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USA
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Posted: 12/10/2014 8:51:54 PM EDT
Hi there!
I'm interested in knowing about how 55gr and 62gr 5.56x45mm would do in a 15 inch barrel in both 1:7 and 1:9? Thanks! |
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Posted: 12/10/2014 9:46:31 PM EDT
[#1]
This is the PRECISION RIFLE FORUM!
Nothing "precise" about 55 gr or 62 gr bullets in a 15" barrel. Did you end up in the wrong forum by chance? |
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USA
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Posted: 12/10/2014 10:56:03 PM EDT
[#2]
Quote HistoryOriginally Posted By captrichardson:
This is the PRECISION RIFLE FORUM! Nothing "precise" about 55 gr or 62 gr bullets in a 15" barrel. Did you end up in the wrong forum by chance? Not at all, I figured that people on this forum would perhaps best know about twist rates, barrel lengths and bullet weights and therefore thought it would be the best place to seek some advice and guidance. Am I in the wrong place? |
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MI, USA
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Posted: 12/11/2014 11:48:15 AM EDT
[#3]
Neither bullet's construction, nor the precision with which the cartridges are loaded are going to give you enough accuracy to notice any effect of twist rate and stabilization. I would guess 55 gr m193 would be more accurate just because it's a simpler construction that would be more concentric than the m855. Both would be very well stabilized in either 1:7 or 1:9, so shoot whichever.
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BOL
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Posted: 4/4/2015 10:40:21 PM EDT
[#4]
In a 20 inch 1/7 barrel 855 will perform better. In carabine barrels both should be fine.
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MS, USA
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Posted: 5/8/2015 6:50:33 PM EDT
[Last Edit: MS556]
[#5]
Government studies, and a separate report by the NRA suggest that 1:9 is optimal for M855, and that at least in carbines, 1:7 had the effect of doubling the group size.
http://www.americanrifleman.org/articles/2014/5/21/testing-the-army-s-m855a1-standard-ball-cartridge/ The same problem persists with the new replacement M855A1 - 1:9 groups are half the size of 1:7 groups. While group size is problematic to begin with at this is not precision ammo, it becomes worse when you double the group size with 1:7 twist. If you are going to shoot this ammo and try to shoot tight groups with it (without laughing) at least stick to 1:9 and get the best it can do. |
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Posted: 10/17/2015 4:13:00 AM EDT
[#6]
Quote HistoryOriginally Posted By MS556:
Government studies, and a separate report by the NRA suggest that 1:9 is optimal for M855, and that at least in carbines, 1:7 had the effect of doubling the group size. http://www.americanrifleman.org/articles/2014/5/21/testing-the-army-s-m855a1-standard-ball-cartridge/ The same problem persists with the new replacement M855A1 - 1:9 groups are half the size of 1:7 groups. While group size is problematic to begin with at this is not precision ammo, it becomes worse when you double the group size with 1:7 twist. If you are going to shoot this ammo and try to shoot tight groups with it (without laughing) at least stick to 1:9 and get the best it can do. Considering the average service M4 rifle has a 1/7 twist, the military must be more than a little pissed I would think. 
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MO, USA
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Posted: 1/31/2016 3:12:47 PM EDT
[#7]
I can't find the articles I read a couple years ago, but generally speaking the heavier grain in the 1:7 (62 gr) and lighter grain in the 1:9 (55 gr). I have one AR with each twist and I can tell the difference.
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Posted: 2/5/2016 12:54:47 PM EDT
[Last Edit: SpeyRod]
[#8]
FWIW, The 55 gr bullet will be stabilized in both barrels. The 62 gr should be stabilized given velocity is not down. Will one shoot better than the other? Twist is not the primary determining factor for accuracy. The individual barrel in combination with the components in the load will dictate which bullet it does best in each case.
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Posted: 2/5/2016 1:07:26 PM EDT
[#9]
M193 and M855 won't ever be very accurate. Either 1:7 or 1:9 will work just fine. I would go 1:7 to ensure compatibility with 77gr SMK and TMK loads.
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