I lapped a barrel a couple weeks ago....

[oldracer]

My very low priced Sharps from Armi had a barrel with many many really bad tool marks and would not group very well, even at 100 yds. Doug Knoell said that many people buy them and then spend the $$$$ for a Badger barrel and have it installed and end with a very good shooting gun for half the price of a full custom Sharps. Before I went that route I decided to try doing a bit of lapping to see if the tool marks would come out AND have the accuracy get better. To gauge the finish I used my Harbor Freight bore scope that even shots video to gather before and after readings.

I poured a pair of lead slugs near the muzzle and used the lapping compound that NAPA sell, which feels like 320 grit. I ran some compound into the barrel with a very small .17 cal cleaning nylon brush and then started slowly working the slugs from the muzzle to the chamber and I had marked the rod so I would not get past the start of the rifling. After 6 passes with both slugs and a very through cleaning, the tool marks were almost all gone. I noted the slugs got looser after 2 or 3 passes since the lead is way softer than the steel.

Today was the big test and the 100yd 10 shot group was with in 1.5 inches on an 8 inch target and the 200yd group was almost exactly the same size! Yikes I thought, maybe I won't have to replace the barrel after all so time will tell and I think the 90 degree marks did have a large affect on the bullet travel down the barrel.

Has anyone else done this lapping with similar results???

[Don McDowell]

I fired lapped a Green Mt. 40 caliber barrel, it helped a lot, but combined with polishing by wrapping 0000 steelwool on a brush soaked in 3n1 it smoothed the innards of that barrel up quite a bit.
I have to trim 45-90 brass down to 2.25 to get accuracy with no leading in my Armi sport made sharps.

[NickSS]

I fire lapped my Marlin 95 lever action in 45-70 and it improved the accuracy a good deal as well as removed the tendency to lead badly. I also about a year or so ago bought one of the cheaper Pedersoli Sharps that Cabella's sells for around $1000. This rifle fouled badly and was hard to clean the first time I shot it. So I loaded up 50 rounds with Jacketed bullets that I had on hand and fired 50 round through it cleaning it after every shot for the first five, then after every fifth shot for the next 25 rounds. Then I fired groups of 10 rounds twice to see how it did. The result was that my group size went from around 4 inches at 100 yards for the first five rounds down to less than 1.5 inches for the last 10 rounds fired. Ever since then this rifle has fired BP loads exceptionally well and cleans pretty much with a couple of patches at then end of the day.

[Civil War Life]

You guys obviously know what you are doing. Could one or more of you write up a procedure for lapping? Also what is fire lapping? Sounds like maybe you use lapping compound on a bullet and fire it out of the barrel? That is interesting. You thoughts on procedures would be very helpful. Thanks,

Terry

[oldracer]

There are several websites that have the procedures outlined (here also) and if I get a chance I can post some links. Basically there are the manual method and fire lapping. I did the manual and there are a couple of ways to set it up.

- First is to make a lead cast near the muzzle end of the barrel and have the lead attach to a cleaning rod. The lapping compound is then put in the barrel and the bore cast is moved back and forth.

- Another way is to cast with something other than lead and lap that way.

- The method I used was to use several bullets that I "slugged" down the bore then drilled in the center and threaded for a 3/16 brass threaded rod, wrapped heavily with tape and then do the lapping. Note these will be tight on the first pass or two and then loosen up.

I used a 22 cal mop brush to put oil based lapping compound into the bore the whole distance from muzzle to chamber and than lapped from the muzzle to the chamber without actually lapping the chamber. In the articles I read one said to use little compound and others said to use a lot of it. In my experience lapping valves and other parts as a Navy nuclear machinist I was taught to use plenty of compound and let IT do the work. I marked the rod first so I'd know how much to run it in and not hit the chamber. The excess compound actually ran out the chamber and into a ziplock bag I had fastened around the shell opening and it took about 5 or 6 smooth passes to have the "lapping bullet" start to feel loose. I would then switch to a new one and did that 3 times total I guess. I flushed out all the compound using patches soaked with Kroil until the bore was clean when looking with my bore scope. I noted there were no tight spots thank goodness as I have read that is a sure sign of bad barrel making and mine just had a bunch of 90 degree tool marks which are now gone!

[Ed in North Texas]

There are several websites that have the procedures outlined (here also) and if I get a chance I can post some links. Basically there are the manual method and fire lapping. I did the manual and there are a couple of ways to set it up.

- First is to make a lead cast near the muzzle end of the barrel and have the lead attach to a cleaning rod. The lapping compound is then put in the barrel and the bore cast is moved back and forth.

snip


An alternative is to roll the sized slug or boolit in the lapping compound (between a couple of steel plates) to embed the abrasive in the lead. Obviously this is necessary for fire lapping, but it also wastes less lapping compound with the manual method as you won't be pushing a bunch of compound ahead of the lead.

oldracer:

Any reason you didn't tap a standard cleaning rod thread (other than already having the brass rod)?

Ed

[oldracer]

The main reason for the threaded rod was for stiffness. My cleaning rods are pretty expensive, if I remember correctly and are some sort of composite material and flex some. I was afraid I'd have a problem and get everything stuck in the bore so I went for safety.

I had read about "embedding" the compound but as I noted I learned many years ago to use lots of compound and let it do the cutting. I bought a can of oil based valve compound at NAPA and it was a couple of dollars I think. I was surprised that they still sold something that was "oil based"!!!

[Ed in North Texas]

The main reason for the threaded rod was for stiffness. My cleaning rods are pretty expensive, if I remember correctly and are some sort of composite material and flex some. I was afraid I'd have a problem and get everything stuck in the bore so I went for safety.

I had read about "embedding" the compound but as I noted I learned many years ago to use lots of compound and let it do the cutting. I bought a can of oil based valve compound at NAPA and it was a couple of dollars I think. I was surprised that they still sold something that was "oil based"!!!

I have a collection of composite and stainless (coated and uncoated). I even still have some GI steel sectioned rods, but dumped all the aluminum rods (except for Shotgun) many years ago. Not flexing is "a good thing" (TM). :bigsmyl2:

As for embedding, it is necessary for fire lapping, just another method for manual lapping. I'm kind of surprised valve grinding compound is still around. I never bothered doing my own when I was fooling with cars, at $8.00 per head it was better to leave it to the automotive machine shop (and I think I just dated myself :-( ).

[oldracer]

I think you did date your age a bit??!! The only time I have seen valves being lapped in the past 15 years or so were the ones (Titanium) that went into my vintage Porsche race car engine. At $125 for each one we treated them very nicely for sure!

I checked with a couple of "new" Navy machinists and asked what they used to lap valves and they both said "what is that???" Glad I retired when I did.

[midnight]

Any one who has overhauled a flathead knows what valve grinding compound is. With it and some Prussian blue you can lap those valves in slicker than s--t. I just used some the other day to lap a hole drilled in the side of an aluminum plate. The cartridge heater slipped right in and now I've got a new heater for a lubesizer.

Bob

[bigted]

thats fun...still lap valves in knucklehead, panhead, shovel head, evo, blockheads...anybody that does go fast work on any engine still lapps valves and knows how to putty an engine to make sure how close the valves get to the pistons as a result of the high lift, long duration cam shafts....and yes i still remember the side valve engines called "flatheads....both ford 6 and 8 cylender and the famous harley in both 45 and 80 inch cid...the 74 inch flattys were and are very rare indeed.

hows that for aging myself???

rifle barrels cant be that much dif in the lapping dept. some do it by hand with slugs n some do it with impregnated slugs shot at slow speed down the barrel.

ive never had problems getting the "clover" cutting compound...any NAPA store either has it or can get it fast for you.

[Gtek]

Valves, bolt lugs, 45 slides, barrel threads, scope rings, scope bases, bores, trigger / sear, on and on. I am a half a century now and wondering what would my life have been without it, those green cans stacked in cabinet. Gtek