The thing you have to watch with the M1 is not just chamber pressure, but the pressure at the gas port near the muzzle; too low pressure won't cycle the action*, too high can damage the operating rod. Which is a Bad Thing. And you can't use the same load information with cast as you do jacketed bullets; a powder that's too slow-burning to safely use with jacketed bullets can be quite acceptable with cast.
I had one other criteria: I've already got a mold for the 150-grain gas-check bullet I use for several cartridges, and
DISCLAIMER: You know the drill: the loads I'm about to list worked in my rifle; they might not in yours. If you decide to try these or similar loads it's at your own risk. Do some research before you decide to follow in my tracks, as I'd hate to year of someone damaging a fine rifle(or their face).
Looking over the information, I decided to go with one guy's procedure: start with 34.0 grains of IMR4895, step up in 1.0 grain increments until you have a load that cycles the action reliably. So I loaded five rounds with 34.0, five with 35.0, five with 36.0. Five because I've got one of the five-round clips, and only 15 total because I didn't know if this bullet would work; a lot of people have said their rifle didn't work well with cast unless using a heavier bullet(and often a slower-burning powder).
Being somewhat short on time, plus it being chilly enough to be a bit uncomfortable(if you read this, Tam: yes, sometimes I am a wuss, my hands get stiff), I went to H&H. So, 30 yard rifle range, and light a bit dim, here's 34.0 grains:
35.0 grains
and 36.0:
The first round of the 34.0 ejected the empty but didn't move the bolt back quite far enough to pick up the next round; all the rest cycled with no problem, and all the 35 and 36-grain loads cycled properly. The first two dropped the cases about two feet to the right; the 36 load ejected forward and a touch to the left. The 35.0 load seems to have grouped a bit tighter than the others, but without a solid rest this is within my margin of error, I may have held a bit better on that group; I think not, but possible. But I think I'll start with the 35.0 for the next testing, which will hopefully be at 50 and 100 yards with a solid bench.Oh, the reason the 36.0 load is higher is I raised the rear sight four clicks; I think they'd require about eight to ten clicks to put it on at 50, which if this runs like the other cast loads should also put it on at 100. We'll see. I'll be able to set up the Chrony and find out velocity, too.
Assuming accuracy holds up at the longer ranges, this should work nicely: recoil was very light, the loads used almost ten grains less powder than milspec ball loads, and accuracy(assuming) should be quite enough for general practice.
I'll mention one other thing: the possibility of lead fouling the gas port or cylinder. I think this would mostly be a problem with a plain-base bullet either driven too fast or cast of too-soft alloy; with a hard-cast and/or gas-checked bullet, little or no problem was reported. I took my rifle down and checked it, and while fifteen rounds isn't a really good test, I only found what looked like one little speck of lead on the face of the op-rod, and it wiped right off. So I don't think that'll be a problem. I've fired a bunch of gas-checked cast bullets in the Carbine with no problem**, so I don't think it'll be one here. Overall, a quite successful test.
*Some people use what seems to be the 'use this' cast-bullet target load, 16.0 grains of 2400 with a 150-170-grain bullet; it won't cycle the action, but reports say it gives good accuracy and hand-cycling drops the brass close by.
**A while back I thought the gas piston seemed a touch sticky, so I took it out; it had what might have been some fouling buildup, but I've been told that can happen over time from lead burning off the exposed base of the standard bullet, too. And since I'd never taken the piston out before, no idea if there'd been some buildup before.
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