1 in 7 twist + 55g = misery?

First time out with a 1:7 18" NEA DMR barrel in a build I just did (that was the only NEA part) led to great disappointment for me.

Winchester 62grain White Box = Best result, 2-3" groups @ 100m (didn't have much of this and didn't test it at 200m)
PMC 62grain green tip = terrible groups, 12"+ at 100m and even worse at 200m

I've since built a 1:9 16" upper that I hope yields better results with lighter bullets, and I've purchased a wide variety of heavy bullets to test the 18" 1:7 because I really want it to see if it shoots.

I like the idea of having an 18" upper just for occasional heavier bullet shooting, because I like to pretend I'm a DM at the range! :D:D:D
 
I have a weird issue going on with my DA556 norc 14.5".

Its a 1:7 twist 14.5" barrel. I was using crappy norc surplus 55gr 5.56 ammo last week. At 50 yards, I could hit a 3 inch square steel repeatedly. When I moved over to the 100 yard range, the bullets were hitting about 12" high. Does this sound super weird to anyone else????
 
tahw said:
Italian sporting goods/Reliable has a good supply of the Barnaul 62G .223
Click to expand...

Thanks i'll make the trip to see one of those guys. Wish they'd list that stuff on their website.

Edit: Italian does not have the 62g Barnaul in stock if anyone is interested.
 
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Bullets do not necessarily have an optimal twist rate, rather they have an optimal RPM range. To determine the RPM its just muzzle velocity in fps multiplied by 720 and divided by the twist in inches, example 3240x720/7=333,257.14 RPM. The jackets of lighter bullets can tear apart at higher RPM's and that depends on the bullet. A 7 twist barrel is not always needed to stabilize the 77 grain or 62 grain ammo, but it is beneficial with the reduced velocities achieved in a 14.5" barreled AR vs a 26" barreled bolt gun for example.
 
Mauser GDog said:
First time out with a 1:7 18" NEA DMR barrel in a build I just did (that was the only NEA part) led to great disappointment for me.

Winchester 62grain White Box = Best result, 2-3" groups @ 100m (didn't have much of this and didn't test it at 200m)
PMC 62grain green tip = terrible groups, 12"+ at 100m and even worse at 200m

I've since built a 1:9 16" upper that I hope yields better results with lighter bullets, and I've purchased a wide variety of heavy bullets to test the 18" 1:7 because I really want it to see if it shoots.

I like the idea of having an 18" upper just for occasional heavier bullet shooting, because I like to pretend I'm a DM at the range! :D:D:D
Click to expand...

This has been my experience since I got my NEA barrel as well. Shoots 55 grain awful, 75 grain fantastic. 3" at best with 55 grain, 1" or less with 75/77 grain. Hand loads or factory.

These days I'm just loading up my 75 grain for ~20 yards....
 
Well, twist rate is just one factor. The same bullets of the same weight and type made by different manufacturers are different. Even the same ammo made by the same manufacturer can vary from lot to lot. Different barrels will also produce different results with different manufacturers ( of different lots ) of the same type of ammo - weight is just one small factor.

I find this on this internet from this site shootinillustrated, that is done with 1 particular carbine, 5X 5 shot groups:

shootingillustrated.com/index.php/26153/green-tip-accuracy-test/

You can see that, with 1 particular carbine, the average group size of M855 from different manufacturer could range from 1.1" ( PMC M855 LAP ) to 2.1" ( Federal XM855 ) all the way to 3.7" ( winchester range M855)

But this is only with 1 particular barrel, you may get totally different results with a barrel made by a different manufacturer.
 
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