Laping Compounds

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  • Last Post 07 February 2012
delmarskid1 posted this 27 November 2011

 Hello. I have been using a diamond paste for honing my straight razors for a couple of years. It is a .1 micron grit in a light grease paste. It is fine enough to use to clean eye glasses. The outfit that I have been getting it from has all different grits to choose from. I got this because it was the finest that I could find. It ain't cheap. 25.00 US for a 5g syringe. Last night I tried it as a lapping compound on my Taurus revolver. I cleaned and disassembled the frame, polished the flat surfaces with an ultra-fine hard stone, and put a small dab of this abrasive in each of the pivot point holes of the action parts. I ground 1 1/2 coils off of the trigger return spring while I was in there. It seemed to respond to the treatment very well. I must remember to clean out the paste before excess wear occurs. I have used this stuff on sear and trigger faces and it polishes up the hardened surfaces. It also gets my razors sharp enough to scare me. I put it on the strop strap. I've pasted the web site. They have all kinds of neato science stuff.

 http://www.emsdiasum.com>http://www.emsdiasum.com

They also sell electron micro-scopes. The ultimate bore scope? Cheaper than a Harley.

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hunterspistol posted this 27 November 2011

Well, a guy can get valve lapping compound from automotive stores and shops. I have some 500 grit clover that's finer than you get for scope lapping. Wheeler Engineering sells a scope lapping kit with 220 and 320 grit, the coarser grades. A little imagination and things work for firearms that aren't necessarily made for them.

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Buzzard Bill posted this 02 February 2012

I have a rifle barrel with a ruff spot in it from sticking a patch in the barrel on a cleaning rod. Does any one have any experience fire laping with valve grinding compound. I have a tube of permatex #34B any suggestions?

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delmarskid1 posted this 02 February 2012

My valve grinding compound is pretty coarse. I'd look for something finer. I've soaked abrasives off of fine abrasive cloth when I was broker than I am now. For your situation my suggestion would be to polish it out with a patch on a rod. Then you will only affect a small area.

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hunterspistol posted this 02 February 2012

Bill, over on CastBoolits, 2dogs, Fermin Garza did a piece on fire lapping revolvers. The idea is to use very light loads that you know work without dangerous pressure. The bullets are rolled on steel plates to imbed the compound (works in soft lead).

Well, I went looking for it but, all the threads you get from the “Search” feature are too many!  Entering 'Fire Lapping' gets you pages and pages of entries.

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runfiverun posted this 02 February 2012

it opens the key word. just as described above will work. if you want fine stuff you can burn wet dry sandpaper and use that grit with some grease to make what you want. i have just used the stuff from napa made some softer cast boolits and rolled them in the lapping compound and fired them with loads in the 14k range. in the revolver i fired 6 and cleaned the bore out then fired again till i could see the bore getting smooth. took about three cylinders full. to polish i made a mix of toothpaste and flitz and done the same thing.

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Ken Campbell Iowa posted this 02 February 2012

the clover grit in 250 to 300 will work just fine for one-grade polishing/lapping.  i recommend hand lapping..it gets easier after you collect the gadgets kit  (G)... if your barrel is mediocre .. firelapping is easier.

400 grit is about the finest that will actually remove any metal.

use of lead-gritty bullets for fire lapping works mostly on the first part of the rifling...for more even firelapping, roll grit into a met...ja...t bullet.

if the barrel is reasonable in the first place, i fire usually FOUR lapping loads, and almost always see an improvement.  the most 250+ grit loads i have fired was about 12, and the barrel never responded... the barrel never shot as needed, and was discarded.


a great project would be for someone with an accurate rig to try polishing the heck out of the barrel innards and see if it gets significantly better ... or worse ...for cast bullets.

in my experience with 22 rimfire, one barrel, a mirror polish, very very fine polish.... made no difference  cleaning or accuracy...  compared to 250+ final  lap.  a sample of one ---(g) ...

trivia r us ..ken

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R. Dupraz posted this 02 February 2012

 

There is an article by Ross Seyfried that I ran across some time back, I just found it again. He reviews the Ruger .44 special Flattop and describes how he fire lapped the bore after finding that the rear was crushed a little too much when it was screwed into the frame.

I found the site again just by Googling Ruger .44 Special.

 

RD

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drhall762 posted this 05 February 2012

Injection mold makers used to use very fine lapping compounds. I haven't worked on a mold in years so it may have changed. The point is a supplier carries many different grades og lapping compounds. Another source so to speak.

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TomG posted this 05 February 2012

My current project is accurizing a new Ruger Blackhawk stainless 357 mag.

Initial accuracy was dismal. Subsequent inspection revealed a tight spot at the the barrel threads and a loose spot under the front sight ramp in the barrel. Cylinder alignment seemed pretty good using custom made range rods. Cylinder throats were on the tight side for the barrel.

I fire lapped the barrel with very hard cast bullets till the restriction in the threaded area was gone. Use very hard bullets and a very light loads so that the bullet doesn't slug up in the cylinder throat or forcing cone. This improved the loose spot but didn't take it all out. Fortunately, the barrel tightened up at the muzzle again. I lapped all the cylinder throats to one thousandths over the barrel ID. I then bought a 5 degree forcing cone reamer and extended the forcing cone from around 11 deg. to 5 deg. per side.

The lawyer trigger in it had a lot of creep and was pretty heavy. I put a spring kit in it and stoned the sear and notch to get the pull down to a reasonable level. I then put the trigger in my surface grinder and ground the sear notch down till most of the creep was gone. It's got one more trip to the grinder to get it perfect. You want to sneak up on this pretty slowly. You have to keep the notch square to the trigger axis and this almost impossible without using a jig of some sort.  

The fire lapping was done with 220 grit initially till most of the tight spot was gone. Then I finished it up with 400 grit. Cylinder throat dia. was matched to the dia. in front of the forcing cone. I would slug the barrel every couple of shot till you get a feeling on how fast it's cutting.  

I'm now getting 2 1/2 inch groups at 40 yds. off sand bags and a 4-12 power Burris scope. That's the best I can hold. I'm sure the gun is better than that now. I may make up a Ransom Rest type rest to get better data on this gun and loads.

The moral of this story is to not try to lap with too fine a grit. For it to work, it must cut aggressively.  Messing around with fine grits only polishes it up but the tight spots are still there.

Also, you don't want a barrel to be too smooth inside. About 320 to 400 grit is best for lead bullets. You want to have a place for the lube to reside on the surface of the bore. Also, if you have too smooth a surface, you have too much contact of the bullet surface with the barrel surface. This leads to more friction and leading or jacket fouling. If there are tiny peaks and valleys the bullet can ride on the tops of the peaks and lube can reside in the valleys. I recieved this from a top notch barrel maker who's barrels win many matches. It makes sense to me.

The quality of the lapping compounds varries from one manufacturer to another. I've examined several brands under a microscope and found that some looked like floor sweepings and some were very uniform and beautiful to look at through the scope with a strong light. I use Clover silicon carbide exclusively. I've never looked at valve grinding compound and don't know if it will imbed in the parent metal or not. I would stick with non imbedding compound and spend the money to do it right. Most any industrial supply place will have silicon carbide compound in many grits.

Whether fire lapping or lapping by hand, I would not finish with anything finer than 400. One custom barrel maker uses 320 and when it breaks down, gives a slightly finer finish. I've examined many custom barrels with a bore scope and all of them looked like they were finished with something around 320 grit.

I once lapped a barrel down to 1000 grit and it didn't shoot any better. My 357 barrel with the 400 grit finish never shows any leading even at 1500 feet per second loads. .

Just my $0.02 worth,

Tom Gray

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Ken Campbell Iowa posted this 05 February 2012

great post, tom; some useful thoughts for tuning up a ruger security six; the innards have been smoothed up but i have been procrastinating about attacking throats,cone, and barrel.

for triggers i too use a surface grinder with a diamond wheel; i find that just dusting the searing surfaces does not clog up the wheel. for jigging i use a magnetic chuck with a small wobble vise, --palmgren type. the sweaty part is the half hour of measuring-before-cutting to get the surfaces square..(g). fwiw, my biggest challenge in a trigger job was an incredibly good shooting 917 marlin..i did get the trigger to a crisp pound or so, but cannot actually explain how that trigger works...vintage rube goldberg .. regards, ken

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smokiejoe posted this 07 February 2012

Be carefull with the valve grinding grits, you may open up the lead more then you want, I put a new M1 barrel on that wouldnt chamber a NOE311284 bullet. 3 shots and I could seat the bullet out more then I wanted, The tube went into the the trash can.Joe

                    Delmarskid 1 - Beloit

   Once worked for the Beliot Corp. in the dryer foundry. 1964, $1.85 a hour

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