Greetings to all,
I have read this forum from time to time over the last few years with great interest and now finally have a reason to post. I am a novice at the cast bullet game and am here seeking advice. I have worked in the firearms trade and have a good working knowledge of barrels and the methods used to produce and chamber them.
I am about to begin work on a project rifle that I will use for “pistol cartridge” lever action silhouette shooting. It is what I call a “gunsmith special", a Winchester '92 in 25-20 with a rotten bore and missing stocks. I will rebore and rechamber the rifle to 32-20. I will be purchasing a chamber reamer for this project and would like to get some guidance from this forums members regarding optimum chamber dimensions for use with cast bullets and smokeless powder. Combining a standard chamber (I have a SAAMI spec reamer) with current production Starline 32-20 brass results in well over .040” gap between the case mouth and the end of the chamber neck. It is my understanding that this is not desirable when shooting cast bullets. I would also like to discuss the dimensions of the throat area of the reamer. It seems that most chamber reamers cut for cartridges that were originally black powder rounds feature a relatively shallow straight taper from the chamber neck diameter down to bore (land) diameter. Chambers for more recent cartridges typically have a more abrupt (90 degree included angle) step-down from the chamber neck to a throat section which is at or just a few thousandths of an inch over groove diameter, followed by a gentle leade angle which engraves the bullet as it passes. To summarize, if you were going to specify a custom reamer in 32-20 for use with Starline brass, smokeless powder and cast bullets, what would it measure and why?
I did perform keyword searches of this forum in an attempt to find relevant threads without much success. If this topic is well covered elsewhere please accept my apologies and if possible, provide a link. Thank you and good shooting.
I almost forgot to mention, any advise on rifling twist rates would be welcome also.