Hand lapping bores for cast bullets

[rvpilot76]

Upon making a bore riding slug, what abrasive should I use for hand lapping? JB, clover valve grinding compound, or Brownell's abrasive grit. The Brownell's stuff is either silicon carbide in 120,180,240,320,400,500,600, and 800 grit or aluminum oxide in 600 and 800 grit. The rifles to be lapped are a #4 Mk.1, 1903A3 Springfield, and an 1895 Marlin Cowboy with exactly 20 rounds of lead bullets down the bore. Any insight as to which grit should be used on the above rifles would be greatly appreciated.

Kevin :smile:

[grumble]

"Upon making a bore riding slug, what abrasive should I use for hand lapping? JB, clover valve grinding compound, or Brownell's abrasive grit. The Brownell's stuff is either silicon carbide in 120,180,240,320,400,500,600, and 800 grit or aluminum oxide in 600 and 800 grit. The rifles to be lapped are a #4 Mk.1, 1903A3 Springfield, and an 1895 Marlin Cowboy with exactly 20 rounds of lead bullets down the bore. Any insight as to which grit should be used on the above rifles would be greatly appreciated."

Kevin, what kind of sandpaper do you use on a Ford, Chevy, and Dodge? <GGG>

Seriously, the grit you use has to do with the amount of cutting you want to do inside the tube, the coarser, the more cutting. A pretty good barrel, use 600 grit, a more pitted or rough barrel, use a heavier grit. Generally speaking, you won't often need anything more coarse than 320 or finer than 900 or 1200.

The carrier really doesn't matter, except for cleanup when you're done. Water based carriers seem to me to be easier to use, but it's a matter of preference.

You can pay extra for the Brownell's stuff or buy the valve lapping compound from NAPA -- grit is grit, and either will do the same job. For cheaper fine grit (about 600-800), automotive rubbing compound will do a fine job on your barrels.

If you want a much simpler way to do the lapping, use a solid cleaning rod with an undersize cleaning jag. Put a couple squares of tee shirt patches on it underneath a denim patch cut from an old pair of blue jeans. The underlying patches act as a pad to allow the denim to 'squish' into the form of the bore. The denim will hold a goodly amount of the lapping compound. Just make sure the jag and patches make a very tight fit in the bore, and overlap your strokes so one area doesn't get too much wearing away from the lapping.

[Bret4207]

One of my jobs in my teenage years was to lap bores in Dads gunshop I probably did 15 or 20 and have no love for it. Doing it the traditional way with the lead lap is slow, slow, slow. I beieve fire plapping is just as effective for overall bore lapping. If it's just one area, like a revolver with a tight throat, then the traditional lap is needed.

[Willbird]

I beg to differ on "grit is grit"

aluminum oxide, silicon carbide, diamond, and CBN are all "grit" but what they do and how aggressively they do it, and whether they embed or break down easily are all very important.


Bill

[Bent Ramrod]

I second Tpr. Bret's motion--lapping with a cast-in slug on a lapping rod is a lot of hard work. Fire lapping is at least shooting, so it is closer to being fun. You have to clean after every few shots, to make sure no lead is building up, but it is much less work. I use Clover 320 valve grinding compound for either type of lapping. My lapping is mainly to shine up a rough bore in a used gun for a modicum of improvement or smoothing out the leade on a newly-chambered barrel. I'll slug the barrels during and after the lapping, but don't generally try for a given diameter.

The big advantage of the hand lap is that you can feel tight or rough spots and give them extra attention. You can also systematically lap a sort of choke into the bore by gradually increasing the length while reducing the number of your strokes from the breech to the muzzle. It takes a lot of strokes to enlarge a bore 0.001", at least with Clover 320.

Setting up the stops so the hand lap doesn't come out of the end of the muzzle to bell-mouth it, and so it doesn't come out the chamber end on the back stroke, necessitating reindexing or casting a new lap, is a real engineering project on the typical workbench with one or two vises bolted on the ends. My makeshift setups are typically good for a lot of bruised elbows and hands and rude language.

I read sometimes in muzzleloading literature that a bore can actually "shoot slick," by which I presume it gets so highly polished by patches that the accuracy suffers. There's been mention of deliberately roughening them up again with emery of some sort. Never have had that problem myself, but it might be an indication that going for the ultimate smooth finish inside the bore is counterproductive.

[grumble]

"aluminum oxide, silicon carbide, diamond, and CBN are all "grit" but what they do and how aggressively they do it, and whether they embed or break down easily are all very important."

OK, Bill, now provide Kevin with something useful, like what he should use. Personally, I doubt very much that any lap other than very expensive diamond lap would "imbed" in a steel barrel. In any event, if done properly, the only grit that could be left in a barrel would be the finest (600+) grit. Even that should be removed with proper cleaning after the hand lapping is completed.

"...It takes a lot of strokes to enlarge a bore 0.001"..."

A THOUSANDTH?!?! Who would want to open a bore that much? Lapping isn't intended to create a new caliber, it's intended to clean up an existing caliber.

It takes 50-60 strokes to clean up most rough bores, and can be done in less than an hour, including reassembly (if needed) and cleanup. It sure doesn't require a complete machine shop and micrometers to make a poor barrel into a better-than-good barrel. If perfection is the goal, go buy a perfect barrel. If good enuff is good enuff for what Kevin wants to achieve, he can do it easily enough.

Further, why talk about how perfection is so difficult to achieve with hand lapping, and then advocate fire lapping, where there is absolutely no control over what happens when the trigger is pulled?

If you want a smoother bore you can fire lap and take what you get, or you can hand lap and control what you end up with. They both take about the same amount of time counting the loading and imbedding grit in the boolits for firelapping. Hand lapping takes a bit of elbow grease, but you end up with a barrel that's done the way you want it. Fire lapping gives you a barrel that's left to chance.

[Willbird]

What kind of grit to use is a good question,

silicon carbide has rounded "rocks" in it and breaks down the easiest, and is least likely to embed.


I would like to know what abrasive Veral's kit has in it.


Bill

[Bass Ackward]

The big advantage of the hand lap is that you can feel tight or rough spots and give them extra attention.



BR,

I am not picking on you, but this is exactly why I hate hand lapping. Even by an expert. Because nobody can know for sure exactly what needs lapping! Every one automatically assumes it is a constriction.

When you feel that tight spot with the lap, what is it that you feel? Is it a diameter constriction? Or is the twist rate a little off? Or is it that two lands might just be a little closer together at that point? There is a BIG difference! And it ALL feels the same to the lapper.

If it is the diameter, then you are pretty much OK. But if the lands are a little closer together at that point and you hone them out, you are also going to expand the bore diameter that may have been perfect there to begin with. Now you just lapped a bulge at that point and maybe made your problem worse.

[MOA Shooter]

You see the measurement .001 referred to often in lapping posts. But truth be told if your removing an actual .001 of metal your sanding off allot of metal. This metal comes from all sides.. land tops, groove diameter and narrows the rifling land. Smith via LBT is one of the first to popularize firelapping, which is also known as throat enlargement for beginners. Should be mentioned that Smith didn't target much on paper preferring to watch impacts on large rocks. You can draw your own conclusions as to those accuracy standards.

Lapping done by barrel makers is just to smooth out tool marks. No or something on the order of a .0001 of metal is removed if that. Mention firelapping or hand lapping to "fix" a barrel and your tube maker would just cringe.

But some do extrol the virtues of firelapping and handlapping. Many times on junk barrels the finish gets some smoothing out meaning less fouling and therefore better accuracy. For every touted success there's a sizeable number of reality checks where accuracy didn't improve or often got worse... much. And once that metal is sanded out your screwed.

MOA.

[Bent Ramrod]

Well, I was just trying to give a proportional idea of how little a lapping stroke actually removes from the inside of a barrel. I only once tried to actually enlarge a bore this way; it was a rebore which, weirdly, was .300" across the grooves, with a similarly diminished-in-proportion chamber like an anorexic .30-30. I finally gave up (without having enlarged the bore enough to matter) and had the thing rebored again to .38-55.

It is true that a tight spot can be other than a narrowing of the bore diameter, but in the old days before bore scopes, the "feel" of the inside was usually all the workman had to go on. I read somewhere once where Harry Pope had a set of 30 or 32 gauge pins, each one inch long, which, lined up in the right order and direction, would describe a 0.001" choke along the inside of a barrel from breech to muzzle. I'd like to see how someone would use a set like that. Probably the lapping in of the chokes in the blackpowder target rifles, with each barrelmaker having his own methods, was one of the reasons for the extreme finickiness of the rifles in the matter of loads and loading techniques that some writers have reported.

My lapping (fire or hand) is pretty much cut and try. A given number of shots or strokes, then clean it out and test the shooting qualities. I may stop the lapping process too soon, but I've never gone far enough to damage the accuracy in shooting.

Allegedly, a hard bullet driven at a low velocity is no worse than one-half a lapping "stroke," but there is that point where the abrasive-coated bullet has to squeeze into the leade of the rifling. Extending the freebore is possible, but would the number of shots necessary to take out small burrs and tool marks or smooth minor pits be enough to do this? Wouldn't enlarging the throat significantly take more fire-lapping shots than anyone would normally take before checking the effect on accuracy?

[Ol'Scudder]

Gents, I wouldn't begin to offer you advice on firelapping a barrel, be it rifle or revolter, but I can direct you to an interesting and informative article on that very subject. The series of articles is written by Marshall Stanton, owner of Beartooth Bullets, and he covers the whole ****terie, from beginning to end in great detail. Hope you enjoy it.

http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/19

[KCSO]

"If I have to lap the dam'n thing I didn't cut it right in the first place"

Harry Pope

I got my tips on hand lapping from Bill Large and Greg Roberts and will not try to put it all in a short post. I have tried fire lapping and consider that it is worthless. If your barrel is not tapered in the right direction fire lapping will only make it worse. If you are going to hand lap you really need a cast lead lap as a cloth patch will not give you the feel you need to do the job right.

It's real tricky to tell be feel what is going on in a tube when you push a lap through and you need to do a few to get the feel. To just smooth a rough bore you need to see how rough it is. I have had some I could lap out with JB's and they came out perfect and some I have had to start with 600 grit Clover. A good all around smoother is the same rotten stone you use fro stock finish work. I mix it with a good grade of oil and wotk it 50 to 100 strokes starting at the breech end. I also thy and work the bore in thirds with only the last 20 or so strokes going the full leanghts of the bore for each grit I use. The idea is to have the bore not only smooth, but to taper to the muzzle. In a hand cut bore this is what naturally occures as your cutter shim progresses down the bore. Bill Large was not big on smooth groove bottoms , claiming that the tops of the lands were more important. Harry Pope wanted both smooth,by cutting only. If you just want to take off a little roughness and don't want to go the whole route, by all means use a cloth patch and your favorite compound. I would start with 600 and finish with rottenstone if the bore was bad or just rottenstone if the bore was in good shape. Try to get a uniform feel up and down the tube. Clean the bore with a good solvent get all the grit out before you shoot it.

[MOA Shooter]

"Extending the freebore is possible, but would the number of shots necessary to take out small burrs and tool marks or smooth minor pits be enough to do this?"


I believe this goes to what grit is used, the alloy hardness and how much umph you put behind the bullet. Then the firelap effect on the throat isn't uniform as in a reamers work. I read Tom Gray stopped firelapping cast BR barrels due to the effect of firelapping on throats. His complaint if I remember reading correctly was primarily enlargement. Most good smiths now polish out the throat sharp edges etc after reaming.



Wouldn't enlarging the throat significantly take more fire-lapping shots than anyone would normally take before checking the effect on accuracy?


Again to grit size. Reason I set this question out again is the number of newbies who grab the idea of firelapping per the net noise and kits available-- which is just something for a few makers to SELL. Without really geting into the cast game in depth and understanding the why's they sand out their barrel and often end up with something that looses a significant amount of potential accuracy.

Grumble I read uses cloth laps which of course isn't the ideal method on the best tubes. But for the junkers why not? If a guy learns what that feel on the rod means how can you really hurt something that's leading and produces patterns vs groups? Just reducing leading is going to mean more consistency no matter the method.



MOA.

[Bass Ackward]

"Extending the freebore is possible, but would the number of shots necessary to take out small burrs and tool marks or smooth minor pits be enough to do this?"


I believe this goes to what grit is used, the alloy hardness and how much umph you put behind the bullet. Then the firelap effect on the throat isn't uniform as in a reamers work.




MOA,

You are absolutely correct with the first statement. No enlargement of the throat will occur unless the bullet swells up. So pressure and bullet hardness have a direct relationship here. I disagree about smiths though. Most good smiths chamber slow enough, keep sharp reamers, and clean their reamers often enough so there are no burrs or a need to polish anything. That is because they can't possibly polish in any kind of a controlled method any better than a bullet will after 20 shots anyway. And you need to fire that to break the barrel in and close the pores. So .... Ol man Shilean said the only difference in the quality of his barrels was 50 shots.

Lapping of any kind comes back to simple accuracy and the misunderstanding of it. The question we need to understand for our own cast uses are, how smooth and how dimensionally correct does a barrel have to be to shoot lead? And does dimensional correctness or smoothness have any bearing on accuracy? Well, if you ever saw the inside of old Mod 52 target barrels you would cringe and say accuracy is totally a seperate issue. But that is a 22 RF. As a result, many people are disappointed when accuracy fails to improve from fire lapping. But should it? Does smoothness and dimensional correctness have anything to do with accuracy? Sometimes yes. Sometimes no.

Example: I have a 700 Rem 06 that shot the Marshall load at 1" right out of the box. When I saw it shoot that well, I dam near blew the gun up locking the bolt when I attempted what should have been just 2400 fps at about 35,000 psi. 500 jacketed rounds later along with a re-crowning job, I can do 2800 fps with ACWW before the mix let's go in "that gun". And the Marshall load is now down to about 1/2".

So depending on your accuracy standard and goals, when was that barrel good enough for lead? Was the accuracy improvement for the Marshall load worth the cost and time of 500 jacketed rounds? Or could I have done the same thing in one day with 20 lappers and just sized a little bigger or seated out a little farther? Or was the accuracy improvement really from the re-crowning? I can't honestly tell ya. But the more dimensionally correct and smoot you are, the higher pressure / velocity ceiling you will have.

This is what makes blanket positions on barrels kinda tough when we all have different goals and standards for lead. When it comes to jacketed accuracy, the only standard is how does it shoot? Oh a small minority of guys MIGHT care how easy it is to clean, but not if it really shoots. :grin:

If it doesn't shoot, thats when everyone starts to worry about barrel conditions and the debates start about lapping or barrel quality.

[MOA Shooter]

"No enlargement of the throat will occur unless the bullet swells up"

Couple things. If the bullet doesn't bump being too hard or not enough psi, the gas is going around the bullet which will blow the grit off the slug on the throat walls. And given bullet to throat clearance is usually 0 to a couple thou I have to think the initial inertia flings enough grit back to give the throat a decent rub.

I read on the net a guy coating the high spots with grit and firing over them slowly. Didn't that idea originate from a guy in this group? Who was he?

MOA.

[Bass Ackward]

"No enlargement of the throat will occur unless the bullet swells up"

Couple things. If the bullet doesn't bump being too hard or not enough psi, the gas is going around the bullet which will blow the grit off the slug on the throat walls. And given bullet to throat clearance is usually 0 to a couple thou I have to think the initial inertia flings enough grit back to give the throat a decent rub.

MOA.


MOA,

No. Not from my testing. I slug before and along the way. I also monitor visually. Your logic makes sence, but reality is that little enlargement takes place if done properly at low pressures with the intent NOT to enlarge. Even on soft steels like 22RF barrels. That is if you start with bore diameter bullets or under and touch the lands for support, I have gone as high as 30 lappers and had no enlargement of the ball seat measured. Tool marks are still there. Lengthening from the angle change, yes. Enlargement no. But it depends what you want to do. Another variable here is bullet diameter and powder speed. You just have to get a feel for what you are doing.

[MOA Shooter]

MOA,

No. Not from my testing. I slug before and along the way. I also monitor visually. Your logic makes sence, but reality is that little enlargement takes place if done properly at low pressures with the intent NOT to enlarge. Even on soft steels like 22RF barrels. That is if you start with bore diameter bullets or under and touch the lands for support, I have gone as high as 30 lappers and had no enlargement of the ball seat measured. Tool marks are still there. Lengthening from the angle change, yes. Enlargement no. But it depends what you want to do. Another variable here is bullet diameter and powder speed. You just have to get a feel for what you are doing.


Bass do you have a bore scope?

When you running those 30 lappers, I assume just fast enough to clear the barrel? How hard a bullet?

Methinks I learned something today. Thanks.

MOA.

[David R]

Aftere reading everything I could, I decided not to fire lap my 308. I did send 20 condom boolits down the barrel and it made a big difference in leading. I have shot up to 2200 fps with no leading, but no accuracy at that speed either.......Yet.

I have about a hundred on those condom things, I will use the rest.

My thought was after reading about the throat enlargment would to put the lapping compound in the barrel after the throat and send a boolit along the way. It would pick it up all right.

One more thought most grit breaks down finer as you use it. This would lap the beginning of the barrel more than at the muzzle. A good thing I guess.

David

[Bass Ackward]

Bass do you have a bore scope?

When you running those 30 lappers, I assume just fast enough to clear the barrel? How hard a bullet?

Methinks I learned something today. Thanks.

MOA.


MOA,

Sure I have a scope.

You have the idea. Just match your bullet diameter to the size of the grit you "need" to use. Personally, I never go below 320 or above 400. Bullets can finish the rest.

I find 14-15 ideal if you match it to something in the 2400 - 5744 burn rate range. Here I will use a tuft of TP for filler.

The guys that really get in trouble here are the ones that start out with bullets sized .002 over bore then wack it with unique or faster. Sure you are going to enlarge over time. After that bullet is imbedded, it can actually be close to .010 over size!

If you really WANT to be sure, then buy a cheap sizer like a Lee. Start .001 below the finished bore diameter you want if possible. Then use the first 5 lappers through the die to clean up the die and open it up. They will usually cut the first .001 pretty quick. Throw those bullets away. Then the die will be nice and round. Load up your bullets and then run them through your sizer.

You can roll the ones you want to fire and run them through the sizer. Roll them again if necessary and size a second time. Five lappers loaded with grit are better than 20 that aren't. It helps to imbed the grit, get's everything closer to the right size so it will chamber, align, and cut the diameter you want.

Get the idea?

[Willbird]

What I think about using firelapping for is to remove the tight spot in a revolver where the barrel is screwed into the frame.

On a rifle I think I would just fit a good bbl to start with..or if it is a period piece just live with what it has to offer as is. But that is just MY opinion.


Bill

[Blackwater]

Willbird, have you done the lapping out of a tight bore at the receiver junction, and if so, just how did you go about it? What grits, how many shots, etc.???

[Willbird]

Not yet blackwater, Mr. Taylor over on Leverguns tells how he did his first revolver.

I'm still opinion shopping.............


Bill

[grumble]

"Grumble I read uses cloth laps which of course isn't the ideal method on the best tubes. But for the junkers why not? If a guy learns what that feel on the rod means how can you really hurt something that's leading and produces patterns vs groups? Just reducing leading is going to mean more consistency no matter the method."

I'll say again: good enuff is good enuff. I'm not a competitive shooter (except against myself), and I'm tickled with 1 MOA, especially if the gun started off as a 6 MOA. For those wanting to shave those last tenths of an inch, the more you put into the lapping the more likely you are to close your groups another 1/4". But getting that last little bit of accuracy will take 10 times as much effort as getting the first and most important improvements.

I've tried using lead slugs to lap a bore, but was unhappy with it, probably because I'm not meticulous or patient enough to spend the time required to do it properly that way. A padded patch that's a tight fit in the bore will do the job very well for the first 90% improvement you'll get from lapping. That last 10% potential improvement is up to y'all.

BTW, it was Aladin on the old Shooters board that came up with the idea of adding the lapping compound directly to the bore, and then shooting through it to lap only certain portions of the bore. As far as I know, he's the only one who's tried it.

[BABore]

I did a fine lapping job on my 1895M 450 Marlin. I started by firing one round of jacketed ammo, then cleaned the bore completely. I repeated this twenty times. Then I fired over a thousand rounds of jacketed bullets cleaning every 30-50 rounds. The bore finish could compare to a fine custom job and it shoots cast bullet great. As an added benefit I got a lot of practice too. :-D :-D :-D :-D


I did firelap a 300 WM with a tent stake barrel. Couldn't make it shoot no matter what I did. As a last resort I firelapped it. The already nasty throat was increase in length by 0.047" after 30 lapping rounds. It did shoot a little better, but was still a tent stake. It's now a 375 H&H.