Maximum velocity using 556 with 16" barrel & 77gr bullet

[ronas]

I chronographed some loads yesterday.

Using 77gr Nosler Custom Competion bullets,CCI 450 primer, 24grs. of Varget. Rifle is 556 OBR with 16" barrel. Velocity averaged about 2450 fps. Is that about the most I can expect with a short barrel.

Have only shot load at 100 yards and 600 yards. At 100 yards I shot 20 shot group which was one MOA, as usual I had two that were a bit out or it would have been a little better than 3/4 MOA.

On the 600 yard target I only shot three rounds which I know estabilishes nothing. The wind was only 5mph but it was swirling. Three shot group would have been about 2 MOA.
I needed 19.5 MOA to get there and that with 64 degree temp, bight and sunny and wind mentioned above.

I also shot 20 shot group of 69 Smks at 100 yards and got 1 1/2" group. Velocity was about 2650 using CCI 450 primer and 26.6 gr of varget

[NotEnufGarage]

The load data on the Hodgdon site says 23.7 grains of Varget is a compressed load with a 77gr Sierra seated to magazine length. Since your rifle is magazine fed, you'll have to stick to a COAL of 2.260" unless you want to single feed rounds.

I did find a match for your load on ammoguide.com (24gr Varget, 77gr SMK) for a 20" barrel and it listed 2750 FPS. Same bullet with 23.7gr of Varget shot from a 24" barrel was nearly identical at 2737 FPS. Both of these loads were seated to magazine length (2.260").

You may want to look into getting a different upper with a longer barrel for this type of shooting. You're leaving a lot of velocity on the table with a carbine length barrel, possibly as much as 300FPS. For that kind of shooting I use either a 20" SS 1/8 twist bull barrel or a 20" 1/7 standard barrel. My 16" upper is just for HD or plinking with the light bullets.

I'm going shooting tomorrow and I'm planning to make up some rounds with WC844 to compare side by side with my 3 different uppers to get a feel for the velocity difference between them. I've heard and read that 4 inches of barrel is typically worth 200 FPS, but I'd like to compare for myself.

Your 69SMK loads at 26.6gr is over the Hodgdon listed max of 26.0 which they show with velocity of 3010, so you're giving up 350FPS with the short barrel there. How do your primers look after shooting those? Any flattening or piercing?



Good luck with it.

[ronas]

I'm going shooting tomorrow and I'm planning to make up some rounds with WC844 to compare side by side with my 3 different uppers to get a feel for the velocity difference between them. I've heard and read that 4 inches of barrel is typically worth 200 FPS, but I'd like to compare for myself.




How do your primers look after shooting those? Any flattening or piercing?

Primers look fine, no piercing or flattening. I might note the primer holes are not wearing as new primers go in snugly. Brass is cleaned ultrasonically then tumbled. Please note CCI 450 primer is small rifle magnum primer. Brass is NATO spec LC 556 from 1991

[hiperfind]

With the latesr batch of wc844 from hi-tech, lot # lc 12160, im seeing mild powder perf. With 25.5 gr putting 55gr fmjbt out of my 16" barrel at 2800-2850. Interesting to note too, was that m193NATO ball clocked at 3150, which is only 100fps less than book value for a 20"barrel. My chrony was at 15ft from the barrel. So, this lot of wc844 is probably near spot on for nato charge values of max 28.5gr.