Bullet Fit to Prevent Gas Cutting

[brad925]

I know that the bullet needs to slug up to seal and prevent gas cutting. But if your barrel has a groove diameter of .456 and you are shooting a bullet that is .458 or .459 does this not solve to problem of having enough pressure to to slug the bullet up to seal the bore? Just reading a piece that was on a sticky referring to an Lasc article in the pressure to slug up 1 -20 alloy black powder would not have enough pressure to do this. Am I way off? Just learning this type of shooting.

[curator]

The diameter of your rifle's "throat" is the most critical dimension, not groove diameter. If powder gas can get past your bullet as it enters the rifling you may get gas cutting despite it being over groove diameter. A fast burning powder may exacerbate this. Lots of .45-70 rifles have groove diameter of .456-.457 but throat diameters of .460-461. My NEI Handi-rifle in .45-70 had this problem and leaded like crazy with poor accuracy, until I began loading cast bullets that filled the throat. It made no difference whether bullets were BHN6 or BHN22.

[Gunlaker]

Black powder definitely has the power to bump up 20:1 and harder alloys. I shoot bore diameter paper patched bullets and they bump up to groove diameter. Even with 16:1 and small cartridges like the .38-55.
With grease grooved bullets most people seem to run them at groove diameter, or maybe a thousandth larger. I've had excellent results that way.

Chris.

[EDG]

Could you leave us a link to that page?
I would be interested to read that. I have used bullets as large as .004 over groove diameter from 20-1 without leading.
I have also used harder alloys at groove diameter to .001 oversize with light leading.


I know that the bullet needs to slug up to seal and prevent gas cutting. But if your barrel has a groove diameter of .456 and you are shooting a bullet that is .458 or .459 does this not solve to problem of having enough pressure to to slug the bullet up to seal the bore? Just reading a piece that was on a sticky referring to an Lasc article in the pressure to slug up 1 -20 alloy black powder would not have enough pressure to do this. Am I way off? Just learning this type of shooting.