Pressure question

[robtattoo]

I think I know the answer to this one but I'm not 100% sure.

I'm loading 77gn TMKs for a .223 Wylde bolt action. Right now I'm loading 24gn of TAC at 2.415" & getting +/- 2800fps from a 20" barrel.
It's too hot. I'm getting cratered primers, flowing along the firing pin & I need to reduce my load. Obvious first option is to drop my powder load & work back up.

But.....

Would loading the rounds longer without touching the lands (I can go out to 2.54") reduce the pressure? I'd really like to stay between 2750 & 2800fps if possible, which means I'm going to be right on the edge, pressure wise at my current length.

 

[Pickettpuncher]

I would drop half a grain and seat them out further and see what it does. Flowing around the fire pin is of little concern for me but if your primer edges aren’t rounded anymore I’d stop there and slowly work back.

 

[SDHNTR]

Assuming you are compressing powder now, backing off the seating depth could theoretically reduce pressure. But getting closer to the lands could also increase it too. I wouldn’t consider this a proper solution for excess pressure.

Primer cratering can also simply happen from too much slop in your firing pin hole of the bolt face. Even without high pressures. I’d look for other signs of pressure too. Ejector marks and wipes, flattened primers. Stiff bolt, web growth, etc.

 

[Molon Labe]

Seating longer will in theory reduce pressure but not enough to make a difference by the sounds of it.

I would change powders.
If you want something with similar burn rate and performance try H4895…plus it’s way less temp sensitive than TAC. Which might be why you are showing signs…did you develop that load in a much colder environment?

 

[Wrench]

Those are easy to get accurate bullets....I'd throttle down and rock on. Typically seating depth changes are good for spread dialing, but to try to use depth as a function of pressure in a rifle....it's fairly insignificant. Flat bottom straight wall cases....absolutely.

Small primer cup thickness can vary from mfrs and if you're on the edge of piercing....then swap primers, nothing may happen, or you may gas cut the bolt and poop your pants.

 

[Tesoro]

Always good to post pic of your hot case heads. You issue is why I just got a 6BR!

 

[robtattoo]

Seating longer will in theory reduce pressure but not enough to make a difference by the sounds of it.

I would change powders.
If you want something with similar burn rate and performance try H4895…plus it’s way less temp sensitive than TAC. Which might be why you are showing signs…did you develop that load in a much colder environment?

Yuuup.
I don't know why I forgot about Tac's temperature intolerance. I built these up in Feb in the 40s. Shot them last week in the very high 90s.
I'm an idiot.