Author Topic: lapping a barrel (Read 1000 times)

zfishingfool · « **on:** March 29, 2006, 11:30:20 AM »

whats the best way to lap a barrel. is it worth it. do you use a cleaning jag or a eye with somthing like J - B bore cleaning compound please let me know . i never did it before,

savageT · « **Reply #1 on:** March 29, 2006, 01:09:02 PM »

I just used a good one-piece steel cleaning rod with a jag tip and placed a patch saturated with J-B Compound and Kroil. Work from the breech forward to the muzzle. The combination works like magic and pulls out all the crud from the rifling such as buried powder and copper deposits. Just work in slow, short thrusts at first, then longer strokes as you begin pulling out the crud. Don't be afraid to replace the patch and compound. You will see an immediate improvement.
Jim

victorcharlie · « **Reply #2 on:** March 30, 2006, 05:14:58 AM »

I don't think JB bore compound is very aggressive and certainly won't hurt anything. If it were me, I think I'd shoot the rifle first and see how it shoots, and how much copper fouling there is before spending to much time trying to fix a problem that may not need fixing.

gunnut69 · « **Reply #3 on:** March 30, 2006, 10:38:40 AM »

The original J-B was designed to not be abrasive and is a great cleaner for really fouled bores. They make a wider line of products now and some may indeed be abrasive. This is not really lapping but more akin to polishing. Lapping involves and abrasive and uses either a cast in place lead lap or a bullet which is embedded with abrasive and fired down the bore. The latter is called firelapping and is of very limited use, as it should be. Lead lapping is a very old school process that is still used by some barrel makers to polish the bores of match grade barrels. All remove metal but the lead lap method is precise in where in the bore the metal is removed and more controlable. Firelapping is much less discriminating and actually accelerates the throat wear in a rifle bore. Fire lapping is however cheap and easy, and that's the atraction.. If you've a bore that fouls quickly or badly(with metal fouling) lead lapping can help. If the bore is pitted and the accuracy disintegrates after very few shots from the metal fouling, firelapping may help, or perhaps not.. J-B is a great bore cleaner.

dave375hh · « **Reply #4 on:** March 31, 2006, 02:08:21 AM »

As Gunnut69 stated proper lapping is done with cast lead laps. If however you only wish to smooth a rough bore you can use a worn out brass brush, ie smaller than the bore size. Wrap the brush with a couple of patches loaded with 550 to 600 grit lapping compound and use long strokes but don't let it leave the bore at either the chamber end or the muzzle. The patches should be a tight fit and when they start passing through easily they should be replaced with new patches and compound. This was the recommended final step that came with a firelap kit I got from LBT. I don't keep any worn out brushes around so I chucked one into a drill and used 40grit cloth backed sandpaper to wear one out. A one piece rod and a bore guide are an absolute must to keep things straight and not damage the throat.

clodbuster · « **Reply #5 on:** March 31, 2006, 04:53:56 AM »

Gunnut69, it appears that you are at odds with what I believe Veral Smith supports in his practices and describes on his discussion topic. It would be interesting to hear your thoughts on the problems associated with firelapping as an accuracy improvement practice.

AkRvrrat · « **Reply #6 on:** April 01, 2006, 07:06:01 AM »

Not only Vera but Marshall Stanton as well. I've used the techniques of firelapping 1 particular rifle due to the "bulges" created by dovetails in my 1895GG. The end result was excellent and accuracies is astounding. With my 425grn hardcast from Beartooth Bullets in the .45-70 with 52.5 grns. of H322 and with a rifle rest @100yds I was shooting a consistent group of .7"--that is some shooting.

gunnut69 · « **Reply #7 on:** April 01, 2006, 08:54:07 PM »

Firelapping in my admittedly limited experience is a kind of last resort practice. The wear produced by the practice is concentrated at the throat and not evenly spaced. this may or may not be a good thing. Also as an aside, any barrel with bulges from sight dovetails should have been replaced. A cast lap is designed to provide a smoothing action over the entire bore. The abrasive coated bullets slamming into the rifling can move a throat out in a big hurry. In badly pitted or badly damaged bores firelapping is a kind of last ditch effort. The cast lap is a technique that will smooth most standard bores.. Without damaging or moving the throat..

AkRvrrat · « **Reply #8 on:** April 02, 2006, 05:30:02 PM »

gn69, you are absolutely correct - if I did not have so much tied up into the rifle from the get go I would have done exactly that. Being that as it is the "damned if I do and damned if I don't" got me. Betwixt a rock and a hard spot. Hind sight being 20/20. Murphys law etc.......
good pointers gunnut69

Casull · « **Reply #9 on:** April 05, 2006, 04:52:18 PM »

GN69, I'm curious as to the difference between fire lapping and cast lapping as it relates to throat wear. It would seem to me that in either case you are pushing an abrasive embedded slug through the barrel, beginning at the chamber. If my ignorance is showing, I apologize. I have very limited experience with fire lapping (performed on a RSRH to remove constrictions at the junction of the barrel and frame and also at the front sight dovetail (with what appears to be excellent results). As a bonus, leading of the barrel has been greatly reduced. It would also seem to my that any dovetailed sight pressed into the barrel would create a bulge (though that bulge might be very small). The only way to avoid any bulge would be to create the bore after the sight was in place. Any way, I am always interested in expanding my knowledge, so if you can explain how my thinking is flawed, I will take no offense.

gunnut69 · « **Reply #10 on:** April 05, 2006, 07:27:22 PM »

Sight dovetails are present in many rifles and usually have little effect on accuracy. In any case it would likely be the pressure of the mill as the dovetail was produced that created the bulge, not the insertion if the sight itself. The difference is in the application. When firelapping the bullet is loaded with the abrasive and into a case. It is then fired into the bore. The throat is the rifling terminus and absorbs tremendous stress as a normal bullet impacts it. The abrasive loaded slug inpacts and the bullet engraves the rifling which wears away the face of the rifling terminus. This forces the thoat further down the bore. The amount is dependant of the grade of abrasive used(fine, coarse, etc) and the number of rounds fired. The same abrasion occurs with a normal firing but is greatly accelerated with the introduction of the abrasive material. In normal lapping the lap is cast in the bore at the muzzle. It is forced thru the bore andslightly extended from the bore to be charged with abrasive. The lap is already engraved so never touches the throat or beginning of the rifling. That plus the normally longer length tends to equalize the bore. If done correctly it can be used to polish a rather poor bore to a very good finish.. Also we must remember the high impact pressure of the bullet fired down the bore tends to shatter the abrasive and make it less effective the further down the bore it travels. This can create a tapering effect and I believe, the reason why some of the operations prouce good results. The tapered bores gradual constriction tends to ameliorate the longer throat and creates a good stable bullet exiting the muzzle.. If the bore is rippled as from firing with oil in the bore the effect is not present.. The bullet is sqeezed and released as it travels down the bore and the jacket is loosened around the core. Accuracy is the pits.. This from some of the initial batch of barrels Ruger produced for the 77/22 Hornet. They were bad enough that the diameter differences were evident with even a moderately tight patch. Firelapping was absolutely no help. A couple of the better ones were helped by cast laps but the factory would replace them free so the incentive was lacking.. Fire lapping is qucik and easy. It can help accuracy but usually produces best results with rifles employing cast(lead) bullets. The throat will be abraded at a rate greater than the rest of the barrel and can usually be measured with an erosion guage of a chamber cast. A cast lap is much slower and labor is expensive. The results are much more controlled and are generally very even over the entire bore. The throat is not abraded any more than the rest of the bore.. I quess it basically comes down to this. Most barrels that are worn out because of throat erosion. It's why the military field armors use throat erosion guage to judge servicability of weapons.. Firelapping is simply an accelerated wearing in of the bore.. Cast lapping is a smothing and polishing of the bore with little or no effect on the throat.. Fire lapping is gaining many proponents because its cheap, fast and easy, and sometimes helps.. regardless of the long term effects.

Casull · « **Reply #11 on:** April 05, 2006, 07:39:30 PM »

GN69,

Thanks for the lesson. I was not aware that in cast lapping the slug was engraved first and then charged with abrasive. With your explanation, I can certainly understand the difference. I was aware of the tapering effect that you mentioned with the fire lapping process, and that it generally works best with lead slugs. I have been reloading my SRHK with hard cast 300 grain bullets from National Bullet. My normal load is 31 grains of H110, and before the fire lapping, I was getting some awful leading. I could probably have switched to a higher grade of hard cast bullet, but as I already had a 1000 of the foregoing bullets, decided to try the fire lapping. As a bonus, it did remove most of the two constrictions in the barrel, and the accuracy has also improved. After cleaning, the bore looks like a mirror (viewed by naked eye, I don't have a borescope). In any event, thanks for the education. I figured if I kept it friendly, you wouldn't beat up to much on me for my ignorance.

gunnut69 · « **Reply #12 on:** April 05, 2006, 07:48:06 PM »

Please excuse me if I come through too brusquely. I try hard to be as civil as possible. The only times I sometimes loose patience is if there's a safety issue involved. I don't totally disagree with it's use.. It has a place.. it's ramification just need to be understood and it can then be added to our arsenal of techniques.. Just for curiousities sake how did you determine there were deformities under the sight dovetails in the bore?

Casull · « **Reply #13 on:** April 05, 2006, 08:32:27 PM »

I slugged the bore all the way through, and I could feel the constrictions at the front sight and where the barrel screwed into the frame (greater constriction could be felt at the barrel/frame area). I then slugged the bore just about an inch or less into the muzzle (just shy of the sight dovetail) and withdrew the slug. Measured both slugs with a micrometer and found the difference. Constriction was about .0015 at the narrowest point (barrel/frame area) and I'm guessing about half that amount at the sight dovetail (based on feel/resistance). BTW, I didn't really think you were being brusque, but based upon my limited experience with fire lapping I thought you might have been dismissing it to quickly based upon "common knowledge" (however, I see you really know your subject and understand the ramifications).

gunnut69 · « **Reply #14 on:** April 06, 2006, 06:02:21 AM »

I always like to try things out a bit before dismissing them.. It avoids embarrasments, of which I have enough, Thank you! Actually I've a 25-20 M92 that need the firelapping used on it. The bore is a bit pitted and leads like crazy. I've used firelapping with cast slugs(home grown materials) but haven't used the kits. Some of these use jacketed slugs which I believe would likely do a more uniform job. Cast bullets tend to slug up under prssure and fill whatever bore there is.. This does little to even an uneven bore.. Also I am hoping the pits will respond better and have their edges softened by the use of the more rigid jacketed slugs.

Casull · « **Reply #15 on:** April 06, 2006, 03:17:07 PM »

I'm not sure about the efficacy of the jacketed bullets with regard to taking the edges off of the pitting, but as it was explained to me, a soft slug is better for removing constictions. Hardcast lead or jacketed bullets tend to spring back more, thus polishing the bore more evenly. This would be appropriate for cleaning up a pitted bore, but when trying to remove constrictions, you want a slug that will not spring back. In other words, it will remove more material at the constrictions and less in the remainder of the bore. I can certainly see your point about the soft slugs upsetting in the bore, but the trick (as I have been told) is to fire them through the bore as slowly as possible. In fact, when I fire lapped my RSRH, I stuck five slugs in the bore out of forty lapping loads. This was no problem, as the tightest constriction was at the frame/barrel area, and I figured that any slugs that only made it part way were doubly effective (since I had to push them back through the same constriction they had just passed through). I don't know if the last conclusion is accurate, but as I said before, the gun is not leading so badly now and accuracy seems to have improved measurably (although I haven't benched it at 100 yards yet - never enough time for fun things).