By comparison, a SAAMI 308 Winchester is 1 3/4 degree per side. By most accounts the 308 is a cast friendly cartridge?
Re: length of leade. Depends on the starting diameter. In sloppy SAAMI throats, the starting diameter is rarely less than 0.002” over groove diameter. Here's some numbers I worked out for a 357 barrel where the throat started at .360 and transitioned to a 0.347” bore:
Let theta be the leade angle per side.
Length = 0.0065” / tan(theta)
If theta = 0.5 degrees then length = 0.75"
If theta = 1.0 degrees then length = 0.37"
If theta = 1.5 degrees then length = 0.25"
If theta = 3.0 degrees then length = 0.12"
From the perspective of the stubby 357 bullets I was shooting, a 1/2 degree leade was a loooong jump to the rifling and didn't shoot worth a darn. It might work great in a 30 caliber rifle with long 180 - 200 grain bullets that could reach out and grab some rifling.
What is the purpose of the leade? To guide the bullet straight into the bore without mangling the bullet? We can agree that the abrupt or missing leades in some black powder cartridges can mangle bullets. A 90 degree leade would shave lead. A 45 degree leade would not be much better. But the 5 degree leade in the 444 Marlin seems to be cast-friendly. For that matter, an 11 degree forcing cone in a revolver is reputed to be more accurate with cast bullets than a 5 degree forcing cone (I'm not sure that I agree, my most cast-friendly revolver to date sports a 5 degree cone).
Point being, how “gentle” does a leade need to be to do its job of guiding the bullet into the bore without damage? Is a 1 degree leade five times better than a 5 degree leade? In my experience, no. 3 to 5 degrees seems to be gentle enough.
A long gentle leade does offer the opportunity to use a matching Ardito-style tapered bullet, if you choose to go that route. It's a proven system.
Just my 2 cents, subject to change as more data comes my way. :)
Thank you for correcting my sloppy semantics, Frnkeore. :)
