Quote Originally Posted by Patrick Chadwick View Post
DON'T TRY IT

I have not yet succeeded in finding anything resembling standards for the .43 Spanish chambering. Any drawings that may exist could only be taken as guidelines.
The bore should be somewhere in the region 0.410" to 0.430" mm, and although the grooves are much deeper than for modern calibers, you have to recognize that this is nearer to a 44 than a 45. You would not try to drive a 45 bullet through a 44 barrel.

The groove diameter will be somewhere around 0.440" - 0.450". Modern handgun bullets are far too hard to be driven through a bore by hand, unless you use the kind of force that is going to be hazardous for your barrel. It will not be feasible to get the degree of upset/obturation/bump-up - call it what you will - that is required to fill those deep grooves.

YOU MUST USE A SOFT LEAD BALL OR BULLET if you want to get the groove depth.

A 429-430 lead bullet might go, but that would only give you the bore diameter, not the groove diameter. OK - that would be better than zero information, which is our present state of knowledge! But if a 429 bullet will not go down with the brass rod method, give it up and knock the bullet out again.

I think the first step is just to roughly measure the groove dia. with a pair of calipers at the muzzle if it's not altogether bell mouthed.

Contrary to Patrick Chadwick, I'm thinking those above bullets may just work.

I believe those Speer bullets are swaged, not cast and are dead soft. So if your bore (grooves) runs 0.447"+ then I think it'll work fine. Just start it w/ a large hunk of nylon or delrin, IF they are the swaged type. I've done similar plenty of times w/ no ill results.

One COULD also reduce the diameter of the rear of a test bullet to reduce the bearing surface. Stupidly, if you have a lathe available w/ collets, just squeeze the back end a bit. Almost no force would be required!