Can I use a standard rubbing compound to lap them?

sure you can but how will you be able to see the results of your work?

quote:

Sure you can, but how will you be able to see the results of your work?

Lampblack?

Could you take the bolt out, take a sharpie to the lugs, work the action for a bit and inspect the lugs?

the problem with doing it that way is that the bolt lugs will show thier contact area because they are wiping over the stationary seats on the action, but they don't give an accurate indication of how they are sitting on the seats. you could have just one small high spot on the seat and the lug shows a big area of contact because the entire lug surface wipes over that highspot. but on the seat it only makes a very small contact area. you need to be able to actually see the seats in order to know you have a decent area of good flat contact on each seat.

Not to mention that with the barrel on you are adding headspace (IF the barrel is already chambered).

great advice as usual. I'll take her to the gunsmith then. Thanks.

You can EASILY lap the lugs with the bolt still on. Use a fired round to give slight backpressure.
Use a Sharpie to mark the back of the lugs to see how much contact they are making.
Any reductions in Headspace are so small as to make no difference.
I was shown this by a couple of different gunsmiths.
Yes it's better to take the barrel off and use a screw in bolt tensioner for a more perfect job, and it's easier to clean out the compound with the barrel off but it's not the only way to do it.................................DJ

Will a paint rubbing or polishing compound work? Does it have to be a special compound?

A method of lapping lugs while a barrell is mounted:


NOTE: Insure your chamber is well under max headspace-if not, set back the barrel or rebarrel etc, and lap lugs/seats first before rechambering!


Cut a FL sized case in half, just forward of the web, then cut the middle section out leaving a head section and a shoulder/neck section, insert a 5-8 lb coil spring smaller in daimeter than the case sections and insert the forward section into the chamber, then the spring, (with extractor/ejector removed from the bolt)coat with dykem or marker etc, then load the lugs with polishing grit and carefully close the bolt on the sectioned head-the spring pressure of the head against the bolt face will insure you have adequate pressure against the lug seats. Work the bolt about 25 times, remove, wipe clean and observe the dykem or marker; repeat until you just achieve 100% contact.

Unless the seat/lugs are really buggered up, you should remove only a few thousandths.

Best!

Any sort of spring loaded tensioning system use to apply pressure to the bolt when lapping will perpetuate unevenness. In addition, such systems will often produce an angled seat and lug. I've seen some good actions which were really screwed up using spring loaded tensioners. Of course, ineptitude on the part of the operator was probably a factor as well. Regards, Bill.

bill is right...
i did exactly that to a little yugo in 6.5x55... got a little too enthusiastic with the lapping and ended up with sloped lugs/seatfaces. this was about 20 yrs ago... a $65.oo lesson on bolt lug lapping! it was done with a lapping tool i borrowed from my gunsmith. the typical, shop-made kind of old barrel theaded section with spring and plunger in it to bear against the bolt face. most everyone has one of these and there's nothing wrong with them, but you have to know what you're doing with them ...it's real easy to end up with junk when you don't have an idea of how the seats should look and how you should go about accomplishing it....it takes surprisingly little lapping to seat things up and you have to be able to see the seats to stop at the right contact pattern, the lugs won't tell you anything about the seats, they are harder than the seats and will eat the seat away easily.

The whole idea of lapping lugs, is problematic, as it will spoil the paralell locking surface, so you in the end will end up with a reducing headspace, acording to how closed the bolt is. In other words, in the extreme, the bolt will become self opening when fiered.

The problem is caused by the nature of the lapping process, where the entrance corners on both the lugs and the seats will be worn mutch more, at they are exposed to the most moovments.
The more you lap, the more undefined the headspace will be.

Another thing is that generaly the hardest part will be the part that wears the most, as the lappingcompound tends to stick to the softest part, therfor it only wears on the hard part, who does all the mowment in relation to the abrasive.
As an excample you can think of why barrelmakers use lead when casting a lap for lapping hard steelbarrels
(because the compound seats into the soft lead, and therefor trawels along the steel surface, creating wear on the steel.)

So if you want to spend time on fixing a improper action, the best way is a real truing of both bolt and action

Bill, What is your recommended method of lapping? How do you apply pressure appropriately/evenly to the lugs/seats? Is any pressure needed?

Also, we know have two theories on which part will lap faster, lugs because they are harder and the grit will imbed in the seats, seats becasue they are softer....

Any really know which is correct?

When we lap barrels, we easily increase the diameter of the bore by 0.02mm without any loss of diameter on our Tin lap

jA,
generally true of two very dissimilar metals...such as a lapping slug of tin or lead/tin and a barrel. when both are considerably closer in hardness, such as bolt lugs and lug seats, they will both wear because the compound doesn't necessarily bed itself in the softer of the two, so it is active on both surfaces. if it were to imbed itself on one or the other, the lapping would never cease....every bolt cycle would reduce one part or the other and headspace problems would be inevitable. the compound is similar to (or for that matter the same as) automotive valve lappping compound. when lapping in valves the compound doesn't imbed on either surface, if it did, a valve job wouldn't last very long at all. the reason for using a softer slug metal is so that the compound will imbed in the working piece and not the worked piece so that the slug doesn't change dimension and the compound is made to contact the entire bore's length. the worked piece(the barrel)then bears the wear from the compound being passed over it.

quote:

Originally posted by Andrew cempa:
Bill, What is your recommended method of lapping? How do you apply pressure appropriately/evenly to the lugs/seats? Is any pressure needed?

Also, we know have two theories on which part will lap faster, lugs because they are harder and the grit will imbed in the seats, seats becasue they are softer....

Any really know which is correct?

I've been at this for quite a while and tried all sorts of systems. Now, on those occasions when I do lap, I use a nylon plug in a barrel stub to apply pressure to the bolt face. The lugs remain in engagement and I make an effort to lap mostly at the bottom of the stroke.
Back in the late '70's, I made up a piloted lap of cast iron and lapped the seats with this. I then faced the lugs in the lathe. Contact was always very good and it was a viable method.
Very often, people are lapping lugs when it is not really necessary. On Remington and Winchester actions, for instance, the bolt is lifted up at the rear by the pressure of the sear on the cocking piece. Since the rifle is usually cycled a lot more empty than loaded, the wear pattern indicates heavy bearing on the bottom(right) lug and no contact on the top. This is a false indication and I believe there is a lot of lapping done when it shouldn't be.
A model 70 I have in the shop right now shows the damage which can be done if lapping is improperly done and, in this case, overdone. To straighten this action out will require an increase in head clearance of at least .013". Already, the safety doesn't work and the lugs and abutments are angled and stepped. A fine old action which is unusable without remedial work as a result of improper lapping. Regards, Bill.