What bullet w/ BP?

I have a 43 Mauser 1871 I want to shoot bp in. What bullet do I shoot. It has .454 grooves and .433 lands. Do I need to fill the barrel with the bullet? Or can I shoot .446. Hawk bullets because they are jacketed.
It’s a special problem to be sure. I could PP but to what diameter? Or sell the gun. It’s a m1871 barreled action with custom stock and set triggers. 25 inch barrel, pristine bore in very good shape. Professionally done hunter or stalking rifle and antique.

I really just want to know what to shoot in it.

That’s the groove of the 71/84. This seems like it’s different technically speaking. With my groove that bullet would gas cut.

I appreciate the info about bullets that fill the bore, but how do you push them into the case. I’ve never had a PP bullet that didn’t bunch up on top of case. I used a .439 bullet, 2 wraps of .0025 paper.

Jackrabbit1957 said:

Might be worth trying a.452 pistol bullet, my trapdoor likes a 255 grain .452 much better than the .405 gr standard ,458 plus it don't beat ya to death.

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I thought of using a .452 plated bullet. Soft lead. But won’t .433 lands distort it badly?

noelf2 said:

I think you can use a 405 grain 45/70 (.457) lead bullet sized down to .452 without a paper patch.

There's a lot of good info for you here:
https://castboolits.gunloads.com/showthread.php?37613-Mauser-Model-1871

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What will happen. It will have .010 engraving on either side. Will the pressure rise.

Big Bore 44 said:

Soft lead will obturate and fill the grooves. If you wish to go the PP route, bell the case mouth a bit more than you normally would. One of the first rifles I loaded for was a 44-40. Grandpa taught me that soft lead was best for BP loads. Properly lubed = no leading.

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How soft is too soft? I was hoping for 9- 12.

hawg said:

You might get by with a BHN of 12 but 17 would be better. Try it and see.

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if hardball is 15 what would be 17?