OK all you experts, I`ve read lots about people being recommended to slug a barrel for the purpose of knowing what size is correct for cast projectiles.

I have a Mauser `98 actioned .308 win with a Schultz & Larsen barrel. How should I go about slugging this barrel without doing damage.

Thanks in advance
Cheers Morton

Take a cast bullet of the appropriate caliber and either squeeze it in a vise or tap the nose with a hammer-to make it bigger in diameter. Tap it into the muzzle with a plastic/wood/rawhide anything not metal hammer. It should leave a ring of lead when it is in, a washer of lead. Now tap it down and through the barrel with a wooden dowel or brass rod or steel rod with masking tape rings every 6" to keep it from touching the inside of the barrel. Or use a cleaning rod with a screw in the brush end. The object is to not damage the crown or barrel. 1/4" wood dowels 3' long work fine for 30 caliber barrels. Push the slug out the breech end of the barrel onto a soft surface.
Measure and record. With odd numbers of grooves you'll need a machinist to measure the diameter.
joe b.

And to add to joeb's suggestion, take a second cast bullet and drive it forward from the breech for ~6" - 12", then gently drive it back out (from the muzzle, as per joeb). The two slugs should measure approx. the same, with the ideal being a slightly larger breech dimension. Btw, it helps to do this with a well-oiled bbl.

quote:

Originally posted by morton3:
recommended to slug a barrel for the purpose of knowing what size is correct for cast projectiles.

Actually, the throat and chamber dimensions may have more influence on the optimal bullet size. Plus, barrel dimensions are usually close to spec on all but the oldest guns, but they are still making firearms with dysfunctional chambers and throats.

For example, yesterday I was talking with someone who has a Winchester 94 357 with a throat that is 0.290" long and 0.370" diameter. If you have a long 0.370" throat, do you really care whether the barrel is 0.357" or 0.358"?

If you only make one measurement, it should be the throat -- the length and diameter of the section between the case mouth and the rifling. This can be done with a casting, either cerrosafe or sulfer. It can also be done with an upset slug.

To make an upset slug, pour a dummy case nearly full of lead, then seat a pure lead bullet in the case. Chamber the dummy round. Now stick a brass or steel rod down the barrel and give the rod a few whacks with a hammer, so that it firmly upsets the pure lead bullet in the throat. The result should be a pretty good impression of the throat and the beginning of the rifling.

There is no cut and dry answer for choosing the best diameter. Sometimes the only way to know is to try several different diameters and see which one shoots best.

Thanks Lads, I understand it all much better now.

Popenmann, I see where you`re coming from also.

I guessing here that chambers with long throats would be highly dependant on an absolute concentricity between chamber throat & bore?

I`m in no way suggesting a short throated chamber would perform without being concentric, just a little more important for the longer throats.

Is the throat machined as part of the chamber with the same reamer ?

I`ve also heard it referred to as freebore, is this correct ?

If the throat was too long, I`m guessing there would be a tendency for the projectile to go into the rifling slightly angled, being unsupported from case mouth to rifling.

So many questions, sorry about that but you blokes have all the answers I need, this is fascinating stuff.

Cheers Morton

Both long and short throats can produce good accuracy, but may require different cast bullet designs. A chamber that is not concentric with the barrel is very bad news in either case. It is desireable for the bullet diameter to be a snug fit in the throat so that the bullet will be forced into alignment with the barrel. A snug fit also minimizes gas cutting.

A full diameter nose gets the nod for a long throat.

A full diameter nose can be used in a short throat, but will have to be seated deeply. A bore diameter nose allows seating the nose out into the rifling, but then it becomes critical that the nose fits the barrel correctly, or else that the nose obturate to take the rifling, as is common practice in BPCR.

"Freebore" is often used to describe long throats. Sometimes it is called the "leade". I am not picky about semantics.

A gentle throat angle is considered helpful. Most modern rifle cartridges have an included leade angle of 1.5° - 5°, but some black powder cartridges and some rifles chambered for pistol cartridges have abrupt throat angles that are not kind to cast bullets. It is by no means impossible to get good results with an abrupt throat angle, but you may have to try a little harder and use a certain bullet design.

It is generally desirable for a cast bullet to engage the rifling slightly when a cartridge is chambered, but that is not cast in stone.

Chambers and throats are generally cut in one operation, but separate throaters are available for about $40. Cutting a slightly longer throat with a more gentle leade is a reasonable approach when you are having difficulty with cast bullets.

Over the years, I have recut throats in .25, .357, and .45 cal rifles. Never hurt accuracy, got some improvement most of the time, and startling improvement some of the time.

This is all new to me, so be patient with this question... What is the medium you use to slug a chamber / throat? Lead, Babbit, Bondo?
Many TIA

Pure lead. If you don't have pure lead, tape-on wheelweights might be soft enough.

sinkers! the teardrop shaped ones.

I bought some sinkers recently at Wally World that turned out to be made from steel! Hard to slug a bore using them

Rick