Bolt lug mating surfaces - checking

[jss]

I imagine that it's quite important with Enfield actions that the bolt lugs mate correctly with the body so that the bolt remains as straight and steady as possible under recoil, for various reasons. I think I have read somewhere that bolt lug to body mating surfaces are checked with engineers blue somehow. Can anyone please point me in the right direction for instructions on this.
Thanks.

Information

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[RJW NZ]

its here someplace?
You can also use a wipe of oil and dust with white powder such as chalk. I've also done it with black marker pen on a de oiled lugs, I'm not sure of the cure etc but even the check will give you some confidence.

[tbonesmith]

All that stuff is in Peter Laidler's articles and archived posts in a sticky in the Lee Enfiels Knowledge Library. Here's a link: Index of Peter Laidler's on-line series of articles.......

[Thunderbox]

Given that millions of rifles have performed just fine with mis-matched bolts, I'm not sure that testing with engineers' blue has any real-world relevance. Given the flexibility in the action and fit of the bolt, I'm sure that any asymmetry simply evens out as the recoil loads build up.

[Peter Laidler]

Ooooooooooooooooooh Thunderbox.................... dangerous! While I agree that many thousands of rifles have performned with mismatched or ill fitting gbolts, I'd disagree loudly that they perform just fine. Putting my physics teachers hat on to bring simplicity into the Q and A, it's liike driving your car with mixed sizes of tyres or cross plies (remember them) and radials. Yep, they'll be fine and get you all the way to Carlisle but a) they're NOT right and b) you could have a lethal mix

Put another way, the reason there are two bearing surfaces is because it NEEDS two bearing surfaces. If it could do with one, then it'd have one. If it could do with one bearing surface, then surely there'd never be a need to number bolts to rifles.

Imagine buying a rifle and the dealer said '........naaaah, no number on the bolt John....., don't need one. It shuts proper and shoots OK'

Just my thoughts..................... But over the years I have tried to tell it as it is from the shop floor right up through the 'system' and impart this hard learned knowledge together with the reasons. Relax the set standards at your peril..............

[Thunderbox]

But presumably there is some sort of "tolerance" as, after all, even a master armourer isn't going to be able to produce a 100% even bearing beyond a certain - albeit microscopic - dimension. Given a production run of a million rifles or so from each factory, there has to have been some sort of compromise or understanding about bolt fit (a) on initial fitting (b) on initial proof firing (c) during the first few hundred rounds of service life. I understand that with other weapons systems - e.g. the multi-lug bolts in most modern military rifles - allowance is made for the individual lugs to reach a final fit through an element of wear during use.

I do check the bolt fit of all of the rifles that past through my hands, and its surprising how few show an asymmetric lug bearing, even when mated with a replacement mismatched bolt.

[jmoore]

Remember this photo?:



Surpmil's Post #51 from the thread below:

Gallery of Dramas. Broken Enfield Parts!

Long lug not bearing maybe, possibly???

[Bruce_in_Oz]

There is a problem with fooling around with vintage original bolts and bodies, of course.
The outer skin of the thrust-bearing surfaces is just that; a skin. Unless, of course, it has been over-hardened, which DID happen from time to time. Once the normal hard skin has worn through, the part is beyond repair, especially in the average garden shed.

I have set up a few No4s and SMLEs, and a Mauser or two, over the years. Lapping lugs is best done with a stripped bolt body and a spring-loaded tool that applies axial pressure on the front of the bolt. However, unless you are working with new components, fresh out of the factory wrapper, you can come unstuck very quickly. I try to aim for a MINIMUM contact area of 2mm x 2mm. If you are using "vintage" components, less will do, as long as there is visible contact on both lugs. On SMLEs it is a case of going for best fit and "close" headspace before even thinking about lapping, if you dare and if you have a suitable jig. Although No4s and 5s have an assortment of available bolt-head lengths, most readers will have noticed the distinct shortage of sizes 2 and especially 3. Some happy campers even have some of the post-WW2 Australian "long" boltheads that were provided to squeeze that last bit of life out of the SMLEs before the L1A1 came on line.

If you are going mad and fitting a newly-made custom barrel, headspace is a cinch: set the barrel back to minimum heaspace, mark it, remove, then machine in the extractor slot. Fiddly bits on the barrel, like keyways or lugs are easier to machine in once the barrel is trued and torqued to the receiver, because you can use the datum of the bottom of the receiver to establish top dead-centre etc.. Well, that's how I do mine, anyway.

As Peter will probably confirm, these "creative" practices are NOT part of the original EMERs / EMEIs at unit or even field level and are essentially "last ditch". The original manufacturing tolerances allowed a mismatch of a few thousandths of an inch between the relative positions of both the bolt lugs and the receiver shoulders, BUT an extremely small tolerance on the dimension for the nominal position of this surface in relation to the front of the receiver and bolt body. There was expected to be some shuffling of components to get things VERY close and only then would "fitting" be permitted: yet another reason that bolt bodies are numbered to receivers.

If you have a rifle with genuine matching numbers and it is only bearing on one lug, you may have a very big problem with wear or distortion. If you are dead keen on shooting that rifle, get it checked out by someone who really knows Lee Enfields and who has a goodly stash of bolt bodies and bolt heads in good to new condition. You may get lucky. You may even be lucky enough to own one or two of those nifty armourer's "master bolts" as seen in previous postings.

It is not a safety issue unless carried to extremes. One of those extremes would be to grind / wear through the hardened surface of the "resisting surfaces". Once that happens, the softer surface exposed will get hammered pretty hard; headspace will increase etc. It will probably not blow up in your face, it will just get a bit brutal on your brass, play hell with effective striker protrusion / performance and may or may not lose accuracy. EXTREME wear will interfere with the timing of all those little bits that shuffle around in the cam-track at the rear of the bolt and the safety / locking bolt. It involves issues of accuracy, function and longevity of your favourite rifle.

[Thunderbox]

I'm not so sure that the designers of the Enfield system haven't taken into account other metallurgical phenomena - such as surface work hardening. Given the teeth-sucking over "wearing through the hardened lug faces", it seems strange that so very few Enfield bolt/receivers either wear out (ie to the point of un-fixable headspace) or exhibit asymmetric bolt lug bearing - given that possibly the majority of Enfields are either now mismatched or have had a replacement bolt at some stage (especially No1s). I'm guessing that there is a process by which an asymmetric bolt has a tendency to wear the "high" point down and/or twist to provide an even bearing during the firing sequence (vide how mobile the front end of a bolt is), and that lug-pocket wear is to an extent counter-acted by surface work hardening - ie the surfaces harden themselves, in the same way that the cog teeth surfaces of a clock mechanism become harder with time.

[Peter Laidler]

Just taking one minute part of that argumant a stage further Thunderbox, can I comment on line 2, sentence commencing 'Given the teeth... down to ......... wear out'. That is absolutely incorrect to the point of, well........., let's not even go there....... In the course of my dealing with a few No4's, I've seen literally HUNDREDS.............., no........ MANY hundreds that have worn through the induction hardened locking lug surfaces to the point where CHS is impossible to achieve.

I appreciate that our Base workshop facilities have the metallurgy facilities to test this. Something that the ordinary dealer probably doesn't have (do any out there have these facilities? Some probably do) so I'm minded to ask the obvious, that how does the average dealer or trader KNOW this? Indeed, it was this VERY point that decided the late 50's trials being undertaken to ascertain the viability of a No4 bolthead.

Work hardening.................. Mmmmmmmmm a much used - or in this case, much MISused notion. I say no more. But my last word here is this. Just make sure that your bolt is correctly fitted to and identifiable to your rifle. The other alternative is to just use ONE bolt for everything. Now there's an idea...................