Before all this internet "info" I shot thousands of 429421s sized at .429 out of numerous .44s not knowing the size of the throats at all. Having measured the cylinder throats of several of those revolvers now at .429 - .432 I am amazed, given the absolute internet "insistance" on perfect cylinder throat fit for any accuracy, that those revolvers ever shot as well as they did. Actually I can't tell a bit of difference between properly cast bullets sized .429, .430 or .431 out of any of them. All those with the standard Kieth load of 22 gr 2400, 17.3 gr of Blue Dot or with 8.5 gr of Unique. Accuracy remains equal and excellent regardless of the bullet sizing.
I know I'm talking heresy here and will be burned at the stake but I think we get too anal about some things. Granted, if the cylinder throats are really oversize, as was the case with a lot of older .45 Colt revolvers, then that can cause some accuracy problems. However the .44s I have and all the others I've used shoot just as well with .429 sized bullets as anything. Fact is .429/.430 is the standard factory sizing for bullets in the .44 and they shoot very well indeed.
If I were you and that is the only .44 you have I'd just size them at .431 and not worry about it. I use .430 now as standard .44 sizing with the exception of my Colt Anaconda and Contender barrel with the 429640HP which requirtes a .429 sizing to chamber into the throats. A .431 sizing of my 44-250-K, 429421s or the group by Lee mould of the 429421 bullet will not chamber into the throats of some revolvers. The .430 sizing seems to fit all with those Keith type bullets. Others have different experiences but those are mine over 43 years using cast bullets in .44 revolvers, single shots and rifles.
Larry Gibson