Thanks for all yalls help.
But I am not sure I'm on the same page so I am going over everything up to now.
Original load
Lapua brass-140 AB 77.5gr IMR 7828 Fed 215 primers
3350 FPS
started working loads with Win Brass and new lot of powder
groups came together with 78.1 gr IMR 7828(Hodgdon)-140 AB---Winchester brass---Fed 215 primers
3480ish average fps after fouling
No heavy bolt lift --no brass shaving off base, only slightly flattened primer
The Winchester brass I am using now is 56.8 grains lighter than the old lapua brass.
My ? is wouldnt the lighter case mean more case capacity allowing more poowder with the same pressure
At this point I am somewhat confused so thanks in advance for your help
Steve Eggers
Steve: I won't pretend to know the answer
sort of a stumper for me for sure.....we would expect that the lighter brass would have more capacity but this may not be so, and the only way I know to be certain is to measure the capacity of both types to find out.
Another issue might be maybe the WW brass is harder,and construction different...it might (emphasis)be able to withstand higher pressure than the Lapua,but since I have not worked with Lapua brass, I really don't know.
You note that you changed lots of powder...this as much as anything would give me pause,as it is not unusual for powders to vary in the velocity they will give from lot to lot.....so you changed two parts of the equation....brass, and powder lots,and either could result in the velocity(pressure) increase.
If you have a 24" barrel I would be a bit skeptical of the velocity......that seems like a lot of vel for a 140 from that case, and while I have not yet run 140's in the Mashburn, I have in the 7mmDakota with RL22 and hit a pretty comfy 3350 in a 24" Krieger,about what you got with the old brass.
I believe the Dakota, the Mashburn, and your necked down 300WM are very close in capacity, so if I saw that velocity in a 24" barrel I would back off and check accuracy again.Those cases might not show signs of high pressure on the first firing, but could be up around the ragged edge...so if it were me, I would run the test again with a charge giving about 3350 again, and see how it shoots and if accuracy and groups come baxck to where they were..
I would not rely completely on the traditional pressure signs in what is likely a custom tube and squared up action, like Johnny B has taught many of us on here; plus you are dealing with a wildcat so best to approach conservatively, fire cases and check primer pockets on subsequent reloads with the same brass.
I'm afraid this does not answer your question, because I really think it would take a lab technician and pressure equipment to give a real accurate answer. For us, working with wildcats of this capacity, I think we are better advised to stay cautious and watch the chronograph for warning signs.
Hopefully others better able to answer will chime in....
