A little stumped load development virgin brass vs once fired

[ripzip]

Ok so I was working on a load with virgin brass for my 6.5 PRC. Found a good node at 3125 with 153 Atip, 60gr of Retumbo, and Winchester Mag primers. Prepped my 1 fired brass I dropped down to 59.5gr and immediately got pressure signs, heavy bolt lift ejector marks and flattened primers. Went home and decided to start my load work up again. Now I get pressure signs with anything above 57gr of Retumbo and velocity only 2970. Barrel is clean with no carbon ring, checked with bore scope. I'm stumped as I was really happy with 3125 but now my good node is only at 2950. That's a big drop in velocity.

 

[nksmfamjp]

I'm stumped. There is missing information, but I don't know what it is!

 

[Shane Lindsey]

Virgin cases will mask pressure as they form. You dropped half a grain, that usually helps it.

I have a 7mag that does this too. Load dev seems to be waaaay different between virgin and fireformed cases. Just have to start low again.

How do you think Norma gets away with factory loads so hot?

 

[ShtrRdy]

Would you happen to be using a different lot # of bullets or primers?

 

[sextonds]

I know it's hard to do these days due to short supply of most components, but if possible, I usually try to do load development with fireformed brass. I'll typically (but not always), fire 50 rounds as a break in while playing at the same time, then start load development with those cases

 

[sextonds]

I also have guns, that fireformed or virgin, they still yield the same result

 

[orkan]

3125 with a 153 in 6.5PRC is insanely hot. Be happy with 2950… because even that is not a slow load. When you're pushing brass that hard, you're bound to lose velocity.

 

[nksmfamjp]

Well since Hodgdon lists 56gr at 2822fps as max, we are all lucky you are here posting about it!

 

[rem.xp100]

Another thought might be what you used to read your speed. I fully trust the Magneto and Labradar but no longer believe most numbers I used to get with a Chrony.

 

[tonyf3]

How many rounds do you have on the barrel.. has it sped up yet?

I have a 7mm that shoots 160 partitions. Virgin brass and new barrel was 70.5 grains Retumbo @3015 fps
2nd/3rd fired brass I had to back down to about 69 grains and velocity was about 2950-2960. 69.5 was too much pressure.
After about 140 rounds and the barrel sped up i had to back it down to 68.8 and velocity settled in about 2960-2970.

 

[LongBomber]

What are your pressure signs? Stiff bolt lift with a click on top?

 

[ripzip]

Well since Hodgdon lists 56gr at 2822fps as max, we are all lucky you are here posting about it!

That was what I thought to. Initially I was only loading to 56.5gr. Then I also had some Berger 153.5's. Called Berger and they told me 57.0 min to 63.3 max Retumbo, I thought the guy was on Crack called back another day and talked to a different guy he told me the same thing. Told him that the case will not hardly even hold 63.3 he said that it was a compressed load. I actually got to 62gr before pressure signs on the virgin brass. That is when I decided to tried pushing the A-Tips a little more and came up with the 60gr load for both the Bergers and Hornady bullets.

 

[ripzip]

What are your pressure signs? Stiff bolt lift with a click on top?

At 57gr I get ejector marks on brass, starting to get a little bolt stiffness.

 

[WildRose]

Ok so I was working on a load with virgin brass for my 6.5 PRC. Found a good node at 3125 with 153 Atip, 60gr of Retumbo, and Winchester Mag primers. Prepped my 1 fired brass I dropped down to 59.5gr and immediately got pressure signs, heavy bolt lift ejector marks and flattened primers. Went home and decided to start my load work up again. Now I get pressure signs with anything above 57gr of Retumbo and velocity only 2970. Barrel is clean with no carbon ring, checked with bore scope. I'm stumped as I was really happy with 3125 but now my good node is only at 2950. That's a big drop in velocity.

Checking the load data I can find with the 153 You're probably going to be considerably over pressure at 3000fps so it looks like you're back into pretty reasonable pressure/velocity range.

The 6.5PRC was never meant to be a screamer, just a good solid performer between 2,850 and 3,000FPS.

I'd say you're lucky to not have seriously damaged your rifle or worse, yourself.