338 Lapua Magnums and 300 Grain Sierra bullets
I've made a lot of these guns. By a lot I mean over 200 in a range of different configurations. Sporting, Competitive, and Tactical.
The 1-10 twist barrel gets the job done reasonably well with 300 grainers. A 1-9.7 twist does it even better.
Personally, I encourage you to use 225-250 grain bullets if your shooting anything slower than a 1-10 for a twist rate.
The throat becomes an issue as well.
To get the velocity from a 300 takes some aggressive loading. This means a high load density if done properly. The 300 is not a magazine tolerant bullet when seated with the boat tail/bearing surface junction just above the neck/shoulder junction on the case. Not in a TRG magazine anyways.
These are the same magazines used in the Dakota Arms, Inc "Scimitar" sniper rifle. A gun I played a significant role in developing and producing for the Royal Jordanian Special Operations Command in 2004-2005 when I worked for Nesika/Dakota as a production manager.
The throat will more than likely become your limiting factor because the bullets will jam into the lands long before the case is shouldered up against the chamber; making for sticky bolts and high pressures. Not good on an already high pressure (62,000 cup) magnum cartridge already stoked up to the high side of a reloading manual. This condition will force you to back off the load and seat the bullet deeper into the case. All counter productive to the advantages of the 300 grain SMK. This is why I advocate the 250's. They run in the gun better and still shoot extremely well.
I found best accuracy by jumping the bullets. Not much, only .005-.010. This was on a gun chambered with a PTG reamer set up with a 1*30" throat angle specific to the 300 grain sierras. Loading them with the bullets sticking out a ways also puts the bearing surface in contact with the bore, right where it should be.
The 250's were also chambered reamer specific and the load used there was factory loaded Black Hills red box with Lapua and (in the early days) Norma brass.
Now, the exception to some of this is when we had another reamer made for the 300's set at a magazine tolerant depth just to try it out. The guns were "ok" but because the velocity was down a bit and (my personal opinion) because the barrel's twist rate was 1-10 instead of 1-9.7 the accuracy just wasn't quite as good as when we stoked up the loads and ran them further out.
Expect recoil to increase a bit also. The sniper rifles didn't have muzzle brakes or any other type of recoil reduction device. A few rounds are more than tolerable on a 12-15lb gun but go prone supporting the rifle only with two hands, a sling, and a shoulder and it'll wear you out after a couple magazines.
As far as accuracy goes, I was able to hold a rock solid 1/2 of a minute on a 10 shot string supporting the rifle from a slung in prone. I never shot them off bags or a rest. This was at a distance of 800 yards. Some of the guys shot them from rests/bags and the groups dropped down into the 1/4 to 1/3rd range. Competitive type heavy bag guns shot about the same with the big advantage being when having to be on the wind. Keep in mind we didn't devote the long hours to perfecting the loads for all these guns, once they shot well enough (under a half minute) we shipped them out the door. Customers routinely got better groups after fussing with the loads more.
Hope this helped.
Last edited by NesikaChad; 07-25-2008 at 10:39 AM.