Thread: 7mm RM rechambering

Hi Grimus,

This is a great idea and I hope you pursue the project and post pictures of your progress. Do have a chat with Kiwi Greg as he has a 7mm 300NM reamer that could make your life easier.

The previous statement that a .30 cal would do better in wind doesn't mathematically stack up when you compare a 300NM running a 230gr Berger Hybrid @ 2934 fps VS a 7mm 300NM running a 195gr Berger EOL @ 3150 fps. In a full value 12mph wind from 3 o'clock with a density altitude of 0ft (sea level) you will have the following holds (excluding aerodynamic jump, spin drift, etc):

300NM @ 2934fps
1000m: 7.60mils up / 1.85mils R
1500m: 15.50 mils up / 3.24mils R
2000m: 28.03 mils up / 4.96mils R

7mm 300NM @ 3150fps
1000m: 6.42mils up / 1.66 R
1500m: 13.08 mils up / 2.91mils R
2000m: 23.68 mils up / 4.56 mils R

MV's are close to actual. You can possibly ramp MV in both up but intent here was to compare apples with apples as much as possible. I'm not sure what barrel length you are running but have a chat to your gunsmith on what will work best for your 7mm wildcat.

Lastly, make sure you have good glass with the required elevation capacity and rail.

Cheers,

JT

Some good advice above.

T3s are great donors for custom or semi-custom builds, but not ideal for magnum cartridges. The action is not really strong enough, the magazine is too short, the barrels too thin and the recoil too stout. The max OAL you will be able to extract an unfired round is 3.5” in a T3.

As others say, the ELD-M 180 in your 7 RM would be the go, but you will need to forget mag feeding. Powders like RE26 and 33 will fix you up. If you want to go .30 cal you will need to be in the 230+ grain projectile range to match the 180s and recoil will be stiffer.

Do you have a reason for wanting a non-belted magnum? I keep reading about blokes who want this but they rarely seem to know why other than reading that belts are superfluous. A belt is not an issue at all and the case only headspaces off it on the first firing anyway.

It’s your choice and you should have what you want, but the T3 isn’t the best choice for your project.

BTW - I have a T3 based .300 Win Mag and it’s good, but not ideal.

.......... and talk to Kiwi Greg. He has a huge variety of 7mm ways to deplete your bank account.