Thread: 375 Lunatic

There’s been a lot of theorising recently about the 375’s and just where they’re going to sit ballistically especially compared with the likes of the big 338’s. Well, we’ve finished our preliminary testing of the first 375 Lunatic we’ve built, and I thought you might be interested in the results. This is basically our full length 338 Lunatic Max opened up to 375 cal. Our Lunatic is based off the 408 Cheytac case which is in turn based on a strengthened version of the 505 Gibbs African cartridge. With around 180gns of water capacity, it is a seriously large capacity case!
The barrel is a 32” finish length gain twist 12 to 7.25” Bartlein, action is one of our worked Barnards, stock is an A5 McMillan finished to our specs with Barnard bedding block installed, and we’ve fitted one of our angled port brakes. The throat was specifically designed for the monolithic Cutting Edge 400gn LD Max, MTAC and HPBT bullets, which require a significantly shorter freebore than conventional bullets of this weight. The CE 375gn to 425gn monolithics are at this stage the only bullets that make the 375 cal worth considering. The 350gn SMK just doesn’t have enough BC to better the 338 version.
And now to the results. It looks like again US869 will be the powder that will produce the most velocity for pressure in this case. We load the Lunatic and other strong cases to 67,500psi in the likes of the very strong Barnard actions. We got to 3025fps for 67,500psi pressure with the 400gn HPBT and 402gn MTAC CE bullets. They only differ in that the 400 has a hollow point drilled for use as a hunting bullet, whereas the 402 is a solid not designed to expand. We’ve corresponded a lot with Terry Holstine in the USA (Augustus on the US forums) who has the most experience with these bullets in this calibre - in his case in the standard 375 Cheytac which is slightly less capacity. Terry has settled on H50BMG/2218 as his powder of choice for consistency reasons, and he’s pushing the 400’s at 2900fps out of his 30” barrel, which makes sense as you’re usually 50 to 75fps behind 869 velocities for the same pressure, and he’s also got 2” less barrel length. We will do some work with a few more powders including 2218 now that we know where the maximum velocity is with 869.
We shot some pretty small groups at 100 yards while doing the load development, and then we shot both bullets on our 1000 yard range this morning. Conditions were a light variable breeze from 1 o’clock with quite a bit of mirage. I dialed 20.5 MOA, shot a couple of foulers at another target, then shot the remaining 8 shots at the target below. We were alternating between a 400gn and a 402gn each shot all the way through the group, as we wanted to see if there was any difference in the way they flew due to the hollow point. As you can see there wasn’t. I dialed no windage as I figured the spin drift would cancel out most of the right to left wind, then just held centre of the 8” bull as best I could in the mirage and fired the 10 shots, with a brief barrel cooling period after shot 6. I did not allow for the wind changing speed, which it did a bit while I shot. The widest 2 holes - shots 9 and 10 - are 6” apart, and the group has 4” of vertical in it. The ES was 14 fps. The BC worked out to be .45 G7 and .9 G1. Terry said he uses .91 to .92 G1 for the 400’s, so our preliminary results matched his pretty closely.
Now we’ll get these bullets out hunting and do some beyond 1000 yard terminal ballistics testing, to see how they compare with the 252gn CE bullets we’ve already tried in the 338 Lunatic. And we’ll try some more powders as I said above. Anyway, I thought I’d get our preliminary results up as I know there are some who are dying to know just how these big 375’s are going to stack up.
Now get out your ballistic programs/I/Andriod phones etc and crunch some numbers and see what you think!

Greg


The 375 Lunatic with 400gn CE compared to a 7mm Rem Mag


The rifle on the shooting bench. Black tape secures strain gauge earth wire


Action, stock, cartridge and Oehler 43 Ballistic Laboratory (Just for you Spanners )



1000 yard target from this morning