View Full Version : .308 bullet choice for a 20 inch barrel out to 600 yards?
Looking for which bullet weight (155, 168, 175, 180), willing to try other weights, would be best out to 600 yards. Not looking for a 1K round, just a good 600 yard shooter.
Failure2Stop
08-16-14, 17:40
175gr
What barrel twist rate will you be using?
I agree that a 175g projectile is a good choice, but I would not rule out a 168 HPBT or a 155g Scenar.
What barrel twist rate will you be using?
Twist is 1 in 11.
A 1:11 twist barrel should work with any of the bullets you mentioned in your original post.
A local shooter told me he had a good load recipe for a 125g bullet that would shoot MOA out of his Remington 700 out to 600 yards. If I can find the recipe, I will PM you.
175gr
This.
The 155 scenar is optimal in a 24" or longer barrel as I understand it. It works on higher velocity than a 20 barrel can give.
I get 3050fps out of the new 155 Scenars in a 20" bolt gun with a can and pushed by 2000MR powder. They're like lasers. Even if you're not getting them quite that fast, out to 600, they'll still post great numbers. It's out at a grand + where they can get funky if you're not pushing them, in my testing, anyway. They're almost cheating. Drop and wind numbers closer to .260 than .308 at the ranges you're talking.
But...175gr has a lot more established loads available and will likely require less experimenting. Ammo availability is another plus, if you need to pick up a box somewhere that are reasonably close to your handloads.
Failure2Stop
08-18-14, 11:39
I get 3050fps out of the new 155 Scenars in a 20" bolt gun with a can and pushed by 2000MR powder. They're like lasers. Even if you're not getting them quite that fast, out to 600, they'll still post great numbers. It's out at a grand + where they can get funky if you're not pushing them, in my testing, anyway. They're almost cheating. Drop and wind numbers closer to .260 than .308 at the ranges you're talking.
But...175gr has a lot more established loads available and will likely require less experimenting. Ammo availability is another plus, if you need to pick up a box somewhere that are reasonably close to your handloads.
I do like the new breed of lightweight 7.62 projectiles, I just have a whole lot of 175gr data that's already established, and it works well even down to 2300 f/s from muzzle.
That said, I live in an "800 and in" realistic application for my 7.62 guns (lightweight, relatively low powered optics), and at those ranges, a smoking 155 might make an appreciable difference.
One thing I noticed about reloading the 155g Scenars, is that I had to be a lot more selective about brass and primers than when developing a 1,000 yard load with the 175g projectiles.
Are those scenars secant ogive?
Well, they're not a 220 SMK nose, but they don't really act like some of the more finicky secants, either. I load them to SAAMI length so I can use them in semis and they still shoot lights out with a good jump to the lands in my bolt gun. Pretty forgiving for OAL in the loads I've developed.
Kinda like the AMAX bullets. Clearly not Tangent, but still don't seem to be jump sensitive.
Yep. They look a lot like a slightly longer, slightly more sharp 175 SMK. The air pocket makes them look like a much bigger bullet.
I shoot a 20" bbl 308 also - blueprinted 40X w/ a Krieger 1/10. I am still playing around with it to develop BR type accuracy. I had been playing with bullets in the medium to heavy weight range (168 - 210). While I got some very very good accuracy out of some loads, I found that with the slower powders, and the heavier bullets, muzzle blast was a serious issue. My developement basically made a U-turn and now I want to start to explore lighter bullets and maybe a faster powder to get the velocity up. The current "best load" I have found is the following:
Lapua brass (neck turned to .0142)(brass is completely prepped) / Fed 210M primers / 40.0 IMR 4895 / 168 SMK's sorted by ogive.
A ten round sample gave me the following #'s
Velocity averages at 2395 (slow!)
SD's are 6.21
ES runs 20
5 shot groups are in the .3 -.4 range.
I tried 175 SMK's, 175 Bergers, and 210 Bergers. I also used 180 SMK's - but be careful - if you are referencing the 180 SMK, the new ones suck (P/N 2220). (Don't know why they even make them anymore). The old ones are lasers. The old 180 SMK's have a boat tail angle of 9 deg and bearing lenths of .400 & BC of .500. The current production 180SMK has a bearing lenth of .462 with a BT angle of 13*. Crappy bullet for LR.
I'd be really interested in the development of loads with lighter bullets - 125 - 155 range. I am mulling various options now - but as usual, have too many irons in the fire.
Interesting thread.
Subscribed
After doing more reading on the subject of using the 308 at 600 yards and under, it seem most are loading the lighter bullets. It was pointed out in another forum to try the 135 SMK and 155 SMK (not Palma). There is so much info out there about the 308, it's not funny, google is almost useless.
After doing more reading on the subject of using the 308 at 600 yards and under, it seem most are loading the lighter bullets. It was pointed out in another forum to try the 135 SMK and 155 SMK (not Palma). There is so much info out there about the 308, it's not funny, google is almost useless.
I hear ya. Right now, my inclinations are pushing me to find a 150 gr (ish) flat base bullet. The one regret I have is putting a 10 twist bbl on this action. Wish I had screwed a 12 or maybe even a 13 or 14 twist on. I know it would feast on 125 - 150gr FB bullets.
12 is pretty flexible. My factory SPS 20" came with a 1/12 (it's not the threaded AAC version that's 1/10), and it stabilizes everthing in the sane realm. It took 220 gr Sierra hunting soft points at sub sonic to get it to start to show instability signs.
I'd love to run some tests and play around with some really slow twist bbls - i.e. bench rest stuff - a lot of those guys are shooting 14 & even 16 twist bbls. Hold on - be right back, gotta go buy some lottery tix...;)
I did a fun test with those huge 220 hunter bullets. They were yawing at subsonic and shooting about 7-8 MOA. I went back and loaded a batch up at a ball park guess for Supersonic with Varget (since Hodgdon doesn't list data for such a heavy bullet in .308), and BAM... those stupid things shot MOA and flew stabile.
I did a fun test with those huge 220 hunter bullets. They were yawing at subsonic and shooting about 7-8 MOA. I went back and loaded a batch up at a ball park guess for Supersonic with Varget (since Hodgdon doesn't list data for such a heavy bullet in .308), and BAM... those stupid things shot MOA and flew stabile.
Interesting - no significant pressure issues? Years ago we used to shoot 240gr Match Kings in 300 Win Mags at 1K. 9 twist bbls and they were brutal - the joke was you needed a mouth guard and tent pegs behind your boots so the recoil wouldn't push you off the matt. I don't miss that punishment at all.
Interesting - no significant pressure issues? Years ago we used to shoot 240gr Match Kings in 300 Win Mags at 1K. 9 twist bbls and they were brutal - the joke was you needed a mouth guard and tent pegs behind your boots so the recoil wouldn't push you off the matt. I don't miss that punishment at all.
:lol:
Yeah... wow. I wouldn't shoot something that punishing no matter how effective it was at reaching. But no... I don't remember any noteworthy recoil, and no pressure signs.
I was just fascinated that the extra velocity added stability.
175gr SMK, 178gr AMAX, or 185 Berger Tactical (Juggernaut)
:lol:
I was just fascinated that the extra velocity added stability.
There have to be specific RPM nodes where bullet designs are stable and will remain stable while losing lots of speed (despite the gyroscopic pull and slight yaw from ballistic drop), I figure this is what defines the good LR bullets from the just OK ones. For my part this is a really useful discussion, and I clearly need to learn a lot more about construction and geometry before looking at handloading -
There have to be specific RPM nodes where bullet designs are stable and will remain stable while losing lots of speed (despite the gyroscopic pull and slight yaw from ballistic drop), I figure this is what defines the good LR bullets from the just OK ones. For my part this is a really useful discussion, and I clearly need to learn a lot more about construction and geometry before looking at handloading -
Oh crap... I just had a flashback to the gyroscopic stability pissing matches we used to have here a year or two back.
As far as the Good vs Bad LR bullets.... all that is easy to dig up. As opsoff1 mentioned, and I've experienced first hand.... the boat tail shape dictates a lot of how a bullet handles trans sonic.
The 175 smk in .308 and 77 smk in .223 handle it like a champ. I tried shooting a Nosler, I think, 168 in .308, and at 1000 yards, that sucker fanned out and would impact anywhere in a 10 yard circle around the target. I didn't know what I was seeing at the time, but after reading the article on the Mil LR .308 round development, I came across the boat tail angle bit.
I'm busy reading up now on trying to figure out why the boat tails are angular (instead of taking a continuation of the secant ogive curve and re-continuing that up to the desire boat tail angle and bullet length) - I'm sure there's logic to it, in the same way that a fairly large meplat makes OTM bullets fly splendidly, but I'm just knowing jumping in and trying to discover how much solid information is out there (instead of relying on just redneck punditry about which magical unicorn mayonnaise load combinations work best in individual rifles).
Final partial derail question - is there a practical limit on weights imposed by SAAMI OAL for the cartridge by the bullet when we're specifically talking about a gas 20" (or shorter) where trying to drive those heavier (185gr+ ) bullets through lossy gas semis starts making extraction or primer pocket issues before those rounds really start to be stable, or is it just a lack of good bullets up in that range for the comparatively low MV of a .308 gas gun since the market for those bullets are for 300WM or similar loads? I've heard similar stuff to your tinkering with 220gr bullets, but just trying to reach a greater understanding on why the 175gr are the generally recommended loads even out to distances where the wind becomes the primary concern.
why the 175gr are the generally recommended loads even out to distances where the wind becomes the primary concern.
175 is the best balance of all factors. It just goes transonic in the 900 yard range if I recall correctly. It passes through really well. It's not jump sensitive.
To me, it's the bullet that lets me do a lot of shooting without a lot of ass ache development and attention to throat erosion, etc.
I'm busy reading up now on trying to figure out why the boat tails are angular (instead of taking a continuation of the secant ogive curve and re-continuing that up to the desire boat tail angle and bullet length) - I'm sure there's logic to it, in the same way that a fairly large meplat makes OTM bullets fly splendidly, but I'm just knowing jumping in and trying to discover how much solid information is out there (instead of relying on just redneck punditry about which magical unicorn mayonnaise load combinations work best in individual rifles).
Final partial derail question - is there a practical limit on weights imposed by SAAMI OAL for the cartridge by the bullet when we're specifically talking about a gas 20" (or shorter) where trying to drive those heavier (185gr+ ) bullets through lossy gas semis starts making extraction or primer pocket issues before those rounds really start to be stable, or is it just a lack of good bullets up in that range for the comparatively low MV of a .308 gas gun since the market for those bullets are for 300WM or similar loads? I've heard similar stuff to your tinkering with 220gr bullets, but just trying to reach a greater understanding on why the 175gr are the generally recommended loads even out to distances where the wind becomes the primary concern.
I suggest picking up Brian Litz's Books. They are found here: http://store.appliedballisticsllc.com/
I'm busy reading up now on trying to figure out why the boat tails are angular (instead of taking a continuation of the secant ogive curve and re-continuing that up to the desire boat tail angle and bullet length) - I'm sure there's logic to it, in the same way that a fairly large meplat makes OTM bullets fly splendidly, but I'm just knowing jumping in and trying to discover how much solid information is out there (instead of relying on just redneck punditry about which magical unicorn mayonnaise load combinations work best in individual rifles).
Final partial derail question - is there a practical limit on weights imposed by SAAMI OAL for the cartridge by the bullet when we're specifically talking about a gas 20" (or shorter) where trying to drive those heavier (185gr+ ) bullets through lossy gas semis starts making extraction or primer pocket issues before those rounds really start to be stable, or is it just a lack of good bullets up in that range for the comparatively low MV of a .308 gas gun since the market for those bullets are for 300WM or similar loads? I've heard similar stuff to your tinkering with 220gr bullets, but just trying to reach a greater understanding on why the 175gr are the generally recommended loads even out to distances where the wind becomes the primary concern.
TehLlama,
Intriguing thoughts. I went over a number of technical papers, articles and books dealing with bullet design. As can be expected, the answer is multifaceted.
Some of the design objectives are truly facinating. The best / easiest way to explain it is to say that it is a combination of manufacturing concerns as well as performance.
From a manufacturing aspect, the die design and difficulty in removing these type projectiles would be problematic = expensive.
The larger consideration is performance. Shadow graph photography showing turbulence / drag of a projectile in flight bears out the design.
Air flow over/around a bullet is basically separated into three types: laminar, transition & turbulent. These three types of flow are found in the "boundry layer"; the thin layer of air that flows around the projectile. From what I can determine the, use of a radiused BT would effectively produce a wider turbulet "wake" behind the bullet. This would increase drag. The use of a conical design reduces the diameter of the turbulence. This aspect will improve (or actually not degrade) the stability of the bullet.
Further - a square base is hugely important for a number of reasons. In simplistic terms, think of it as a bearing surface - off kilter (not perpendicular to the bore) and the propellant gasses will upset the flight.
The conventional boattail design decreases drag when a bullet is in the transonic flight. The boattail effectively reduces drag in all stages of flight but it’s in the transonic stage where the greatest drag forces are applied to a bullet. The transonic velocity is were the bullet is decelerating from supersonic velocities down to subsonic velocities, between about 1250 fps to 1050 fps.
Other reserachers found in testing, that a rebated boattail design provides even more benefit. The rebated boattail designs simplifies the design of bullet swaging dies vs the conventional boattail. It has been proven mathematically and experimentally that the rebated boattail design is superior to the conventional boattail: it imparts more energy, in velocity, to the bullet on exiting the muzzle; it allows the bullet to fly through undisturbed air after exiting the muzzle because the hot gasses are deflected out to almost right angles to the bullet’s flight instead of flowing up past and into the flight path of the bullet; and because of the step from the boattail to the shank of the bullet it makes a 90 degree angle to the bore when fired, this 90 degree angle greatly reduces the hot gasses ability to flame cut the rifling.
Also - reasearch has shown that the best "angle" for a boat tail - one that reduces the drag coefficient best is aproximately 7 degrees.
So - bottom line - For boattail lengths between 0.5 and 1.5 calibers, conical boattails have lower drag than either the ogival or concave configurations.
I know this doesn't completely answer your question - but hopefully it will provide a little better insight.
If you want more data - check these references:
1) Optimization of Boattail for Small Arms Bullets, by Kneubuhl, Defense Procurement Group 2, Ballistics Division, Ministry of Defense, Switzerland. (Presented at the International Symposium on Small Arms at Quantico, Virginia, 1983). http://www.ntis.gov/search/product.aspx?ABBR=PB85143758
2) The Effect of Various Boattail Shapes on Base Pressure and Other Aerodynamic Characteristics of a 7-Caliber Long Body of Revolution at Mach = 1.70, by B.G. Karpov, US Army Ballistic Research Laboratories APG Report No. 1295, 1965. www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0474352
I had to googlize this rebated BT idea....
http://www.corbins.com/images/rbt-muz.jpg
The Lapua 170gr (iirc) featured exactly that, a partially rebated BT with a much shallower BTA, and from unverified sources it was a superiour replacement possibility for the 169gr SMK, but being foreign sourced lost out (and now the 175gr SMK is the de-facto standard), although part of that may have been the exposed lead lock base playing some role too. My guess is that having a small stall zone back there that allows displaced turbulent flow paths to meet again somewhat smoothly is preferable to having vortices of varying size trying to overlap in that wake area; I had thought of the back edge of the bearing surface being given a more favorable angle to allow for unhelpful gas blowby would be a drawback, but if there's no external ballistic advantage, then I now see how the simpler to manufacture conical ones are better across the board, especially since the flow around the bearing surface should be able to achieve a laminar boundary layer independent of a bow shock region regardless of ogive shape, so the shallow boat tails just reduce the amount of turbulent low pressure air being dragged behind. I'm a bit out of my depth past this, so I'm quite curious
I guess the last mystery to me is why there aren't many hybrid ogive rebated boattail bullets out there - seems like the ticket for 'do everything pretty well'.
The Lapua 170gr (iirc) featured exactly that, a partially rebated BT with a much shallower BTA, and from unverified sources it was a superiour replacement possibility for the 169gr SMK, but being foreign sourced lost out (and now the 175gr SMK is the de-facto standard), although part of that may have been the exposed lead lock base playing some role too. My guess is that having a small stall zone back there that allows displaced turbulent flow paths to meet again somewhat smoothly is preferable to having vortices of varying size trying to overlap in that wake area; I had thought of the back edge of the bearing surface being given a more favorable angle to allow for unhelpful gas blowby would be a drawback, but if there's no external ballistic advantage, then I now see how the simpler to manufacture conical ones are better across the board, especially since the flow around the bearing surface should be able to achieve a laminar boundary layer independent of a bow shock region regardless of ogive shape, so the shallow boat tails just reduce the amount of turbulent low pressure air being dragged behind. I'm a bit out of my depth past this, so I'm quite curious
I guess the last mystery to me is why there aren't many hybrid ogive rebated boattail bullets out there - seems like the ticket for 'do everything pretty well'.
The 170 is their "Lock Base" which is technically a rebated boattail FMJ - but not really what we are talking about here. It is more of a FMJBT with a distinctive base closure process that reduces the exposed lead.
Look at their D46 bullet (awesome BTW - been around for decades)
Their Scenar and Scenar L are more conventional designs - tangent / secant ogive with conical BT's.
Rebated boat tails provide the benefit when the bullet is in transonic flight - which for a typical 308, would be out in the 850-900yard area. They don't provide really any added benefit before that. That is more than likely why the big mfr's don't bother - too small of a crowd that need / want that aspect. (follow the $$)
Years back we tested a cool bullet - Hammett 80gr (.224) RBTHP - rebated boat tails - saw no difference at 600, but they flew beautifully past that - way past that. No one at the time considered shooting the M16/AR15 at 1K. We were firmly stuck to our M14's for LR (literally :lol: - "Firm Grip" spray on adhesive) I still have a few boxes of those bullets - he doesn't make them anymore - used to be really big in the .17 cal crowd. I may have to dig them out and test them at 1K.
shark101au
09-14-14, 12:58
168/175 gr SMK or 155/168/178 A-Max will all work really well. I typically use 168 SMKs out of my AR-10 and 175 SMKs out of my 22 inch M24 clone.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.