I've heard that 55gr. ammo is better suited for 1/8, 1/9 twist barrels. Is it correct that accuracy is not optimized shooting 55gr. through a 1/7 twist barrel? What are the pros/cons to it?

Technically speaking 55gr might not be optimized in a 1/7 twist but really it should be fine. Even 50 grain bullets shoots very well in my 1/7 twist barrels. 55 is usually what I shoot.

1:7 Twist shoots 55gr just fine.

One of the best 100yrd groups I've ever fired was 1:7 hornady VMAX handloaded with Win748 powder.

52gr match rounds will also shoot very tiny groups.

1:7 can also shoot 77gr bullets which are the choice for long range shooting, or killing things.

typically 55gr FMJ is not going to shoot tiny groups in any rifle


imagine these winchester turds snipping towards your target...

Yes.

It works.

Well good, because American Eagle M193 is cheap and plentiful, and that's what I've been shooting. It's also what I stock up on. Can't see paying extra for M855.

My 1:9 S&W shoots 50 and 55 grain more accurately than my 1:7 and 1:8, but the 1:7 and 1:8 shoots it just fine.

all barrels like different ammo. Buy a 20 round box or two and try it.

It depends on how fussy you are.  I have a DDM4V5 with 16 in 1:7 barrel. All I have ever shot out of it is 55 gr FMJ.

At 50 yds I get all rounds into a 1 inch square.  At 100 yrs the group is smaller than my fist (about a 3inch group).  At 200 yds its smaller than my open hand (about 6 inch group).  All "A" hits on IDPA type of a target.

I'm using PMC and IMI M-193 55gr FMJ.

Most every weight of bullet should shoot well in a 1:7. It may not be the most ideal twist rate for the 40 and 45 grain bullets but as long as they don't have paper thin jackets designed for .22 Hornet velocities you should be fine.

Actually 1:7 isn't "ideal" for anything you will be shooting through a typical AR15.

Nothing that you can load to magazine length needs faster than a 1:8. The M855 that the OP mentions is best in a 1:9.

Typical lead core 55gr is best shot in a 1:12. There are some extreme examples of thin jacketed lightweight bullets that can self destruct in flight due to excessive rotational speed from 1:7 twist - it's happened to me.

The faster you go, the more eccentricities in the projectiles as well as gyroscopic effects become pronounced.

That said, it's a statistical measure and many/most will never be at the level of performance or ranges where those effects become noticeable in individual examples.

With large numbers of examples however, the differences can be detected. Take for example the original M16A2 design process where M193 failed accuracy specifications with 1:7 twist. Or much later when Colt swapped out a few thousand 1:7 barreled rifles for 1:9 for a large metro police department that couldn't get consistent accuracy with their 55gr duty load.

For general use, range plinking etc it will be fine. For any serious use you need to be using something better anyway, and you can test it beforehand in your particular barrel and see how it does.

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