6.5x284 RL 26 Pressure question

[L. Perry]

I am stumped. New Bartlien barrel on a Surgeon xl action.
This is the 6th barrel on this action all 6.5x284 Norma.
I have been reloading precision ammo for 30+ years.
So here is the problem, Brand new Lapua Brass all the same lot, 8 lb. jug of RL26, Same 500 count lot of Berger 140 hybrids, Same lot of 210M primers.
Worked up an excellent load of 55.5 grs of powder 30 thou off the lands, Under .50 of an inch at 200 yrds. No pressure whatsoever, Shot 200 rounds with that load at 3150, extreme spread of 8 for a 10 round group. No trouble out to 1000.
Prep all the brass, neck size only with .002 neck tension, load up 10 to make sure everything is cool. Shows pressure, hard bolt lift and some ejector marks. Doesn't shoot for shit either. Always calibrate chargemaster before I load and let it warm up. What is going on? I am baffled, not that that is that hard to do!

 

[L. Perry]

It is not the dreaded carbon ring either, Cleaned it and checked with the hawkeye.

 

[Supersubes]

How fast is it going with the now once fired brass?

 

[L. Perry]

Didn't have time to chrono it today, Impact was all over so can't go by that either, May have time toward end of week to chrono.

 

[Supersubes]

So did you run through 200 pcs of virgin brass, and now the same load you developed in virgin, you’ve loaded in the fired brass? That’s how I read it. If so, the fired brass produces more pressure than virgin. It’s a little counterintuitive, but this is a typical situation. You know the gun likes your components, just do a small charge work-up to get back to proper pressure/accuracy.

 

[Steel head]

So did you run through 200 pcs of virgin brass, and now the same load you developed in virgin, you’ve loaded in the fired brass? That’s how I read it. If so, the fired brass produces more pressure than virgin. It’s a little counterintuitive, but this is a typical situation. You know the gun likes your components, just do a small charge work-up to get back to proper pressure/accuracy.

I’ve had this happen a few times.

That’s why I never look for a pressure limit with virgin brass.

Narrow ladder or whatever testing regimen you use below your current load and you should be GTG.

 

[L. Perry]

I am going to try that, just never had this happen before. Went up to 57 grains with an 10 thou. jam before I hit pressure. Also going to try my old load of N560 in the once fired brass and see what it does. Don't really know why I just didn't stay with that worked really well for 7000 rounds.