important factors in terms of precision rifles. You're obviously going to want to free float the barrel as well.
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