J-B paste for fire lapping?

[Shuz]

From what I've read, it appears that J-B paste is mainly a bore cleaner. Has anybody used it with success as a fire lapping product?

[Outpost75]

I have blended equal parts of JB paste with beeswax and Crisco and used it successfully as a BP lube to smooth up rough, soft iron barrels, including muzzle-loaders and cap & ball revolvers, and it seems to do the job well IF you have a SOFT bullet with GENEROUS lube capacity, you keep the loads down at BP levels, you use the blend over a period of time, several hundred rounds, cleaning normally with hot water and Dawn detergent between sessions, and inspecting after each session until you get the bore condition and results which you want.

[DougGuy]

If it's been sitting a long time, pour the oil off the top and use the paste in the lube grooves in place of lube, this works. You'll have to flare the case mouth extra large, seat the unlubed boolit partway, pack the paste in by hand, then seat and crimp. I used this method with 50 full power loads of 8.5gr Unique under a 255gr K type LSWC in a Blackhawk and it worked great. The downside is the gun will be a total MESS in your hands by round 20, and you may want to take some brake clean and hose it off periodically.

This was years before there were many articles published detailing rolling the boolits in abrasive and using only mousefart loads. I had heard of firelapping but didn't know how to do it or where to follow up on it, there was no internet back in them days, gunrags and shotgun news was all I had. I just took a bottle of JB that was broken open on the shelf and had been sitting for I bet 10 years and went for it!

That BH was full of tool marks in the grooves from one end to the other. It got rid of all of those but the most prominent ones which it polished nicely, and it cut groups in HALF. I was very happy with the results afterwards.

[Jtarm]

I'd just save myself the trouble and buy the LBT compound. I still have half the bottle I purchase 20 years ago.

[Outpost75]

In my experience the LBT compound is much more aggressive and works mostly on the throat and origin of rifling, enlarging diameters there as well as removing the tool marks. The JB paste blended into soft lube and used with a "Biglube" design BP bullet in soft alloy works more by axial compression of the bullet as pressure rises, distributing the lube and abrasive mix down the bore in a "greasegun" effect, rather than having the powder blast splash it all into the throat and forcing cone at once.

Not sure what LBT uses as his abrasive, but JB is 800-grit garnet in a grease suspension. While it gets the job done, it does so GRADUALLY, you have to be patient. The advantage I find to this technique is that even with soft iron barrels it is hard to over-do the job with JB, whereas with a more aggressive abrasive treatment you can actually change throat and forcing cone dimensions, which you may not want!

[Shuz]

The rifle I have in mind doing this with is a Savage Mdl 11 in .308 Winchester. I loaded up 5 rounds with 4g of Red Dot behind a Lyman 311466 that was sized to .309 and had a hardness of Bhn 14. I hand applied the J-B paste to the multi grooves of the 311466. After firing,I then cleaned the bbl with Ed's Red, a brass brush and a tight fitting patch. I'm wondering whether I should repeat this procedure, or shoot some groups and see if there was any improvement. Based on what I've read, I'm inclined to run at least 5 more down the bore to see what happens. Stay tuned!

[Rattlesnake Charlie]

The J-B paste is very fine grit. I think you'll need maybe 20 to see much improvement. I have used much coarser grit on barrels to start the cleaning up process.

[yeahbub]

It depends on what sort of lapping chore you're trying to accomplish. Slug your barrel to determine what it's condition is, so you know if you've made progress. It's common to find a "reverse taper" condition where it's tight at the breech and looser at the muzzle or loose spots or constrictions. Ideally, it's better to have a consistent bore and grove diameter from end to end, or slightly looser at the breech and tighter at the muzzle. If you're just wanting to smooth a good barrel to a consistent diameter and finish, or round over the edges of minor salt-and-pepper pitting, JB will do the job, and at a leisurely rate, as Outpost75 notes. If your task is to remove egregious tight spots that act like a bore obstruction when you slug the barrel, more aggressive abrasive types are probably in order. In such a case, I begin with 280 aluminum oxide rolled into dry cast boolits between two steel plates, which are then washed with mineral spirits, dried, and hand lubed with something soft (automotive DoorEase works well, or shortening in cool weather) and inserted in an unsized fired case with 3-5gr of something fast, like Red Dot, Universal or similar, but just enough to reliably get them to exit the barrel. If stout charges sufficient to obturate the boolit are used, there will be a definite increase in throat/leade dimensions others warned about. Once the more obvious constrictions begin to wane, finer grades can be used (Crystolon 400 to 600 from http://www.us-products.com/category-...how=100&page=1) to finish the job. A sample-sized 1 oz. jar will lap a number of barrels. But if you have JB, it's a good place to start.

A note on grading abrasives: each company has their own in-house standard to grade size and what they call it, so beware that one fellow's "fine abrasive" may be very different from someone else's "fine". It was once suggested to me to "just use some fine valve grinding compound and it'll work great." The "fine valve grinding compound" I wound up with was obviously much coarser than the smooth grey toothpaste-looking stuff used by the fellow who suggested this. Opperating on "a little knowledge is often a dangerous thing", this led to a lot more diving for details before I lapped my first barrel.

[1bluehorse]

With about 3 minutes of research on this site you'll find exactly what you're looking for in kit form. There's some really good info in the Tech notes and the kit sold here is as good or better than what you'll find anywhere. I've used it on many barrels rifle and pistol and it's an excellent product.

[sigep1764]

I had to fire Lapp my Kahr CW9 as it had a very short lead with very sharp rifling that tended to lead up. 20 rounds rolled in JB paste and a quick scrub, it was good to to go. very little leading if at all after that. Good stuff and will use it in the future.

[Shuz]

After fire lapping 5 more; with 3g this time, of Red Dot and the 311466, I am still not getting the accuracy of each 5 shot group to be similar. I shall try 10 more.

[DougGuy]

I had to fire Lapp my Kahr CW9 as it had a very short lead with very sharp rifling that tended to lead up. 20 rounds rolled in JB paste and a quick scrub, it was good to to go. very little leading if at all after that. Good stuff and will use it in the future.

That Kahr barrel needed throating. They have a very abrupt rifling with NO freebore at all at the end of the chamber. Still needs throating even after firelapping so you don't have to seat below what specified COA is in loading data just to get it to reliably chamber ammo.

Check post #77 this is for a CW45 but the same exact issues plague the CW9: http://www.kahrtalk.com/showthread.p...745#post354745

[Rattlesnake Charlie]

As Veral Smith of LBT directs the abrasive grit should be embedded into the bullet by spreading the abrasive on a steel plate, laying the bullet on the plate, then placing another steel plate on top and gently rolling the bullet through the abrasive. The idea is to embed the abrasive into the bullet itself. I've used this method to fix some awful barrels. Using a very fine abrasive such as J-B paste will take many more than five bullets down the barrel. I suggest five of 320 grit, clean the barrel, then another five of 320 grit. Clean the barrel and take a look down that CLEAN barrel. You can at that point decide if you need another round of 320. If not, do the same routine with 400 and then 600 grit. If you want a really fine polished bore continue with finer grit. I think Clover goes to 1200. As Veral said you can not get the bore larger than the diameter of the bullet you are using to lap with, so don't be shy. And, since the result will be a slightly larger diameter at the breech than muzzle things only get better.

[sigep1764]

That Kahr barrel needed throating. They have a very abrupt rifling with NO freebore at all at the end of the chamber. Still needs throating even after firelapping so you don't have to seat below what specified COA is in loading data just to get it to reliably chamber ammo.

Check post #77 this is for a CW45 but the same exact issues plague the CW9: http://www.kahrtalk.com/showthread.p...745#post354745

It sure didn't have much of a leade at all and absolutely no freebore. I use the 358-147 Elco HP mold in my 9mms to counter it. I should have sent it to you, but the the JB and this boolit ended up working out. I could never get used to the trigger as the way it is designed, the trigger pulls up slightly as it breaks over center. It always forced my shot a little low. After a few thousand rounds, I traded it in on Walther PPS M2.

[CraigOK]

The brass you use for this process needs to be discarded after?

[Shuz]

The brass you use for this process needs to be discarded after?

I've read that one should discard brass used for "cat sneeze" or fire lapping barrels, but I don't know if this is a "truism" or just another old wives tale. A dental pick inserted down the neck of my fire lapping brass did not detect the dreaded ring that is the precursor to an incipient head separation.

[CraigOK]

I've read that one should discard brass used for "cat sneeze" or fire lapping barrels, but I don't know if this is a "truism" or just another old wives tale. A dental pick inserted down the neck of my fire lapping brass did not detect the dreaded ring that is the precursor to an incipient head separation.

What about grit left behind that could hitch a ride down the bore?

[Rattlesnake Charlie]

Discard brass used for fire lapping?
Nonsense. Just wash it up in some warm water with dish detergent, rinse well, then dry.

What about grit left behind that could hitch a ride down the bore?
Didn't we sent grit down the barrel on purpose? Any left in the brass will not be a problem for long.

This ain't rocket science folks.
It is like getting a smooth finish on a piece of lumber with increasingly finer grits of sandpaper.
It works!

[Shuz]

I loaded up 10 more J-B Paste and the 311466, and fired them, but I haven't had the chance to go down to the range to see if there was any improvement. I also loaded up the 5 cases I used for the fire lapping with my 16g of 2400 and the RCBS 30-150, and saw no problems.

[Victor N TN]

In the past I have made my own "lapping bullets" out of soft lead. I rolled them on my work bench while holding down a course file with a lot of weight. After this roll the almost knurled bullets in extra fine lapping compound wet with a little heavy oil or light grease. Be sure to dry off the base of the bullet before loading into the cartridge case.

But I have had better luck by hand lapping the same method custom barrel makers use.