- Joined
- Oct 25, 2004
- Messages
- 3,178
A new thread was requested, so here it is.
How to slug:
You'll need a slug and something to drive it with. The slug should be pure lead or nearly so, large enough to engage the rifling fully but not so large that it can't be pounded in. Fishing weights work well for this. To drive the slug a cleaning rod will work in a pinch but is not a good idea. Use a wood dowel slightly smaller than the bore and several inches longer than the barrel. Cut it into 6" lengths to prevent breakage.
Clean the bore thoroughly and leave it well oiled. Grease up the slug and pound it through. It should not take much force. Pay attention to the feedback that you're getting from the dowels. Ideally it will feel the same all the way down. If the slug is moving an inch or two each time you tap it and it suddenly moves eight inches (or, even worse, starts moving under hand pressure alone) you've got a loose spot.
Why is this important? Bullets are picky. They'll bump up a bit to fill a slightly loose bore (assuming the pressure behind the bullet is high enough) and they'll squeeze down into a constriction but they don't like it; the more we deform them, the worse accuracy will be. The real killer is when a bullet has to do both -- squeeze down, then bump back up again. You'll wind up with gas cuts and mangled jackets and the target will notice.
Now, you know and I know that all weapons have a nominal bore diameter, so if we know that we're good, right? Wrong. Slug some of your factory firearms and be prepared for a surprise or two. Even today, the occasional lemon gets out. (Fortunately, unlike with milsurps, you can send the lemon back and get a new one.) In WWII and before, there was no CNC machining, less precise metallurgy, and sometimes a war going on. Work was hurried, workers were sometimes not properly trained, worn tooling was used longer than it should have been, etc. After being built the rifle was issued to a soldier who may or may not have cleaned it properly (or even at all) and may have been fired far more than it should have been. The result is some variance in bore diameters and if it's too loose, accuracy probably isn't going to be very good.
How loose is too loose? Ideally, jacketed bullets should match groove (not land) diameter; cast bullets should be .001-.002" larger than this. Sometimes you can get away with being .001" under. Usually not. Jacketed bullets tend to handle such abuse better than cast but no bullet will perform at its best like this.
Sometimes we have other problems -- for instance, my M44 with the oval bore. Slugging will reveal these as well.
Loose spots or constrictions inside the bore are often caused at the factory. Sometimes they can be fixed. Sometimes they still shoot. Sometimes they're goners. It has to be taken on a case-by-case basis.
Hope that helped.
How to slug:
You'll need a slug and something to drive it with. The slug should be pure lead or nearly so, large enough to engage the rifling fully but not so large that it can't be pounded in. Fishing weights work well for this. To drive the slug a cleaning rod will work in a pinch but is not a good idea. Use a wood dowel slightly smaller than the bore and several inches longer than the barrel. Cut it into 6" lengths to prevent breakage.
Clean the bore thoroughly and leave it well oiled. Grease up the slug and pound it through. It should not take much force. Pay attention to the feedback that you're getting from the dowels. Ideally it will feel the same all the way down. If the slug is moving an inch or two each time you tap it and it suddenly moves eight inches (or, even worse, starts moving under hand pressure alone) you've got a loose spot.
Why is this important? Bullets are picky. They'll bump up a bit to fill a slightly loose bore (assuming the pressure behind the bullet is high enough) and they'll squeeze down into a constriction but they don't like it; the more we deform them, the worse accuracy will be. The real killer is when a bullet has to do both -- squeeze down, then bump back up again. You'll wind up with gas cuts and mangled jackets and the target will notice.
Now, you know and I know that all weapons have a nominal bore diameter, so if we know that we're good, right? Wrong. Slug some of your factory firearms and be prepared for a surprise or two. Even today, the occasional lemon gets out. (Fortunately, unlike with milsurps, you can send the lemon back and get a new one.) In WWII and before, there was no CNC machining, less precise metallurgy, and sometimes a war going on. Work was hurried, workers were sometimes not properly trained, worn tooling was used longer than it should have been, etc. After being built the rifle was issued to a soldier who may or may not have cleaned it properly (or even at all) and may have been fired far more than it should have been. The result is some variance in bore diameters and if it's too loose, accuracy probably isn't going to be very good.
How loose is too loose? Ideally, jacketed bullets should match groove (not land) diameter; cast bullets should be .001-.002" larger than this. Sometimes you can get away with being .001" under. Usually not. Jacketed bullets tend to handle such abuse better than cast but no bullet will perform at its best like this.
Sometimes we have other problems -- for instance, my M44 with the oval bore. Slugging will reveal these as well.
Loose spots or constrictions inside the bore are often caused at the factory. Sometimes they can be fixed. Sometimes they still shoot. Sometimes they're goners. It has to be taken on a case-by-case basis.
Hope that helped.
:thumbup: 
