"Lapping Patches"

[roundball]

There have been a few recent references on the forum to lapping bores, with a variety if approaches.

Wonder if another approach could be to "lube" some patches with lapping compound and have a range session dedicated to "shoot/lapping" the bore with 40-50 shots using patches like that??

 

[Stumpkiller]

Yep. It's called "fire-lapping" and I've always been afraid to try it. It's mighty hard to add metal back if you get carried away. I'd try two and check before I fired off 40 or 50.

We used to get the same effect with 'surplus' ammo that had fulminate of mercury and glass in the priming compound. 40 rounds and the barrel's throat was 1/4" further out. :shocking:

 

[LRB]

Don't do it!!!!!!!

 

[roundball]

I've seen the term fire-lapping before...thought it simply meant just shooting the rilfe in..."firing" it at the range to gradually break it in that way...didn't know it meant with "lapping compound patches".

Also, fire-lapping might create an uneven amount of lapping wear in different sections of the bore, due to the difference in velocity / thrust as it was moving down bore?

 

I firelapped an 1860 Army Uberti with no apparent ill effects. I loaded a normal charge and ball in all chambers then covered each ball with grease based 400 grit Clover compound. I repeated the loading and fired 4 chamberfuls this way, then cleaned as normal. The barrel shown like a mirror but without some sort of scientific method for actual measurement of the bore surface, I don't know if any good was accomplished. I would not be afraid to do this with a rifle but would not use anything coarser than about 320 grit. I think you are less likely to cause damage this way than if hand lapping carelessly or improperly without a bore guide.

 

[jtmattison]

I brought up this very subject a while back.
If I remember correctly, many folks on here recommended against it.
I didn't do it.
Lapping the barrel with a tight patch wrapped around a brash bore brush works great for me.

Huntin

 

I'm not recommending fire lapping one way or the other. I studied on it and could not think of a valid reason not to try it. My only concern would be using too coarse a grinding compound but the same caution would apply to the hand method. A barrel is essentially fire lapped to a small degree every time it's fired, which is why many rifles shoot better after a few hundred shots. However, if I was to do it on a rifle, I'd only grease the patch liberally with grinding compound and put no extra in the barrel on top of the load that might cause an obstruction. I would also pull the breech plug after I was done so the barrel could get a good scrubbing.

 

[shmrck1]

roundball
if i were you i would not do it!!!!
I am snake-eyes

 

Bad idea unless done verrrrrrrrrrrrrrrrry carefully.
Say you lube your patch with a liberal amount of 400 grit some-thing-or-another and 80 grains of gee-whiz behind it.
Got any idea how much pressure that would generate? Neither do I but I'll bet it'd be a good deal higher with a patch full of fine sand than Stumpy's excellent lube!
If you MUST lap the thing (why you wanna lap it anyawho?) then use the patch on the ramrod method.
By the way, Ross Seifried, or whatever his name is (gun writer) plugged fire lapping in several articles. I'm talking high powered rifles. Seems a bunch of fine barrels ended up with erroded throats in short order.
But then Ross recommended a cup full of 4fg in your favorite shotgun too!
:bull: :bull:
If it don't need lapped, DON'T LAP it. :blah:

 

[roundball]

If my barrels were any more accurate I couldn't stand it so I don't have interest in "lapping" anything...and if there was an accuracy problem, I'd send it back to them and let them figure it out anyway...my personal feeling is that it would be a little arrogant of me to think I could or should attempt to improve the condition of a TC or GM bore.

After seeing all the discussions about lapping I just had the thought and asked the question if it would work better putting the stuff on a patch, rather than the steel wool, the scotch brite pads, etc, etc

 

roundball: I have lapped several T/C bores that were pretty rough, but I used the patch, ramrod, jag, and elbow greas. I bought lapping compound from Brownells, 400 and 600 grit non imbedding compound and this slicks up a rough bore really well. Did accuracy improve? NO! :curse:
But then I never could get the 1:48 twist in calibers .50 and .54 to work for me.
(Please, no 1:48 debates again.)
I understand your question better. I don't think "fire lapping" would be a good idea, UNLESS one used very light charges of powder. It likely would polish the bore quite nicely that way.
I owuld stay away from valve grinding compound. I had a friend that used the 240 grit on a pre-64 (dummy!) M-70 and ruined the barrel.