I remember a while back reading a thread on the subject of lapping lugs. There are several and I tried to search for this particular one and can't find it. Anyway, at some point in the thread a comment was made something like "just don't use one of those spring loaded things". I assume this referred to something along the lines of whats shown in Kuhnhausens book. So my question is, what's wrong with using that type of tool? It seems in my inexperienced mind to be just what the doctor ordered as far as alignment goes.

Just trying to learn,
Ron

It may have been one of my comments.

Don't know about anything in any Kuhnhausen book (another story) but I was referring to a device intended to put pressure on the bolt face in order to keep the bolt lugs in firm contact with the receiver lugs while lapping.

IMO the spring-loaded device is totally the wrong thing to use.

The lugs should be hard-fitted, that is, the pressure supplied to them should NOT be spring-loaded. The spring tension will encourage the bolt lugs to follow the peaks AND valleys of the receiver lugs while the use of a hard-fitting adaptor will apply cutting pressure to ONLY the peaks, or at least mainly the peaks. The solid (versus spring-loaded) pressure will tend to lap the surfaces more evenly as well as more rapidly. JMO.
Regards, Joe

That makes sense. Then again, many of your answers do.
I will be trying your "back and front of the mag box touches, sides have clearance" method soon on a commercial 98 that had much internal damage due to oil soaking and bad inletting. If I ever get the thing finished and shoot it, I'll post my results.
Thanks, JDS.

quote:

The lugs should be hard-fitted, that is, the pressure supplied to them should NOT be spring-loaded. The spring tension will encourage the bolt lugs to follow the peaks AND valleys of the receiver lugs while the use of a hard-fitting adaptor will apply cutting pressure to ONLY the peaks, or at least mainly the peaks. The solid (versus spring-loaded) pressure will tend to lap the surfaces more evenly as well as more rapidly. JMO.
Regards, Joe

I've actually made barrel/chamber stubs for doing this, it's a good project for a student smith. Just thread and chamber a barrel stub and make a close-fitting dummy plug the size of a cartridge case. Simply screw the stub into the receiver and chamber the plug, then tighten the stub until the plug just barely bears on the bolt face when it's locked. Then lap by working the bolt handle up & down, applying minimum force at first with the stub's threads and gradually increasing the pressure as the lapping progresses. When you get more than about 75% contact on both lugs, evenly, then it's time to think about stopping.

The beauty of this method is that the stub and plug don't really need to be machined perfectly, not at all. As long as they are in line with the bolt raceway then they'll serve their purpose admirably, a beginneer can fab several as learning projects before actually tackling a real barrel chambering job.

I'm not a BR smith and certainly not a toolmaker or even a very good machinist so others here may care to correct this description and berate me for it. Please feel free.(grin)
Regards, Joe

I was thinking up something like this after you explained the pressure lapping. The pressure lap seems like it duplicates firing. If chambering practice wasn't going to be part of making this, the hole in the stub could be a simple ID with matching plug, boltface end squared up with the dia., assuming I'm following you right.

quote:

Originally posted by walnut:
I was thinking up something like this after you explained the pressure lapping. The pressure lap seems like it duplicates firing. If chambering practice wasn't going to be part of making this, the hole in the stub could be a simple ID with matching plug, boltface end squared up with the dia., assuming I'm following you right.

You're absolutely correct; it's really pretty simple and requires nothing but a little time.

I try to use something like garnet for the lapping, it's NON-imbedding and easy to clean up with no worries about future unwanted cutting from the imbedded residue.
Regards, Joe