Slugging a barrel

rudyj

This is new to me, but I have seen people say they have slugged their barrel. What exactly are they talking about, and how do you do it. Any help is appreciated.

dcs shooters

You push a pure lead slug through it to get the diameter of the bore.
Most of the time there is a question about the proper bullet size.

Rocky Raab

Yup. It's a very valuable test, even if you aren't trying to match cast bullet sizing. Properly done, slugging a barrel can tell you if there are tight spots, loose spots, possible rust pits, a "choked" rifle barrel, or a "frame pinched" revolver barrel.

You push a lubed lead slug through a clean and oiled barrel with a rod, feeling how it progresses all the way, and then measure the slug with a micrometer. The passage tells you a lot by feel, and the micrometer tells you the exact groove depth.

nononsense

rudyj,

There are two dimensions to the inside of a rifle barrel (or pistol).

1) The bore diameter (top of the lands).
2) The groove diameter (bottom of the grooves).



Soft lead in the form of a lead ball or bullet is pushed into the barrel forcing it to conform to the shape of the lands and grooves. Some folks have suggested lead sinkers for fishing as well. It's important to choose a bullet or ball close to the bore/groove size so you don't get it stuck.

Pushing it completely free of the barrel allows you to measure it with a set of calipers to get accurate dimensions. These dimensions are used to select the proper bullets for reloading or the proper ammunition to shoot if you don't reload. The reasoning is that some barrel dimensions are too close to see the difference but the difference is enough to raise pressure, maybe to an unsafe level.

Example:
8x57 Mauser (0.318")
8x57 Mauser (0.323")

There are others of course.

Best.

jonk

It's a good idea to do with any gun, especially an vintage piece. For instance- I have a 1903 Springfield that while it should nominally measure .308/.300, has a .310/.301" measurement, for the lands and bore respectively. I got noticeably better accuracy by switching to a .310" bullet (which you should only do if it chambers freely).

For cast lead it is even more important. Most non-US military guns run a bit over nominal spec. Take the .303 Enfield for instance. Nominally the lands should run about .311". I've seen some that run up to .318". If you try running a .311" lead bullet down that bore, not only will accuracy be horrible, you'll lead the snot out of it to boot. General rule of thumb is, run jacketed at or 1/1000" below measured groove diameter, cast lead at least 1/1000" above it (and sometimes more depending on rifling depth).

rudyj

Thanks for all of the good information, it is greatly appreciated. I have been reloading for some time but never knew what slugging a barrel was for. Thanks again.

13a19195

There is an excellent tutorial located at:

http://7.62x54r.net/MosinID/MosinSlug.htm

I use 1/8 oz. "egg sinkers." Pretty easy to do, once you get past the notion of hammering a piece of lead the "wrong way" through the barrel.[:D]

rudyj

13a19195
That is a really good explanation, and how to. I really appreciate the information. Thanks a million.