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Posted: 1/29/2011 2:38:27 PM EDT
I will primarily be shooting either 55 gr or 62 gr out of my rifle. What do you all recommend?
Link Posted: 1/29/2011 2:40:34 PM EDT
[Last Edit: 1/29/2011 2:42:38 PM EDT by FMJ]
Originally Posted By BrunBrun:
I will primarily be shooting either 55 gr or 62 gr out of my rifle. What do you all recommend?

1/7 can do about everything

I shoot 45 to 77gr

I like 1/7 & 1/8

BTW 1/9 might not be able to shoot heavy 75/77gr bullets accurately
Link Posted: 1/29/2011 2:41:59 PM EDT
1:9 is better with .22 conversion kits
Link Posted: 1/29/2011 2:43:03 PM EDT
Link Posted: 1/29/2011 2:51:01 PM EDT
Originally Posted By jwb47:
look here

Exactly what I was looking for

What bullet weight can I shoot in my (1/9, 1/8, 1/7, etc.) rifle?

This is undoubtedly one of the questions that is asked the most. The answer depends on many things, but here are some rough guidelines for those that don't care about the details:

1-in-14"55gr or less
1-in-12"35gr up to 55-60gr
1-in-9"45gr-75gr, possibly up to 77 if you're lucky
1-in-8", 1-in-7"45gr - 80+gr
To find out for sure if your bullet will stabilize a given bullet which is on the fringe, you'll have to try it out in YOUR rifle. Some people's 1/9 can't stabilize 75gr bullets, while others can get away with 77gr bullets in theirs. Technically, it isn't about the WEIGHT, but the LENGTH of the bullet, as well as air density and velocity. A simplified method for determining the minimum rifling twist rate for a given length of bullet is given by the Greenhill formula. A Google search will show many sources for those interested in a more in-depth discussion. If you have the length of your bullet, and just want a look-up table to see what twist rate you need, refer to this page. If you really enjoy the in-depth mathematical treatment of the subject, check out these pages.
Link Posted: 1/30/2011 6:54:26 AM EDT
1/7 is what all the military M4's are chambered in , if having a "correct" battle rifle is important to you. 1/9 seems to be a much more common civilian chambering ––-

I dont shoot expensive 75 or 77 grain bullets, so its not an important issue for me, like yourself, most everything i shoot is 55 or 62 grains. Neither the 1/7 or 1/9 are any better or worse than the other in my rifles with those bullet weights (i have both, but in different configurations) It becomes much more important when you are shooting at the extremes in bullet weight

That said –– when i think i need a 75 to 80 grain pill, then that is usually a sporting application (for me) and i grab a different rifle chambered in .243. That heavy a bullet out of a 16" barrel is too slow and has too much drop (again –– for my use , others like 'em though)

Others said 1/9 works well with .22 conversions, but going a step further still, an old 1/12 M-16 upper i have works even better for that –––– but then again, considering the price of an old M-16 upper plus a conversion kit –– its almost easier to buy a dedicated barrel for that use anyway if you want ultimate .22 accuracy.

Link Posted: 1/30/2011 7:18:18 AM EDT
Originally Posted By InfiniteGrim:
1:9 is better with .22 conversion kits

+1 This is pretty much what I go by.
1/7 better for 69gr+, 1/9 better for <55gr and .22 conversions.

For example I sold a used 6520 1/7 barrel in favor of a new BM superlight 1/9 barrel for my gf's build since she'll only be shooting 55gr/62gr and .22 conversion.
Link Posted: 1/30/2011 7:30:25 AM EDT
[Last Edit: 1/30/2011 7:30:25 AM EDT by Zhukov]
AR15 Discussion FAQ, entry #3.
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