February 2012 Issue - Target Shooter Magazine

Bergara & their new...
No Gunsmithing Barrels...
this job in ‘slow motion’, taking the ultimate care
and attention to detail in all machining stages, never
needing to ‘cut corners’ to match the time/money
criteria laid down by professional gunsmiths.
He explained to me how the time and hence fee
charged by various gunsmiths often varies widely,
purely down to some of this balance and one other
quite surprising facts – including the action being
re-barrelled. Much as he tried to avoid the issue (I
know Vince loves Remingtons for the way they are the
access route for many, including me, into this sport
of ours) but, as the consummate precision shooter,
engineer and machinist, he winces at the thought of
working with one. Had it been a BAT or Stolle, I’m
sure his eyes would have glazed over and I now know
partly why. I LOVE Remington 700s, at 50 years old
this year they are the granddaddy of nearly all modern
precision rifles with their footprints and design
ethos but, they are as individual as women – in that
no two are exactly the same - and in the same way,
individually unique and challenging if a precision job is
to result.
A love/hate relationship
If you are working on a £1000 BAT action or
something similar, the significant measurements, to
within one ten thousandth of an inch, are all carefully
laid down in the technical specification of the action
- consistent from one action to its brother three
years from now. The action-face is square to the
bolt raceway which is central to the barrel-threads –
exactly as it should be! When working with a factory
rifle, such as the common old Remington 700 used
here, all the measurements to do with the thread on
the barrel tenon, bolt nose clearance and headspacing
of the cartridge must be done after taking careful
measurements off the actual action being used –
some are good and some are not so good! With the
threading/chambering job on the BAT or Stolle - you
don’t even need to have the action in the room.
With a Remmy (much as I adore them) the action is
continually measured and offered up to its barrelthread
to check fit and tolerances at all stages. I know
any factory-made mechanical component has a plus or
minus tolerance on it but these are all unique. I have
renewed respect and understanding for those who do
this job day in and day out and, if the same machining
care and attention is given to both actions during a rebarrel
job, the Remington WILL take longer, if done to
the same standard.
Anyway, from back in September, the precise numbers
of threads per inch and tenon diameter evade me
but the barrel tenon (the section that screws into
the action) is threaded and has a shoulder cut into it
that will meet the face of the closed bolt with a few
thousands of an inch to spare.
Being a Remington, the face of the barrel, before
chambering, needs to incorporate a bolt nose recess
(part of the iconic `three rings of steel`) and allowance
must also be made for the thickness of the recoil lug,
in this case a precision ground custom stainless-steel
one from Brownells.
Machining techniques and styles are often
personalised with experience but, there are certain
unbreakable rules associated with thread pitches,
angles and feed-rates for standards as near as perfect
to be achieved. Vince had a few well thumbed,
beautifully oil and fingerprint stained `bibles`
of equipment settings and records of previously
worked-on actions to ensure correct specifications for
subsequent barrels. He has the time to be confident
in his exclusion of all considered variables and if this
means slowing down the work rate, so be it.
So, we now have a threaded barrel that fits the action
and mates to the bolt with the correct bolt-nose
clearance - the next stage is to cut the chamber. This
is where real patience comes in, as we were not using
a roughing-reamer to rip out 95% the chamber but a
finishing reamer that must be driven more carefully
to maintain the finish and of course, not destroy this
precision tool.
As most of Vince’s reamers are tight-neck or wildcats
of some description, we had to borrow our standard
243 reamer from Osprey Rifles. The reamer is
attached to the tailstock of the lathe via a floating
reamer-holder that allows the tail of the tool to
position itself precisely to the last ‘n’th degree whilst
it is guided from its tip by a ‘pilot’ - carefully selected
Checking headspace with the ‘go’ gauge
Job done – the recess is peculiar to Remington – their
‘third ring of steel’
from a set that will closely and snugly slide into the
rifling. This guides the reamer accurately along the
bore centreline and hopefully, we end up with a
chamber with negligible ‘run-out’.
At this point we also fitted the muzzle-flush nozzle
to the muzzle end of the barrel (not yet finished or
crowned). This will drive a pressurised stream of
cutting fluid back towards the reamer and ensure that
cutting was well lubricated and all swarf flushed back
along the flutes of the reamer to exit the barrel at the
breech end. This prevents any swarf accumulating in
the reamer flutes and scoring of the chamber.
About to feed in the reamer. Once cutting starts we
will increase the flushing oil pressure
The reamer is driven into the bore extremely slowly
and smoothly and regularly withdrawn completely
to inspect it and the chamber and ensure the flutes
were clean with no build-up of metal on the cutting
edge. Now, during this withdrawal and re-insertion of
the reamer, the cutting fluid pump must be turned off
and on - with careful timing – otherwise it can have a
tendency to spray everywhere...!
Bergara & their new...
No Gunsmithing Barrels...
Under Vince’s guidance, I took it very slowly and
eventually I was able to ‘feel’ how the reamer was
cutting. During machining, the swarf produced is a
good sign to the machinist of machining quality, if
he can speed up or slow down the feedrates and is
also a good indicator of the barrel steel quality and
consistency.
STOP!
Coming to the end of the chamber reaming process,
we need to start checking where we need to STOP,
i.e. set our headspace or in simplistic terms, the size
of the chamber, relative to the shoulder and bolt-face.
To do this we use `go` and `no-go` gauges, which are
specific to our cartridge.
Basically, we want to continue cutting until when
the barrel, recoil-lug and action are screwed tightly
together, the bolt will close on the `go` gauge but not
with the `no-go`. It sounds simple but you have to
anticipate the amount that the barrel will nip up into
the action when fully tightened so how many `thou`
to leave spare to take this into account as there is
only a few thou. difference in the two gauges. Again,
when working with a custom action, the ‘nip up’
will be negligible but with a factory action it can be
significant.
This is a critical stage as, if you go too deep, there is
only one cure, that is to re-cut the barrel shoulder and
trim a bit off the tenon which means adjusting the
bolt-nose clearance and is undesirable in terms of both
time and physically, metal that has been removed
cannot be glued back on. I doubt you will ever find
a gunsmith who wants to be disturbed to any extent
during these processes, all critical to 0.001 inches,
never mind explaining it and teaching it along the way
and, bless Vince’s patience, I buggered it up!
Vince is a true gent and basically returned back to the
start to tweak a few details but eventually everything
was perfect, a job we were both technically happy
with - concentric chamber, perfect headspace and
thus complete at the action/chamber end of the
barrel. To finish the job, we removed the blank and
turned it all round so that after once more re-clocking
36 37