What to do about headspace after #4 bolthead?

[Timmer]

Okay, first of all my Model #4 Mk1 rifle's head space is okay (gunsmith inspected). However what do I do when the headspace gets to big when the bolt head is currently a #4? Do I add a spacer? Try a different #4 head? Rebarrel? Any suggestions? Thanks.

Information

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[Alan de Enfield]

Firstly I doubt you will increse the headspace enought to worry about it unless you plan to shoot 10s of thousands of rounds.

Secondly - are you sure its a size 4 bolt head ? Of all the folks on this forum I have only ever heard of 3 size 4 bolt heads being seen (EFD had two). Can you post a pic of it ? If it is a size 4 its probably worth more than the rifle.

Measure the bolt head true size :



What size is it ?

About a year ago I did a survey of over 100 bolt heads to see if the "size" corresponded to the actual dimensions - to some extent it did but it was possible to get (say) a size 1 bigger than a size 2, or a size 2 bigger than a size 3 and so on. The actual results are :

*Size 0 = 0.620" - 0.631"
*Size 1 = 0.622" - 0.635"
*Size 2 = 0.630" - 0.640"
*Size 3 = 0.632" - 0.640"

If you ever do need a new bolt head then maybe you could use a lower size and actually get tighter headspace.

* These meaurements were taken by different people using different verniers / micrometers so there is potential for errors.

Another way of reducing the headspace is to try different bolt bodies as they can 'compress' (reduce in length) due to continued recoil and wear at the mating surface with the bolt head. A 'new' bolt body may be 'longer' than your 'old' one.

Another thing to watch for is bolt head over rotation :







Over-rotation Pictures Courtesy of Ed Horton

[Peter Laidler]

There was a thread some time ago about 1950's trials aimed at establishing the viability of a higher size bolt head. It was deemed that............ anyway, someone will repeat the findings but the long and short was that if you can't get CHS with a No3 bolt head and a new bolt/bolt head, then it indicates a worn body

[Alan de Enfield]

There was a thread some time ago about 1950's trials aimed at establishing the viability of a higher size bolt head. It was deemed that............ anyway, someone will repeat the findings but the long and short was that if you can't get CHS with a No3 bolt head and a new bolt/bolt head, then it indicates a worn body

CHS - Body and bolt wear
Posted By: Peter Laidler
Date: Mon 28 Apr 2008 9:17 am
You should all read and re-read this if you have ever thought about CHS, body wear or fitting a new bolt, especially in response to the recent thread about the matter.
I was having a chat to one of the most senior examining Armourers at a huge Base Workshops at Warminster a few days ago. Long retired, he was a 1930's apprentice and one of the very strict examiners. I was asking him about chroming bolt heads to get longer life out of heads bolts and bodies when he reported back something that was VERY interesting.
He said that during the mid 50's, there was a plan mooted to make a No4 size bolt head available so as to decrease the number of old wartime/tired/just plain worn out rifles being condemned as unfit simply because of insufficient CHS. The alternative was to increase the MAX CHS to .078".
He was involved in this project as the research Officer, so was in from the start. The PROBLEM was that once the BOLT, Inspectors, Gauge (a calibrated slave bolt used to test wear) plus a calibrated No2 bolt head (No3 not permitted at Base/Factory don't forget) had been inserted into the inspectors gauge bolt, then making a further bolt head available was palliative and not a cure because these simple tests indicated that it was the BODY that was worn and not the bolt or the face of the barrel. And thinking about it, while it's obvious really, it's absolutely correct!
Another problem they encountered was that with the speed of wartime production, the induction hardening of the bodies was at best, mediocre, and at worst, sometimes virtually non existant. The hardening sometimes had no depth and it was tested at Base Workshops by the old IZOD impact test method. Apparently, all manufacturers were as bad or good as each other including Savage and LB (I bet that has shocked a few of you who were probably lead to believe that some makers were 'better' than others......)
I spoke about resurfacing bolts but he just shook his head sternly and wagged his finger as if to say. 'No, it's the BODY that's worn beyond the point of no return and once the hardness is gone, then there is no cure.'
There, that's straight from the horses mouth and it doesn't come any clearer or louder than that. If you cannot get CHS with BOTH bolt lugs bearing evenly using a No3 bolt head, THEN trying a new bolt, then it is the BODY that is finished. Sorry about that.....................

[Edward Horton]

I found this on a Golf Course, it was very strange day everyone was yelling Foooour!

[S-A-M3]

I came across a bolthead stamped 4 earlier this year, only one I have ever
seen, used it recently to headspace a tidy No4 Mk11! Was a few thou longer than a 3, used it because it didn`t overthread. It didn`t have any markings on it so I assume it was a commercially made one? Australia? Does anyone out there know?

[Peter Laidler]

No4 boltheads are a bit of an enigma. Maybe someone ought to do a steel analysis on one and compare it with a bog standard No 0,1 or 2.

I say this because it can't/won't be a factory made bolt head (?) because FTR/Base Workshops would reject bodies that wouldn't CHS on a 0 1 or 2 bolt head using the GAUGE, dummy bolt, armourers. And there was never such a beast as a No4 bolthead in UK or NZ military service

Can anyone identify any other marks on a No4 bolt head? What about a visible proof mark?

[Enfieldlock]

I have two.

One is brand new, .642 in length. Marked with an "M" and the broad arrow.

The other is "well used", .642 long. It has an "F" or "E" and "2??" in a box".

A search through 3-400 units came up with only two of the beggars.

[Badger]

Okay, first of all my Model #4 Mk1 rifle's head space is okay (gunsmith inspected). However what do I do when the headspace gets to big when the bolt head is currently a #4? Do I add a spacer? Try a different #4 head? Rebarrel? Any suggestions? Thanks.

If you want to learn more about the very basics of "headspace", Parashooter published an excellent teaching article in the Technical Articles for Milsurp Collectors and Re-loaders(click here)

Headspace 101 for .303's (click here)

Regards,
Badger

[Parashooter]

Badger, please consider replacing that version of "Headspace 101 . . ." with the current iteration, which contains some added information and removes the controversial lubed-case approach. (You might also remove the obsolete e-mail address. I have a new one I don't post but can be reached through this board's PM feature.) Thanks.

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Several generations of American shooters have been convinced by bad information that something mysterious and scary called "headspace" should be checked and re-checked on almost any surplus rifle, especially Lee-Enfields. The truth is less interesting but still worth knowing.

Stripped to its essentials, with a rimmed cartridge like the .303, headspace is simply the distance between the front of the bolt and the back of the barrel. It's the space where the "head" (rim) of the cartridge fits when the rifle is loaded.



Since there has to be some room to allow for varying rim thickness, the headspace is normally a bit more than necessary - giving what I call "head clearance", a little extra space so the bolt can close easily, even on the thickest rim allowed.

In addition, Lee-Enfields and their ammo were often made with a fair amount of space for dirt, mud, snow and other battlefield debris between the chamber and the cartridge's body and shoulder ("Body/shoulder clearance"). Since the cartridge is controlled by its rim, this clearance doesn't do any harm (except to handloaders who insist on full-length sizing).

When a full-power .303 cartridge is fired, a whole string of events occurs.



1. The firing pin shoves the case forward, rim against the breech.
2. The primer detonates. If it's not heavily crimped in place, it backs out, shoving the bolt and barrel as far apart as it can.
3. The thin, forward part of the case expands to fill and grip the chamber while the bullet moves out of the case and down the barrel.
4. The solid case head can't expand and grip the chamber, so it moves rearward, re-seating the primer, stretching the case walls just forward of the head, and stopping when it hits the bolt face. (In rear-locking actions like the Lee, the bolt and receiver also compress/stretch to add a little more movement. The higher the pressure, the more they move.)
5. If (and only if) the amount of head movement exceeds the elastic limits of the case, the cartridge separates into two pieces.

New cartridge cases can normally stretch a lot before breaking. Even with a minimum rim .054" thick and maximum "field" headspace of .074", the resultant .020" head clearance is well within the limits of new brass and it's very unlikely a new case will separate even if the headspace is somewhat more than the field maximum (which is pretty rare).

OK, but if one does separate I'm in deep trouble, right? Not really. It seems the short "cup" left behind the break is pretty good at keeping most of the gas where it belongs. Here's a demonstration -

First I took a case that had been reloaded with heavy loads enough times so it was stretched near breaking.


I loaded it with a 180-grain bullet and 40 grains of 4895 - a reasonably stiff charge about 2 grains under "maximum" - and fired it in a much-abused Savage No.4 with a clean sheet of typing paper wrapped around the receiver.


When I opened the bolt, the separated head extracted. (The front piece of the case fell out when I happened to turn the rifle muzzle-up while removing the paper.)

The sooty paper shows where some gas escaped. No rips or holes, just a little soot - and only where the bolt meets the barrel. Had I been shooting from the shoulder and wearing glasses, I probably wouldn't have noticed the leak at all.

The point of all this is that excess headspace, even a bit beyond normal limits, isn't the terrible danger we've heard so much about. It's not a good thing for consistent ignition or long case life (although handloaders who neck-size or adjust F.L. dies carefully can control this) - but it's not a disaster waiting to happen.

Unless you're consistently getting broken cases when firing new ammo or brass, there's not much reason to be worried about headspace in these sturdy old Lee-Enfields. Relax and enjoy!

Handloading

If you handload for a .303 with generous headspace, there's no need to mess with bolt heads - changing the rifle's clearances to yield longer case life. You can control head clearance simply by changing technique.

When you fire a new case for the first time, use an improvised spacer ahead of the rim - anything from a precision metal washer to dental floss can work to hold the the cartridge head firmly against the bolt face and eliminate or reduce stretch even if head clearance is significant. Another way of accomplishing the same end is to use a bullet seated out far enough to jam into the lands, "headspacing" on the bullet instead of the case. Such techniques are useful only if the rifle has excess headspace. With normal headspace, initial stretch isn't enough to worry about.



After you've fire-formed your new cases they will fill the chamber fully, stopping on the shoulder just like a rimless cartridge. If you neck size, you'll have zero "headspace". If you have to full length size, adjust the die so the cases chamber with just a bit of resistance in the last few degrees of bolt rotation.

Finally, don't try to turn a .303 into a magnum. Keep the pressures below the limit and you reduce the small amount the bolt and receiver compress/stretch on firing in a rear-locking action.

With these techniques you can make your .303 cases last for dozens of loading cycles, even if your "gauge headspace" is well beyond the .074" field spec.

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To demonstrate how we can control head clearance using only the shoulder, I filed off the rim of a once-fired Remington .303 case. After adding an extractor groove to fit a Mauser-size shellholder, I neck-sized, reloaded and fired this case 19 more times.



The load was a 180-grain jacketed soft-point over a lightly-compressed charge of IMR 4350 (giving an average velocity of 2310 fps for the 19 shots and listed at just under 39,000 CUP in my IMR data booklet). The test rifle was a 1943 Lithgow S.M.L.E. Mk.III*. 20 shots was enough for a practical test, I sectioned the case to examine the web/body junction area where thinning normally occurs.


This case, fired 19 times with no rim, has not stretched or thinned at all. I'm sure it could have continued for at least another 20 of these moderate loads.

It's clear to me that the .303's shoulder, alone without help from the normal rim, is entirely adequate to maintain "headspace" when sized in a way that preserves the shoulder location. Those handloaders who experience poor case life with neck-sized handloads should look for other factors to explain premature case failures. The most likely source of trouble is high pressure. More pressure means more action flex and that means shorter case life.

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Just to demonstrate that there's nothing new (except computer animation), here's a page from a 1937 book I found online several years after first posting "Headspace 101 . . ."