Barrel Lapping

Bill, you'r an individual

Bill Leeper said:
Unlike many others, lapping a barrel is something I will often do. What's more, I have no trouble with lapping a barrel after chambering. For some reason, barrel lapping has come to be regarded as a mysterious operation which is more likely to cause harm than do good.
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I have found it is entirely possible to do all sorts of things which most say not to do. For instance:
Don't remove the lap from the barrel. You'll never get it back in place. I do this all the time. In fact, I will index the lap around in an attempt to uniform the land and groove dimensions.
Don't lap from the muzzle end. I actually find this to perhaps be the best way to lap the throat area.
You can't lap gain twist barrels. Because I don't appear to know any better, I lap them all the time. Works good.
I consider firelapping to be a technique for the inept.
or as an act of desperation. As gunsmiths, we should have some idea of what it is we are trying to do before we do it. Regards, Bill.
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As I never ever had the slightest intention to shoot in competitions my need for lapped barrel is Zero. I've never owned a rifle that wouldn't shoot at least 30mm/100metres even with a powder thrown charges.
A friend of mine who is an accuracy orientated freak who always wants to improve on everything, has ruined every single barrel that he had lapped.

Your lapping techniques are quiet unique to say at least, but I won't despute your claims.
I'll put my balls on the line if an individual who hasn't have a clue about lapping any barrel, will improve the accuracy of a finished barrel by hand lapping it.

Shoot well
Peter
 
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The earth is still flat, yes?

To this day I remain amazed, at people, that eschew the thought of lapping a barrel themselves.
One of the most prominent rimfire gunsmiths of our time, has, on at least a few occasions, attempted to convey his techniques used to lap a barrel.

Learn to slug and lap, then learn to read the wind, or not. But know this, a fella that can lap his own barrel, is usally the one going home with the wood.
 
If you don't want voids heat the mold before pouring, I use wheel weights for the lap. I never toss the short ends of barrel so when I need to do a chambered barrel I find one as close to the bore as possable and use it.
 
I use nearly pure lead but with a very small amount of tin; perhaps 1 or 2%. heat the end of the barrel up to about 300 degrees or so. Minor voids are not a problem. Regards, Bill
 
Are there kits that one can purchase? I've seen one in brownells sold by neco, I have also seen fire lapping but I dont know how well fire lapping works. Thanks for all the advice and encouragment I was about to rule out doing this myself.
Thanks bored184
 
Barrel lapping

First off through devouring various articles on lapping barrels I have done this. Its not that hard to do it if you have a bit of patients and a some what OCD I first had to understand principles of why I was going to lap my new M70 Special Edition 300 Mag Fagen well for one thing the barrel was rough it would take some 60 or so patches to clean it and accuracy as not what I expected from an all be it modern factory rifle...I purchased the laboratory grits from NECO it comes in 4 grits 220, 400, 800, and 1200 these grits are in a bit of mineral oil and must be stirred as the grit does settle somewhat, also I had purchased some 30 cal. lead slugs to slug the bore. I just wanted to take just enough off to smooth the rough spots...But being a SAMMI spec rile I didn't want to get too lap happy.

First I started by cleaning the bore with solvent and then Brownell's JB compound, as to remove all remaining copper from the bore surface and then back to solvent and then dry patches until no blue streaks can be seen. Once this step is complete then its time to take the initial measurement by running the first lead slug down the bore. I used a wood dowel and a small hammer to slowly bump the slug through the bore and with a good digital micrometer took three measurements of the land groves on the slug and wrote them down on a note pad and then average them. I then cleaned the bore to remove any lead fowling from the slug. Get used to this cleaning as you will have to do this between switching grits and slugging.

To make the lap I used pure lead that I salvage from a nuclear flow sensor box. I'm sure one can find pure lead on the market and not have to go trough the lengths I had to to get it, but pure lead is a lot softer than lead that has tin or antimony in it...I suppose one can use other lead, but I prefer the pure stuff as it makes for a softer lap. Once its been cleaned and slugged, then cleaned again your ready to make the lap. I start by setting up the action and barrel in a vertical position as plum as one can get it ( lab clamps on a rod with base work great for this) with a cleaning rod and a regular patch and jag attached push it all the way through and tie a piece of jute twine (burlap thread) to the rod just below the jag and warp it just to the point it will pull through the bore this will center it.A bore guide is a must Now pull the jag back until it is about an inch from the crown double check for centeredness, pre heat the barrel just hot enough to where you cant pick it up with your bare hands now pour your molten lead in till it just comes up but not out of the bore if it does well you'll have to make a new one as the lead will collapse and cannot be pulled through. If done right you should see the lead bead solidify just below the exit once you stop pouring. Note: I used an under sized push jag with the point cut off, which aided in breaking off spent laps.

Once your lap is made place gun in a sturdy vice on the bench and place a C-clamp on the edge of the bench in front of the bore at a distance to only allow 1/2 to 3/4 of the lap to exit. I use a piece of rubber and wrap it on the C-clamp so the lap has a soft point of contact. Coat the portion of the lap with your first grit (220) and here will be either easy or kind of hard to pull through depending on how rough the bore is. With a sturdy grip and force pull the rod back through the bore until you reach the beginning of the rifling....One must determine this distance as every rifle is different. Pull back and forth without removing the lap from its molded position, if you do so you have to make another lap. As far as how many strokes there is no predetermined number its all done by feel. In this particular rifle the throat and the last 4 inches of the bore needed attention the most.

Initially on this rifle it felt pretty tight at first pull of about 4 to 6 inches in and then smooth for say 4 inches and back to tight, then smooth again these points of tightness were the high or rough spots. After a few passes it became easier to push and pull once this happened I removed the jag and broke off the lap and cleaned and dried the bore, re-slugged the bore took measurements and wrote them down and made another lap for the next grit....Like I said before 'its a feel thing and as you progress through the grits it becomes really smooth especially after the 400 grit and feels as though you not doing much at all...You can skip the 1200 polish grit but why hell you came this far why not polish it....

I wasn't expecting miracles I just wanted an easy bore to clean and as a bonus this rifle shoots ragged holes at a hundred yards not counting fouling shot for about 40 to 50 rounds and then will throw them just outside an inch as the rifle becomes too fouled and it cleans up in 10 patches or less....This is a chore but with a little attention to detail it can be done...If your still scratching your head on this you may need either hands on or some illustration, but do not attempt if your not fully confident to do this.
 
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A friend has been doing quite a bit of experimenting lapping finished match grade barrels that he had slugged to find out what he was dealing with as far as internal dimensions. The trick to it all has turned out to be getting the right finish so that they will break in properly with regard to jacket fouling. Also, since one of the popular abrasives, aluminum oxide, breaks down to finer sized particles during the lapping process, there is the issue of how often to charge or change laps and what the sequence should be to arrive at the desired final finish. He has also been able to improve the accuracy of some factory rifles. The main issue that determines whether a given barrel is suitable for this is how big the bore is, in relation to bullets to be used in it. If it is too large, it would seem to make little sense making it larger, at least as far as fine accuracy is concerned.
 
I believe I read that Hart barrels are slightly under bored and then lapped up to spec. I'm with Boyd especially dealing with factory rifles one would want to exercise caution not lap out of spec. Which begs to question does the rifle have potential for accuracy in the first place and or is it a good candidate for lapping i.e. new rifle like in my case the rough bore was holding it up and once properly done one can tweak a factory rifle and sometimes you get fine wine and even if you don't more than likely it'll be better than what you had to start with. I might add I moly prep the bore and bullets to not only reduce fouling but to aid in fouling if that makes sense. I do however believe what you can expect after lapping the better the condition the barrel is in to reduce vibration.
 
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Say what you will about post-manufacturing/post-chambering barrel lapping but Bill Calfee is now getting close to $3,000/barrel for his fine tuning with a poured lap. He is also getting close to the $10K mark for a finished rimfire benchrest assembly....and has a waiting list.
 
When I saw this thread I couldn't help myself, so I joined to put my two cents worth down, since there was a void in information on this subject and its been awhile, since I've immersed on this subject. I thought there might be some extra critical information, or some simple tidbit detail that would be worth its weight in gold. After all this site is titled 'Benchrest Central, so I know there are others who's experience and expertise far exceed mine when it comes to accurizing, particularly this subject, so that being said jump on in fellas....

I must add I noticed the extreme caution from some of the post and there's nothing wrong with that at all 'Yeah! you wouldn't want to do this willie nillie....It would be one of those steps that I wouldn't want left out if one were to blue print and true the action on that high dollar barrel, but if were talking those kinds barrels more than likely they been already lapped, however if your action is not sporting a lapped barrel such as probably most modern factory rifles off the shelf keep in mind they have been CNC machined, so at that your a lot further ahead than back in the days when there were no computer assistance in machining, you more than likely have way better than 50/50 chance of getting more out of that new factory rifle.....Like my old man used to say "cut on this side of the line... If your feeling confident and want to tackle this chore one can never be too intimate when touching a rifle's private parts.
 
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alinwa said:
I think that using lapping grit finer than 220 grit is asking for fouling issues.....
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Well I suppose that maybe true for some, but I'm confused with an earlier statement you made....Starting with 220 and then working through to the finer grits is exactly the point of what your supposed to do, so why would that be asking for fouling issues? (just want you to clear that up.... So what do you find incomprehensible? If one understands what their trying to accomplish and needs just that extra piece of information to try their hand at lapping and has the common sense not to go too far as to remove to much metal, as to alter the dimensions that will create problems.... Were talking just enough metal to smooth and polish the bore....Like I said before you can feel what's happening when your running those laps through the bore especially the first two grits... I don't have my notes handy, but were talking several hundred thousandth of an inch just enough to nock the roughness off....In the polishing phase your pretty much out of the woods, since were in the micron size grit at this point....The goal is not to expect giant gains in accuracy, but to shoot for an easier bore to clean....But don't be too surprised if you inherit startling accuracy. I would say my biggest hang up was how many strokes for each grit particularly the coarse 220, 400 to say how many strokes would depend on how rough your bore is, so lets just say I went through two laps with 220 grit while short stroking over the rough spots with the first.... clean the bore and starting with a fresh lap with the same grit I did full runs through the bore right to the point where I couldn't feel rough spots anymore at 400 grit I pretty much did the same routine the rough spots were faint at this point and 800 and 1200 I just focused on polishing.....
 
Well I'll admit its is hard to convey without illustration...C'mon jerry I understand this thread is old but its got a lot of room for information....Really I'm not trying to create a pissing contest here.....
 
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