Reloading M84 Trapdoor. Relationship between OAL & PSI/CUP

Is my approach a sound one?

  • Yes, start low and work slowly and carefully.

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  • No, the logic is flawed, you're going to be pulling a breech block from your eye socket.

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Possibly the Hi-Tek coating is different than what you are using and the OP is not using Black Powder.

I use Eastman powder for those 45/70 bullets. I have used some bullets that had Hi-Tek coating and it did not appear to be as thick as the PC bullets. I know he is not using black powder however whenever I mention PC bullets and black powder without stating they get lubed when using black powder it always starts a “you can’t use PC bullets without lube and black powder debate”
 
Wanted to circle back here. Spent some time over on CastBoolits and ran into Larry. He was a great resource of information, and I've read his info also besides a few PMs back and forth.

He told me to essentially calm down about OAL on such a large case. He recommended - as some of you did here - that I just roll/taper crimp at the crimp groove, even if that sets the bullet into the rifling, and let er rip. I did that... and it was fine.

I loaded the .460 GT Bullets 390 gr over a 21-25gr charge of A5744. I didn't use any Dacron, although he recommended it. Each charge was pretty consistent with a spread of about 20fps. Each grain increase raised FPS by 30-50fps on average.

For grins, on the last 4 bullets at 25 gr, I tried what some have described, I tilted the barrel up to settle the powder against the primer and then slowly lowered the gun and aimed.

I was shocked. A5744 is listed as a less case-location sensitive and less case-full sensitive powder. The two shots with a "regular" aim and fire were 1165 and 1162. The two shots with the powder settled against the primer were 1223 and 1238. The extra ignition gave the same fps impact, in my testing, to equal a nearly two grain increase in powder charge. I'll use the dacron next time.

I checked the rifling throughout the shooting, and there was some more fouling down near the chamber - but minimal leading. The first shot welded a bit of lead onto the exterior of the case neck. After that, no more leading visible on the outside of the cases. For reference, the 405gr HSM bullets would weld lead to the outside of the case neck on EVERY shot, and leaded up the barrel to poor accuracy within 5 shots.

My loads today (20 shots) left a bit of lead in the barrel - a single scrubbing removed it entirely. Worlds better.

All in all it went really well. My best groups were the 23 and 25gr charge (3" @ 50 - although if I remove a single flier on the 25gr load the remaining 3 shot group was 1"). 21gr min FPS was 995, 25gr max FPS was 1238.

I'm going to load up the bullshop 405gr HB bullets next, along with the 425gr solid base. I'm still looking to try a soft lead 405gr HB cast at .461 and see how that does as well. I think I'm still a shade undersized.

Thank you all for your help and direction.

Lastly - I received the Wolfs TrapDoor book - what an incredible reference work. I've thumbed through it a couple times, and really read into portions here and there. I'm amazed at the level of work that he (and those that helped him) put into it.
 
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