20” barrel 6cm pressure issues
- Thread starter PRCDEATH
- Start date
Are you in the rifling? What is your speed? I run 107smk, 42.2gr h4350, cci200 in hornady brass(leftovers from factory ammo). Mine is running 2995 in a 22" proof
That is interesting. I just finished a 6 creed work up a little while ago a good bit higher with H4350. Finished at 42.1 and tested to 42.7g with only slight ejector swipes. Still easy bolt lift with no other pressure signs. Same bullet but Alpha brass. My only thoughts are maybe tight chamber and also re measure the distance to lands and loaded rounds to verify you are truly off the lands.
105s in a 20" getting 3080, I know why you're seeing pressure. Can't remember charge, but re16 in lapua with 105hybrids in a 20" ai barrel is 2950, and it's a warm load.
First thing I would do? Bore scope your barrel and see how dirty it is. My 6 CM speeds up with the increased pressure from about 3080 to 3150. Seems to happen right around every 250-300ish rounds and then requires a decent cleaning. My buddies Savage with the factory barrel was even worse, 100-150 round cleaning interval, and his velocity would spike from 3020 to 3140 and he would blow primers. Not sure about your rifle, but the Berger Hybrids dont need to be that close to the lands to shoot well. I run the 105 and 109 Bergers 20 thou off the lands, but Ive seen guys run 60 thou off with no issues. Sometimes being too close will give you pressure signs.
Myself? Im 3080fps with a 109 Hybrid, 41.2gr of H4350, Peterson brass, 20 thou off the lands, CCI BR4 primer from a 22" Rock Creek 7 twist. No pressure signs, but when the barrel gets dirty the velocity spikes, I see heavily flattened primers and accuracy goes out the window.
OPs jump is 30 thou(.03) or I'm completely retarded. I usually run 105s @.020/20 thou off. If your velocity is correct, 3080, that load is damn hot in a 20" barrel. I'd be ecstatic with 2950- 3000 in a 20" barrel. I'd cut your charge and find another accurate node in that range. Hot August day or smoked bolt face will ruin your day. 80fps doesn't make much difference in wind hold, with same bullet. Maybe .1 at 800-1000yds, not enough to play with fire.
Nope not retarded. I misread that thinking 3 thou.
My biggest concern is that he is seeing pressure at sub 40gr. That should not be the case with any 6CM. Im pretty average right around 41gr with all my 105-109 loads for Bergers, and Sierras with no pressure signs. I've seen guys take a 105 over 42.5gr with no pressure but that is a barrel killer.
Generally I'd agree about charge weight, but if he's actually getting 3080fps in a 20", he's making pressure somewhere to get there. OP, what chrono are you using and is it accurate or dope verified at 600+yds? If it were mine, I'd cut powder to be in the 2950fps range and retune for accuracy.
What brand barrel was used?
How much neck clearance? Already been asked but I didn’t see an answer.
Have you used same lot # of H4350 in any other cartridge to verify burn rate? I’ve some lot #s of H4350 be be appreciably quicker than “normal”.
