I have searched this site and reviewed the Ammo Oracle information but can't find an answer to this question.   I am shooting a M4A3 with a 1 X 9 barrel twist.   How much difference in accuracy will I notice between a 55 gr and 69 gr.?  I have been shooting 55 gr and have had difficulty getting good groups (could be me)    I was reading that the 1 X 9 twist is more optimum for higher grain ammunition.  Does that mean 55 gr will not perform well in that barrel?

Thanks in advance.

No. 1:9 is the sweet spot for ARs in terms of accuracy but it's achilles heel is that very heavy bullets (70+gr) don't stabilize with a 1:9. 69gr?? are you referring to 69 or the popular 62 gr? I would not fire anything heavier than 62 grain through a 1:9 barrel if accuracy at distances was necessary.

What kind of ammo have you been shooting?  If you have been shooting 55 grain wolf or xm193 then switch to say Federal Gold Medal Match 69 grain SMKs you should see quite a difference.

Test results on my 1/9 twist, 18" JP barrel shot at 100 yards with three shot groups are as follows:

- Hornady Vmax Moly 40 grn. bullets grouped 3/16"
- Hornady Vmax 55 grn. bullets grouped 9/16"
- Sierra 69 grn. BTHP match bullets grouped 5/8"

Conclusion:

1/9 twist barrel will shoot 40 grn. to 69 grn. with acceptable accuracy.

Hope these facts help you.

The one in nine is fine for 69 grain bullets....no question. I have been using them for many years to shoot varmints out to 500 yards. The same rifles shoot bullets as light as 45 grains very accurately. Some one in nine will shoot 77 grain bullets but not all one in nine will. The SMK 69 grain bullets have 7-10" twist barrels only stamped right on the box. The only way to really know what your rifle likes is to try some and see.