Enfield No.4 bolt lug tolerances.

[aric84]

Would anyone know what kind of tolerance there is on the length / position of the bolt lugs on a No.4 enfield? Reason I ask is that I took possession of a Savage built rifle with a mismatched longbranch bolt. The combination had such gross headspace and uneven lug engagement that the bottom short lug was dented from firing. The other long lug had at least. 015 clearance between the lug and the receiver. The bolt would also close on a case with a .030 shim behind it and still have play!

I obviously have not fired it like this and am thinking of fitting a new bolt to the rifle. I did try fitting a couple other bolts from my other rifles and the headspace was much tighter, almost no movement when pushing the bolt forward on a closed case. There was also some engagement on both lugs so I do not think the receiver is damaged. The damaged bolt would move forward by what appears to be at least .030" with case in the chamber.

So really the question is, are No.4 bolts usually a pretty close fit, barring setting headspace it a new bolt head or is there a high chance of getting another short bolt?

I believe the original damaged bolt is a longbranch one.

 

[trevj]

I would suggest posting the question over in Milsurp. There are guys out there that can tell you the dimensions of the various sizes of bolt heads, and what fits what that might close things up, but they tend to be more focused upon their areas of expertise.

A 30 thou gap between the case head and the bolt seems a tad...excessive though.

Back when I first started out in the CF I was a weapons Tech on an Air Base, and worked in the Small Arms Shop where we maintained FN's, LE rifles, Sterling SMG's and Browning HP Pistols, as well as a smattering of assorted other firearms.

We had all the gages we needed, plus bins of parts. Could I recall what the dimensions were supposed to be after almost 40 years though? Nope! It was something we looked up in the manuals.

LE chambers were never meant to be as tight a fit as a more modern cartridge calls for. If you dig about the web for the min/max cartridge sizes and the min/max chamber sizes of a .303 British, and compare the same dimensions from say a .308 Winchester, the differences in the 303 are quite a bit wider.
Add to that the Military need to work well enough, in ALL conditions, including much mud, and the military arms are a little looser yet in their chamber specs, but they still had pass and fail specs to meet.

The bolt should close on a Go Gage, but not a No-Go gage. I am reasonably sure the Field gage is set to indicate the maximum allowable chamber including wear that was considered acceptable. Been a lot of years, we just looked it up and followed the inspection checklist, eh?
But off the top of my head the difference between a go and no-go gage for a modern round is on the order of 4 thou or so. That would require some independent verification, as my coffee levels are pretty low right now too! Even I wouldn't bet on it being gospel!

Someone on the Milsurp side is more like to be able to give you some clearer dimensions, as well as give you an idea if you are in a recoverable situation for being able to use factory ammo.

Worth mentioning that if all else fails and all else checks out, you 'might' be able to make up custom fitted loads, fireformed to the chamber dimensions, that would only work in your rifle. But that is another whole show too.

Cheers
Trev

 

[aric84]

I believe that no go is .074 and this is way beyond that. I believer the bolt was mucked about with by someone and they took a pile of material off. The extractor will not even snap over the rim when closed on a chambered case, it just rests on the edge. One I get a replacement bolt I am going to scrap this one as it is unsafe.

I am hoping the receiver is okay and I can salvage the rifle. I will try asking about in other forums as well.

 

[Potashminer]

Go to Mil surp site and read Peter Laidler articles on setting up a Lee Enfield - he has detailed step by step to fit and check bolt body to receiver, set up firing pin protrusion, select and check bolt heads regarding overturn and headspace, etc. Both bolt lugs must bear evenly in the receiver. A headspace gauge set for 303 (like other rimmed cartridges) is essentially verifying the range of total "play" or slop from bolt locking lug surface to forward face of cartridge rim - no part of the cartridge case body is involved in rimmed case headspace checks with a head-space gauge. With a bolt body that is within tolerance and fitting properly in a receiver that is itself within spec, once can select one of the "0", "1", "2" or "3" length bolt heads, that fits that bolt body with correct overturn, to set the headspace - the distance from bolt face to forward edge of the rim. The 303 headspace gauges I have are marked min - .064", max - .069", field - .074"

 

[englishman_ca]

Difficult to give an opinion without the thing in my hands but i would suggest that there is something wonky with that bolt.

Often these ex service arms are worked on by civilian owners who have no real idea as to what they are doing. It sounds like that somebody has been filing or dremeling at this bolt. What you describe is scrap.
I have seen the front face of the bolt body shortened to allow the bolt head to screw in to give better firing pin protrusion. It does allow the pin to stick out further but screws up headspace big time.

You mention that you tried other bolts and the fit of things seemed more in line as to what you would expect.

Junk the bolt and find another to replace it.

There is a procedure for the fitting a bolt, all critical steps. info can be found on line as mentioned above.

 

[aric84]

The bolt was definitely ground at some point for some reason. Brought it to the gunsmith's and he set me up with a new bolt and headspace is now well within tolerance. I smoked the lugs and I have perfect engagement on the top lug and fair engagement on the lower lug. Much better. I will read over the aforementioned articles and decide if I should lap it a bit or just shoot it as is.

Thanks for the help guys.