No.4 bolt heads specifications

[bow]

Hi ! i'm planning to build bolt head for enfield No.4: i'm not alone. Two friends of mine are metallurgical engeneers and machinist so we could try... Now i need some data:

-- the threads on bolt heads..what is it?
-- What iron should we use . i red somewhere that bolt heads were manufactured using grade "5" iron. Could we use "6" or "7" ?

Information

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[Peter Laidler]

The first question anyone will ask is WHY do you need to remanufacture bolt heads Bow?
The second is this. IF....... and I seriously question this......... IF your friends are matallurgical engineers (or metallurgists but you didn't quite say that.....), then they will EASILY be able to establish EXCACTLY what the material spec of the bolt head is. That is a simpe fact.
Even if they are just simply good engineers, they will EASILY be able to use a shadowgraph - or even a simple steel ruler to establish what the thread form is.
Something just doesn't ring true here. And here's another point to ponder. If you want to make an extended bolt head to, say extend the life of an un-C.H.S.able rifle, then don't bother. The body is worn out/through the induction hardened surface of the locking shoulder

Just my 2c's worth. Any thoughts JM, Bruce from Oz and Son?

[bow]

The first question anyone will ask is WHY

Because i have a No.4 in mint condition made in 1950 at Long Branch arsenal. Bore is 0.302, very tight and good looking. It seems to be the perfect rifle. But...it mounts a "3" bolt head, 0.339" long.. Headspace checked is o.072" so bolt doesn't close fully on a 0.074 gouge , I believe the rifle is safe to shoot but brass has short life. Soldiers do not reload during the war; shooters will do.

I checked bolt tennons using engeneers blue and it is fitted very well, as for your instructions Peter. In conclusion, the rifle is very good... well bedded, good bore. Probably it was wide-headspaced at its birth in 1950 and never touched.

[Alan de Enfield]

But...it mounts a "3" bolt head, 0.339" long.. .

Are you sure ?
Do you mean 0.639" ?

0.639" is not a 'large'size 3 and there are many, many number 2 bolt heads that are 'bigger' than 0.639"

[Brian Dick]

Your rifle is fine in my humble opinion. Why fix it if it isn't broken? People can't seem to grasp that bolt heads came in different sizes for one reason and one reason only, production expediency! If a new rifle took a #3 to pass the .074 gauge, then that's what was used. Neck size only your fire formed brass and it'll last twice as long as full length sizing, shoot and enjoy your rifle! I challenge you to fire it enough to need a longer bolt head in your lifetime.

[jmoore]

If you use small rubber/neoprene o-rings at the base of the cartridge for the first firing your brass will never know what the headspace measured. It'll last just as long or longer than can be achieved by any other method.

[bow]

Do you mean 0.639" ?

0.639" Alan... i did a mnistake on writing.

---------- Post added at 07:56 PM ---------- Previous post was at 07:53 PM ----------

If you use small rubber/neoprene o-rings at the base of the cartridge for the first firing your brass will never know what the headspace measured. It'll last just as long or longer than can be achieved by any other method

But ith o-ring will reduce headspace first time the brass is shot..but the second time , withouth o-ring , it will be stretched ... What i hadn't understood?

[Ridolpho]

Thanks Bow for asking a question I've been wanting to ask (ie. why doesn't someone build some new large size bolt heads?) and thanks to everyone else for answering said question! My specific rifle of interest is a 43 Longbranch that had one of the 6 groove barrels installed in the 50's and in very good condition. It headspaces (and shoots) OK but the bolt head measures 0.642 leading me to wonder where I would go from there if I shoot it a bunch and it opens up.

Ridolpho

[Alan de Enfield]

Here is an extract from a detailed 'thesis' By Peter Laidler on Headspace.
You can find the full article in the Milsurps Library.

If you cannot get headspace, even using the very relaxed criteria I have discussed here by using a new bolt and a No3 bolt head, then I’m afraid that it means your body is knackered. This quaint old Armourers technical term indicates that it’s seen better days ….., it’s xxxxed! You COULD allow yourself up to, say, .078” headspace but the technical opinion reached during research into this during the 50’s is that it’s a palliative and not a true cure.

[Beerhunter]

I hope that my many American friends will forgive me but I only see this obsession with head-space manifesting itself on the "other" side of the pond. Other than Alan's interesting and may I say, valuable research on the variation of bolt head sizes, we just don't seem to worry about it over here.

I am extremely pleased that others (Brian) are pointing out that the primary reason for the sizes was manufacturing. (Earlier Lee-Enfield bolt head being individually sized to the rifle.)

Peter when I was a Cadet Armourer (We were mostly responsible for keeping the guns clean!) at school in the early 1960s, I don't remember the REME blokes ever replacing or suggesting that a rifle needed a new bolt-head, due to wear - EVER. Did you?