Bolt HeadcFitting Question

[Alan de Enfield]

It is "plug and play", all the way. According to ALL of the original technical literature I have seen, for No 1 Mk 111 rifles, there was ONE "standard" bolt head, with a "qualified" thread and a set distance (with the usual tolerances) from face to the shoulder forward of the thread. No "Shake and Bake" assembly here.

My understanding from the instructions to armourers manuals is that the No1 MkIII bolt heads were anything but 'plug and play' with every one needing to be individually fitted to each rifle to ensure correct headspace and overturn. This is further supported by a post by Peter Laidler on May 5th 2008 where he states :

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.


Then, of course, there were the two different (non-interchangable) designs of bolt heads - the Mk1 and the Mk2
(photo from member 'Bear')