300 rum pressure problem??

[Snootch]

I have a savage with the muzzle brake that can be turned on or off. I took it to the range the other day to work up some test loads. I settled at 99.5 grains of RL 33. It showed no signs of pressure and shot under .5 moa at 100 yards. Today I took it out to chronograph and check groups at 300 and I had a little bolt lift and casings showed some signs of pressure. I went home pulled some bullets and re weighed, still at 99.5. Nothing has changed and temperature was a couple degrees cooler today then last time. The only thing that I know I did different was had my ports closed on my brake for there was someone shooting right next to me. Could that cause an increase of pressure?? I won't have time until next weekend to test. Would like to see what you guys think...

 

[Barrelnut]

How did you prep your brass between trips. Full length resize? Neck only? Trim neck lengths, etc?

Sounds like the necks may have grown past spec. or maybe seating depth of the bullet changed (intended or not). Seating bullets closer to the lands can increase pressure.
Also an oily chamber can beat the brass up.

 

[Snootch]

Brass is from the same batch that I got ready for loading , size, seating depth everything is right on. I can't understand what changed.

 

[screech]

I don't know why your pressure would change but I would try h1000 in it. Every ultra mag I have ever dealt with shoots h1000 well. Weather it be with a 180gr.nbt up to a 230gr.berger they all seem to like h1000 just my experiences with ultra mags and I'm not saying I know everything about them but I've owned 6 in the past and helped out around 4-5 more with there's