Mr. Stanton,

I have recently received a copy of your "Technical Guide". You certainly present a very convincing argument for fire lapping the barrel of any new or problematic firearm.

My question concerns the slugging of the barrel of a muzzle loader to gauge where problems might lie within the barrel. The "Technical Guide" addresses several types of firearms, however muzzleloaders are conspicuously absent from that discussion.

Aside from a meticulous cleaning of the barrel and the application of a lubricant such as WD-40, what would the procedure be? Would one slug be pushed down the entire length of the bore? Or, would several slugs be required to gauge constrictions at various stopping points? Also, silly as it may sound, how does one get the slug out after pushing down the lenght of the bore? Would one use a standard ball puller, or perhaps a CO2 ball expeller?

thanks,
hbennett

For a slug, there are some REALLY big oval egg sinkers available on the market, and their size goes large enough to handle up to .54 caliber Muzzle Loader applications. As you have surmised, it does take a few slugs for sizing determination and for constriction identification.

The best bet is to get the appropriate sized egg sinkers (yep, take the micrometer to a takle department), then start a slug into the muzzle. Then using a traditional ML ball screw, insert the screw into the existing hole in the egg sinker, and extract the sinker. This is sinker #1, and it will give the groove diameter at the muzzle of the gun.

Start a second sinker into the muzzle, get a firm grip on the sinker by again using the traditional ball screw attached to your ramrod/range rod and use that to push the sinker down into the bore until constriction is encountered, push past the constriction, then retrieve back up, throught the constriction again, and retrieve the egg sinker. This is sinker #2, measure and compare with the measurements of #1, it will give you the amount of constriction for that tight spot in the barrel.

Then it's time to fire-lap, lap the bore as discussed in the article online:

http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/48

Then periodically check for constrictions using this method throughout the lapping process of the ML.

You are right by the way, about the absence of mentioning ML's in the Tech Guide. At the time of its writing, I didn't even think about, or consider lapping them.... I don't know why, it just never occurred to me!

Thanks for the questions, and let us know what you find!

God Bless

I've observed on many occasions the lead slug used for measuring a barrels interior show some inadequacy. A soft lead slug larger than the groove diameter of a barrel can be swaged into the bore and even though it is larger than the bore it can leave space between the lead and the bottom of the grooves.
The grooves are what one is uaually trying to measure so if the lead slug doesn't get to the bottom the measurement would be erroneous. Cap&ball barrels are really good for showing light in the grooves after an oversized lead slug is inserted.

Put an oversize lead slug into a bore. Push it in a ways. Look thru the barrel at a window,or better yet a flashlight, and observe the light showing thru the grooves. Mostly the corners of the grooves.

Lead is somewhat elastic and when the lands of the barrel force lead backwards off the lead slug it also pulls lead out of the grooves enough to leave a space.Not all barrels do this. It seems to be dependent on the depth of the rifling. Muzzleloaders usually have deep rifling and show the light between the lead slug and the bottom of the grooves. Anyhow the proper way to slug a barrel is to remove the breech plug. If the plug can't come out or the person doesn't wish to do that the lead slug can be pushed to the breech face and wacked to upset the lead and fill the grooves. If the plug comes out then an opposing rod needs to be inserted to be able to "bump up" the lead to insure it actually fills the grooves completely. Several positions naturally are used to measure different parts of the barrel so the measurement shows any constrictions. If the lead slug is just pushed in all the way and pulled out it shows the smallest diameter across the grooves only.
If a person wants to measure a barrels interior properly then the use of "Cerrosafe" is the key. It is an alloy made for measuring bores and chambers. It is melted like lead and poured in the chamber or barrel to a certain position and left to cool. Naturally the barrel has to be blocked off with something so the melted cerrosafe doesn't just run out. The cerrosafe doesn't shrink when cooled to any appreciable amount so that isn't a worry. The cerrosafe plug poured in,cooled and pulled or pushed out will give a really close measurement.Cerrosafe is reusable and comes with an instruction paper. You know about warming the barrel prior to pouring the cerrosafe and all.I think that aspect of lead being forced into the lands of a rifled barrel and pulling lead out of the grooves a small amount when the lands push lead backwards causes some problems with shooting lead. I guess there is a reason that lead bullets sized right to or.001-.003 oversize for the grooves of a rifled barrel are considered optimum.