Bob in NH : What is your take on the erratic pressures seen in the 7mm
I've heard/read that it is caused by the shallow neck angle combined with a shortish neck.
Not much different geometry on the MashburnSM, or is it ?
Interested in your observations
Cheers
338:
I haven't seen any evidence of this despite sometimes pushing the cartridge pretty hard. As a WAG I think I have loaded for 15-20 7RM's myself,and been around quite a few others belonging to friends.
The only thing I know about the issue is what I have read. My understanding is that it isn't erratic pressures but wider swings in pressure;I also recall some correlation to worn throats but can't be sure.
In any event I never worry about it.
I can't see what a shallow shoulder angle would have to do with anything. You never hear this stuff about the 264 Win Mag even though I have found that cartridge to be FAR more temperamental at top end, and it has the same shoulder angle.And of course there's the 8 degree shoulder angle of the 300 H&H; and the 17 degree shoulder angle of the 30/06 and 280.
So where is the problem with the 7 Rem Mag shoulder? There probably isn't one.
It's said the longer necks draw heat away from the throat; so theoretically the short necks on the 7 RM and 243 make them vulnerable to more rapid throat erosion. The 300 Win Mag has a short neck, too. You never hear any problems with that.
The 7mm Mashburn has a few more grains of powder capacity and a longer neck. This contributes to more flexible bullet seating and higher velocity. The Mashburn has always been a better design.
But there ain't no flies on the 7 Rem Mag. Personally I would pay no attention to the results they get in ballistic labs and the pressure swing stuff. IME back yard hand loaders are highly unlikely to be affected by any of it.
Most all of us could not identify it if it did happen anyway.
Im sure what they see in the ballistic labs is true but if it were all so onerous, the 7 RM would not be the most popular belted magnum and a Top Ten BG cartridge every year since it was introduced. The rest is just trivial distraction.
