Problem with No4 MkI Bolt

[browningautorifle]

it looks like I have a Longbranch bolt head.

That's right...

[RobD]

dewey, from your initial post, it sounds like your bolt head jumps out of the track on firing - not on cycling the bolt - is that correct?

[dewey1424]

dewey, from your initial post, it sounds like your bolt head jumps out of the track on firing - not on cycling the bolt - is that correct?

Yes sir. That is correct - it pops out when fired. It cycles OK when dry fired or using a snap cap.

[Micheal Doyne]

That don’t sound terribly safe!

[Bruce_in_Oz]

There is something DEFINITELY awry if the bolt-head "jumps" up on firing. There should be a section of the guide-rail still engaging the bolt-head. Furthermore, the extractor should be in the appropriate narrow recess in the rear of the barrel and held against the radiused ramp surface by the extractor spring. Another factor is that there will be a difference in "bolt float' between feeding ammo from a full mag and dry cycling.

If the bolt is flopping all over the place during dry cycling, either it is badly worn, the Body is seriously worn, or, embracing the power of "and", BOTH important bits are totally flogged out.

Quickest test is to "borrow" a brand-new bolt body; one that is JUST a bolt body, i.e., nothing fitted. Run it into your rifle and compare the vertical play, just before lockup. If there is significantly less, a NEW bolt body may get you out of trouble for a few thousand more rounds. If the "slop"is just as bad with the "new" bolt body, your rifle body is in pretty dire shape.

[RobD]

I think a professional gunsmith needs to help you with this. Brian Dick [see post no. 3 above] is the top man in the USA for Lee Enfields. I wouldn't shoot it until it has been fixed.

[Brian Dick]

I think he means that it pops out when he retracts the bolt after primary and secondary extraction. Looking at the pictures, I can't for the life of me see how it can pop out upon firing. I've never seen or heard of that happening with any Lee Enfield Rifle. How about a clarification?

[dewey1424]

I think he means that it pops out when he retracts the bolt after primary and secondary extraction. Looking at the pictures, I can't for the life of me see how it can pop out upon firing. I've never seen or heard of that happening with any Lee Enfield Rifle. How about a clarification?

I have taken this rifle to the range twice since I bought it last fall. The second time, earlier this month, the sequence was this. I loaded a single round and closed the bolt. When I fired the rifle, the bolt stayed in place but I could not withdraw the bolt. In each case, I had tried to raise the bolt handle to eject the case when I encountered a stuck bolt. But I could manually raise the bolt head to the vertical position with my thumb and then remove the bolt. It appeared to me that the bolt head had jumped the track. This happened 3 times at which point I reached the same conclusion as Mr. Doyne. [Slow learner.]

I have since tried loading a snap cap again from the magazine and from lying on top of the magazine. It loads, the bolt stays in track, and it is extracted OK, with the bolt head staying in the track. Whatever the problem is, it appears to be associated with firing, but I didn't think to take any pictures of the problem when it occurred.

I have put 19 rounds through the rifle. I believe I would have noticed this behavior the first time I took it to the range. In between the first and second visits I stripped the bolt head and rechecked the headspace with the 0.071 gauge.

Here are some more images.




As you can tell, I'm new to these rifles. The only thing I could think of is that front part of the channel is worn or bent up, the bolt head is too wobbly or worn, and/or I didn't get the bolt reassembled correctly... or I did not correctly assess the sequence of events.

Is it possible when loading a single round to close the bolt and fire without the extractor engaging the rim or to commit some other "operator error" that could cause this behavior?

Is it possible that a worn or damaged throat that wouldn't show up in a headspace check could cause this problem?

Thanks to all who are weighing in on this problem. I would prefer not to relegate this one to wall hanger status, but if it can't be made safe then needs must.

[Surpmil]

Your bolt head overturn should not be more than 12° if I remember Peter's comments correctly.

Furthermore, your bolt head does not have the necessary chamfer at ether end of the guide rib, as per the bolt head shown above. A little surprising considering it is a Long Branch made bolt head.

Get out the needle files and go to it?

The bolt head retaining slot on your rifle does not look worn enough to condemn it, nor cause problems if the bolt head rib is properly chamfered.

[Bruce_in_Oz]

That photo showing the rear of the chamber looks odd. You should be able to see a clearly-defined "collar" in the body, just behind the actual barrel face. The barrel should not be touching this "collar" (known as the "inner ring" because No4s breech up on the front of the Body, as opposed to all its predecessors, which, like a Mauser, breeched up against that inner ring.

Another part of the "mechanical safety" designed into the Lee Enfield family is that the the very front of the blot-head enters this close-matching aperture in the rear of the breech ring, thus centralizing (more or less) the bolt-head with the chamber.

IF that aperture is oversized, the bolt-head alignment will not be as good. If the bolt-head alignment is "wonky", so will be the bearing of the locking lugs. If the bolt assembly can be "drifted" to the right, the left lug will disengage. Thus, on firing, the initial back-thrust will be primarily on the RHS locking shoulder. Asymmetric back-thrust in an asymmetric (or any other) body will produce undesirable wave / vibrations that no amount of fancy bedding will overcome.

If, somehow, the rear of the breech ring does NOT closely surround, the very front of the bolt-head, there WILL be problems The bolt cannot move off-axis to the left because of the substantial support from the left side of the Body. As the bolt closes, the extractor engages its slot (or at least, it SHOULD) and this tries to pull the bolt-head to the right. HOWEVER, at the same time, that inner breech ring is "capturing" the bolt-head and centralizing it.

In the unlikely event of a catastrophic overload, or a seriously faulty cartridge case, the relatively soft body will not shatter like a grenade, but the slightly less substantial right side of the body will "stretch". NOTE; what is envisaged here is not something caused by a few extra grains of powder, but like an overloaded proof cartridge or worse. Even then, what is more likely to happen is that the extreme pressure (and temperature), will blow out via the primer pocket. Again, the engineers thought of this. That is why the extractor has a bit of "air-gap" around it and there is a vent port directly opposite on the left side of the breech ring. These features prevent a "scary" event escalating into something MUCH worse. Lee Enfield vent "case blow-outs" from the front of the receiver. Herr Mauser's designs conveniently allowed the generous bolt-lug guides to allow escaping hot gases to vent rearwards, hopefully dissipating as they went. That is why Mauser type rifles have that rather large shroud over the rear of the striker assembly. It's a SHIELD against stuff that can blot out your eyesight.

SMLEs and earlier are slightly SOFTER in the body than No4s. When they "blow up", they tend to bend more readily; the earlier pattern ones the the magazine cut-off slot slightly moreso. They also wear in the bolt-head retention area; to the point that the bolt-head can disengage from the body when only halfway closed. This of course takes a a LOT of action manipulations, dry and live.