Headspace gauges

[rmkey]

I have a Enfield No 4 that after the extractor is removed will close on a "no go " gauge. However, after firing the primer is backed up indicating excessive headspace. Am I missing something? I have a second and third Enfield that also closes on the same gauge with no indication of excessive headspace. Go, no-go , field gauges. I thought if a specific gun closed on a no close gauge it was at least safe to shoot.

I know you all think I have excessive headspace and right now I do!!!!!

 

[1911Tuner]

No Go

Depends on where the excess is coming from as to whether it will show the classic signs or not. If it comes from the chamber being cut too deep, it won't. If it comes from worn or deformed locking lugs or their recesses, it will if it's bad enough. The first isn't dangerous. The second is.

Positive headspace...whether out of bounds or not...usually comes from a combination of both.

 

[Iron bottom]

The go gauge tells you if the firearm is safe to fire with the longest in spec ammo. You will not crush the case, in other words. The no go gauge tells you if the firearm is safe to fire with the shortest in spec ammo. The case will not back out of the chamber far enough to blow out. There are some special situations, of course, but I would be very careful with a firearm closing on a no go gauge.

 

[jlmurphy]

A NO-GO gauge represents a maximum chamber dimension and if the bolt will close on it, it is not safe to fire, it means the chamber is at minimum too big. There are longer gauges called field gauges that represent the absolute max and are sometimes used. The brass cartridge is inadequate to hold the pressure of a high power rifle round, the chamber must be close fitting or the case will explode and probably injure the shooter. The Go gauge represents the minimum chamber dimension and means the chamber isn't too small. The gauges have their length engraved on the sides.

 

[1911Tuner]

Gauged

Go/NO GO directives on the ordnance level state that all weapons must bolt on the GO and none may bolt on the NO GO gauge. Any weapons that fail either test are deemed unserviceable and turned to the armory for repair and adjustment.

That said...and to restate a point...Failing the maximum NO GO check doesn't definitively show whether or not the weapon is unsafe to fire...nor does bolting on the GO gauge guarantee that the weapon is safe to fire. It only proves that the weapon is within or beyond allowable chamber stop shoulder to boltface dimensional tolerances. If the weapon passes both tests, it is in all liklihood safe to fire and fit for service.

 

[shooter503]

Several posters are confusing rimmed versus rimless headspace here.

The 303, being rimmed, headspace does not consider chamber dimensions, that's another problem. In practical mechanical terms the 303 headspace only compares two dimensions. The first is the distance from the face of a closed bolt to the face of the rim support surface in the barrel. The second is the allowable thickness range of cartridge rims. That is why 303 headspace gauges are merely short buttons representing the cartridge rim area instead of full length cartridge shapes.

By searching "303 british headspace gauge" you can read several very interesting web articles.

Many 303s have what we would consider to be "oversize" chambers. Remember that the military certainly did not intend to reload used brass and the rifle must continue to function even with a dirty chamber. Therefore, what we would consider as an oversize chamber in a commercial rifle was acceptable to the military.

If you are backing out primers your headspace is excessive. If the rifle is in good condition merely fitting the next size of bolthead might help.

 

[shooter503]

RMKEY,

This is a really crude experiment but it may throw some light on your problem. Find a fired case with the thinnest rim thickness. Remove the primer. Lightly polish the base of the case against fine emery cloth placed on a flat surface to remove any burrs that may be present. Cut the case off about 1/2 inch up from the rim. Measure and record the rim thickness if you can. Get an assortment of shim metal with known thicknesses, oftentimes this can be found in serious model shops in both brass and steel. Brass is easier to cut and is OK for this purpose. You might need 1 thou., 2 thou., 5 thou. and 10 thou. Cut a few small discs from this material slightly smaller than the case rim diameter. Good scissors will work fine.

On each of your rifles remove the extractor. Put the cut-off cartridge in the chamber. Select combinations of thicknesses of shims and put these between the bolt face and the cartridge until you can just feel the bolt rotate fully closed. Record the combined thickness of the shims used with each rifle. You now have a comparative measure of the distance from the bolt face of each rifle to the rim support face on the barrel. If you have measured the cartridge rim thickness accurately with a little math you can calculate the actual dimension. Do not put too much trust in this last value because measurement errors can be quite high but it is a good comparison figure.

From what you have said I would expect the thickness of shims used to be more on the problem rifle but there could be a more subtle factor at work here. Let us know what you find out.

 

[Clark]

Per SAAMI 303 Brit:
The rim of a 303 case is .064" - .010"
The chamber rim of a 303 is .064" + .015"

That is .025" slop on the headspace of the rim.
The same story for the shoulder = another .025" slop on top of the rim slop


Headspace?
What Headspace?

And then there is the paper thin bolt body with the lugs at the rear that compresses under SAAMI pressure to .003" back.

The longer bolt heads can no longer be found.

What do I do?
0) Design my own headspace requirement
1) Select brass with uniform rim thickness.
2) Silver Solder a shim on the bolt face while the rest of the bolt head is in a heat sink.
3) Load for low pressure, not low velocity, that means a slow powder.

 

[shooter503]

Actually Clark I have quite a little stash of longer 303 bolt-heads. Unfortunately, not enough to start donating them.

That little paper-thin bolt body you refer to has survived military use in every continent of the World except Antarctica for 100 years. It has proved faithful in two World Wars, many more minor skirmishes and use in various bush-wars by so many nations and rag-taggle armies that they are uncountable. I even saw a 303 pictured in Sudan recently alongside the AKs. The 303 has killed masses of wildlife for sport and survival in every ex-colonial part of the World often with zero care. It has been successfully converted to handle the 7.62 NATO (308) cartridge. You really must step back and look at the reality of this, what appears to be to you, such a delicate firearm. You make a valid technical point but - a technical point has never been sharp enough to drop an enemy soldier.

My suggestion to RMKEY, subject to getting the required data, is to temporarily be prepared to exchange bolt heads between his three rifles. I am not making this suggestion now. I am saying, when we have the facts and have considered a couple of ideas, he may be able to put his favorite 303 into use by de-commissioning one of the other rifles by exchanging parts.

As information. In the past when I have re-barrelled a 303 I set the (what I would call) rim clearance to 10 thou. using custom made gauges. I have found this works with the majority of commercial brass. I do not use surplus ammo. I do not shoot 303 enough to justify using suspect, possibly corrosive, ammunition.

 

[rmkey]

Any way to correct problem

There are no No 3 bolt heads available. Since the rimed 303 headspace is measured only between the bolt face and the cartride rim it would seem some type of steel washer-shim behind the bolt head and bolt body would serve to close the headspace?

 

[shooter503]

I am a little uncomfortable about the idea of heating the bolt head excessively. It is, after all, a critical component.

I have not needed to buy any new bolt heads since I was lucky enough to get a few spares some time ago. I got mine from UK.

I think I would investigate some sort of cool build up process such as chrome plating (performed by a specialist, not your local plating shop). I do not know the latest "state of the art" on this but I know they can do pretty amazing jobs on repairing other machine components. The full range of bolt head size increments was only 15 thou. from a "0" through a "5". I would think a chroming job should provide that much thickness. If you need more thickness than this you should stop and examine the action very carefully before proceeding in case Bubba owned it once.

What you do not want to do is change the bolt-head to correct an undiscovered mechanical problem in the action. What is happening in your rifle is that the cartridge case is being held forward in the chamber somehow (by the extractor or by the firing in on impact on firing, could be several items). When the cartridge fires the case is expanding to grip the chamber walls so the cartridge case is locked in position. However, there is excess space between the bolt-face and the back of the cartridge head. The high pressure gases are forcing the primer out of its pocket until the primer hits the bolt-face. This is not a good situation. Slightly more primer movement and you will, at least, have a face full of gas and bits of primer case blasting about. If you are using safe ammo. this excess space can only come from wear in the locking lug area or incorrect components in the rifle, such as a rifle put together from a bucket of parts with no armorer inspection.

 

[rmkey]

Where in the UK?

I am willing to pay for a bolt head. Does the place you got yours still exist?
I am pretty sure the rifle is sound. All numbers match and I have had it several years. The ammo I was last using was commerical Federal 303 when the primer backed up. The rifle has a No 2 head. Why couldnt I cut a steel piece from material such a mechanics feeler guage and place between the NO bolt face and the No 2 bolt head?
I have obtained another stripped bolt but could only get a No 2 head -but problem is probably the receiver. The Enfield is my favorite rifle. I have loads of MN's and (M39's pretty good as well). K-31s, 1903 Springfields and 1917 "Enfields". But I have to say my favorites are the Brit Enfields. I even love my Ishapore which is more accurate than I would have ever thought. I really like the feel of a No 1 Mk 3 but they are pretty much gone.
The rifle being so well preserved it just seems there surely must be a way to save it. I cant help but wonder if longer bolt heads are not available why doesnt someone investment cast them like Ruger does their parts. I would have to be profitable. Now I am rambling.

 

[shooter503]

RMKEY

Some primer extrusion is not unusual with commercial ammo. As Clark says these rifles were ISSUED with what we would consider too much headspace. That's the difference between a sporting and battle rifle. I am not going to say that primer extrusion is OK - my attorney would kill me. Can you measure the extrusion?

Right now I am contacting a friend in Australia - he is one of the World's best scroungers. I have told him I will take a few dozen of any long bolt heads he can find. If he can help I will add to this post.

By the way, I got the bolt head count wrong - shouldn't use my terrible memory. There were 5 bolt head sizes 0 through 4. 4 is very uncommon and the only two I saw I bought. These were from the old AJ Parker company in Birmingham, England. I think most of the Parker inventory was bought out by someone from New York State.

There should be bolt heads in UK, South Africa, Canada, Australia not to mention the US. Heaven knows where they have gone - they must have been made in the millions.

If you read the old gusmithing books they tell how to deal with situations like this but I am not going into print to mention the methods in public. Most would not be approved in our present legalistic society.

Lets see what happens in Oz.

 

[rmkey]

Prime extrusion

The primer back out was totally eliminated with the use of Greek mfg ammo. circa 1969.

 

[shooter503]

RMKEY,
Please see PM.