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Posted: 1/18/2015 1:02:45 AM EDT
Ok, I completely understand that a 1X7 will stabilize a heavier bullet for a longer distance. BUT what effect might a 1X7 have on a 55 gr FMJ at a longer distance?. Does the faster twist rate have any detrimental effect on a lighter bullet at a longer range? I shoot a LOT of 55 gr FMJ punching targets and all kinds of stuff when just out shooting but now I am all but done building a 16 inch carbine with a 1X7 twist barrel and am just curious about what to expect from this twist with lighter 55 grain bullets when I go shooting LONG. Any first hand experience would be appreciated.
Link Posted: 1/18/2015 1:49:40 AM EDT
[Last Edit: 1/18/2015 1:54:42 AM EDT by AR-4C]
Chapter 5 — Section V. Ballistics of FM 3-22.9 will explain more in detail the differences of M855 vs M193 when using a 1x7 twist barrel.


Figure 5-32 Ammunition Impact Comlarison

5-92. The M16A2/A3/A4 rifle and M4/M4A1 carbine fire both M193 and M855 ball ammunition with little difference in accuracy to a range of 500 meters. The M16A2/A3/A4 and M4/M4A1 and their ammunition are more effective than the M16A1 at ranges out to and beyond 500 meters due to better stabilization of the round.

5-94. Figure 5-32 (B) shows two 25.4-centimeter (12-inch) shot groups fired by the same skilled marksman at a distance of 274.2 meters (300 yards) using an M16A2 rifle.
— The shot group on the left was fired and zeroed with M855 ammunition. The shot group on the right was fired using M193 ammunition.


Figure 5-35. M855 zeroed at 25 meters; M193 fired using M855 zero.


Table 5-11. M855 zeroed at 25 meters; M193 fired using M855 zero.
Link Posted: 1/18/2015 5:11:39 AM EDT
Well we now know that a 1/6 twist will put 35s damn near moa, consistently so I think the 1/7 is too fast for 55s argument is over, it's not too fast.
Link Posted: 1/18/2015 11:19:22 AM EDT
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Originally Posted By nateebobo:
Well we now know that a 1/6 twist will put 35s damn near moa, consistently so I think the 1/7 is too fast for 55s argument is over, it's not too fast.
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Didn't want to start an arguement. Just wanted to know what I might be in for. Thanks guys.
Link Posted: 1/18/2015 12:36:45 PM EDT
By definition, an “unstable” bullet is one that will have a gyroscopic stability factor of less than 1.0 at the muzzle. A typical 55 grain FMJ bullet will have a gyroscopic stability factor of approximately 3.7 when fired from a 20” barrel with a 1:7” twist. [CaptainObvious] 3.7 is not less than 1.0. [/CaptainObvious].


The following demonstration compares the results of firing four 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist. The first barrel used in testing was 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. The second barrel used in testing was a 20” Colt HBAR, also with chrome lining, a NATO chamber and of course a 1:7” twist. The longer barrel with the 1:7” twist was purposely chosen for the increased muzzle velocity coupled with the 1:7” twist. Both barrels had free-float handguards.

Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Naturally, the wind conditions were monitored using a Wind Probe. The set-up was very similar to that pictured below.






Four 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.

As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel. Those groups were also also over-layed on each other to form a 40-shot composite group; the results were nearly identical to those obtained from the 1:9” twist barrel. The composite group had a mean radius of 1.01”. The two composite groups are shown side by side for comparison.







Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the “overstabilization” claim is largely inconsequential. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris performed tests comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, (well into the downward slope of the trajectory where the Internet Commando claims that all manner of evil befalls the “overstabilized” bullet), and the accuracy results from the two different twist barrels were also nearly identical.

Quality, modern lightweight bullets (40 to 55 grain) of typical copper-jacket/lead-core construction can shoot superbly from fast twist barrels. Typical 55 FMJ bullets do not fall into the quality category.


The group pictured below was fired from a 1:7" twist Noveske barrel using 40 grain V-MAX bullets.






The 10-shot group pictured below was fired from a distance of 100 yards from a Noveske barreled AR-15 with a 1:7” twist using 55 grain BlitzKings.





The 3-shot group pictured below was fired from the same 1:7” twist barrel with the 55 grainBlitzKings for the Internet Commandos in our viewing audience.






The next 10-shot group pictured was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.






A 14.5" Colt M4A1 SOCOM barrel,with its NATO chamber, chrome lining and 1:7" twist manages to shoot quality 55 grain bullets quite well.







...




Link Posted: 1/18/2015 12:54:31 PM EDT
What grain is recommended for 1:8 twist?
Link Posted: 1/18/2015 2:42:33 PM EDT
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Originally Posted By Legion7:
What grain is recommended for 1:8 twist?
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Anything that will fit in the magazine and most if not all that are even too long. It all comes down to what you're barrel likes, pick a few match rounds of different weights and try. Also varmint bullets are usually very good, if you want something cheap to put groups on paper try the american eagle 50 grain varmint tipped stuff available everywhere, it's never shot bad from any barrel I've tried it in.

Molon can tell you far more than I can on any of this stuff, if he swings back in here, check the thread in the ammo section that asks this very question as well.

Op, I wasn't being a dick and didn't mean to come off that way, sorry. It's just that ever since those damn charts came out everyone states what on them as gospel rather than trying and finding out for sure. Not to mention the legions of 1/7 barrels out there shooting m193 everyday and doing it quite well. It's just annoying to see people turned away from 1/7 based on nonsense and ending up with something that can't can't deal with the heavy loads. Truth is if your never going to use anything other than bulk, cheap ammo it doesn't matter what twist you go with anything will get the job done but if you plan on ever shooting heavies or using mid to heavy all copper Barnes type bullets for hunting, you'd be a fool to go slower than 1/8. Again not trying to sound like a dick, I just type that way sometimes sorry again.
Link Posted: 1/18/2015 3:12:16 PM EDT
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Originally Posted By nateebobo:



Anything that will fit in the magazine and most if not all that are even too long. It all comes down to what you're barrel likes, pick a few match rounds of different weights and try. Also varmint bullets are usually very good, if you want something cheap to put groups on paper try the american eagle 50 grain varmint tipped stuff available everywhere, it's never shot bad from any barrel I've tried it in.

Molon can tell you far more than I can on any of this stuff, if he swings back in here, check the thread in the ammo section that asks this very question as well.

Op, I wasn't being a dick and didn't mean to come off that way, sorry. It's just that ever since those damn charts came out everyone states what on them as gospel rather than trying and finding out for sure. Not to mention the legions of 1/7 barrels out there shooting m193 everyday and doing it quite well. It's just annoying to see people turned away from 1/7 based on nonsense and ending up with something that can't can't deal with the heavy loads. Truth is if your never going to use anything other than bulk, cheap ammo it doesn't matter what twist you go with anything will get the job done but if you plan on ever shooting heavies or using mid to heavy all copper Barnes type bullets for hunting, you'd be a fool to go slower than 1/8. Again not trying to sound like a dick, I just type that way sometimes sorry again.
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By nateebobo:
Originally Posted By Legion7:
What grain is recommended for 1:8 twist?



Anything that will fit in the magazine and most if not all that are even too long. It all comes down to what you're barrel likes, pick a few match rounds of different weights and try. Also varmint bullets are usually very good, if you want something cheap to put groups on paper try the american eagle 50 grain varmint tipped stuff available everywhere, it's never shot bad from any barrel I've tried it in.

Molon can tell you far more than I can on any of this stuff, if he swings back in here, check the thread in the ammo section that asks this very question as well.

Op, I wasn't being a dick and didn't mean to come off that way, sorry. It's just that ever since those damn charts came out everyone states what on them as gospel rather than trying and finding out for sure. Not to mention the legions of 1/7 barrels out there shooting m193 everyday and doing it quite well. It's just annoying to see people turned away from 1/7 based on nonsense and ending up with something that can't can't deal with the heavy loads. Truth is if your never going to use anything other than bulk, cheap ammo it doesn't matter what twist you go with anything will get the job done but if you plan on ever shooting heavies or using mid to heavy all copper Barnes type bullets for hunting, you'd be a fool to go slower than 1/8. Again not trying to sound like a dick, I just type that way sometimes sorry again.


No problem at all. Just way more info than I needed. I just SIMPLY want to know if a 55gr FMJ would perform about the same, worse, or maybe even better out of a 16 inch 1 X 7 twist compared to the same round out of a 1 X 9 twist. Either way, I am very close to finding out for myself. I have completed the build and function tested the gun and results were just fantastic (not my first build by any meens) and just need to wait out the gail force winds we are having at the moment. I have just never ran a 1 X 7 twist 16 inch barrel. and wanted to hear from someone that has with 55 gr FMJ that might could tell me what to expect. It really wasn't intended to be any kind of really technical question. I am pretty much a simple and practical man and all the charts and technical data meen pretty much nothing to me. I dont even bother reading or looking at them. The possible differances between barrels and ammo used could easily distort those written results. Thanks for the help and either way soon as this wind lays I will find out for myself....Thanks again.
Link Posted: 1/19/2015 12:37:00 PM EDT
I shoot anything that will fit in the magazine and chamber in the firearm. I pick the ammo with the best grouping stock that and my zero is on that ammo. After that whatever is on sale that goes bang is fair game for training.
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