View Full Version : Larger Threads At End of Barrel?
EzGoingKev
07-26-17, 17:14
I was looking at some barrels for sale here (http://ar15performance.com/5_56_223_wylde) and am seeing some barrels having 5/8x24 threads which is typically used on .30 caliber barrels.
The reasoning is listed as:
"NOTICE*** THIS BARREL HAS 5/8-24 threads to keep the bore at the muzzle from swelling like most barrels threaded 1/2-28. The tighter bore at the crown gives better accuracy."
I would love to see people who have experience with a barrel configured like this. It would be great if there was some comparison data.
Would I would not love is posts from people with no experience with these barrels, posts from people who had ask where the bullets go, etc.
.625" threaded .223/ 5.56 barrels have been known to be better than the .500" threaded ones for a "bell mouthed muzzle" for a long time now. Even before the initial AW ban, this was done by some. Supply and demand really limited this better offering. Even now, there is still little demand.
This is pretty much the reason that KAC uses .750" threads on their SR-25's now and for a while.
The question really is to how this effect compares to other precision or accuracy issues for a lifespan of use?
There's a lot going on in a barrel, look at the "needs" and apply those while reducing negatives. Many guys have been using 7.62 MD's on 5.56 platforms for a potential for some time now.
Theoretically, the crown of a properly stress relieved barrel shouldn't swell due to the smaller muzzle thread.
But from a structural standpoint, our view is that 5/8-24 threads are actually a better match for .750 gas block journals, while 1/2-28 threads are a good match for .625" gas block journals.
Barrel profile continuity can be a key feature and appropriately sized threads contribute toward this goal.
Larger threads are stronger, stiffer and exhibit less flex. Period.
Many muzzle devices are available in either thread pattern, especially as the 300BLK and 6.8SPC variants have grown in popularity.
It seems there is also a trend toward using smaller 30 caliber suppressors to handle anything from 5.56 to 300BLK.
These tend to have 5/8-24 threaded mounts as well.
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/481917400.jpg
Our SPR barrels feature the larger threads for all the above reasons.
http://www.blackrivertactical.com/concrete5/store/#!/BRT-16-OPTIMUM-SPR-STAINLESS-Barrel/p/79720046/category=1852006
EzGoingKev
07-26-17, 20:07
This is pretty much the reason that KAC uses .750" threads on their SR-25's now and for a while.
OK so I read that and googled "3/4" thread muzzle break" to see how common they were and to get an idea as to what calibers are normally associated with that thread size. Interestingly enough this was in the results.
http://bulletin.accurateshooter.com/2015/04/muzzle-threading-dont-remove-too-much-steel/
Great article.
Most barrels do not exhibit the same kind of static bore expansion demonstrated in the videos, but obviously it can and does happen in certain circumstances.
For a little comparison,
5/8" threads on a 22 caliber bore have approximately the same wall thickness as 3/4" threads on a 30 caliber bore.
Both could be considered larger, heavier duty combinations.
The "standard" 1/2" threads on a 22 caliber bore and 5/8" threads on a 30 caliber have roughly 2/3 the wall thickness of the heavy duty versions.
And if you really want to look at thinner walls, my Keltec Sub2000 has 1/2-28 on 9mm. Then again, a blowback PCC isn't a match grade gun.
I wonder whether anyone profiles the barrels first and then rifles them, it seems like that might be possible too.
EzGoingKev
07-27-17, 10:09
Our SPR barrels feature the larger threads for all the above reasons.
@ Clint, prior to releasing your SPR barrel did you do any testing that compared 1/2" threads vs the 5/8" threads?
SomeOtherGuy
07-27-17, 13:38
I have two of Harrison's 16" 5.56 NATO barrels with 5/8x24 muzzle threads. I have not done any rigorous testing, but they seem to be relatively accurate.
If you can find a muzzle device you like with those threads - and he makes all his options with those threads - then I see no disadvantage. I imagine that the overall weight would be a break-even since the greater mass at the tip of the barrel is offset by less mass in the muzzle device.
EzGoingKev
07-27-17, 13:43
I have two of Harrison's 16" 5.56 NATO barrels with 5/8x24 muzzle threads.
Pardon my ignorance but googling multiple derivatives of harrison ar barrel did not bring anything up. Who is Harrison?
SomeOtherGuy
07-27-17, 15:00
AR15 Performance, the company you posted about, is owned by a man named Harrison Barnes. He posts on here occasionally as Constructor. So when I said "Harrison's barrels" I meant those sold by AR15 Performance.
EzGoingKev
07-27-17, 15:04
OK. I know he posts here as Constructor but I had no idea what his actual name is.
Keep in mind, some muzzle devices are optimized for a particular caliber (i.e. Precision Armament hybrids). Differences in gas volume and bullet "seal" may reduce the performance for a device compared to it's advertised effect. Also, pretty much every 30 cal device weighs more than it's 22 cal equivalent. Just some things to consider.
Sent from my ZTE A2017U using Tapatalk
Bruin's statement is true, but in the past at least, many were more concerned about gas pressure imbalances that can effect precision/ accuracy. They wanted more of a distance from the projectile OD to the bore ID of some devices. Not meaning all by any means.
To the OP though, the base barrel's manufacturing process has an influence into the degree of this. Also, it is known that reducing thread diameters smaller than the normal ones can magnify this greatly, i.e. 1/2x28 .308 barrels, etc..
EzGoingKev
07-27-17, 17:25
I would love to see some chrono info for two barrels, same ammo, same day, etc with the only variable being the thread sizing at the muzzle end. Some groups too. Preferably the testing would have been done without any muzzle device installed.
Probably too much to ask for.
Also, without an intent to derail this discussion, but with an intent to expand that if desired. We could look into some differences between having that portion of the barrel in a extension tensile force, or more of a compressive force, and what we would register to for possible MD's. etc..
I would love to see some chrono info for two barrels, same ammo, same day, etc with the only variable being the thread sizing at the muzzle end. Some groups too. Preferably the testing would have been done without any muzzle device installed.
Probably too much to ask for.
You'd need a lot more than 2 barrels to get real data from.
EzGoingKev
07-27-17, 17:53
You'd need a lot more than 2 barrels to get real data from.
I got a feeling asking for 2 barrels is going to be 2 too many.
Yeah, it gets complicated more than that.
Before and after threading should give you "a good idea". That should eliminate barrel to barrel variance.
I'd expect it to have more to do with accuracy than velocity.
SomeOtherGuy
07-28-17, 07:58
I would love to see some chrono info for two barrels, same ammo, same day, etc with the only variable being the thread sizing at the muzzle end. Some groups too. Preferably the testing would have been done without any muzzle device installed.
Probably too much to ask for.
It might be easier and cheaper to find an engineer willing to do 3d modeling of the forces on the muzzle end when the bullet passes based on the differing thread types. A while back someone posted an interesting strain model for the gas block area comparing set screw, pinned and clamped types of gas block.
On the other hand, I see no downside to the larger diameter threads, so if a barrel you want is available with them just try it out. If the barrel you want only comes in 1/2x28, there's your answer.
3D model FEA shows approximately 50% higher stress at the thread root due to bore pressure when comparing the smaller threads to the larger threads.
The Texas State Highpower Rifle and Texas State Junior Highpower Rifle Teams have been shooting barrels turned from Shilen blanks by Nez Rongero this way for a few years now.
Keith Stevens won last year's President's Rifle Match at Camp Perry with a Rongero-turned Shilen with the 5/8s muzzle thread. Nez has these barrels nitrided before turning them into rifles.
This would be an interesting topic.
What are the general effects?
We could look into some differences between having that portion of the barrel in a extension tensile force, or more of a compressive force, and what we would register to for possible MD's. etc..
The possible differences in radiuses acting as a fulcrum axis for deflection for some possible MD's for some barrel profiles. This is kind've a thread drift for the OP, so you can email me Clint if you like. It's mostly the concept of continuous curve for use Vs a curve that has deviation(s) to that curve that more resembles different arcs combined.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.