If there is anything I have learned in the past 36 months....it is that full bore hard cast slug/bullets react the exact same way as smaller hard cast bullets! All that we all have learned (the hard way) about cast bullets still apply, they are just bigger.
I see quite a variation in the rifled shotgun barrels. Groove diameter varies from under .727" ot over .730".......so slug bullet diameter is important. Leading is not a bad problem on hard cast in these barrels......why I am not sure. Pressure?
Now.....Why would it not be possible to fire-lap one of these barrels if you wanted to? I was thinking about a series of tight fitting cut wads with grit on them? With a very light load of some powder like Unique.....you could blow out quite a stack of wads? What do you all think?.....James

Follow up....We just loaded and fired a new primed 12 ga-3" hull loaded with 12 grains of Unique-one .200" hard nitro card and three 1/2" hard Alcan cut wads. Retrieved wads show they filled out completely, having the rifling marks on them.....no grit.
So, What do you all think?........James

James, For once I will disagree with you! Sure took a long time coming for this one, but finally we get to actually argue! :D

I'm no fan of fire lapping, seen far too many good guns destroyed by it.

Here's my beef:

First, you have no control over what's happening from the time the hammer falls. Slight variations in hull/case thickness, mis-allignment in the chamber and so forth ... while these are often tolerances that don't mean squat to the results, when you take to fire lapping, they mean everything!

I don't care if you're using wads or bullets, the minor tolerances seen on chambering that are usually corrected by the forcing cone now become a major problem because instead of correcting error, the correction factor is now being cut down. The abrasive used does not care if it's cutting the forcing cone or the bore or the rifling. It's cutting as it goes and will cut at anything that gets in its way.

Most gun makers use a lot of care cutting the chamber/forcing cone/throat so that it is alligned as best possible with the bore. Now, you chamber a round that is loaded with cutting agent and blow it through through so it can wallow out the cone/throat to match its mis-allignment. Once you bugger this up, you may as well forget about the bore because no matter how good the bore is, if the bullet does not enter it properly, it ain't worth crap.

Think about this, if all the cases/hulls were perfect, we wouldn't need the cone/throat at all now would we? It's there simply because no matter how much care you put into loading a round or manufacturing a case or hull, there is going to be some amount of tolerance and if not for this allowable tolerance, most guns would never work properly at all.

I know a guy who went out and bought a new S&W 429. Front of the cylinder was bored about .002" too small. He ignored my suggestions to send it back and let S&W fix it or at the very least take it to the competent machinist I knew. He read all about fire lapping on the internet and enlisted the help of another friend who was "the fire lapping king". Together, the two of them managed to take a gun with a minor problem and turn it into a gun with major problems. They managed to open up the cylinders but they were not cut concentrically, they also managed to bugger up the forcing cone to the point where jacketed bullet would strip copper off as they passed through. He finally ended up sending it back to S&W who were more than happy to charge him for the new cylinder, new barrel, installation of both and return shipping. Now he had a brand new $450 gun he spent about $750 on not counting all the time and materials wasted!

The machinist I suggested he use has lapps he made himself. To open the cylinder up .002", it would have taken about 1 hour and cost him $75.

The only way to properly lapp a bore is with a long lapp and by hand so you eliminate the errors instead of creating more damage. You've got to stay out of the cone/throat completely unless this is what's buggered up and then the only recourse is to possibly have it re-reamed but in most cases you'll find replacement will be the only 100% cure. On cylinders, you need to use a piloted reaming lapp or you will do more harm than good because they will never come out round.

Hello Friend Mark and All........Sorry, Mark, but you missed your chance again! If you read my previous posts, I have always been leery of fire-lapping, prefering my old method of lead lapping. You bring out some good points....and I wanted feedback.
What I might do is make up a rod tip that will hold a series of felt wads and polish the bore with that? Greg Sappington sent me some cerium (sp) oxide that he has been using on bores. He has had some excellent results with it. By applying a little oil on the wads and rolling the edges in the oxide, it might work?
If you relly feel the need to jump my case (in fun I hope!), go over the Shotgun Wold's Slug Section and join the shotgun sabot shooters! They have been calling everything Ole' Dixie makes Flying Bricks and not good for much! They seem to be looking for a 200 yard slug load? They get very upset when I bite back....those Northeastern fellows can pop off at the mouth, but can't understand why someone comes back at them?
Oh well! Such is life!......Regards to All, James

No fun here James, I'm really PO'ed at you and if you don't send me some free Dixie slugs I may actually mean that! :D :D :D

Of course it's all in fun, I haven't had a reason to disagree with you till now but I see even this time it seems I can't do it! :( LOL

I'll agree, I use felts for light polishing, leather if it needs a little more smoothing and lead for when it needs "work". Easiest way to make a mandrell for the soft lapps is to get a 4" long 8-32 or 10-32 machine screw or piece of threaded rod (whichever fits your cleaning rod). Cut the head off and touch-up the threads so it'll screw into the rod. Run a 5/32" or 3/16" bit through the center of the wads, slide them over the t-rod, put a washer & nut on the end and snug it down. Harder you crank the nut down, tighter the lapp gets in the bore.

Something to keep in mind, super sharp edges on the rifling lands is not necessaroly a good thing, knock the corners off a little and accuracy will settle right in. Leaving the rifling real sharp more often than not ends up causing variation in the accuracy, goes back to my comments as to why you should burnish a new rifled bore right from the start.

I never used the cerro whatever so I can comment on it. Depends on what I need to do as to what I go in with. If it's just a light polishing, I use Top Bright. If I'm looking to burnish the bore and don't have an steel or bi-metal jacketed ammo to run through it, I use my non-embedding iron compound.

First thing I'd do is push a slug through by hand and see if there's any tight/loose spots and make the plan of attack from there.

Great returns, Mark......Thanks. The barrel in this Mossberg 695 is not near as smooth as the Hastings barrels we have, It also runs tight.....for sabots?
I'll keep you updated........James

How tight is it? Bore tight or groove depth tight?

Mark and All.......yesterday, Little Hank and I put on kinda show up in the North end of Dixie County (Guntown) for a group shooting Tri-Ball II. We also shot a couple of prototyge ASSA Target Loads in the "Pig"......730"-730 gr @1050'/". The holes showed that there was some bullet tipping????? This same load is Very accurate in a Hasting barrel (.717"land-.728"groove). We drove a Terminator in the Pig's barrel and it appears as tight as .725" in the grooves? I think the slug is swagging into the barrel, when fired, slighly off line??? These prototype loads had heat treated slug/bullet that a very hard. I don't plan to use them in the final production run. The fellows are going to retest with a slug/bullet about 10bhn........More later, James

The cerium oxide has the interesting quality of being herder than annealed steel, but not as hard as Full hard steel. mIt has not shown any type of wear on steel in my experience. It will remove fouling, and help smooth burrs. I tried to test it on a buffer at 3450RPM on steel to see if any damage would result.`after several seconds. no change was visible. This type of abrasive is intednted for glass cutting, not for steel. However it is much safer for the bore than Aluminum oxide, silicon carbide, aqnd sapphire abrasives. I am sold on this material for cleaning, and burnishing.

Greg S

Followup on the Mossberg 695 ("Pig")......turns out that the ported barrel did not like the double (2) Alcan Air-Wedge over powder wads! Went back to our regular BPI X12X OP wads and now nice little round holes in the target!.......strange?
Regards, James

Mark, to get back to a point you made.... any decent reference on the source would have said to fix cylinder throat diameters BEFORE lapping barrels. 0.002" is way to much to lap, should have been reamed. Then lap barrel - if needed at all.

They simply used the wrong tool for the job. Can't make a foolproof process.... always can find a better fool! Course those guys might have screwed up the reaming, too.....