Lapping a barrel

[cynthialee]

How long would it take to lap a CVA barrel smooth by hand?
What lapping compounds would be the ones to use?

 

[bubba.50]

I've had fairly good results usin' a jag a couple calibers smaller than bore size, green scotchbrite, and valve grindin' compound from the NAPA store.

how long it takes kinda depends on how bad the barrel is to start with & how easily yer arm gets tired.

 

[Larry Akers]

The correct way to lap a barrel is to cast a lead slug around a screw (or other carrier)in the barrel and re-cast as the slug wears. I have made laps from leather discs, which are oversize for the bore (ie .500 for a .45), stacked on a machine screw to a length of 1/2 - 5/8" and use a multi-grit valve grinding compound. You can also fire-lap the barrel by using the valve grinding compound as a patch lube.
As Bubba said, how long it takes depends on how bad the bore is.

 

[Scota4570]

Lapping, using a cast lead slug, always from the breech end. Use a fat steel rod with a guide, a big bulbious handle, and wear leather glooves. Cast the lap on a piece of all thread. Use two nuts around leather washer to keep the moulten lead from leaking down the bore. Use valve grinding compound, 120 to start and 240 to finish, maybe 320 if I am feeling ambitious, then a little steel wool and semichrome for the final polish. I take enough steel to make a choke, maybe .0005". I might cast 5 #120 laps, one each of the smaller grits. I add wood screws to the laps to swell them between grit aplications. It takes several hours and my hand usually gets a blister.

The CVA breech plug will be a problem to line up perfectly and reinstall the drum.

 

[bubba.50]

I would pretty heartily recommend that you NOT try to remove the CVA drum & breechplug! yes, it has been done but probably ten times as many have been screwed up as have been re-installed successfully.

 

[cynthialee]

I am not touching that drum and plug.

The plan is to get the compound and just zone out on the barrel while watching the tube until it is done. I am guessing it will take awhile.

 

[kansas_volunteer]

Lapping with a cast lead lap is the only way to get a truly smooth bore. Scotchbrite pads probably only knock off a few burrs. Take one of those pads to a steel cooking utensils or similar and see how long it takes to get a polished surface.

I've had a 5/16ths rod welded to the axle of the front hub from a bicycle. Reassembled the thing became a lapping rod free to rotate the working end of the rod was notched to keep lead on the rod from working it's way off, as the all thread rod would.

Cotton string wrapped around the rod, and a tight fit in the bore will stop the molten lead from running down the bore.

You really don't need to polish with much more than a 220 grit.

I don't know how the CVA breech plug is fit, but I wouldn't hesitate to pull the plug on a T/C or similar. A beech plug wrench for lack of a better word used to be sold by T/C for the purpose of removing the breech plug. I still have mine.

When casting a lead lap it helps to heat the barrel before pouring the lead. Use lead as it melts at a lower temperature than some alloys of lead.

 

[bubba.50]

no, scotchbrite won't lap a barrel---by itself, neither will a lead slug---by itself. that is the reason you use valve-grinding compound or some other form of abrasive with either one.

but I DO like that bicycle hub/rod idea. :thumbsup:

 

[54ball]

Ok....

With a good rod and cleaning jag with scotch bright, various grades of steel wool, you,can significantly improve a rusty barrel.

This will hit the high spots and smooth over the big pits. On a really rusty barrel it will be easier to load but after a few shots it will foul and will never load as easy as a new barrel but it will be usable and even accurate.

Lead lapping is a little more involved and will improve a pitted barrel more so than a jag with abrasive. It is more work and in my opinion valve going compound and lead is too aggressive, I would go with a very fine polish compound like the wax based compounds for stropping chisels.

On a CVA, as mentioned you will have to work from the muzzle.

Refreshing...

This can also be done from the muzzle with care. Traditionally a good wooden rod was used. This rod was notched for the lead slug to grip the rod. You want your slug say 2 to 3 inches long. The barrel should have enough rifling left to imprint on the slug.
A small piece of steel is filed to the same shape as the raised groove on the slug. Then teeth are cut into this piece of steel. This little piece of steel is dovetailed....wider at the base. The lead slug is dovetailed to accept this "cutter".
When placed into the dove tail this cutter should match the raised groove on the slug near perfectly. The dovetail for the cutter should be in the middle of the slug so the cutter follows the groove.
After the cutter is made it is hardened.
One groove is cut at a time. Paper is used to shim the cutter for a deeper cut.
One groove is cut....the tool is then repositioned for the next groove.
This will eventually refresh the barrel except for the area just ahead of the breech.
A .45 may finish out to say a .47...

While maybe a good historical display.....

In the real world you can get good results and see improvement with just steel wool and or scotchbright pads on a jag.

 

[Billnpatti]

How long would it take to lap a CVA barrel smooth by hand?
What lapping compounds would be the ones to use?

You didn't say why you wanted to lap your barrel. Is it new and has sharp edges on the lands and tool marks in the grooves? Is it rusty and needs to be polished up to remove the rust? I have never polished up a badly rusted or pitted bore and cannot recommend the best way to do that job but I have polished up some lightly and moderately rusty bores and smoothed up some new ones with just Scotch Brite on an undersized jag. It needs to be a fairly snug fit. It may take as many as 400 or 500 strokes to get it polished. I change the Scotch Brite patch after about every 50 strokes. I flip it over and use the other side after about 25 strokes. A Scotch Brite pad will give you plenty of patches for polishing your bore so no need to try to get more than about 50 strokes from each patch. Don't waste your time and effort using a worn patch. I put a drop or two of oil on my Scotch Brite patch. Fasten down your barrel and stroke away. When you have finished about 500 full length strokes, wipe out your bore with a clean dry patch and use a bore light of some kind to check to see that you have gotten your bore as polished as you want.

 

[kansas_volunteer]

The best way to lap a barrel is from the start, lapping it before it is rifled will leave the tops of the lands polished and the bore concentric. After rifling lapping will polish the grooves.

Unless you have a barrel the maker or someone has already lapped it's almost certain you will feel rough spots and tight spots as you work the lapping rod. You'll know when it's smooth.

It isn't likely you will have a cold hammer forged barrel formed around a mandrel, but this sort of barrel should not be lapped as it will already be very smooth inside. Lapping will only scratch it up.

I do like the idea of using leather as a lapping slug. I think it might work as well as lead.

 

[M. De Land]

The trouble with leather is that it is springy. Lead is not and maintains it's cast profile width until it is worn down.
I don't like lead bump up slugs either as they do not swell uniformly their full length.
I cast a slug and use it recharged every 50 trips up and back for 5 cycles for a total of 250 round trips then clean the bore and cast another. It is the only accurate way to keep it's length parallel to the bore.
Also lapping a bore to completion removes perhaps two or three ten thousands and not much more.
It usually is good for taking out the tight spots but will never remove a pit that are any deeper.
Lapping also takes more off the land than groove bottoms as they are the high points in the bore. A land is being lapped on it's top and both sides but the groove only on its face.
I once did a barrel that took 2500 round trips total using three different grades of lapping compound, 220, 340 and 400. Valve grinding compound is far to course in my opinion.
One needs never go over 400 grit. It must be remembered that the grit size initially applied wears and fractures down with use cutting progressively smoother just as sand paper does.
The lap rod should have a bearing T handle and never used without a down bore muzzle guide. I use rimmed brass cases with the primer pocket drilled out to lap rod diameter.Keep the grit covered rod entirely off any part of the bore.
I should also be stiff enough not to flex contact with bore while in use.
Here are some of my lap rods and associated equipment:


The case is a down bore muzzle protector/guide.
Picture of the jags and string dam for casting the slug.

 

[M. De Land]

Barrel in vice with lap rod and string dam behind the jag for casting the lap. Heat the barrel with a propane torch for a few minutes before casting to get out the lap wrinkles.
I usually anoint the bore with a bit of gun oil before casting. When it begins to smoke the barrel is hot enough to pour the lap.

I make my laps about 2.5 inches long and always apply the lapping compound from the breech even in chambered cartridge guns. It can be done from the muzzle but it is always better from the breech if possible if you hope to work in choke.
Also one does not have to apply grit to the whole length of the lap. It will work up over the entire length in a couple of trips up and back.
Once the lap is poured one does not want to loose index until removed for a new one.
Keep it in barrel index and charge only the lower half or third. Besides a fully grit covered lap can jamb up in the barrel and have to be melted out and you have to start over.
Also, after the cast and before charging the lap, oil the bore and run the lap up and back several times.This will make the first trip with the freshly grit covered lap possible.
Let the barrel cool down from the lap casting process before you begin or it will not be the same diameter as when cool.

 

[M. De Land]

The green tool in the first set of pictures is a lap stop that is clamped on to the muzzle end so you don't push the lap out to far and loose barrel index.
No two lands and grooves are exactly the same especially in cut rifled barrels so maintaining index is important even in modern buttoned and forged barrels.

 

[hanshi]

I've had good luck fire lapping one of my rifles. Just used ball & thick patches rubbed well with JB polishing compound. Made a real difference.

 

[Zonie]

A number of years ago, I sketched up this lead lap design.

After the lead has worn from the lapping operation it can be removed and placed with its ends between the jaws of a vise.
Tightening the vise just a little bit will cause the diameter of the lap to enlarge.
As we are only talking about a couple of thousandths of an inch or so, it doesn't take much compression with the vise jaws to refresh the lap.

(Right click on the link and select "open link in new tab". Then open the new tab that pops up to see the picture. Left click on your old tab to instantly get back to the MLF.)
http://img.photobucket.com/albums/v85/JAMESKING/xtra/lap.png

 

[Scota4570]

That is a simmilar idea to what I do. I cast the lap on a piece of all thread. I use jam nuts around leather washer to prevent lead leakage. String is fine too. To incrementally expand my lap I drill a hole down the middle of it and use a drywall screw.

#120 valve grinding comopund works. It is not possible to lap a pitted barrel to smooth with fine abrasives. Using very fine abrasives, you could work it until your hands bleed and not make any progress. You need to actually remove some metal. After it is uniform, pitfree, and has some choke. I use finer abrasives. Get real deal,aluminum oxide grease based abrasive, clover used to sell a little double ended can. Mine lasted 30 years. The kind that break up and goes away will not do.

I have never removed a CVA breechplug. I would speculate that if the mating shoulders we relieved a hair, it might be easier to align it precisely and reinstall the drum without damaging anything.

I'm not sure any of this helps Cynthia. She was asking about polishing a barrel and called it lapping. For her goal steel wool or Scotchbrite and some Semichrome metal polish will make the bore sparkle. Use a bore guide to avoid crown damage.

 

[M. De Land]

Well, it will bump up on both ends and part of the length but it won't be parallel and apply equal radial pressure its full length as would a fresh cast especially if two or three inches long. Longer laps, up to a point, track better and more uniformly level the bore than does a short one. Actually a level bore will shoot just as well as one with choke in my opinion. Tight spots are no good as well as a long taper toward the muzzle especially with conicals.
Patched balls seem to do fine with even long cones in the muzzle.
A patched ball will alloy more bore problems than a lead bullet and still shoot well as long as it is not torn.

Also cleaning rods are not the best choice as they usually are not stiff enough to avoid flexing into the bore wall when pushed on a freshly charged lap and almost never have a T handle or good thrust bearing on them.