Some words of advice. Like Swamlord says. Go for the 300 NMI. Or the 338 NMI. The 7 is way to finicky and touchy with a negative investment to rewards equation. Having worked on the cartridge for 10+ years and refusing to submit to the obvious we kept at it. Many reamer design changes (6) were made in efforts to find the "best" way to make it work like we dreamed. When Lapua brought out brass things improved somewhat but we had already been using 423 Dakota brass made by Lapua so we had already reached the limits of the designs we had in reamers.
Things became very apparent after hundreds of rounds and numerous barrels burned. Yea stubbornness played in a lot here.
Here is what we found. The 200 wildcats went away so that left the 195 Berger's.
The 195 Berger's will not stabilize at high speed. Once speeds go over 3250fps this bullet goes crazy. Groups open drastically. 8 twist and 8.4 twist both. 26 inch long. Keep them at or under 3250 and it's a one hole tack driver. Copper fouling in the barrels (Proof Research) was horrible at the upper speeds. Other bullets were pushed over 3400 fps. The Hammer hunter in 177 grains was a winner in the lighter 180 class bullets but with its BC is a long range deterioration game. Past 1k really had problems with wind. That's enough there for another thread somewhere. 180 hybrids started to vaporize out of the barrels at times at 3250 fps and above. 180 eldms are just to explosive at under 500 (tested in a 7saum at 3030 fps at the muzzle. 4 elk and 2 deer from 400 to 630 yards) with the velocity they could be pushed to in this case so we didn't use them. Maybe the 190 Atips will perform better?.
Also when things got above the 3250fps range the rifle began to have drastic torque added into the recoil which added to accuracy issues.
These rifles are 10 pound rigs designed for hunting.
Powder selection is limited for this highly over bore hotrod. Retumbo,RL33 and N570 being the 3 most able to give these velocities with the heavies. Add RL26 for the 180 weight class. Tested 8133 and LRT with result that were not what we needed. 50bmg gives slower velocity and it runs out of case capacity before pressure is reached.
RL33 was to erratic with temp changes!
Then we found that N570 caused rapid throat erosion in the 7mm bores. One barrel was toast in 200 rounds. So now N570 is out on the 7 bore size for us now. Side note is in the 30 cal it performs without the throats being melted so far.
I believe the 28 Nosler is at the tops for case effectiveness and use for the 7mm bore.
When this barrel burns out On my 7 it's going to have the 30 version put on it. 230 Berger at 3200fps is serious elk medicine.
Just my 2 cents from experience
