Size of #4 MK 1 Bolt Heads?

[kscchtrainer]

Not sure which forum to post this question, so I'm asking here.

Where can I find the actual front to back dimensions in either inch or metric specs on the 0, 1, 2 and 3 numbered bolt heads for the No. 4 MK I?

I have a #4 with a 2 marked bolt head that I think is slightly out of spec. It measures from .633 inch to .636 inch as you measure it at different points (front face to back shoulder on the threaded end).

Haven't found any dimensional specs in the manuals I have here.

Thanks for your help.

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[kscchtrainer]

Is there noone out there that knows the proper sizes for the No.4 MK I bolt heads? So far I've not been able to find the information on the internet or in any publication I currently have.

Any help would be greatly appreciated.

Also looking for a #3 size bolt head if anyone has an extra they would be willing to part with.

[Badger]

Here's an old post I made a few years ago, so I'll repeat it here in the hopes it might helps somewhat.....

Although I'm clueless in gunsmithing and virtually anything mechanical (ask claven2 ..... ), I discovered some interesting stuff last year about Enfield headspacing. While trying to fix a problem on one of ~Angel~'s No.4 Enfields, where the primers on her .303 S&B commercial ammo seemed to be backing out way too much, I found that apparently one can't just go and install using the marked bolt head numbers to correct a headspace problem.

So, out of curiosity I began measuring with a highly accurate digital micrometer, some of the bolt heads mounted on her No.4's

I used the following standards, as per the Enfield Armourer's Manual.:

#0 .620 to .625"
#1 .625 to .630"
#2 .630 to .635"
#3 .635 to .640"

The bolt head marked #0 that had failed a British military .074 "field guage" measured .630, which seems to indicate to me it should be marked at the high end as a #1 or at the low end of being a #2. Also, I have another one marked #1 and it measures .632, which should make it a #2. So, I simply put another loose marked #2 I had in a parts box, that actually measured .064 and it worked fine. I'm not exactly sure why the differences, except perhaps the poorer manufacturing tolerances for the era.

Before I did any of that, again using a standard British military armourer's guage, I checked the firing pin protrusion first as per Enfield Armourer's Manual. It was .044 and the spec called for .040 to .050, so I assumed it was fine.

If you want to learn more about "headspace", Parashooter published a good article in the Technical Articles for Milsurp Collectors and Re-loaders(click here)

Headspace 101 for .303's (click here)

Regards,
Badger

[kscchtrainer]

Thanks Badger,
I'm not worried about the headspace in my No. 4 MK I, as it passes the .074 gauge test just fine.

I am trying to come up with some spare parts in case I run into problems in the future. I have some little gunsmithing experience, having taken an armorers course while in the US Army, albeit that was years ago, and most of my actual work has been done on 1911 type handguns.

I've been acquiring or building the tools and gauges necessary to properly maintain both my 2A and #4. I have another lathe session scheduled at a friend's home machine shop to construct a striker removal tool.

You mention the Enfield armorers manual. I've got the Canadian maintenance manual on the No. 4 MK I that you pointed me to, but I don't think that's the armorer's manual you speak of. That one I haven't found in PDF format yet. The manuals available for download that you mentioned don't seem to contain the dimensions you just posted for me, hence my query.

Thanks again for your knowledge and help -- this stuff is starting to become a lot of fun.

[kscchtrainer]

Badger,
I finally got a chance to take that No.4 MK I that I got as a freebie (and was looking for the #3 bolt head for) to the range yesterday. Ammo used was manufactured in Serbia with PPU headstamp (Prvi Partisan, I believe), 174 grain FMJ Boat tail. Excellent accuracy, just over MOA at 100 yards and just a tad low. I believe it would have been spot-on at 100 meters.

Cases show no primer setback or signs of pressure, only an approximately 1/4" shiny ring just forward of the rim.

After the range session, the bolt face and interior of the action was still clean, no powder residue whatsoever, unlike that which you get with a semi-auto.

Checking case length: Speer reloading manual lists max case length as 2.222"
I measured 10 unfired cases and got a min of 2.208" and a max of 2.212". I then measured 10 cases fired cases and got a min of 2.2025" and a max of 2.2145". Not much stretch and well within tolerances.

This old rifle is in very good condition other than the fact the wood is really beat up, and pretty doggone accurate to boot.

[krinko]

Here are actual measurements of 48 No4 boltheads.
#0---11 examples---.627-.632".
#1---17 examples---.630-.634". 1 example---.626".
#2---10 examples---.633-.638".
#3---8 examples---.635-.641". 1 example---.625".

Most of these are on rifles---with the exception of the .625' #3. It's a brand new BSA made piece and probably "new" because it was so far out of spec.
At any rate, I suspect this is a representative sample.
-----krinko