For you G-smiths, how do I go about lapping a bolt to my action? I have a M-70 and a CZ 550 that could use it.

Why would you lap it? The cocking piece keeps the top lug from contacting until the explosian slams it back. The bullet has left by that time.
Butch

I worry that the bolt body has too much clearance inside the bolt bore of the receiver. This clearance makes lapping problematic. The lugs could be lapped with flat contact when the bolt body is at one angle inside the bolt bore, but not at another. The Mauser bolt body is too busy with features to sleeve.

I am just an amateur gunsmith, but for 98 Mausers, I have:

I drill and tap a hole in the bottom of the receiver near the recoil lug.
I screw a 5 pound spring ball detent into the hole.
http://www.brownells.com/aspx/...0BALL%20SPRING%20KIT
http://metalworking.mscdirect....CTLG=54&PMT4TP=*LTIP
I notch the bottom lug on the bolt so the detent can get started.
This pushes up on the front of the bolt body.

I put the trigger assembly on the receiver. The sear will push up on the cocking piece if the bolt is cocked. This pushes up on the rear of the bolt body.

I cut a cartridge case in half and put a coil spring inside.
I put the cartridge with spring in the chamber.
I put Dykem blue mark up on the lug contact surfaces.
http://www.use-enco.com/CGI/IN...943768&PARTPG=INLMK3
I put valve grind compound on bolt lugs.
http://www.cylinderheadsupply.com/clovercompound.html
I turn the bolt a few hundred times, until the blue is gone on enough area.
I clean out the action and clean off the bolt.
The bolt is now at the top of the receiver bolt bore when cocked and and the bolt lugs fit is flat over some area, so they won't dent and change headspace with hot loads.
When the rifle fires, the bolt should not rattle around in the receiver bolt bore.

Bill Leeper, a real gunsmith and then some, tells me that old gunsmiths a long time ago used to use the spring balls like I am now.

Unless a person addresses alignment issues from the muzzle back, simply lapping the lugs in an attempt to improve groups is a waste of time. Lapping lugs as part of an accuracy makeover is usually only necessary if the surface and finish you just machined is rough. Of course each job is different and will have to be judged on it's own merits.

Whatever you do, I would recommend pulling the barrel. Not only does it make the job less invasive, and clean up a lot easier, it gives you a chance to examine the condition of the receiver's lugs, which represents half the job.

Rae59, I'm not clear on just exactly why you want to lap your actions, there are several good reasons for lapping but everyone here has assumed that it's the lugs that you want to lap. I personally lap most bolt actions to obtain smoother operation rather than better accuracy since most of mine are hunting rifles. Can you give further details?
Regards, Joe

Drilling and tapping "near the recoil lug" causes me some concern..Can you clarify that part?

Lapping an action is done prior to barreling and chambering !

How come?
Butch

Lapping an action is usually part of the truing process, but it does not have to be. Critical "fit" tolerances can be affected by lapping is why it should be down prior to fitting the barrel.

Lapping can affect trigger operation, safety operation, and headspace.

Thanks JD. It is not the lugs I am wanting to lap, it's the bolt rails on the two rifles that need some work. On the M-70, there is a high spot that causes the bolt to get tight when it nears the lug grooves. The CZ 550 is just plain flat rough on the rails. Any directions would be appreciated.

Rae, these days I use the lapping compounds from Brownell's but in the past have used Fine & Coarse valve-grinding compound you buy at the auto parts house or industrial supply store. Either will work but I prefer the greater range of grits available with the Brownell's products. Please be advised that you need to keep the coarse lapping compound AWAY from the bolt lug recoil surfaces in the receiver, and also please be advised that some (most) lapping compounds will tend to imbed into the softer metal and thus continue their abrasive action after you want it to stop. Be sure to use plenty of hand-scrubbing and liquid flush to remove all traces of the previous grit before beginning a finer one. I use garnet for anything I can since it's non-imbedding but it's not available in the coarser grits.

Sometimes I begin with 200 but that's fairly coarse for almost all uses, depending. Anyway, even if I begin with 200 I usually don't cycle the bolt more than maybe a dozen times at the very most before flushing the action and going to a finer grit, 300 or 400.

Be very careful with the coarser grits, go very slowly. After a while you can tell when the grit has done its job, or most of it, and I recommend flushing and checking progress at frequent intervals at least until you have reached 600 grit.

I also lap the bolt and cocking piece ramps at this time, but I use a much softer mainspring to make things go easier during the bolt cycling. Needless to say I remove the entire trigger assembly during this entire process. I don't normally lap beneath the extractor collar but will clamp it tight while rotating it with kerosene for a lube. That's a trick used at Springfield Armory on the NM 1903s.

By the time you get to 600-800, you'll be cycling the action several dozen times or more for each grit. As the grits get finer, the cycle time must increase in order to achieve a good polished surface finish. I sometimes go to 1200 grit, it's amazing just how slick & smooth you can make an old clunky Mauser or, especially, an old 1917 Enfield or Rem 30!
Regards, Joe

Thanks J.D.

Lapping bolt lugs into full contact with the integral lugs does one thing. It creates a camming surface between the two(so basically nothing). A properly trued action and bolt need no lapping to create full contact, as the surfaces will be true already. However, when the bolt is closed, the only lug that will have any contact is the bottom lug anyway(as Butch pointed out). Simply because the trigger pushes the bolt up until it contacts the top of the rear action bridge when it is cocked. One of the main reasons that Benchrest actions are made to the extremely tight tolerances that they are, is for this very reason.

Misunderstood your post. The raceways can be handled like new guy did his mauser. It is a couple threads below. Yes, my CZ was rough at first.
Butch