338-378wby load development questions.

[Gregg C]

Started working up a load for a 338-378 Why using Retumbo under 300gr Berger Elite Hunters. Start with looking for max load in my rifle, one round each load, 1/2 gr increments till 1/2gr under listed max, Then increase by .2 from there. Hodgdon web site lists 100grs min to 106.5grs max. Got heavy bolt lift and extractor marks at 106.6grs. Back off to 105.0 and perform seating depth test. 30 rounds loaded and shot at 105.0grs Retumbo, absolutley NO pressure issues. I am stoked, right ? Picked out a couple groups to fine tune, and loaded up 30 more at that charge. Got to the range this a.m.- first shot, extractor marks. Light, but still there. Next one same. 3rd round, no marks. 4th shot, a little heavier mark, 5th ( and last ) had heavy bolt lift. What the heck is going on here ?
Only 2 things were different. 3, counting weather, but at merely 25°F difference (50 two weeks ago, 75 today) I think it can be eliminated as a determining factor. One, I raised my sizing die to size the neck only. Now takes a bit of effort to close the bolt. Or, maybe this is it, different lots of powder ? I opened another bottle. The ES was better, at 20 fps, but 5 rounds is not large enough of a sample to really tell. Unless it was NO variation. Thoughts, any one ?

 

[Gregg C]

Not many shooting this cartridge, I guess. So, for someone who might get one and learn on it, here is what I did to overcome this last dilemma. Pulled bullets, resized, full length this time, and put the powder back one grain less@ 104. Shot well. No pressure woes. Settled on a seating depth of .078 off lands.

 

[jbs2014]

Not many shooting this cartridge, I guess. So, for someone who might get one and learn on it, here is what I did to overcome this last dilemma. Pulled bullets, resized, full length this time, and put the powder back one grain less@ 104. Shot well. No pressure woes. Settled on a seating depth of .078 off lands.

I have seen differences from lot to lot with Retumbo. I had a good load with 133 grains behind a 420 grain bullet in .408 Cheytac, switched to a different lot and had to up the charge to 135 grains. I need to just buy 32 LBs or more from the same lot to alleviate this issue since I have use Retumbo in 3 different calibers.

With new 338-378 Weatherby brass, my load for a 275 grain bullet was 106 grains of Retumbo for 3056 FPS and a 10 FPS ES. However, when I took once fired brass and set the shoulder back .001 it messed everything up, ES was up to 22 FPS and the velocity went up to 3077 average. Same lot of powder, primers, and bullets. So it seems that the .001 shoulder setback on the once fired case changed things a bit. I will likely have to drop the charge a few tenths of a grain to get it where I need it.

 

[Gregg C]

Wow, that is weird. I have been struggling with horrible ES-100 plus fps over 25 shots. I got it down to 20 before I learned about lot to lot changes, so am making progress. Now just need to see if everything is repeatable. Glad to see I aint alone shooting that cartridge. Keep me posted on your progress, if you don't mind. I find it heartening to hear that low ES actually can be achieved in that case.