How do you lap a barrel?

S

skeetlee

Active member
So does anyone here know how to lap a rifle barrel blank? I have a shilen chrome moly 6mm blank that i bought from midway for 125 bucks. I understand that these barrels are not lapped at all from shilen. My question is, how do you lap these things and is this something one can do himself?? thanks lee
 
I took a tour of a barrel manufacturer's plant a few years back. They had a bottom pour lead pot (RCBS) mounted high on a steel column that was one of the supports of the metal building. What I saw was the lapping of the bore, after reaming the hole, before rifling. A metal rod, that had a ball bearing handle (perhaps a cleaning rod) that had some sort of jag designed to stop the lead and have some of it poured around it, was inserted through the un-tapered blank, within a few inches of the far end, ( I assume that there was some residual oil in the bore from reaming.) and the assembly was lifted up so that the open end of the barrel was pressed against the pour spout of the lead pot long enough for a slug to fill the end of the barrel. After a brief pause in the upright position, the barrel was clamped in a vise that was mounted at a convenient height, the lead slug was pushed out an inch or so, the end was trimmed so that it could be pulled back into the bore. Then it was pushed out most of the way, and then a small soft brush was used to apply what appeared to be a mixture of oil and abrasive, then the operator began to push the lap back and forth, the full length of the barrel. As we left, I saw the finish lapping area, where contoured barrels were being worked on. It looked to be something similar.

A few years ago, through a friend, I was able to get a factory chromoly chambered barrel for my Savage. After having if for a while, I changed my mind about my plans for that rifle, and sold it to a friend, for what I had in it. At first he thought that he had made a bad purchase. It copper fouled quite a bit. I advised him to keep shooting it. He did, and within a couple of hundred rounds, it stopped, and has been an accurate, easy cleaning barrel since then.

I think that for you to lap your barrel would risk more than you will probably gain. I would either sell it, or chamber it and then be prepared to shoot it a bit, to smooth it out some. With some of the reports that I have seen on the copper remover that Montana Extreme offers I think that this may not be as much trouble as it would have been a few years ago. Lapping barrels is a matter of experience and feel. Barrel makers are in a good position to learn because their mistakes mostly cost their labor. For the rest of us, it could be a major undertaking, and a lot more expensive. Good luck with your project.

Boyd
 
Agree with Boyd

I've lapped a few of the inexpensive Midway barrels-----with the help and oversight of a friend, a retired machinist who'd done a lot of internal lapping in his work days.

I've also seen lapping done at a barrel maker's plant-----they have a good setup for this and inspection equipment that most of us wouldn't have. Plus the experience to know how to do it right.

We made jags for the laps out of brass 8-32 threaded rod and used a cleaning rod to push the laps.

Without a borescope or air gauge, we didn't know what we were acomplishing----but we could feel the tight spots. We quit lapping when the tight spots were relieved.

These barrels are accurate enough for 223 PD guns but nowhere near as accurate as a premium barrel. I don't have a before-and-after reference to compare the fouling of these barrels to an unlapped barrel but fouling isn't excessive.

I was able to get three of these barrels for less than one Kreiger barrel but don't think I'll repeat this exercise, even though the barrels have done pretty well in the dog towns.

To each his own.

A. Weldy
 
If it's a Shilen, it use to be you could get Shilen to lap it for a fee. Yes, you can learn to do it yourself. A learning curve of 25-50 failures should be about right.
 
Charles,
When you buy a new Shilen CM you can have the blank lapped for an extra fee. I don't think they would do it for free. The problem with lapping a chambered and crowned barrel you stand a chance of both ends being a little larger. It ain't good for accuracy. I would take Boyd's advice.
Butch
 
This is a shilen blank unchambered. i will call shilen tomorrow and see if i can send it in. That sounds like the best idea yet. Lee
 
Lapping a barrel

There are several ways to accomplish lapping. Yes, you may loose 1.5 inches at the muzzle. I bought several hundred unsized lead slugs with lubricant rings. I shoot several squirts of non detergent 30 weight oil down the barrel. I distribute it well with a nylon brush. I thenb use a lead bullet slightly oversized to the bore loaded up with 180 grit valve lapping compound. I drive the lead bullet into the barrel with a smaller than the bore brass or aluminum rod. I then work it back in forth from one end to the other. I lap the first 1/3 of the barrel an extra 15-25 strokes to give the bore a slight taper. If you feel tight spots you work them until the resistence is the same all the way down the barrel.
Nat Lambeth
 
Butch Lambert said:
Charles,
When you buy a new Shilen CM you can have the blank lapped for an extra fee. I don't think they would do it for free.
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What I said, right?

The problem with lapping a chambered and crowned barrel you stand a chance of both ends being a little larger. It ain't good for accuracy. I would take Boyd's advice.
Butch
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I didn't realize the Midway barrels were already cut & chambered. Of course, you're right about that.

Edit

Nathan, I believe some valve grinding compound is silicon carbide, no? Use to be, anyway, That's not what you want to use in a barrel. Aluminum oxide only. Or maybe all valve lapping compound is AO these days?
 
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I've also lapped quite a few barrels (25 or so I guess) after learning from a barrelmaker. It really is not that difficult, but you won't find barrelmakers freely giving advice as they are somewhat protective of their exact grade of lubricant, abrasive, etc... What will work is aluminum oxide and most any type of grease (150-200 grit). I gave my buddy some rendered bear fat to try and it worked very well too. If you use a silicon carbide abrasive such as Clover Compound, go with a finer grit as it doesn't break down like the aluminum oxide will. Cast a lap in the breech end with the rod sticking out the muzzle (use PURE lead) and put a small amount of compound on it the lap and start lapping. Don't work the muzzle as much as the breech end, and after a few passes, you can push the rod completely out and index it to a different groove to either 'even things out' or just for the hell of it. Feel for tight spots and work them out, after a few strokes wipe off the excess compount off the breech end of the barrel as the lap can load up too much and get pretty tight. The first inch or so will look a bit galled from some abrasives 'rolling' on the lap before embedding in the lead, so initially lap the breach end a bit more. When your about done, take a couple full length strokes and if part of the lap comes out the muzzle, you can tap it in by keeping the rod straight and tapping on the back of the handle with your palm. If the lap feels too loose, you can also slug it up a bit by putting a brass rod in the bore on the breech end and with a mass against it give the rod handle a rap with a mallet (go light). With button rifled barrels (22 cf is what I most often do) you can lap out 95% of the reamer marks in 5 min. or so. A borescope is pretty much necessary I would say too... If you want to 'practice' and you have a borescope, get some factory take-offs and have a go at it with them. Same deal there, cast from the breech and push the slug out so you can nip off the chamber and throat cast. It can be a little tricky lining up the cast with the bore, just take your time and rotate the rod side to side as you pull it in until you feel it lock into the rifling. There is a fine line on finishes also...you don't want it TOO smooth. If you look in there with a borescope and it looks like a mirror with very minimal longitudinal marks, it's gonna foul like a SOB....A tight patch and Flitz can do that after a few hundred strokes...I found that one out after a last resort effort on a factory 270 barrel. Now I guess I should end this with IMO, and in my experience...which is not as great as many here, so this is just what works for me.
 
Just to add... all of the stainless Shilen barrels are lapped...
 
I called shilen today, and yes they will lap this barrel for 40 bucks. Now i need to decide if i think its worth the 40 bucks?? I also asked the nice lady if the chrome moly barrels were air gauged and she said they only offer one grade on the chrome moly. I then said "so this could be a select match grade you simply just dont know, is that right" She didnt act like she knew what i was asking, and said no we only offer one grade. I said ok. So i still dont know what to think. If they dont check them, or maybe they do check them, how do they know how true the bore diameter is? I just dont understand. I know Butch has had some really good luck with these barrels but i have also read were some folks say they arent worth the trouble. the problem is, i dont know those other fellas that say they arent worth a hoot, so i wont hold what they say for a grain of salt. Anyone here other than Butch shoot these chrome moly barrels? My barrel is a 1.250 straight 6mm 8 twist, and i am thinking about chambering it for a 6ppc then use a throater for something like 88gr berger bullets. Thats my idea. Lee
 
Lee,
The CM barrels are all match grade. Some would meet select match, but they sell them all as match grade. Lee, you can ask a lot of guys a lot of questions,but you need to visit a barrelmaker to really understand what you are asking. I would definitey have it lapped.
Now a heavy bullet quick twist 6ppc doesn't sound very good to me. I believe you need to make it a 6BR. Just my opinion.
Butch
 
Quite a number of years ago I bought a Shilen barrel from Brownells. I had been using the West Virginia and Wilson barrels up to that point and this was supposed to be a big upgrade?? Anyway, the barrel was a CM 10 twist 7mm barrel, about a #4 contour. I built a 7mm08 on a Ruger tang safety action.

It had 8 lands/grooves believe it or not. I believe it was called the 'Lone Star' grade back then. I could hold a bullet up to it and the copper molecules would jump off the bullet and into the rifling! It fouled that bad, funny thing was, it still shot.

I put 2-3000 rounds through it, killed 25 or so head of big game with it when a buddy just had to have it. He traded me a Pre-64 220 Swift for it and has been killing stuff ever since. The 220 Swift was a dumb experience; 14 twist wouldn't stabilize any decent bullets and too light to use for prairie dogs and too dang heavy to call coyotes with it. I traded it off myself!

I don't think they make those 8 groove buttons anymore but that rifle shot pretty dang well for a $120 barrel!
 
Dennis,
I used to use a lot of the Lone Star grades until they found that they all made match tolerance. They still have the 8 groove buttons.
Butch
 
A lot of people used to tell me "Never use a Shilen on a magnum, those little grooves wear out too fast". I have a 300 WBY barrel that I got 2800 rounds through before I pulled it and it has 12 lands/grooves. It still shot pretty decent, just not as good as was.
 
Butch Lambert said:
Dennis,
I used to use a lot of the Lone Star grades until they found that they all made match tolerance. They still have the 8 groove buttons.
Butch
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Butch

Can you convince Shilen to make stainless select match barrels with that 8 groove button again? I hear they shot very well.
 
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