7mm Mag loads

[Clark]

I have had 7x57mm rimmed Norma brass get loose primer pockets when I did not expect.

Usually all brass is about the same for rifles. I got sever lifetime supplies of RP 7mmRM brass once fired from St Marks testing. [I got an amazing deal on Vmax bullets there today. My computer is a fishing pole.]

If I get the chrono to match the Quickload predicted velocity, then the QL predicted pressure is useful to me.

This was QL predicted at 108 kpsi
That is a loose primer pocket.
Don't do that. My VZ24 did not like it and needed valve lapping compound.

I have (4) Bolt rifles I chambered in 7mmRM and (2) factory 7mmRM rifles; Browning 1885 and Ruger #1.

In all (6) rifles I have been running the same load 140 gr Nos Bal Tip 3400 fps QL says is 77 kpsi.

That is a couple grains backed away from change in extractor groove diameter which is a couple grains backed away from easier primer insertion after one firing.

I am soon to build more 7mmRM rifles, and will probably switch to IMR-4451 instead of H4350. I will probably stick with the 140 gr Nos Bal tip, but I could get lucky with Nos 150 gr long range accubonds. I have not got lucky with 142 gr 6.5mm long range accubonds, so hope is shrinking.

 

[Turok01]

The 7mmRemMag was SAAMI registered in 1962 at 61 kpsi and it should have been 65 kpsi.
It was registered at 3.29" over all length and it should have been registered at 3.34".

But that does not go half way to explain why published loads are so wimpy.


There must have been a push to make the recoil less than a 30-06 or one blew up in an executive's face, or some idiot had a job that year, or someone hated Remington, ....... or something.

30-06 loads are not wimpy.

From what I've read on the 7mm Rem the pressures are held lower than most other cartridges because it has larger pressure variations from shot to shot.

I can't recall what the actual variation is in terms of psi, but if it's 3000 psi and your load is running 65kpsi as a max you'll quickly end up in an over pressure situation where you stand to pop primers and or damage your gun.

Pressure variations aren't limited to just the 7mm Rem, many other cartridges have them too, it's just that the 7RM has higher variations.

SAMMI published some numbers on this. Will have to see if I can dig it up.

Neil

 

[Pathfinder45]

It ain't that hard to get 3,000 fps with 150 grain bullets from a 24" barreled 270 Winchester with select powders. Seems like you fellas ought to be able to safely attain 3,200?