7RUM Pressure

[ptpyron]

I have recently had my Remington XHR 7mm RUM chamber shortened to accomodate loading Berger VLD's. I had to have this done due to the factory chambering left my bullets a whopping .467 from the lans and grooves. Dennis Olsen of Plains Montana did the work and explained this left little to no room for error on my loads. My question is by shortening the chamber and allowing my bullets to rest a mere 0.0010 off the lans and grooves, how much increase in pressure will I have? If I load with Retumbo powder @ 84 grains for the 168 vld's what would this be compared to the max saami load?

Rifle info:
Remington XHR 7mm RUM
barrel removed and shortened .467 from the chamber end
shooting Berger 168 vld's with Hogdon Retumbo powder
COAL of 3.668

Hope this makes sense....

 

[rscott5028]

The only way to know if it's safe is to back down to a minimum powder charge and work up safely.

If you seat bullets that close to the lands in a hunting rifle, you may want to measure the OAL of every cartridge to be sure you don't get one too long and stick a bullet in your chamber spilling powder everywhere when you have to eject a live round.

-- richard

 

[ptpyron]

Thanks, yes I do measure every round for that reason. I guess the real question I was trying to ask was, Can the size of the chamber effect the pressures to where 85 grains in one rifle may yield 2900 fps and in a different rifle the same charge yield 3100 fps?

 

[rscott5028]

Thanks, yes I do measure every round for that reason. I guess the real question I was trying to ask was, Can the size of the chamber effect the pressures to where 85 grains in one rifle may yield 2900 fps and in a different rifle the same charge yield 3100 fps?

If you modify the chamber, throat, lead angle, jump, case volume, etc... the pressure will change. If the pressure changes, the velocity will change.

I would not expect it to make a 200 fps difference based on the info you provided. But, I don't think any of us here know exactly what was done to "shorten" your chamber/throat.

-- richard