Bolt HeadcFitting Question

[browningautorifle]

etching in the bolt face.

Yes, I've had that and sometimes a bit worse.

[tiriaq]

^^^^^
The backthrust is not taken by the threads, but by the rear of the bolthead being in contact with the face of the bolt body.

[MAC702]

Too, I think a leaking primer could be construed as a pierced primer. Which is a firing pin length issue...

If he's "blanking" the primer, with bits of primer cup actually blowing into the bolt, that would be a clearance issue between firing pin and the hole in the bolt head, necessitating bolt head replacement. I recently replaced an AR-15 bolt for this issue, after a few years of hot long-range loads went through it.

But if it's just etching on the boltface, I don't see that it's either.

[browningautorifle]

that would be a clearance issue between firing pin and the hole in the bolt head, necessitating bolt head replacement.

Yes.

I recently replaced an AR-15 bolt for this issue

Agreed, I did one of those a few years back, had several fine pits burned into it.

To see if the firing pin protrusion is an issue it would need to be checked. One of the things you look at, when the parts get swapped by collectors there's little thought given.

Anyway, that wasn't the issue he was suggesting after all.

[Alan de Enfield]

If a bolt is clocked in spec, the threads do not bear cartridge thrust in practise. Bolts are made of hardened steel, while bolt heads are made of either wrought iron or mild steel that is hardened on the bolt face and the rail lip. The threads aren’t hardened.

So if it’s clocked in spec, the bolt head will bear on the bolt face after the first few rounds are fired, as the threads will plastically deform enough to fit itself more fully to its bolt.

Like this :

[togor]

^^^^^
The backthrust is not taken by the threads, but by the rear of the bolthead being in contact with the face of the bolt body.

In both rifles I am working with, with original bolt heads, the back of the bolt head comes into contact with the face of the bolt body slightly past alignment with the rib. IIRC a few degrees of this is considered okay. I'm seeing about 1/8" of over-rotation possible at the surface of the rib.

This means that when the bolt head is aligned to the rib, those surfaces are not in contact, and the recoil is on the threads.


Now as dumb beginners luck would have it, this new bolt head just purchased bottoms out exactly in alignment, *and* the measurement from bolt lug to bolt face matches the original bolt head to within .001" on the Maltby '42.

I agree that a proper set of headspace gauges is the way to really know what one has. But sometimes, if one is careful, a small incremental change from a known good system is possible without putting the rifle into a dubious state.

[Surpmil]

I am assembling a new bolt head of matching #0 as insurance against leaking Winchester 41 primers....

How would a new bolt head improve over what you have now?

As for the question of the threads "taking a beating" I'd suggest that the distribution of load over a dozen or more threads is far greater and the loading therefore much less than over the shoulders at the mating faces of the bolthead and bolt body.

[togor]

How would a new bolt head improve over what you have now?

As for the question of the threads "taking a beating" I'd suggest that the distribution of load over a dozen or more threads is far greater and the loading therefore much less than over the shoulders at the mating faces of the bolthead and bolt body.

Well the design is what it is.

I'm looking at a new bolt head not because of the thread pounding.

I'm looking at it because I might find myself shooting some 80+ year old ammo and I'd rather not etch the original bolt face if a primer leaks. Just a precaution.

Rifles have collectible value, so enjoy them, but take precautions.

I suppose they allow a little over-rotation in the fitting of the bolt head on the assumption that the bolt head and bolt face will take the pounding once the threads loosen up a bit and get out of the way

[Surpmil]

Well the design is what it is.

I'm looking at a new bolt head not because of the thread pounding.

I'm looking at it because I might find myself shooting some 80+ year old ammo and I'd rather not etch the original bolt face if a primer leaks. Just a precaution.

Rifles have collectible value, so enjoy them, but take precautions.

I suppose they allow a little over-rotation in the fitting of the bolt head on the assumption that the bolt head and bolt face will take the pounding once the threads loosen up a bit and get out of the way

I wouldn't worry about it unless the bolthead you have looks sub-standard or compromised in some way. And if it does there are plenty of NOS ones out there you could replace it with if you have HS gauges or a vernier you can measure the existing one with. Only the HS gauges will show whether the BH face is square to the chamber of course.

As for the old ammo, be patient with hangfires and if necessary take advantage of the unusual ability of the rifle to recock without unlocking the bolt.

[Bruce_in_Oz]

Lee Enfields have HELICAL lock-up. Thus, basic measuring gear will be of little use.

It is "plug and play", all the way. According to ALL of the original technical literature I have seen, for No 1 Mk 111 rifles, there was ONE "standard" bolt head, with a "qualified" thread and a set distance (with the usual tolerances) from face to the shoulder forward of the thread. No "Shake and Bake" assembly here.

Caveat: POST WW2, (early 1950's), Lithgow did a run of "longer" series bolt heads. These rare and exotic items have LETTER size designations. If you have bolt-heads with a letter "M" stamped on them, that is NOT a "size", but indicated that hey were made from "Mild Steel" and then case-hardened and finish-ground. Earlier "unmarked" No1 rifle bolt heads were made from "malleable cast iron". The idea was to NOT have high "hardness" but general toughness. (Resist wear and NOT shatter in the event of a catastrophic cartridge case rupture. The entire purpose was the wring the last bit of functionality from the old girls before the mass adoption of the L1A1 rifle. These nifty new-fangled gas-operated jobs ALSO had a "graduated" locking shoulder system of inserts to achieve "spec" headspace AND "retention" grab". Once the gun-plumbers "ran out of numbers", the body was condemned and destroyed or used for "non-firing" roles like cutaway instructions rifles or as "levers" and such on grueling obstacle courses. (Try hoisting a succession of diggers in battle order over a ten-foot high wall, with an M-16). The FAL / L1A1 was ultimately late-19th century engineering with marginally better metallurgy.