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From: toby@stein1.u.washington.edu (Toby Bradshaw)
Subject: Re: Action Truing
Organization: University of Washington, Seattle

#First, the barrel, bolt and trigger group is removed.  Then a diamond or other
#good lapping compound is put on the bolt's locking lugs.  After the bolt is
#put back in the reciever, it is closed and opened so the lapping compound
#will smooth up and make 100% full contact on the entire mating surfaces of
#the bolt and reciever lug recesses.  What this does is make sure the bolt
#bears evenly and completely on the reciever.  Doing this prevents the fired
#shot from causing the reciever to vibrate in different directions from shot
#to shot.

A minor nit here.  The best smiths will true both the lug abuttments
in the receiver and the back of the bolt lugs before lapping.  Plain
lapping is better than nothing, but it is perfectly possible that
the bolt will "cam" into the abuttments unless they are trued.  That
means that unless the bolt handle is absolutely, all they way down
for every shot, the headspace will vary.

Of course, with a good custom action the bolt and receiver threads
WILL be in line, and all this stuff can be skipped (after checking,
of course).  Some BR gunsmiths will go to the trouble to re-cut
factory receiver threads oversize to get them on the same centerline
as the bolt.  This gets expensive.  You're still stuck with a
right bolt/right port (slow) receiver and a flat-faced (slow)
bolt, and the cost of factory action + work is pretty close to
what a custom that needs no work would cost.  Hence the prevalence
of Stolle, Hall, and Wichita in the BR winner's circle, where
re-worked Rems used to be pretty common.

-Toby Bradshaw
toby@u.washington.edu


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Action Truing
Organization: Hewlett-Packard Fort Collins Site

Toby Bradshaw (toby@stein1.u.washington.edu) wrote:

: A minor nit here.  The best smiths will true both the lug abuttments
: in the receiver and the back of the bolt lugs before lapping.  Plain
: lapping is better than nothing, but it is perfectly possible that
: the bolt will "cam" into the abuttments unless they are trued.  That
: means that unless the bolt handle is absolutely, all they way down
: for every shot, the headspace will vary.

Truing the receiver's lug contact area and the bolt lugs separately was
tried in the 1960s.  Machine rest tests showed that for highpower match
rifles, it didn't make any difference.  But it sure might be important
for a benchrest rifle.

Camming the bolt the last thousandth of an inch forward does not seem to
be a problem.  With both types of truing done, tests have shown that the
bolt must be all the way down to its stop anyway.  With the bolt about
5 to 10 degrees shy of being fully closed, groups open up about one-half
to one MOA.  But again, this is with highpower match rifles; stool-shooter
rifles may dance best to the beat of a different drummer.

: Some BR gunsmiths will go to the trouble to re-cut
: factory receiver threads oversize to get them on the same centerline
: as the bolt.  This gets expensive.

Yes.  And then the barrel's tenon must be turned oversize to fit.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Bolt Face on M1A.
Organization: Hewlett-Packard Fort Collins Site

Kwong Wong (blkcat!Kwong.Wong@uunet.UU.NET) wrote:
: Bolt face on my M1A is not square with chamber when gun is locked up.

A very common thing with service rifles.  Few if any are trued up even by
'smiths who rework them.

: It seems that the rear of the bolt does not contact the bottom of
: receiver (where clip guide is) and magazine pressure pushes bolt out of
: alignment.  Any ideas on what I can do to square off bolt face or modify
: receiver?  This condition makes brass very hard to reload.

Squaring the bolt face requires two things to be done:

  * squaring up the front of the reciever perpendicular with the axis of
    the barrel shank threads.  This requires a jig in a lathe turning on
    centers that fits the threads in the front of the reciever.

  * then installing a bolt face truing jig that holds a carbide cutter
    parallel with the shank threads, screws into the front of the reciever
    and is cranked by hand to true up the bolt face with the bolt closed.

There's no other way to get a bolt face trued up with the chamber that I
know of.  Any other method is only close, but not square.

Or, you could swap your bolt for one that headspaces correctly and fits
better.  Otherwise, such is the fate with many aftermarket service rifles.

BB


 
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