Wayneo,i've been using trailboss for some plinking loads. if i could get 1000 fps using TB and 350 grain JHP's, would that be a suitable hunting load for whitetails - <100 yd shots.
I agree with Bearcat, subsonic velocity will not be enough to expand the jacketed HP bullet with any authority unless you hit big bones. However, there may be a cast bullet option you may want to consider.
GT Bullets has a good selection of pills for the 45-70 with hollow points and he uses an alloy that is soft enough to expand.
Here are two examples. I have ordered several different calibers and designs over the years. All were high quality. Much better than any other mfg I have used. Also, this could be a good reason to start casting your own. If you cast you can dial down the hardness to 30-1 and have a quick expanding flat point bullet at subsonic speeds.
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jd,I don't own or shoot a 45/70, but I can vouch for GT Bullets. I bought my first batch of 500 for .357 mag back in the early summer - immediately fell in love with them. The next month I ordered 100 count samples of both .44 mag and 30-30 and got hooked. My latest order was less than half what it should have been but was the first of November, just before GT announced a long wait time. I'm due to get this order of .44 mag and 30-30 bullets around the first of February .... I hope. I believe that PDP is right on the spot recommending them, and if you're dead set on a Trail Boss load to push them, you'll probably be able to find something that works.
Like you, I ordered several samples before getting on a larger quantity. Both of the 32-20 hollow points are great, 115 and 100 gr. I still have a gas check bullet mold for the 32-20 and have sold the others. His quality is that good. The 148gr 38/357 swc hp and 45 ACP 180 hp target are also great. I also like that I can order as cast without lube. I can size to my need and use a softer lube mix that works better than the hard crayon lube all have to use to hold up in shipping.
My last 500 order was for the 130 gr HP 30 cal. I shoot them in a 30-06, 30-30, and 30 carbine T/C Contender pistol.
Being currently all but confined to shooting long guns off the bench, I've really gotten hooked on cast boolits in the lever guns. For the last 3 years, thanks to some of my favorite internetsuperhighy enablers, the mixture of cast boolits pushed with pistol powders has become addictive. That GT 150 gr HP gas checked bullet with a proper dose of AA#7 will amazingly shoot MOA groups at 1700 fps at 50 yds, closer to 1-1/2 moa at 100 yds, from my 30-30. Not having a 45-70, I won't have the satisfaction of tinkering with it, but I sure would like to hear a success story of a GT bullet load in a 45-70.
I wish I'd had the funds at the time to go ahead and order 1000 of both the 44 boolits and the 30-30 boolits .... might as well add 1k 357 bullets to that wish list too since we're looking at a minimum of 3 month wait time.