I would be foolish not to except your offer in sharing with me how you slug your barrels. I have done it once and I’m sure there is a mush better way of doing it. Once I know what the bore is i wil, order up the dies and expander.
By the way, if you decide to try loading Black Powder for your Rossi, you will find almost no fouling escapes into the mechanism. The thin brass at the neck is why, it expands at the relatively low pressure developed by Black Powder to completely seal the chamber. Almost all of the fouling goes down the bore, very little gets into the mechanism. Which is a good thing with a '92 because they are a pain to take down for cleaning. Generally speaking, a rifle chambered for 45 Colt will have a lot more soot getting into the mechanism because the thicker brass does not expand to seal the bore as well.
If you want to try loading Black Powder, here is where I buy my Big Lube bullets:
http://www.whyteleatherworks.com/BigLube.html
I use the 200 grain Mav-Dutchman bullets in my 44-40 and 44 Russian Black Powder cartridges.
Anyway, without further ado, here is how I slug a barrel. Sorry, but it is a little bit long:
Slugging a Barrel
There are lots of ways to slug a barrel. Here's how I do it.
First off you need to come up with a slug. I have used all sorts of things to slug barrels. Ideally, your slug should be just a few thousandths larger in diameter than the grooves you are slugging. If it is too big, you spend a lot of effort driving it into the muzzle in the first place. I have used soft cast bullets, hard cast bullets, soft lead round balls, whatever I have laying around that is just a tad larger than the bore I am trying to measure. I have even taken a 44 caliber soft lead round ball and hammered it down to a rough bullet shape in order to slug a 30 caliber rifle. Some folks also use lead fishing sinkers, if you can still buy them where you live.
When I slug a rifle I lay the gun down on a soft towel on my bench. Or else I support it in a felt lined rifle rack. I do not jam it in place so it does not move. I allow it to slide slightly with each hammer blow, hence the soft towel or felt to protect the finish. I used to slug bores completely dry, but lately I have taken to running a patch dampened with Ballistol down the bore. You don't have to soak the bore. Frankly, I don't think it makes much difference if the bore is lubricated or not, I've done it both ways and don't really see much difference.
Whenever possible, I will slug a bore from the chamber end. However with revolvers and most lever guns it can only be done from the muzzle end. I start with a short rod, only around 8 or 10 inches long. It is much easier to control a short rod when you are whacking it than trying to whack the end of a 3 foot long rod while still trying to hold onto the gun. I grasp the muzzle in my left hand, and jam the slug into the muzzle so it holds still. I also hold the rod in place with my left hand, leaving my right hand free to use the hammer. I place the end of the short rod on the center of the slug to get it started, grasping both the muzzle and the rod in my fist. I like to use brass rods. Some prefer wood, but I find wood splinters and shatters. I start with a brass rod about 10 inches long. I have a few lengths. 5/16" diameter brass will work for everything from 38 (.357) on up to 45.
Most any hammer will do, I have a nice 8 ounce ball peen hammer that works well.
The key here is to not hit the muzzle with your hammer. I start with the short rod. Getting the slug completely into the bore is the hardest part. Once it gets into the bore, it moves more easily. Don't be scared, I have never gotten a slug stuck in a barrel. Just be careful. I change the short rod to a longer rod long before my hammer gets anywhere near the muzzle so I don't risk striking the barrel. I change over to a 3 foot rod to run the slug all the way out the bore of a rifle. I keep a soft cloth by the chamber, so the slug will fall out onto the cloth without marring it.
With a revolver I stand the gun up with the barrel horizontal and the butt resting on the towel on the bench. The procedure is the same. I grasp the muzzle and the rod with my left hand, I jam the slug into the bore, and I control the rod with my left fist. The right hand is for the hammer. A 12 inch long 5/16" rod usually works for all my revolvers.
A few facts about slugging a barrel. The slug only measures the narrowest diameter of the rifling. If there is excessive wear near the chamber, like with some old rifles, the slug will slide along easily through the worn part, it has already taken the shape of the narrowest part of the bore. With a new gun, this should not be a concern. However with an old gun, it can give you a feel for if there is wear in the bore.
The slug must completely fill the rifling grooves. If the slug did not completely fill the grooves, any measurement you take off of it is meaningless. When your slug emerges, look for lengthwise drag marks on it. You should see these marks on both the low spots on the slug, corresponding to the lands of the rifling, and the high spots, corresponding to the grooves. If you don't have drag marks on the high spots, you may not have completely filled the rifling grooves, and any measurements taken from the slug are not as useful.
I hear a lot of guys say you have to measure a slug with a micrometer so you can measure it right down to the .0001 level. Frankly, I think a standard caliper is fine for measuring a slug. Measuring down to .001 is fine, particularly on a dial caliper, where you can interpolate what the dial is telling you between the tick marks. A digital caliper will round off to the nearest .0005, so you may not get as accurate a measurement. But using a micrometer that measures down to .0001 on a soft lead slug is overkill, in This Cowboy's Humble Opinion. Just the act of closing the tool on the slug will deform the lead a couple of tenths, killing the usefulness of the accuracy of the micrometer.
Obviously, you want to measure across the high spots of the slug, to get your groove depth diameter. This is simple if the rifling has an even number of grooves, so that you are measuring across the diameter of the slug. Some barrels though, like many S&W revolvers have 5 grooves. It is very difficult to get an accurate measurement on a slug run through a barrel with an odd number of grooves with a caliper or a micrometer. If you try to add the depth of one side of the rifling, there will usually be some error involved. It ain't impossible, but it is tough.
Slugging a bore is really very simple, I have made it sound complicated. It usually only takes me about 5 minutes to set up to slug a bore, and about 5 minutes to run the slug all the way through. The key is finding a suitable slug just a little bit oversized, and don't whack the muzzle!