mchaley
02-09-10, 08:07
For the past five hours or so I've been reading about twist rates and bullet stabilization. I'm far from being an expert but I've learned a lot. I wanted to go through some key points that I read to get some feedback. Some of these are quotes from M4Carbine.net and other sites.
If your barrel has a 1x12" twist - you are limited to 55 grain ammo.
If your barrel has a 1x9" twist - you can shoot either the 55 grain or 62 grain (actually up to 69 grains reliably)
If your barrel has a 1x7" twist - you can shoot the 55 grain, 62 grain, 75 and 77 grain - even all the way up to 80 grains reliably
As far as ammo choices:
First choice BY A LONG MARGIN would be the 75 or 77 grain ammo it fragments beautifully from point blank out to many hundred meters.
Second choice would be M193 or equivalent 55 grain ammo if fragments reliably from point blank to around 150 +/- meters.
DISTANT third choice would be the SS109/M855 62 grain ammo which is not a reliable fragmenting round at any range.
Once a bullet is adequately stabilized, the riflings' rate of twist has no further influence on bullet accuracy. Light .224" bullets suck for accuracy at longer distances merely because they drift more in the wind.
Other random "facts" that I picked out:
The difference in 55gr in 1x7 and 1x9 is hard for me to see unless I'm using really high powered scopes even then it's pretty nill.
I think the 1 and 9 is just as accurate as my 1 and 7 barrels but most of the barrels that are 1 and 7 are made from 4150 steel and that to me is more important.
Faster twists will show better accuracy with longer bullets.
Longer bullets are usually heavier as well.
with proper ammo selection the 1/7 can accurately shoot 45gr-77+gr bullets!
The U.S. military 62 grain ball (ss109) will work nicely in a 1/9 twist, but also works nicely with the 1/8. The very light bullets, say 55 grain & less, work nicely with a 1/12 to 1/13 twist.
Shorter (which USUALLY means lighter) bullets can be fired in barrels with tighter twist rates than in necessary but longer (which USUALLY means heavier) bullets cannot be shot in barrel twist rates that are slower than what they need. So the most versatile barrel twist rate is one that is tighter as it will shoot all bullet lengths/weights.
My notes:
Quality ammo matters more than twist rate.
faster twist for longer (usually heavier) rounds whereas shorter twist rates are for shorter (usually lighter) rounds.
1:9 and 1:7 are the most popular
1:7 barrel will wear out faster than a 1:9
Longest lasting barrel will be a non-national match, chrome, 1:14 barrel
Best barrel for the best bullets is the 1:8 for the Sierra 69 grain or 80 gr VLD Sierra
A 62gr bullet fired from a 1:12 barrel will start tumbling at 100yds.
When in doubt, try it out.
I've been researching twist rate and accuracy. From what I've read, a 1:7 will handle everything. Lighter rounds may suffer in accuracy but chances are it's less to do with twist and more to do with inferior ammo. A 1:7 will wear out faster than a 1:9 especially when lighter rounds are used (45gr varmint rounds for example) because of the higher pressures.
If you want a tack driver you should get a 20" stainless steel match grade barrel with heavier Sierra ammo.
If you want the best all in one barrel you should get a 16" chrome lined 1:7 barrel and use anything from 55gr to 80 gr ammo. With a normal aimpoint you won't be shooting for extreme accuracy past 200-300 yards anyway.
What are your thoughts about this? Am I on the right track for the most part? I sure hope so because the next research project I'm going to do is on barrel metal composition.
If your barrel has a 1x12" twist - you are limited to 55 grain ammo.
If your barrel has a 1x9" twist - you can shoot either the 55 grain or 62 grain (actually up to 69 grains reliably)
If your barrel has a 1x7" twist - you can shoot the 55 grain, 62 grain, 75 and 77 grain - even all the way up to 80 grains reliably
As far as ammo choices:
First choice BY A LONG MARGIN would be the 75 or 77 grain ammo it fragments beautifully from point blank out to many hundred meters.
Second choice would be M193 or equivalent 55 grain ammo if fragments reliably from point blank to around 150 +/- meters.
DISTANT third choice would be the SS109/M855 62 grain ammo which is not a reliable fragmenting round at any range.
Once a bullet is adequately stabilized, the riflings' rate of twist has no further influence on bullet accuracy. Light .224" bullets suck for accuracy at longer distances merely because they drift more in the wind.
Other random "facts" that I picked out:
The difference in 55gr in 1x7 and 1x9 is hard for me to see unless I'm using really high powered scopes even then it's pretty nill.
I think the 1 and 9 is just as accurate as my 1 and 7 barrels but most of the barrels that are 1 and 7 are made from 4150 steel and that to me is more important.
Faster twists will show better accuracy with longer bullets.
Longer bullets are usually heavier as well.
with proper ammo selection the 1/7 can accurately shoot 45gr-77+gr bullets!
The U.S. military 62 grain ball (ss109) will work nicely in a 1/9 twist, but also works nicely with the 1/8. The very light bullets, say 55 grain & less, work nicely with a 1/12 to 1/13 twist.
Shorter (which USUALLY means lighter) bullets can be fired in barrels with tighter twist rates than in necessary but longer (which USUALLY means heavier) bullets cannot be shot in barrel twist rates that are slower than what they need. So the most versatile barrel twist rate is one that is tighter as it will shoot all bullet lengths/weights.
My notes:
Quality ammo matters more than twist rate.
faster twist for longer (usually heavier) rounds whereas shorter twist rates are for shorter (usually lighter) rounds.
1:9 and 1:7 are the most popular
1:7 barrel will wear out faster than a 1:9
Longest lasting barrel will be a non-national match, chrome, 1:14 barrel
Best barrel for the best bullets is the 1:8 for the Sierra 69 grain or 80 gr VLD Sierra
A 62gr bullet fired from a 1:12 barrel will start tumbling at 100yds.
When in doubt, try it out.
I've been researching twist rate and accuracy. From what I've read, a 1:7 will handle everything. Lighter rounds may suffer in accuracy but chances are it's less to do with twist and more to do with inferior ammo. A 1:7 will wear out faster than a 1:9 especially when lighter rounds are used (45gr varmint rounds for example) because of the higher pressures.
If you want a tack driver you should get a 20" stainless steel match grade barrel with heavier Sierra ammo.
If you want the best all in one barrel you should get a 16" chrome lined 1:7 barrel and use anything from 55gr to 80 gr ammo. With a normal aimpoint you won't be shooting for extreme accuracy past 200-300 yards anyway.
What are your thoughts about this? Am I on the right track for the most part? I sure hope so because the next research project I'm going to do is on barrel metal composition.