How do you "slug" a barrel?

[mallc]

Just bought a Mosin M91/30. One of the threads on this site says to be sure to slug the barrle to determine whether it uses .310 or .311 bullets.

How do you slug a barrel please?

Thanks,
Scott

 

[Wiljen]

I like to start with an egg sinker just bigger than bore diameter and push it through with a brass rod just under bore diameter (never anything harder than the bore) and a mallet. Once the sinker is pushed all the way through - measure it at its widest and narrowest point. The widest should be the groove diameter, the narrowest is the land diameter. You usually want a cast bullet with driving bands slightly (.001-.003) larger than the groove diameter and a nose at land diameter or just a hair over (.001). For jacketed bullets, match the groove diameter.

 

[res45]

+1 there Wil,here are a few pics to go along with his explanation to help you out.

http://www.surplusrifle.com/reloading/slug/index.asp

 

[Sunray]

Hammer a cast .30 calibre bullet(it'll expand enough. A sinker will do, but may not have a lot of measuring surface) through the barrel, preferably from the chamber end, using a brass rod and a plastic mallet and measure it with a micrometer or vernier calipre.

 

[dmftoy1]

The best luck I've had for a Mosin is using 00 Buckshot pellets. You get 9 if you break open a 12 gauge 2 3/4 shell. They have the advantage of being soft lead.

Have a good one,
Dave

 

[David Wile]

Hey Mallc,

You might want to slug your barrel in three places: one slug for the first inch or so beyond the throat, a second slug for the last inch or so at the muzzle, and a third slug going all the way through the barrel. You may get different readings at those three places on older military rifles.

A soft or pure lead ball or bullet a bit larger than the bore makes the job a lot easier. For example, an 8mm bullet cast in soft lead would work real well for most 30 caliber bores. For the throat end measurement, you need to remove the bolt or whatever to get access to force the slug into the barrel an inch or two. Then use a brass rod from the muzzle end to push it back out. For the muzzle measurement, start the slug down the muzzle an inch or two, and then push it back out with a brass rod from the breach end. For the full length measurement, simply push a slug from the muzzle through to the breach with the brass rod.

If you remembered to keep the three slugs apart, you can measure them with a micrometer for both lands and groove measurements. If all three slugs are the same, your barrel is likely to have had very good care.

Best wishes,
Dave Wile