lapping the bore

[Bert]

What is the material/technique that some of you all use to lap the bore?

 

[mgcrumster]

Bert, The book, "Shooting and Winning with the Champion's" by Don Davis, has a in depth article regarding bore lapping by Web Terry, Web is a Benchrest barrel builder/shooter with tons of experience. I think this book is out of print, but can be found on the net at used book suppliers like Alibris... Best wishes.. Mgcrumster..

 

[Blizzard of '93]

get a 3" machine screw that fits thread of your cleaning rod. likely 10-32. on the head wrap steel wool around until it is a snug fit in the bore and run it in leaving about 3/4" exposed. pour lead in the barrel, let cool and pull the 'lap' out. charge it with fine valve grinding compound by smearing on and rolling the lap over glass firmly pressing.
insert lap into bore and expend some elbow grease. try to keep the rod centered in the bore as you go back and forth. it will take awhile and you may have to recharge the lap with grit.
I have used 3M handpads with good results to 'shine' a bore up. make a 'patch' out of it and use next size down jag to scrub the bore.

 

[J.D.]

Lapping is not to be undertaken lightly. Improper materials or techniques can seriously damage a bore.

Valve grinding compound is to be avoided at all costs, as is polishing with an abrasive on a cloth patch.

VAlve grinding compound is not consistent in grit, and will not provide a smooth bore. The larger grits within the nominal size grit will cause scratches that can cause problems of their own.

Abrasives on a patch will wear the edges of the lands, essentially wearing out the barrel.

Using patches of green scrubbie pads on a smaller jag works well to remove sharp wire edges from lands that cut patching, but worthless for anything else.

I also suggest The book, "Shooting and Winning with the Champion's" by Don Davis as an excellent resource for lapping equipment techinque.

 

[spitpatch]

Simple. Shoot it a lot!! Thats what works best for me after many years an many guns.

 

[LRB]

Well said JD. It seems many people have little understanding of what lapping really means. You said it all better than I could have. True lapping is nearly an art. I have done a little, but only on barrels that had such problems that I could do no harm.

 

[gmww]

I've been wondering the same thing about lapping. In Modern rifles they sell stuff that you roll a lead bullet it and fire lap.

I was wondering if a patch with JB Bore shine around a RB might do the same thing.

 

[J.D.]

I was wondering if a patch with JB Bore shine around a RB might do the same thing.

I'm not an expert on lapping, by any stretch of the imagination, however, I wouldn't even consider fire lapping this way.

IMHO, there are only two reasons to lap a bore.
1. a rough bore that can be improved by lapping.
2. A bore of inconsistent diameter.

By inconsistent bore, I mean there are tight and loose places in the bore. Proper lapping will even out the variations in diameter.

Lapping just for the sake of lapping is NOT a good idea.

IF one should decide to fire lap a ML rifle, IMHO, only hollow base minis or bore diameter maxis should be used. By bore diameter I mean groove to groove diameter, not just land to land diameter. Gotta get down into the grooves if you are going to do any good.

It is also necessary to roll the bullets in proper 220 and 320 grit lapping compound. The simple act of correctly rolling bullets in compound is more complicated than one would think.

Very light powder charges should be used, jsut enough to expand the skirt on minis, or just enough to eject the bullet.

A thorough cleaning between shots is also necessary. Gotta remove any lube, grit, and fouling if you expect to get an even lapping.

IMHO, its MUCH better to remove the breech and do it right.

IMHO, the only reason to fire lap, considering the aggravation involved, is on a production gun where the breech plug cannot be removed.


Wick,
Thanks for the compliment.
I have done several barrels. All a little rough. All turned out very well. I did have a lot of support and a lot of instruction prior the process.

One production gun was fire lapped, the others were lapped conventionally.

Again, I'm not an expert, but I did my homework prior to the attempt, and I did learn a lot from a coupla experts.
J.D.

 

[faw3]

JD has it right , Ive always done it from the breach end and beive thats right , isnt it?? someone??? Also just shooing a few 100 balls thru seem to do the same thing. Fred :hatsoff:

 

[J.D.]

JD has it right , Ive always done it from the breach end and beive thats right , isnt it?? someone??? Also just shooing a few 100 balls thru seem to do the same thing. Fred :hatsoff:

Yep, it's best to go in through the breech.

Shooting a few hundred balls will usually slick things up enough, and sometimes it won't.

The key word is "enough." Some barrels do need sharp burrs removed from the lands, or machine marks smoothed. Most new barrels don't have as many issues and will shoot in very well after a break-in period. A few won't.

An addendum to my last post, as a result of the rediculously short edit time, any minis intended for fire lapping need to be bore diameter, land to land diameter, so's the skirt will completely fill the grooves.
J.D.

 

[410-er]

I used 0000 steelwool on a jag and oil.Start stroking.Wash with soapy water.It might not be the most scientific but it worked wonders!I do this now on all muzzys I get.New or used.

 

[LRB]

That is not lapping. That is removing burrs from the edges of the lands, which does no harm, but if you went to far using anything coarser, you could do damage by rounding the edges to where they may not grip the patch as well, and accuracy may well suffer. True lapping polishes the surface of all angles evenly, and as JD said, removes tight, or loose sections in the bore, when properly done.

 

[Blizzard of '93]

you are wrong there JD, pouring a lap in a rough bore after it has been cleaned with brushes will clean it up fairly well, I have done this several times. mostly on guns that had been 'cleaned' after firing and set aside for some time. this procedure got the rifle to shoot PRB's. they were basically 'unshootable' before I did the casting/lapping procedure after brushing/cleaning. some of them were so rough I used 'coarse' compound to start with. your mileage may vary. this will not remove bad pitting but will make an 'unshootable' bore shoot fairly well with PRB's. my apology if you mis-understood my reply. even a 'new' bore should be treated with caution. :thumbsup:

 

[faw3]

Well put about some will shoot better , I've always got a kick out of guys that wont touch a mirror smooth barrel, a lot of the older one wasnt 15 to 30 yrs ago, Ive had some that have ? well it looks like someone took a knife to the land and took chips out, but do the last 5 to 9" of that barrel right and Ive got some great shooters out of them. Fred :hatsoff:

 

[Scota4570]

The process of lapping a bore is surrounded in mystery and myth. I've lapped about a dozen barrels. It is not difficult and you wont hurt anything, if you use common sense. IF you are ham fisted step away. I have examined barrels microscopically before and after, I lapped them. Proper lapping, IMHO, won’t hurt the average button barrel. Remember, good quality barrels are lapped. You would be amazed at the tight, loose and rough spots in a barrel that looks good to the eye. I normally put a slight choke in cast bullet barrels and a significant choke in round ball barrels. A choked round ball guns is so easy to load and all of mine shot well.

I lap with wheel weights cast on a machine screw. I use leather washers to center it. I use tapered wood screws to expand the lap. I use a steel rod and guide. I use valve-grinding compound. I start at 80 and progress down to 320.

I am trying to remove material! I want the bore to be uniform. This may take half a thousandth to get it all trued up on a crummy barrel. I take the burr off the breech end with a Dremmil stone. You need a tiny bit of taper to put the lap back in. Heat the barrel to make the lap cast without wrinkles.

Initially I charge the lap at the muzzle end. Mark the 12-o'clock in the lap. Expose the lap and smear a little compound on it. Pull it back in. If you tak it all the way out you may loose your index or have it bind. All the lands and grooves are not exactly the same. Hose the inside of the barrel with oil from the backside and into the muzzle. It should always be swimming in oil to float the steel out and prevent binding. Once the lap gets loose add a little more compound. Once that won't tighten it screw the wood screw in a bit. Recast the lap when it won't tighten or it get buggared. Don't roll it on glass to add compound. The slightest damage to the lap will jam it. Once you have a choke you will need to tighten it up before you can do any cutting. Do that thought the muzzle with the screw. You can also tap it with a brass drift to upset it.

You will wear a blister on your palm with #80 before much happens to the bore. Sorry guys, all this business of ultra fine special abrasives is bunk. BTW use real grease based valve-grinding compound. That water jell stuff that breaks down is useless. Grit imbedding in the bore it a myth. Look at the barrel you just draw filed and polished, see any grit in it from the sand paper?

Have fun, practice on a junk barrel the first time.

 

[Blizzard of '93]

good read and my point exactly Scota. I have salvaged unshootable barrels using a cast lap and valve grinding compound. I also use oil in the barrel when lapping(forgot to add that). it would take many strokes with coarse to do much damage. I also do this with good barrels to get tight spots (usually near sights, barrel wedge pin hooks and rib screws) out. shoots better particular with slugs.

 

[J.D.]

Right on Fred. New barrels with chatter marks, or too sharp edges on the lands can be improved with judicious lapping. Gotta do it right though, no half assenine techniques.

Blizzard,
REad closer, smoothing a rough bore is one of those reasons to lap. Again, gotta do it right.

I was taught that the lap should never be removed from the bore, unless it is marked and reinserted in the proper grooves. The "lands" on the lap need to be mated to the groove it came out of.

I was also taught that the lap should be a coupla inches long. I don't know if length of the lead lap really matters, other than longer laps carry more grit. Long laps also bridge the loose spots in the bore better.

While steel wool and green scrubbies work well for removing heavy rust deposits, personally, I would use something other than steel wool to make a dam to form the lap.

I use several layers of canvas patches pierced in the center to fit on the screw. The patches are a little larger than the bore and sandwiched between a coupla nuts, smaller than the bore.

IMHO, Canvas is easier on the bore than steel wool.

The rougher the bore, the coarer the grits needed in the beginning. I would still avoid valve grinding compound. It might work ok on a real rough bore, but there are better, although more expensive, alternatives.



Scota
That is exactly the reason I feel that lapping for the sake of lapping is not productive. Too many people don't know what they are doing, and don't want to do the research to learn how. And, unfortunately, common sense isn't all that common any more.

Your mention if a guide is important too. Mine is essentially a bolt of the same thread of the breech plug, drilled through a little larger than the diameter of the rod.
J.D.

 

[BS]

This is a link to an old thread showing my set-up. It worked very well. :grin:
Link To Old Lapping Thread

Bruce