I have a number of 40-65 die sets that came to me cheap after the Browning BPCRs in 40-65 were discontinued. It seemed for a while no one but me wanted them.
A few years back I started measuring and recording the neck inside diameters of my dies. The intent was to find the largest neck diameter to minimize the potential for moving the neck off center due to excessive sizing.
Here is what I found
4 RCBS Cowboy FL dies = .421
2 Late model Lyman FL = .421
2 Redding FL dies = .416
1 Redding trim die = . 416
1 RCBS date code 1965 = tapers at the base of the neck = .430 at end of case .418.
(made for the .406 bullet)
I shoot .409 and .410 bullets and I use an expander the same diameter as the bullet relying only on a little spring back to grip the bullet
As you can see the dies are all too tight for the modern .408 to .410 diameter bullets and barrels - especially the Reddings.
It looks like with a minimum .409 bullet and minimum .009 thick case walls a .427 neck internal diameter would be close to ideal. A case sized in this would give an internal diameter of .409
One of the Cowboy dies is not a set but is a single die that I can modify by lapping with barrel lap.
The old timer 1965 RCBS die appears to match older tapered chambers though the larger expanders and bullets will straighten out a lot of that taper.
Discussion of BPCR loading techniques, SAFETY, Case Cleaning and Prep, Indexing, BP Choice, Primers, Wads, Compression, Drop Tubes, Vibration, Load Testing, etc.
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