55 gr or 62 gr ...?

Dave, sounds like you need to do a bit of reading up on barrel twists too. 1:9 is fine for both, a 1:12 is what the original M16's had for 55gr M193. 1:7 is useful if you want to shoot 80gr+ bullets, but usually does fine with lighter bullets too.
 
I've used 40,53,55,62, grain in my 1-9 twist,without any issues. It does like the 53g the best. 55 g is the cheapest to buy,if you use a lot of FMJ.
 
For sport shooting the difference between 55gr M193 and 556NATO 62gr is moot. Look at Winchesters on line ballistics calculator select 250yd zero, comparing the 55grFMJBT to the 62gr head to head in drift and drop to 500 and see there's no practical difference almost ballistic twins, hence why pay more for the coveted NATO round when there's lots of good 55grFMJ's around for practise and marksmanship practise in your favorite AR-15 of any type.
 
55 grainers have shot amazingly well in every 1 in 7" twist I have owned. I am not sure if there is a bad choice between 55's and 62's if you have anything in the 1-10" to 1-7" twist range.
 
I just started reloading for my 1-7 twist in my Colt HBar again after getting lazy for a few years when loaded ammo was reasonable. I tried the 55 gr Vmax bullets and couldn't get much better than 1 1/2 and some 2 1/2 inch groups at 100, I was able to get the 68 grain Hornady match to do .9 to 1.1 inch in my latest reloads.
Probably not a good comparison of the 2 bullet types but my M14S likes the 168 and 175 grain Vmax bullets as much as the Hornady 168 grain match so I was surprised with the AR results with the same bullet type/design.
Rodney
 
BattleRife said:
55gr, because it is cheaper and much easier to find.
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That's right. The 1:9 twist which is the most common on commercial AR's will handle 55's and 62's
just fine, but 55's are widely available. I've got a Bushmaster that will shoot both with virtually identical groups.
If you want to really drive yourself crazy you can read up on minor chamber differences between 5.56 and 223.
I recall an article in a recent Gun Digest (2013?) describing chamber reaming. But, that's for another thread.
Enjoy your AR!
 
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