Gunsmithing Hand lapping factory bore

[bohem]

Another forum (6mmbr.com) brought up a point about hand lapping factory barrels.

The general idea seems to be a plastic bristle brush, some 0000 steel wool and JB Bore paste.

Put a plastic or wooden stopper in the muzzle so you don't pass the lapping equipment through the muzzle.

Count 50 or so strokes through the barrel and watch for crud buildup and clean appropriately throughout the 50ish passes.

Result is a lapped bore that will shoot better and clean easier.

Anyone ever done this? I'm intrigued and very nervous to try it at the same time. I was thinking about doing it to a Turk Mauser first. If it screws it up no one will ever know, and I have several 8mm turk barrels on the shelf I could replace it with if I REALLY screwed the pooch.

If it works well I was considering this treatment to a 204 that I'm getting in soon. I don't have money for a custom barrel, I'm impatiently waiting and thinking about how I can improve something (even though I don't have it yet, anyone else know the feeling?)

 

[Dans40X]

Re: Hand lapping factory bore

Slug & hand lap is a better option.

 

[Victor N TN]

Re: Hand lapping factory bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DANS40X</div><div class="ubbcode-body">Slug & hand lap is a better option. </div></div>

++1...

Once again Dan is on top of the situation.

If casting the bore isn't an option, a tight fitting patch on a jag will work. I have had to use 2 patches on an undersized jag before. But the main thing is to get a very snug fit to hold the lapping compound in place. I usually finish up with 400 to 600 grit Clover brand lapping compound mixed with a little heavy oil to keep it in place.

 

[bohem]

Re: Hand lapping factory bore

I take it you mean make a lead slug, roll it in polishing compound and shove it through the bore?

EDIT: I see someone else has clarified, thanks.

Casting the bore isn't a problem for me, I don't have a 20 cal mould but I can just turn a larger lead slug down on the lathe.

 

[WRM]

Re: Hand lapping factory bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">I take it you mean make a lead slug, roll it in polishing compound and shove it through the bore?

EDIT: I see someone else has clarified, thanks.

Casting the bore isn't a problem for me, I don't have a 20 cal mould but I can just turn a larger lead slug down on the lathe. </div></div>

You cast the lead into the bore, so it matches the rifling. And you NEVER completely remove the lap from the bore until it's complete....

Bill

 

[bohem]

Re: Hand lapping factory bore

Victor, Dan, WRM, thanks.

If I cast it into the bore and don't remove the slug until the job is finished am I putting lapping compound into the bore before casting or do I cast, removed, coat in compound, reinsert and THEN not remove until lapping is finished?

 

[Dans40X]

Re: Hand lapping factory bore

A jag & patch works also as Victor in TN has described.

Scope the bore.
Do not reverse direction-push the jag/patch all the way down the barrel past the crown.
Remove the patch & jag from the rod,extract the rod.
Flip the patch on the jag.
Push it through the bore.
Remove patch/jag.
Discard first patch.
Compound up another patch.
Push through bore.
Flip patch & push through once more.

Run 2 wet patches of bore solvent through bore.
Run 2 dry patches through bore.
Run 1 wet & 1 dry patch.
Scope the bore.

I prefer 400/600/800/1200 grit silicon carbide compound in an oil base solution.

The above procedure is for dirty//copper fouled/button rifled production barrels - ONLY.

 

[WRM]

Re: Hand lapping factory bore

Lap is cast inside barrel onto rod fitting, so you can swab it back and forth through the bore with the rod. Lapping compound is applied to that portion of the lap extending past the end of the barrel and pulled back "in". Just do not push/pull the lap all the way out, or you have to start over.

It is generally not performed on finished barrels, because often the last inch or so at each end is cut off.

I'm familiar with the concept, but have never actually performed this process.

Cheers,

Bill

 

[bohem]

Re: Hand lapping factory bore

Thanks guys. I'm going to try this on an 8mm barrel first to practice before I put it through a barrel on a functioning rifle.

 

[WRM]

Re: Hand lapping factory bore

I'd recommend the patch routine as described above. Lead lapping really is for before the barrel is chambered and finished.

Good luck,

Bill

 

[bohem]

Re: Hand lapping factory bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body"> Lead lapping really is for before the barrel is chambered and finished.
</div></div>

Thanks, the patch method seems like the easiest way not to screw up when I don't have any experience with this.

 

[Victor N TN]

Re: Hand lapping factory bore

When I cast a bore I actually have a cleaning rod end that I put in the barrel, submerge the end of the barrel in the lead pot and draw back the rod a couple of inches and let it cool in an upright position. (Oil the bore right before you do this.) Then when the lead cools I pull it back through and apply the lapping compound to the exact reverse of the bore.

If you're using an old pitted barrel, don't do the casting thing. Pits in the bore can stop the lead slug fast in it's tracks.

Good luck with this project. Remember to stop and look several times along the way. Once metal is removed, you can't put it back.

 

[bohem]

Re: Hand lapping factory bore

The 8mm I have in mind actually is a nice barrel, my dad and I bought about 25 mausers at one point and turned a number of them into new creations. Thanks for the advice on the pitted barrel, the one I'm going to use is pretty nice, no pits, no dark areas, but I'm sure it was never lapped before it left the wartime factory.

 

[BLAWTON]

Re: Hand lapping factory bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body">Lap is cast inside barrel onto rod fitting, so you can swab it back and forth through the bore with the rod. Lapping compound is applied to that portion of the lap extending past the end of the barrel and pulled back "in". Just do not push/pull the lap all the way out, or you have to start over.

It is generally not performed on finished barrels, because often the last inch or so at each end is cut off.

I'm familiar with the concept, but have never actually performed this process.

Cheers,

Bill </div></div>

Yes i see that. Well if your casting a lead lap for the barrel removing it is not a problem if you can get it back in without bending it or crossing the rifling. Best thing for you to do is take a rod just under the size of the barrel and make a brass fitting about .005 smaller then the land bore size of your barrel. Prop the barrel upright and make a ledge to set in on so you can control the length of the lap. for a small barrel like a 204 a 2-2.5" lap if preferable cause its very easy to bend. I would use a 240 to 400 grit lapping compound. always lap the back more then the front but dont go crazy. You can feel if its getting loose by the resistance you have on the lap. You want a small amount of taper from bore to muzzle but to much is just as bad. I use a alum handle with some washer or bearing to allow it to spin freely in the bore. Dont force nothing or you will wear off the sides of you lands and that will not be good for the life of your barrel. This is not a easy task and i would suggest you calling someone who has done it alot to get some extra hints. I would be willing to help you out if needed. But again you cant replace metal you have taken out so be careful!!!

 

[BLAWTON]

Re: Hand lapping factory bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body">I'd recommend the patch routine as described above. Lead lapping really is for before the barrel is chambered and finished.

Good luck,

Bill </div></div>

To solve this problem i will take and just barley cut the neck off of a case and drill a hole in the primer area. apply some very thin tape to the outside so you dont scratch the chamber in it and it will keep you from lapping your throught out of the barrl.

 

[pac-nor338]

Re: Hand lapping factory bore

You can lead lap the barrel but not a good idea with the action on. I work for Pac-Nor and we sometimes lap chambered barrels but you have to be careful not to scrach the chamber. Personaly I wouldnt even try Laping a barrel that is full of reamer marks aint gonna make your gun shoot that much better.

 

[BLAWTON]

Re: Hand lapping factory bore

Thats true its would help alot if you were experienced at it. Some people we have hired have taken close to a year most of the time before the get good at it. It takes a nack to feel how the bore is doing without having the proper equipment to measure how its going.

 

[bohem]

Re: Hand lapping factory bore

Thanks guys. I'm all ears at this point (or eyes, as it may be) and I appreciate the information.

I want to see how it shoots before I do anything, I was told on a 204 Forum that some shooters have had to lap the factory barrels.

The ideal thing for me would be to just put a match barrel on it and be done, but the cost of making the tooling to get the action loose, buy a reamer, buy a barrel, etc. would cost me close to what the rifle did even before I had to buy my dad a case of beer for his time.

I don't doubt the rifle will shoot well, but I was hoping that this would be a relatively straight forward process that would help with barrel life and accuracy without too much risk of ruining my stick.