Spare
bolt heads issued from the factory were actually oversize and marked
with a small ‘S’….., but nobody can tell me by how much! Other
Armourers of the period have told me, only yesterday over a frantic
phone call, that this is incorrect but they WERE all to the longest
specification. Whatever it is/was, there should be room to stone to
size. And THIS is where Armourers were always taught DON’T OVER CHS. Or
in this case, should that read don’t UNDER CHS. If your rifle closes on
the .074” NO GO gauge, this is what you do. Go to the No1 bolt head
drawer and select half a dozen bolt heads that don’t overturn by more
than 10 degrees (later, 15 degrees was permitted to make best use of
remaining spare parts stockpiles), the bolt face is not ringed
sufficient to allow the escape of gas past the primer and the striker
hole is not greater than .084” dia. Try them all until you get the best
fit. If necessary machine or stone the bolt head square and true until
it closes over the .064” gauge and doesn’t close over the .074” gauge.
The point at which the bolt doesn’t close prior to the .050” limit is
academic because so long as it doesn’t go/close, it’s passed the test.
Now,
how you shorten the bolt head it is up to you. You can machine it in a
lathe if you like but some are quite hard, or surface grind but I was
taught that the best way was to rub the face down on a sheet of ‘400’
wet and dry carborundum paper on a sheet of glass, just covered in slow
running water. Go round and round with equal pressure, rotating the
bolt head slightly every so often, taking a gnats knacker off at a time
for several minutes and trying it again and again. Every so often,
smear a smidgin of engineers blue on the rear of the .074” gauge and
close the bolt head lightly against it to ensure a crisp round witness
mark on the face of the bolt. This is the acid test of it being
perfectly square to the bore. Be sure to remember these old Armourers
technical words such as ‘gnats knacker’ meaning something too
insignificant to be measured and ‘smidgin’, indicating a quantity
equivalent to a gnats knacker.
That
is very basically it! Once again, this is weeks of practice in the
classroom and on the bench with discussion groups all put into one
short period. And if we destroyed a rifle or bolts and boltheads while
learning our trade ….., who cared so long as we learned and got it
right eventually.