Issue with AR zeroing

Thread starter #1

CassGA

Senior Member
I have a Sig M400 with a 1:7 twist. I have 55 gr .556 FMJ that i have been shooting through it and cannot get it to group at 100 yards. At 25 yards, Im getting sub 1/2" groups. However, if i back up to 100 yards, they are all over the place, with no consistency. Attached is a picture of my grouping at 100 yards. This is from a bench. I have tried 3 different brands of bullets and two different scopes, all with similar results. Are the 55 gr too light? Im going to pick up some 62 gr to try. I understand the twist and that a heavier bullet benefits from the faster twist, but I also was of the understanding that 55 gr would be fine with 1:7. I hope the heavier bullets help but hate that i already have 500 rounds of 55 gr. Any other ideas? Thanks
 

Attachments

ringorock

Senior Member
I suggest you shoot some more weights then come back looking for answers. 55 gr should be ok in a 1/7, but you just never know. What scopes were you using. What mount? What rest? Trigger weight? We can't help you until you run gamut and provide more info.
 

transfixer

Senior Member
55gr can be okay with 1-7 twist, but will likely never be as accurate as heavier rounds, 55gr is ideal for 1-9 twist, and 1-8 is considered a good compromise allowing you to shoot both the 55gr and the heavier rounds, up to about 70gr with acceptable accuracy, some of it depends on how fast the 55gr loads are running, loaded for maximum fps they prbly won't group well, ideally something 62-69 gr will shoot best out of a 1-7 twist
 

transfixer

Senior Member
A lot of AR manufacturers are using barrels with 1-7 twist, I guess because that is currently what the military is using, and the military is using 62gr or 63gr rounds, but in the aftermarket the cheapest ammo is .223 55gr ,, not 5.56 62gr, and there is a difference, the 5.56 stuff you have will be travelling faster than an equivalent .223 55gr load, as the 5.56 is loaded to higher pressures . you could try some .223 loads and see what you get ? but the heavier rounds will be the most accurate I'll bet
 

Knotwild

Senior Member
FMJ stuff probably won't shoot very well. In fact most of the manufactured ammunition I have tried in ARs hasen't done well. I did have great luck with 77 grain Sierra Match King commercial ammunition, but it was in a JP rifles 8 twist barrel. It was SSA, but I don't see it listed on the Shooters Pro Shop site today.

If your barrel is marked 5.56 then try 5.56 ammunition in it. If .223, then try .223.

There are tons of different weight bullets and brands out there. About all you can do is check off the list of things like the trigger, is the gas tube touching the receiver where it enters, etc. Then start trying different brands/weights of ammunition. If you find one that works well, buy a thousand.
 
The 1 in 7" twist in our gun safe blows up full power 55 grain loads. 55 grain loads shoot very well in our 1 in 8" and 1 in 9" rifles. As others have said, 77 grain match bullets are your best bet. SMKs are the bees knees, but some of the other ones can also shoot very well out of fast twist ARs.

But I usually recommend trying a box or two before committing. Send me a PM, I may be able to give you some cheapo boxes of 77 grainers to try.
 

bfriendly

Senior Member
Seems we have all been through it f you got the new and popular 1:7. Mine no likey 55 gr, but loves 69s or pretty much anything thereabouts. You’ll have a smile in no time👍
 
Top