Good bullets for .45/70 black powder load?

You can but you will have a terrible mess in the barrel. You should be using lead with a blackpowder lube.

Like he says, lead bullets are what you need. Preferably fairly soft ones.
Jacketed bullets would excessively wear an original trapdoor barrel, and increase pressures unsafely with black powder I would think.
A replica trapdoor would be okay with jacketed bullets and smokeless loads intended for weak actions (documented in a reloading manual), but using black powder with them might again increase pressures unsafely, I would think.

You need to slug your bore to determine the groove diameter, to determine the best bullet diameter.
Probably .460" would work, lubricated with a good black powder lube, but it all depends on what the groove diameter actually is and whether the cartridge will chamber.
With quite soft lead bullets of .458" the bullet may obturate to fill the bore with the usual compressed load of BP and deliver good accuracy, even if the bore is a bit larger.

I'm sure that the BP cartridge pros can give more and better info.

If you were looking for an ideal bullet, a 405 hollow base with big grease grooves would be first choice. Fortunecookie45lc has some great videos discussing black powder 45/70 bullets.

Lyman 457124 lubed with SPG and shot as cast if around .459-.460.

If you have to use a jackted bullet you can use a lube cookie under the bullet. But there is no reason to use a jackted bullet, stick with lead there cheaper. The lead will be less pressure which is a good thing.

Many who are far smarter than me have said shooting jacketed Bullets in a original trapdoor is not a good idea as the steel is not the same as modern ones. I cast Lee 405 HB and 500 grains Bullets 20 to 1 lead tin with a 50/50 beeswax and olive oil.
If Virginia Jim is still looking at this post you need to do some research on loading for and shooting the trapdoor.

Howdy

This is the bullet I use in 45-70 with Black Powder

https://www.midwayusa.com/product/1010755057?pid=763241

Driftwood Johnson said:

Howdy

This is the bullet I use in 45-70 with Black Powder

https://www.midwayusa.com/product/1010755057?pid=763241

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72 cents each holly cow. If that doesn't convince you to cast your own nothing will.

AJC1 said:

72 cents each holly cow. If that doesn't convince you to cast your own nothing will.

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I bought a whole bunch or these years ago, they were not as expensive back then. Besides, the lead count in my blood is too high and I am not allowed to cast bullets anymore.

Virginia Jim said:

Thanks to all. I have a lot of sites bookmarked on loading the Trapdoor. I’m going to do some more looking and go with a lubed lead bullet of the correct diameter.

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Finding big bullets to slug is harder for me than the smaller ones. I normally use shotgun pellets. I'm curious if carefully swaging a pure lead bullet would be the easiest.

You can slug a bore with a slightly flattened pure lead ball. You can also round out a lead fishing weight. Anything that is slightly over groove diameter can be used to slug a barrel. I have also slugged barrels with standard hard cast bullets with good results.

The trick is how many grooves are in the in the bore.

My Trapdoor left the factory in 1883. It only has 3 grooves. I cannot speak for all Trapdoors, but that is the story with mine.






It is easy to get a measurement on a slug shoved through a bore with an even number of grooves, you measure across the slug between two high points and you are measuring groove diameter. With a bore that has an uneven number of grooves, if you measure across the slug with calipers, you will be measuring from groove to land. Then you have to add the depth of one groove to get the real number. This is pretty tricky, I have never been really good at it. It is tough to balance the depth measuring end of the calipers on the edge of the groove and get an accurate measurement.

I probably slugged this barrel with these bullets years ago, but I don't really remember, so I just redid it. These are the .458 diameter bullets that I always use in my Trapdoor and my Sharps. I measured one of the bullets and actual diameter is running between .4580 and .4585. After slugging it was about .455 across from groove to land, add about .001 for the depth of the groove. So that means my Trapdoor probably has a groove diameter of about .456. Give or take something for the wobble of my caliper.









The grooves are very shallow, but I did get good drag marks across the high spots, corresponding to the grooves. That means my slug pretty well filled the grooves. I have always had good results with these bullets in my Trapdoor and my Sharps. Dunno if I could do better, but at least the rifling gives them a good spin and they don't keyhole. The bore of my old Trapdoor is actually nice and shiny without any pitting.

P.S. Yes, there are techniques for measuring an odd number of grooves using a V block, but I have never tried it.

A Hornady 50 caliber ball is what I used to slug my Trapdoor.and took it to a local gun builder who had the right micrometer to measure odd grooves. It came out at .4608 and cost me $15.00.
You will find that is about normal with some going to .463 and slightly more.

Today I slugged a new Marlin Cowboy 1895CB 26" inch .45-70.
I used a .490" dead soft round lead ball that I use in muzzle loaders.
I have an excellent Starrett dial caliper that sees light use that I trust.
The 6 groove barrel measures .4565"-.457" according to the slug driven from the chamber to halfway up the bore, and about .456" from the slug driven a few inches in from the muzzle.
From on-line searches around .457" was what I expected.
Good news since I have 200 x 405 grain bullets measuring .458"-.4585" that should work well with around 36 grains of Reloader7 (RX7) for around 1350 FPS and only about 12,000 CUP.
Should be a good powder for old BP .45-70 rifles.

Reeferman said:

It came out at .4608 and cost me $15.00.
You will find that is about normal with some going to .463 and slightly more.

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I wonder how large a bullet diameter can be used, loaded into a case?
Are the chambers generous in size or do you need to use a nearly pure lead bullet that obturates?

Old Stumpy said:

I wonder how large a bullet diameter can be used, loaded into a case?
Are the chambers generous in size or do you need to use a nearly pure lead bullet that obturates?

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I would be very hesitant to make any blanket statement on the older guns. Even the much more modern mosin, or 7.7 have chambers and ware that would only have me say your going to have to cast the chamber to be sure.

I use a 405gr lead bullets that I picked up in an estate auction, they are soft and expand when they hit anything hard. I am going to clean them and try powder coating them since the lube is falling out. Remember to clean your brass with water and Dawn soap after shooting, I have a plastic coffee container I drop them in while shooting. I like the smoke and smell and am surprised at how accurate my imitation is.

Old Stumpy said:

I wonder how large a bullet diameter can be used, loaded into a case?
Are the chambers generous in size or do you need to use a nearly pure lead bullet that obturates?

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Both of the Lee 405 HB and the 500 grain bullets drop at about .463 or so with about a 30 to 1 lead/tin and I size them to .460.