Lapping compound in barrel

[bigbuckdn]

I read a lot on here about using lapping compound on a new barrel now my rifle is my first build I am going to shoot it for the first time next week or the week after. I know that it will require some break in time but is lapping the barrel nessasary :idunno: I have built a couple of custom modern rifles would never consider lapping the bore I gues if i was having a bad problem ripping patches maybe?
oh yea my barrel is a 36" gm 1:70 twist

 

[Birddog6]

99% of the ML bore I have seen lapped succeeded only in rounding off the rifling & making a nice crisp new bore look like sh.. :idunno: I have two suggestions....

1: Take a long jag 1 caliber smaller than the bore size, put some 0000 steel wool on it & some penetrating oil for lube & swab the barrel about 100 full strokes. That will take off any burrs from rifling & make it slick as a whistle. Then swab it dry & go shoot it. Some like to finish this with JB Bore paste or toothpaste, but I can tell no dif by doing so.

2: Do the same thing with a piece of Scotchbrite pad. The famous Getz barrel company has done this for over 30 years, & we know well of the quality of their barrels.

3: Leave it alone & go shoot it 200 rounds.

I always go for option 3. It gets the barrel broke in & you broke in at the same time & gets the sharp edges off both. :grin:

Keith Lisle

 

[ohio ramrod]

Lapping new barrels is a way of reducing "breakin time" . I personally would never lap a barrel before shooting it to see if it is shreding the patches. If the barrel doesn't shred the patches lapping will be of no benefit. If the patches are shredding, lapping will smooth out any sharp edges. :hmm:

 

[paulvallandigham]

Run a cleaning patch down the barrel, dampened with a bit of spit, and see if you can feel it pulling on the threads in the patch. If it is, you have burrs on the edges of the land, and doing some mild clean up will save you lots of frustration shooting a new gun that won't shoot good groups, and tears holes in your patches.

I use a double patch, oiled, and then put Pearl Drops toothpaste on the patch, to run down the barrel. The Toothpaste has a VERY FINE abrasive in it, and its enough to remove the feathers( burrs) on the edges of the land, and also polish the land a bit. 50-100 stroked, and several patch changes- when the patch turns Black, its time to at least flip it over, or to use a new patch, with more toothpaste- will do the job. Then, go shoot it.

READ YOUR SPENT PATCHES. if you are getting tears from burrs, they will be located at the corners of the lands on the patch( both grooves and patches leave marks on patches.)

A properly sized, and lubed patch will come out with fringing on the edges, from being whipped back when it hits the air in front of the muzzle. In the middle, the patch will be "whiter" than the rest of the fabric, and almost dry of whatever lube you used. Then you will see a dark brown to black ring where the patch makes contact with the bore, and in the rings you will see straight marks representing the lands a grooves.

What you don't want to see is Black STREAKS coming from the lands and going forward of the ring. And you don't want to see any tearing, or holes in the patches. Tearing is rips into the center, and through the ring( if one even is visible), not the whipped fringe on the edges.

Some barrel crowns are too sharp, and cut patches as you start the PRB down the muzzle on the sharp edges of the lands. You will have to use a lag bolt head, or the butt of a file handle, to back some abrasive cloth to go down and polish the edges off the front of the lands to stop this.

All these are things you can do with a new barrel before ever firing a shot out of it. It prevents a lot of frustration at the range, if you take cared of these problems before going TO THE range. :hatsoff:

 

[jerrywh]

I agree with birddog. I never lap a barrel until I see if it shoots Ok or not. Then if it doesn't shoot to my satisfaction I lap it with scotchbright and WD40.
Sometimes I will drill a hole in a ball and put it down the bore with the correct patch, then I pull it back out and see what the patch looks like. If it isn't cut I leave the barrel alone.
Same goes for coneing. Listen to Birddog, he is uaually right.

 

[Capt. Fred]

I had patches getting torn in a Colerain barrel so I did Birddog's method #1. Probably stroked it 50 or 60 times. I think I switched the steel wool 2 or 3 times. I could actually feel it getting smoother. Worked great, no more ripped patches. It probably would have smoothed out eventually from shooting, but I don't have time to shoot as much as I'd like to so I took the quick and dirty route. :thumbsup:

 

[bigbuckdn]

thanks to you all yea I will shoot it first see where i am at go from there I have all summer to break her in 120hours of build time no sense rushing things.

 

[Zonie]

To me the term "lapping" indicates that some sort of an abrasive is used and I would never suggest that this be done on a new barrel.

I do know that deburring and breaking the very sharp edges on square cut rifling is an expensive process so it is not done by the barrel maker. (After doing my process it is easy to understand why they wouldn't want to invest the time it takes.)

As these sharp edges can and will cut a cloth patch I always use a piece of #0000 steel wool wrapped around a cleaning jag with a little oil for lubrication to break the sharp rifling edges.

Maybe 50-100 strokes, changing the steel wool every 20 or so seems to do the trick.

I also always use some 600 grit wet/dry paper to break the sharp edges where the rifling meets the crown at the muzzle.

With these sharp edges removed, my new guns barrels never tear a patch and there is no need for a 100-200 shot 'break in' period before the gun is shooting like a champ.

 

[A.Merrill]

Go to a auto parts store get some valve lapping compound. Use it as your patch lube for the first 50 or 80 shots. It's called fire lapping. You get to shoot and lap at the same time.Good Luck AL

 

[bigbuckdn]

thank you both for the added imput seems to be several ways to do this I will be shooting sunday for the first time i will post up results then go from there.

 

[Zonie]

Personally, I would be afraid to use valve lapping compound to fire lap a barrel.

I have a can of it which actually has two lids and two compartments, one "course" and one "fine".
Even the "fine" is far more course than anything I would use in a barrel that I wanted to be smooth and easy to clean. But then, maybe some valve grinding compound has become available in the last 30 years that is much finer?

 

[Birddog6]

? Clover? I think the brand is. Old brand, had some Very Fine & Ultra Fine, and may tell the grit size on the can..
But not sure you could even buy it anymore. I have some that is ? 40 yrs old or more.
But I still wouldn't fire lap a ML barrel. Don't see any reason to, as they are mild steel & clean up very easily. NOT the same as modern steel barrels use for modern rifle barrels.

Keith Lisle

 

[longcruise]

Personally, I would be afraid to use valve lapping compound to fire lap a barrel.

That is absolutely excellent advice. I have successfully firelapped many barrels and have heard the horror tales of ruined barrels. It seems that the ruined barrels were firelapped with valve grinding compound. My successful firelapping has been with dedicated firelapping compounds either from LBT or the Wheeler Kit.

 

[Zonie]

Yup. Clover brand.
It came in handy when adjusting the valves on a Ford Flathead.

For you young folks those engines had solid lifters with the valve stem right on the lifters so in order to adjust the valves you either ground the stem off or you lapped the valve seat.

The lapping compound was also used on newer engines to get a good gas tight seat between the valve head and the seat.

Anyway, I can't imagine a good reason to use a hard abrasive to lap a muzzleloader unless the bore was so badly rusted that doing so would be a last chance at saving it. Even then, if it isn't done correctly by using a expanding lead slug it would probably do more harm than good.

That's my 3 cents worth. :grin:

 

[Kentuckywindage]

use jb bore paste, its non abrasive and does a hell of a job on fresh or old bores. I just finished my GPR's barrel yesterday. Smooth as silk and loads smoothly.

 

[Longsmoke]

Chuck, it's a Green Mountian. Go shoot it, I have not had one GM barrel that didn't shoot well from the first shot.

The only thing I have ever had to do to them is as Zonie said, polish the crown with 600. The way it comes new can be hard on the patch if your load is tight.

Bruce

 

[ohio ramrod]

Having worked as a tool and die maker,mold maker, tool grinder, auto mechanic , as well as working on guns for over fourty years I can tell you there are several grades of "coumpounds".Some as hard as diamonds (actually fine diamonds). Some as soft as talc. Grinding compounds being the most abrasive and comes in different "grits", lapping coumpounds which are finer , and polishing coumpounds which are less abrasive and comes commonly as fine as 6000 grit. And can be special purchased even finer. Each has it's place in smoothing and polishing. :hmm:

 

[Vaino]

The bore of my .54 cal. Hawken shredded patches w/ a powder charge above 80 grs 2f and after approx. 30 strokes w/ a green Scotchbrite pad, my elk load of 120 grs. is very accurate and the patches are not cut at all. When using the Scotchbrite, don't withdraw the pad out of the bbl or the "mouth" of the bore can get belled.....Fred

 

[J.D.]

IMHO, lapping a new bore is nothing new, however, unless one is into shooting X's at 100 yards, lapping is isn't worth the time and trouble it takes to do a good job. For those who do a slipshod job, lapping a new barrel will probably cause more harm than good.

IMHO, fire lapping a ML barrel with compound spread on a patch will wear a barrel out pretty quick, especially if the "lapping compound" is as course as valve grinding compound.

The intent of proper lapping is to remove tool marks and minor constrictions in the bore that will reduce accuracy.

Proper lapping is done with a lead lap cast in the bore, impregnated with a fine grit compound. Again, this removes tight places in the bore, in addition to removing minor tool marks. Only about .0005 of material is removed in lead lapping, and that can take several hours.

Remember that over doing lapping with course abrasives will only wear a barrel out faster than normal.

That said, removing burrs in the rifling is best done with a green pot scrubber, aka green scotch brite pad using roughly 50 stokes in and out, as described above.

So, the question you have to ask yourself is, do ya wanna wear your barrel prematurely, or do ya wanna just remove the burrs left behind from machining the bore?

God bless

 

[bigbuckdn]

again thanks to all I desided to shoot it first
and it shot great burning some patches but not realy cutting them I will play with loads and just let it break in on its own hunting season is a long way off lots of shooting to be done and it shoots ok now so it will only get better.