Having trouble closing the action on my No4 Mk1*, need advise please.

Sorry if I sould a bit contrary chaps, but....... IF the bolt head is jumping out of the bolt head track on a Mk1* and the gap in the trackl guide is chipped, then there is ONLY one repair. Anything else is palliative and not a cure. Take the bull by the horns, read back on a thread where I explain the REME/Army method of repairing it, and get on with it - properly.

It's not a difficult job....., just fiddly and a good mig or tig welder should be able to repair it in minutes. There's no hardened or important surfaces near by, it ain't going to distort then all you've got to do is to undercut carefully with a fine toothed hacksaw blade.

Peter is spot-on.

There is a caveat or two.

IF the bolt body and/or the action body is sufficiently "flogged out", the bolt-head will "float" up and down as it is cycled back and forth.

IF, furthermore, the bolt head lacks the tiny chamfers on the "rib", it is very likely that the guide-rail on the body will start to suffer chips rather quickly. I understand that this "chamfering" of bolt-head "ribs" started in Canada sometime in the late 1940's.

Another factor, closely tied in with the "looseness" of the bolt is the effect of a fully/mostly filled magazine has on the "tilt" of the "loose" bolt body. I have long harboured a suspicion that some of this damage can be sheeted home to "dry cycling" as there is almost ZERO vertical pressure applied to the bolt body by an empty magazine. Ditto the "style" of the operator's working of the bolt. Note that as you retract the bolt you are applying an upwards force on the bolt handle. This in turn depresses the front of the bolt. When that happens, the bolt head lug will rotate with the inner edge of that flat guide surface acting as a fulcrum. That MAY explain why the corner at the REAR of the gap seems to suffer the greater damage.

Or am I barking up the wrong tree here?

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Originally Posted by Peter Laidler

Sorry if I sould a bit contrary chaps, but....... IF the bolt head is jumping out of the bolt head track on a Mk1* and the gap in the trackl guide is chipped, then there is ONLY one repair. Anything else is palliative and not a cure. Take the bull by the horns, read back on a thread where I explain the REME/Army method of repairing it, and get on with it - properly.

It's not a difficult job....., just fiddly and a good mig or tig welder should be able to repair it in minutes. There's no hardened or important surfaces near by, it ain't going to distort then all you've got to do is to undercut carefully with a fine toothed hacksaw blade.

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Thanks Peter, I am very interested in this article! Would I find it in your link of indexed articles? I could not find such a post in your links or searching the forum. Would you know more specifically I could use as a search term?

---------- Post added at 08:57 AM ---------- Previous post was at 08:53 AM ----------

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Originally Posted by Bruce_in_Oz

Peter is spot-on.

There is a caveat or two.

IF the bolt body and/or the action body is sufficiently "flogged out", the bolt-head will "float" up and down as it is cycled back and forth.

IF, furthermore, the bolt head lacks the tiny chamfers on the "rib", it is very likely that the guide-rail on the body will start to suffer chips rather quickly. I understand that this "chamfering" of bolt-head "ribs" started in Canada sometime in the late 1940's.

Another factor, closely tied in with the "looseness" of the bolt is the effect of a fully/mostly filled magazine has on the "tilt" of the "loose" bolt body. I have long harboured a suspicion that some of this damage can be sheeted home to "dry cycling" as there is almost ZERO vertical pressure applied to the bolt body by an empty magazine. Ditto the "style" of the operator's working of the bolt. Note that as you retract the bolt you are applying an upwards force on the bolt handle. This in turn depresses the front of the bolt. When that happens, the bolt head lug will rotate with the inner edge of that flat guide surface acting as a fulcrum. That MAY explain why the corner at the REAR of the gap seems to suffer the greater damage.

Or am I barking up the wrong tree here?

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This seems to have merit. In my original thread I stated that if there are cartridges in the rifle then the frequency of this happening drops to about 1 in 4.

---------- Post added at 09:02 AM ---------- Previous post was at 08:57 AM ----------

IMO this one part of the Mk1* "design" that is an Achilles heel. I know it was a wartime expedient but I think the No4 Mk1 is a better rifle. The caveat being that I am not an expert, just a fan.

---------- Post added at 09:06 AM ---------- Previous post was at 09:02 AM ----------

My particular rifle was lightly used, the barrel is in excellent shape with no detectable wear. This damage probably came about from too much cycling of the action in an empty rifle. I am also going to look into the angle of the cocker spring binding up inside the bolt and causing the bolt to want to turn.

Can someone wot is better wiv comp'ers bring this article up?

Nope, I don't agree that this is a design flaw as such. When the last No4 Mk1* and 1/3 rifles were leaving UK Military service in 2000 or so, from Cadet Forces, they were all pretty well flogged to death but there were still thousands - or hundreds of thousands still in good serviceable condition. If that gap is the exact length of the bolt head, then that is the answer to the problem. Once the gap increases in length, the increased length just exaggerates the window of opportunity so to speak where FURTHER chomping away of the good material can occur.

I'm of the opinion that your striker spring theory is based on fuzzy logic. In true mechanical terms, when you close the bolt, the action............... Nope, fuzzy logic I'm afraid! Just my opinion based on mnothing more than a bit of experience

Good point about the "window", so to speak, of opportunity.

M-1 / M-1A shooters will be aware of a related issue when the operating rods start to wear or are distorted / "misaligned", and begin to run "hard" in the receiver. In this case, it is the op-rod that gets trashed, rarely the receiver. (The joy of properly heat-treated 8620!)

Can the damage to No4 Mk1* receivers be repaired? Never tried, but, a visit to my friendly TIG welding brother may be in the offing. Getting the correct filler rod and current could be interesting.

Pack most of the body into damp mineral sand, TIG it up and carefully grind away the "blobs"with Dremel cutting discs?

However this is all fairly pointless if the body and bolt are dimensionally "shabby".

We used to put a length of copper plate into the full length of the undercut and make good the slot at each end with mig or gas where necessary. Then we had a handle which would take a hacksaw blade, We'd use this from the rear to get the right undercut. Done loads of them. Once they'd gone through the workshop they'd come out like new

One other (somewhat unlikely) possibility;

Has this rifle been fitted with a replacement barrel?
If so, I wonder if someone has twisted the action a bit, by shoving a bar through it to unscrew it from the barrel?

Just a thought, as that'd maybe cause the bolt -head to misaligne on closing.

All the best,

R.

I had a Long Branch Mk.1* through here a couple of years ago that had the exact problem that Richard suggests. I don't think it applies to the OP's rifle with the badly chipped rail but it sure stumped the crap out of me at the time. The rail wasn't chipped on this rifle and when the bolt was drawn to the rear, the bolt head automatically jumped up through the gap anyway. The owner had removed the barrel using a breaker bar through the magazine well and twisted the receiver/body ever so slightly. He also faced off the shoulder of the barrel one full turn in a lathe to tighten up the headspace to his nonexistent match specification so he ruined a perfectly good barrel in the process too. I agree with Rob that when the action wrench is seated properly on the shoulder of the receiver/body at the front, no amount of torque should twist it in theory. That being said, there's still a reason why real Armourers used a slave bolt with no extractor to reinforce it during the process.

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Originally Posted by Peter Laidler

We used to put a length of copper plate into the full length of the undercut and make good the slot at each end with mig or gas where necessary. Then we had a handle which would take a hacksaw blade, We'd use this from the rear to get the right undercut. Done loads of them. Once they'd gone through the workshop they'd come out like new

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I'm afraid that doing this would make the rifle worthless as a collector. So I guess I'll just have to live with it, I'll try some heavy grease in the bolt threads and perhaps create some washers for the striker spring. Anyone know the dimensions that I would need to make these washers?

I won't buy another Mk1*, my next one will be a No4 mk1 or a Mk2!

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Originally Posted by cthulhudarren

I'm afraid that doing this would make the rifle worthless as a collector.

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Pretty much worthless as a collector or a shooter the way it is now.

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Originally Posted by cthulhudarren

I won't buy another Mk1*,

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That's your prerogative. But don't condemn the Mk.1*'s just because you bought a stuffed one due to a total lack of basic knowledge.