Reducing loads and still overpressure

[shawnb]

Hey guys, i have been shooting my 30-375 ruger and i am having to reduce my loads to keep within the same pressure. My normal load was 80.5 gr of n570 and am now down to 78.5gr. Everything is the same, brass,powder lot, etc.

Ive cleaned everything and still getting more overpressure. Last night i fired 4 rounds waiting in between a couple minutes. And on the 4th shot. My primer was completely flat and had to hit the bolt back with my hand. The first shot had absolutely no flattening and extracted very very smooth.

Im puzzled? Never had this happen.

 

[shawnb]

I will add that bolt lift was perfectly smooth. It just couldnt pull the bolt back like normal.

 

[RockyMtnMT]

May need to aneal the brass. Have you chronographed the load? Is the vel changing?

Steve

 

[lancetkenyon]

Have temps changed since you did load development? Some powders are temp sensitive once you hit a certain ambient temp. RL26 shows no pressure until you hit about 84°. So a round sitting in a hot chamber could be spiking pressure.

 

[shawnb]

Brass is annealled, reduced loads are shooting to the same poi at past 1200 yds

 

[shawnb]

Temps are consistent. And i dont chamber until im ready to shoot.

My one thought is a carbon ring? I noticed on my muzzlebreak that the holes are very fouled with carbon. So much that it flakes off like rust does. I cleaned with wipeout but not sure if that could get rid of a carbon ring?

 

[cjuve]

Might be worth a look with a bore scope

 

[NW Hunter]

I found my carbon ring by noticing my base to ogive measurement got shorter.

 

[dok7mm]

You can run your cleaning rod in the bore, then attach a new brush at the brake. Pull the brush, from muzzle to chamber slowly, but same amount of pressure. You should notice a tightness, that tells you where the carbon build-up is located.

I would strongly suggest you have someone knowledgeable scope your barrel. Just because a patch comes out clean means nothing as to how clean the barrel is. It usually just means your solvent of choice isn't softening the carbon/copper enough to stick to a patch. JMO

 

[tankgijohn72]

Barrels speed up over time, especially with a large overbore. You will likely see what looks somewhat looks like alligator skin in the throat area if you boroscope it. The larger the overbore, the faster the pressure/velocity climbs. I haven't ever worked with a 30-375, but spent a lot of time with the 300 Norma Mag. Pressure/velocity climb can continue into well into the hundreds of rounds. So, the approach you have taken by dropping back your powder charge is pretty much the only thing you can do.

 

[Pdvdh]

Hey guys, i have been shooting my 30-375 ruger and i am having to reduce my loads to keep within the same pressure. My normal load was 80.5 gr of n570 and am now down to 78.5gr. Everything is the same, brass,powder lot, etc.

I've cleaned everything and still getting more overpressure. Last night I fired 4 rounds waiting in between a couple minutes. And on the 4th shot. My primer was completely flat and had to hit the bolt back with my hand. The first shot had absolutely no flattening and extracted very very smooth.

Im puzzled? Never had this happen.

Hornady brass?
Is the barrel melonite treated?

 

[Lefty7mmstw]

I'd guess you are getting carbon buildup, whether a "ring" or simply filling the grooves in the throat is a moot point. You've got to scrub the dogcrap out of the overbores once in a while to get the carbon out if you don't keep up on it. I've had a few rifles start running over pressure like you are stating; every time it's been a throat issue and usually carbon. You may even have to go to JB's bore paste to scrub the crap out.

 

[gohring3006]

I'm in the carbon ring camp.

 

[tankgijohn72]

It is possible that there is a carbon ring present. But barrels do increase in pressure/velocity over time. I JB borepasted (heavy scrubbing, tight fitting patch)a barrel every 100 rounds until 500 rounds. Pressure/velocity climbed continued throughout the duration. All same ammunition, no reloads.