Originally Posted by str8shoot
I bet it is the powder. A faster powder will expand that case faster (before the burning powder comes up the case neck). I think that load actually needs a little more pressure.
Retumbo is a pretty slow powder for the 7 mag. It works well for the heavy bullets. I prefer h-1000 to retumbo and I shoot mostly 160-180s in my 7mags. If I were gonna try some 150s I'd use H-4831, it seems to work pretty well with most weights.
Hodgdon lists a max load of 72.5 gr Retumbo with a 150 partition. I really think you are under pressure with that load, have you tried higher charges of Retumbo? Do you haven't any other powders on hand to try?
As far as bumping the shoulder, I actually had to grind down the bottom of my die to be able to bump my shoulder just .002. I removed enough material that my shell holder wouldn't touch the die when it is set up correctly.
Hope any of this helps.
Str8shoot, I think you may be correct!
Of course, the powder is just part of the question in this "multi-variate" problem.
Yes, i think 68.9 gr is below the max recommended charge for Retumbo (though it is not listed specifically for 150 gr bullets in my Barnes manual), . . . but seems to produce very good velocities, very consistently at 2964 fps (+/- 9). As such, it is a very efficient load, but . . . may be part of the reason I'm seeing the powder fouling on the shoulder and neck . . . especially if these cases have been overworked by 3 cycles of FL resizing with .008" of shoulder movement. I like the Retumbo because it seems to have a bigger sweet spot, in terms of consistent performance in the face of changing temperature.
I have tried higher charges of Retumbo, up to 70.5 gr with 150 gr bullets (and up to 73 gr with 140 gr bullets) . . . but I do not know whether the same shoulder fouling occurred. I will have to look at that again.
I also have IMR 4831 powder on hand, which has also been very good in this gun, and seems to produce higher pressures. So, I think I will try that again for comparison, though the recoil seems to go up while the velocity goes down. (Not as efficient a load.)
I have not tried the H1000. I was planning on trying some VIT N560, but everybody seems to be out of it at the moment. I think it would produce higher pressures, too.
If I can get this powder fouling to go away, I'd be happy to stick with the Retumbo,
so I'll try getting these dies set up to produce just 0.001" of shoulder bump, and I may try annealing some cases, too. I hope this "problem" will go away by getting my dies set up, and reducing the work hardening on the cases.
Naigi, I don't really care what the cases look like . . . so long as they look like they are still in one piece (as opposed to a short piece sitting on the shooting bench, and a longer piece wedged in my chamber). My original question still stands: Is powder residue on the shoulder & neck a safety issue?
I don't have a good feel for when one is getting close to case head separation, though I know a guy who lost a good gun (35-338 wildcat) to it. I don't want that to happen on my 7mm Rem Mag, which I just sunk over $3k into rebuilding.
Jinx . . . I do now! ;-)
Justgoto, thanks for the picture! Know I know a little more about what to look for.
Mikecr, thanks for the note. I think you're right, the brass was getting worked beyond what was necessary for minimum bump, though I need to go back and try to sort out which head space measurements came from which die adjustments. (I may need to just start over, and so am trying to get a press set up here at my house so I can try adjusting the die and making more measurements. I may need to go get more brass and start over, too . . . though everyone seems to be out of Nosler brass for 7mm Rem Mag. I would like to try to stick with the same brand of brass, just to eliminate one more variable, though I suppose I could try another.)
Thanks for all the input, guys!