How to hand lap a factory barrel?

[Texas10]

IF you don't want or can't afford a good quality bore scope, get a endoscope for about $35 on Amazon and you'll see enough to know you have carbon rings, copper in the bore, dirty chamber or throat before wasting your time trying to perform a CBTO check on a new bullet. Perhaps most importantly you'll also confirm your cleaning methods are doing what you expect. I consider some kind of bore scope or endoscope as minimum equipment for anyone even half serious about shooting accurately.

IMOP, a good quality bore scope is one of the greatest sales tools for any gunsmith. One look down a factory new barrel and he'll have you ordering a new custom fit barrel for more that you paid for the entire rifle. Not that it's a bad thing, mine you, but many a new factory barrel replete with railroad track lands will still shoot sub 1/2 moa all day. Sure it'll copper up sooner, but you can afford a whole lot of copper solvent for the price of a new custom.

As others have noted, bad looking rifling is not necessarily an accurate indication of ability to put bullets on top one another.

 

[FrankG]

You want to lap a barrel properly....you need the right mix of lead a good handle with bearing and a straight steel rod (you can cheat and use a good one piece cleaning rod). You have to pour a lead lap into the barrel onto the rod.

You need some lapping compound. After the lap you poured is cool you apply the lapping compound and stroke the lap back in forth in the bore. How many strokes? That can vary.

That’s the short version. You don’t learn how to finish lap a barrel on one barrel.

Lapping is meant as a final polishing process. If your lapping to change size of the bore of the barrel that is wrong. You can end up bell mouthing the ends of the barrel etc...

I would suggest recrowning the barrel afterwards.

I’d shoot the barrel first and see how it shoots. If it shoots ok and doesn’t foul badly don’t worry about it.

Later, Frank
Bartlein Barrels

 

[msinc]

This is a ten year old thread, but it looks like there is still some interest in this subject. I did a thread on lead lapping a barrel a few years back. It seemed to be well received by all of the nice folks that read it. You can read it if you search "lead lapping a barrel?????". It's in the Gun Project Questions and Gunsmithing section. I did it back in the days of photobucket and all the photos are now red x's. It has been too long and wont allow me to edit and replace the photos. I can re-post it if anyone is interested to see how I did it.

 

[BRGUY]

At least Frank finally gave a decent answer to the question.

After I finish making a barrel and before everything is finished and ready for chambering, I take a clean stainless steel rod with a ball bearing handle, and fit a brass bushing about 4" from the end of the rod, that will keep the molten lead from traveling any further down the bore. The 4" or rod in front of the bushing is "ringed" and once the 100% pure molten lead is poured into the bore, it grips the rod and keeps it from sliding or moving around.

Now, about 2 1/2" of the lead lap is pushed out the end of the barrel blank, and a lapping compound is smeared around the lead lap. The lead lap is pushed and pulled through the bore, and you can feel where any tight, loose or rough spots are anywhere along the length of the bore.

When the lead lap starts feeling loose, you push it about half way out the barrel, and lightly tap the very end of the lap. This causes the lap to swell and fit tightly in the bore. If you let the lap get too loose, it will cause the sharp edge of the lands to round over.

Depending on the condition of the bore after manufacture, I usually start with an 800 grit lapping compound, 600 grit is it rougher than expected, and normallu go up in grit 200 at a time, and finish with either 1,200 or 1,500 grit.

A barrel blank is always cut off by an inch or so at the muzzle after lapping, and chambering takes care of the other end.

Me personally, when making and lapping a barrel for my self, I will normally stop the final lapping 4" from the muzzle, so after I remove the 1" from machining and lapping, the last 3" of barrel is just a little bit tighter than the rest of the barrel. My .308 barrel that was finished yesterday is .3080 + .0000 - .0001 from the chamber end and the last 3" air gages at .3077. Most varmint shooters ask that I make their barrels the same way. Does it matter? I cannot prove one way or another, but after 40 years of barrel making, at least for me and the ones who ask for it, I'm not about to change a thing.

 

[FrankG]

I didn’t get into a ton of details are there are many variables to doing this as BRGUY pointed out. What each person has for access to equipment and how they use it will effect how the process works and the overall results.

As an example we make our own lapping compound. Most often we use 180 grit but take that with a grain of salt as what we use quickly breaks down and I’ll say it will break down to about a 1000.

Same as the lead. We mix our own as well. Too hard of lead or too soft will have a different effect. Too soft a compound of lead and the lapping compound will imbed itself more into the lead and not be as effective. Too hard and you have the opposite happening.

Also at times I have finish lapped factory barrels. Some barrels have been so rough that after pouring the lead you could not pull the lap thru the barrel at all. Just ended up melting the lead out to pull the rod out. That can give you an idea of how rough some bores really are and how cheaply some barrels are made.

I know of manufacturers that don’t even bore ream the barrel after drilling and just go and pull a button thru it.

I was truly impressed with some brand new (Dec. of 1945) Vickers Machine gun barrels I purchased when I had my water cooled Vickers. The finish inside the bores for what was essentially a wartime produced barrel was pretty nice. Those where cut rifled. I finished lapped the bores and they looked fantastic. I still have one of them. Even the bluing on it is awesome and can put some of the new stuff to shame as well.

 

[sdean]

My last two stck Remington barrels flat hammer.

My 308 is a J-lock tactical and it will shoot .25 MOA with 168 match loads. A legit .25 MOA. ti is not even bedded. It is insane.

I just bought a stainless SPS to replace my old tactical in my favorite stock. I took the guts of the gun, put in my old trigger, and bedded it in the stock. After breaking in the barrel, and having the barrel rechambered to 223 AI it shoots ALWAYS under .5 MOA. My old tactical would shoot just as well but it had more fliers.

PS: I shoot moly. I do not give a crap what anyone says.

There are a lot of factory guns that would group well if you ignored the flyers.

 

[gambleone]

Thread is from 2009 bro. Half those posters are probably mia bro

Yes, one is that i know of. It's a crap shoot. You may be able to bring a factory barrel to life by lapping as preacher stated in his post of 2009, but being an off the shelf factory barrel, you're not sure what you're starting out with. You might find yourself putting a lot of time & effort into something that will not turn out. imho.

 

[JohnMill]

Anyone still around and still interested ;Google "Lapping a bore with a poured lead lap" That will take you to an old conversation with Gordy Gritters and some other folks. I think its from a long ago Benchrest Central thread. I'd post a link if I could find it on this mess that is my computor