RL15 in 223; should I be using magnum primers?

[TheGerman]

I'm at my witts end with this. While I can make hits and have hunted with the round, it groups like shit at times and I'm not sure why.

Take 3 rifles with me, shoot the first 2 and have crazy small groups. Shoot the RL15 rounds and sometimes under MOA, sometimes 2 inch groups. I can't explain it.

The only thing I can think of at this point is that I should be using small rifle magnum primers for RL15 in a 223/5.56 case. Or is this just a bust for my setup and try something new? I ran the whole range from 23.5 to 25.0 grains of powder and ES is always somewhere in the 20-30 range, highest S/D was 13.8 with most under 10. What gives?

77g TMK
Federal 5.56 brass, FL sized and shoulder bumped back .004
RL15 powder
CCI small rifle primers

Shooting out of a full spec Mk12Mod1 with the Douglas contract barrel.

 

[Hawk in WY]

What's the twist rate of the problem barrel?

 

[jambau]

I agree. 77 gr is a long bullet. You may not be spinning it.

 

[kd185]

I agree. 77 gr is a long bullet. You may not be spinning it.

X2

 

[Longshot85]

77gr Tmk and Mk12 were designed to work together, as long as the barrel is proper Mk12 spec the twist rate should not be the problem

 

[TheGerman]

77gr Tmk and Mk12 were designed to work together, as long as the barrel is proper Mk12 spec the twist rate should not be the problem

Yep, its the correct contract Mk12 barrel. 18" 1 in 7

I was reading somewhere (cant remember where) that you SHOULD use magnum primers with RL15. Not sure if that was true or not, but after isolating everything else and coming up with no culprit, other than changing powders, I was thinking maybe there was some weird ignition issue going on.

 

[308pirate]

Reloder 15 is one of the bar none favorite 223 powders of NRA highpower rifle competitors. I used it over nearly 15 years and made master with it in 3 seasons.

It is not as easy to tune as Varget and IME likes to be loaded hot. My favorite load was 24.7 of it in Lake City cases lit by a Rem 7 1/2 primer with a Hornady 75 HPBT on top. Works just as well with the Sierra and Nosler 77 gr HPBT, but obviously one would have to work up to it.

All my rifles were Wylde chambered in either 1/8 or 1/7 twists.

There is a ton of experience with heavy bullets in ARs in the highpower world. We, after all, were the ones who drove the idea long before anyone else even dreamed that the AR-15 could be a capable 600 yd performer.

BTW, the Sierra TMK was not around when Mk212 was developed (copied from HP competition loads basically) and whether the barrel is "Mk12" spec or not has fuck all to do with the problems you're having. So long as you have a quality barrel with a 1/8 twist or faster, you can find a spot where any 75 - 80 grain bullet will shoot.

How much are you jumping these bullets? I've never used the TMKs and maybe they are less tolerant to jump than their HPBT cousins. Try Remington or CCI BR primers. Get some Lake City or Winchester brass.

I'd look at your load development method. After trying almost everything I can think of, OCW works the best. Loads that don't seem like they should work based on chrono numbers will sometimes surprise you when you take them out.

 

[-=boone=-]

TMKs are very sensitive to seating depth. More so than a smk, Nosler cc, Nosler RDF, hornady BTHP. You may or may not get them to be reliable accurate.

Find a charge weight they seem to like and start at 2.260 and reduce by .005 increments on depth.