I think you should try a few more grains of those powders and lose the crimp. The 5744 won't burn clean at low pressure anyway and crimping can cause accuracy problems and isn't needed in a single shot. Some people have really good results with 12-13 grains of Unique with the 405. Of course, unless you have a pressing need for a light load, you should get serious and go ahead and use a 500 grain bullet and black powder now.

Jump on the other guys good advice

Lot of things can affect results, most likely problem is the bullet and bullet fit. Next would be bullet pull then how much it engraves the lands on loading.

Least likely to cause trouble is 4759. I would stick with 4759 until you get 2 moa groups. Too many variables one time often hides the true problem.

Iron sight, big side hammer,  round forearm gun, in a large caliber using store bought bullets not tailored to the gun. 2 moa is pretty darn good, and that’s if it's a good Sharps and you have good eyesight.  Irons general rule is 1 moa lost to sighting error alone. You read about better groups rarely see them. I would not expect 1 MOA  out of a iron sighted 45/70 with any load. 

Only exception to the 4759 advice is it's been discontinued, might be better off working with 4227 which is going to stay in production and hardly any different than 4759 burn rate and results.  I bet 75 % of the shooters on this board use 4227 or 4759 for cast bullet loads.

Boats

John,

Rifles I shoot Black and Smokless I almost always use two molds. Black will bump up on firing. Smokless with light pressure loads, that are safe in old rifles, don't have much bump, proper bullet is larger, as much as .002. Mold throwing for Black can get away with bore size, needs larger grease groves to carry more more lube.

45/70 one problem with .460 bores and smokeless is oversize bullets may be difficult to chamber. Very common Trapdoor problem, not so good with Smokeless powders much better with black due to bullet fit.   

Sounds like a interesting rifle, keep us posted

Boats

Quote:

Yes - Black powder instead of smokeless
And due to the large metplat on the 405 HB, seating it 0.020 off the leading bore cuts with a crimped case - the bullet is not being presented to the center axis of the bore

Buy some Paul Jones Postell & Creedmoor cast & lubed bullets ... (You need to Login or Register to view media files and links)
Load with 70gr FFg powder and the case bell crimped only to remove the bell.  COL so the ogive is touching the leading bore cuts or engraved to be able to thumb seat.

Results?  Out of 25 shots @ 100yds - 14 bullets in the ragged hole with vernier & globe sights
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now I gota say the above group is what I call a wallet group. I have several and hope for more at every trip to the range. argie1891

I just stopped by the powder "pusher" yesterday and he had a new shipment of 4lb 4759 for $80 so I picked one up. However I use 4198 in the 45-70 for reasonable results. Check the land depth. I have had Borchardts that would only do well with black due to the shallow groove depth.

Charles