Just wondering how many of you have ever slugged a barrel, to determine actual groove diameter?
What prompted this is I have a Marlin 1895 in 45/70 (actually, I have two of them...an older one with micro-groove rifling, and a newer one with ballard rifling), and recently tried some cast, plain base, 340gr bullets made in a Lee mould. They dropped from the mould right at .457 diameter (wheel-weight lead), so there was no way I could size them to .458, or .459. (would have preferred .459) I tried them anyway, with a modest charge of IMR 4198, driving them to about 1300 fps. Accuracy was extremely poor...couldn't hit the broad-side of a barn, from INSIDE the barn! (ok...a slight exaggeration, but you get the idea) The highest velocity reading on my chrono was about 1380 fps, with all the rest being less. (but still more than 1200 fps)
The barrel suffered extreme leading after about 10 shots, and had to be brushed out with a bronze brush, to get all the lead out. (yes...the bullets were lubed properly) This was with the older rifle with the micro-groove rifling. I didn't have time to test the newer gun, which might have been perfectly happy with those loads...
After some contemplation, I did some searching on the web to see if anyone else had suffered the same problem. Yep...plenty of them! Turns out the groove diameter for the Marlin 45/70 is spec'd at .4587" diameter, not .457". If that is the case, then trying to shoot .457" bullets through them isn't going to work out too well. I can just imagine all the high temperature gas blow-by....
This lead me to wonder how to slug a barrel, to find out for sure. I found a couple "how-to" videos:
Both videos appear to know what they are talking about, so I'm gonna give it a whirl with my Marlin and see what's up with this barrel...
So...who has slugged a barrel? Did you do it the same way these guys teach, or some other way? Can you use a regular lead bullet, instead of a round ball? What if I "fatten" up one of those 340gr slugs a few thousanths or so in a vise, then try to use it as the "slug"??? (I don't have a 45-cal lead ball)