Ishapore No1 MKIII* hard closing bolt

[Parashooter]

The videos show an extractor mortise with some burrs. Smoothing those out might help.

As for "how much should be taken off the contacting edge?" - the answer is "enough but no more". From an engineering standpoint, we really need only enough bolt face remaining to support the base of the cartridge, not counting the rim (which isn't directly subjected to firing pressure) - so one could put a fairly serious chamfer where it's jamming without meaningful reduction of the normal pressure containment system. On the other hand, there shouldn't be any increase in the visible gap between bolt head and receiver ring when the bolt is closed - since a good fit there is part of the system that directs escaping gas away from the firer in the event of a ruptured case.

But before chamfering the bolt head, at least try deburring both the extractor and the barrel mortise into which it fits when the bolt goes forward.

[Peter Laidler]

Nope............, DEFINATELY the bolt head fouling the rear of the breeching ring. Just chamfer the top right hand edge of the bolt head, sufficient for the bolthead to cam its own way down so that it slips INTO the breeching up ring instead of tending to abutt against it.

Not an approved method of repair so far as I can ascertain but if this was one of ours, we'd have gauged and tested it with a slave 'gauge' bolt that the examiner would have had and then certified it ZF............ the death knell for all weapons

But if you can make yours serviceable with a small chamfer, then go ahead

[Parashooter]

Agreed, Captain, we can see that the bolt head is jamming against the receiver ring. My question is exactly what it pushing it up/over there only when a cartridge is present? If it's the extractor (as you indicated in post #27 here), is it due to extractor deformity? In normal operation, the extractor bears against the inclined mortise surface, withdrawing its hook from firm radial contact with the cartridge body, and the presence of a cartridge shouldn't affect pressure on the spring as the bolt is closing. I suspect the extractor is either too long (perhaps the 7.62 version) or is burred/deformed.

Regardless of the root cause, a small chamfer certainly seems a practical remedy.

[Lucite]

From what I can tell its a number of things, the magazine follower, the front left tab on the magazine and the extractor all combined to cause this

[Brian Dick]

All are problems most likely associated with excessive slop in the bolt runway of the body. Give the bolt head the chamfer as instructed by Peter and I'd bet it'll be good to go.

[Lucite]

well I took some 800 grit sand paper and made a slight chamfer which really didn't do much, but my main concern it taking too much off and creating a safety hazard.

[Brian Dick]

It won't create a safety hazard if you use care. Use a sharp file but go easy. I don't think 800 grit sand paper will give it more than a polish.

[Parashooter]

. . . my main concern it taking too much off and creating a safety hazard.

If you compare the size of the bolt face to that of the cartridge rim, you should see that there's room for a substantial chamfer without compromising cartridge support, even without considering that, with modern solid-head cases, there's no real need to support the portion of the rim that extends beyond the case body's major diameter. It is, however, important to limit any chamfer to the portion of the bolt head that is enclosed within the receiver ring when the bolt is locked. (In the illustration below, the portion of this area that isn't enclosed was blackened with a marker to highlight the enclosed, unmarked, portion.) Extending a chamfer beyond the enclosed portion would provide an undesirable escape path for gas and debris from a split case or blown primer, instead of directing it to the gas escape hole on the left side of the receiver ring and the ejector cut on the right.



It seems very unlikely that any serviceable SMLE would require a chamfer anywhere near as large as that indicated by the green lines. A 45-degree chamfer with face width under 1/32" should be more than enough.

[Peter Laidler]

Lucite, from these 4x pages, can I reasonably assume that you aren't a technical sort of person........... In much the same way as I'm not a computer person!

You can be rest assured, in the nicest possible way, that 800 grit is going to be hard pushed to chamfer a fingernail, let alone chamfer a block of tough steel that has been case hardened to boot. Attack it with a grinder as shown by Parashooter

Other forumers also take note that the front magazine lips should be absolutely and totally clear of the barrel of the bolt. They are simply to hold the nose of the bullet until it strikes the feed ramp and THEN, that action unhooks the bullet from the left or right lip and leaves the nose of the bullet to wend its weary way up the feed ramp and into the chamber.

If the front feed lips can be forced up so as to touch the bolt body then it indicates that the magazine is defective where the top front edge contacts the MAGAZINE STOP FACE at the front of the magazine well OR that the actual magazine stop face in the body is worn away. Yet another defect that will ZF a No1,4 or 5 rifle

[Lucite]

Lucite, from these 4x pages, can I reasonably assume that you aren't a technical sort of person........... In much the same way as I'm not a computer person!

I am a fairly technical person but I am also fairly new to guns and I want to make damn sure I know exactly what I'm doing so I don't kill/ maim myself especially when it comes to modifying the bolt head.

A 45-degree chamfer with face width under 1/32" should be more than enough.

okay so under 0.031 is all I need to know