1968 MP5 with no serial number

[Peter Laidler]

I wouldn't do ANYTHING else to your deactivated former weapon Clarkie. It has been to the PH, got the cert and correctly marked. You would be unwise to tamper with it in any way. Just my opinion.............

BP, your thread 40. The difference between the D&B inert and the real McCoy was that the D&B L86 was more reliable!

[Gil Boyd]

Agree with that philosophy Peter from a lawful Police standpoint.
The Deactivation certificate will reflect the weapon in question at the time it entered the Proof House and recorded accordingly as to what they had in front of them, presented for deactivation.

[mrclark303]

The ex Enfield "Foyer Display" marked L86 isn't mine guys, it belongs to a friend.

As you know, Enfield built these up from parts, as display non firearms, no one really bothered about them back in the 1980's.

The trouble is the potential live components that could be directly reused

I have only had a quick look at this particular example, I am sure Mike can give us a proper run down, but from my quick inspection, the bolt carrier appeared live and reusable, the TMH looked like it would be usable with a little work and the receiver appeared to be unmolested.

I guess the main legal issues center around the restricted (proof marked) components, like the bolt carrier and reciver.

Not sure about the legal position of the TMH??

[Peter Laidler]

I'm not sure that the bolt carrier could be categorised as a proofed or load/pressure bearing part to be honest. It does exactly what it says in that it just carries the little breech bolt/block. The BB locks into the upper receiver lugs. The question is this. Would it fire and remain locked of the carrier wasn't present. The answer is yes. The TMH is not a proofed part, just like the L1A1 and bren butt slide. However, I would argue that an L1A1 WOULD NOT remain locked if the BBC wasn't present.

[mrclark303]

That raises an in interesting question Peter, I wonder what would happen if you dropped an L1A1 breech block into battery without the bolt carrier and fired the rifle?

Would the bolt remain held by the locking shoulder during firing or would it ride over the ledge and boom!

[browningautorifle]

Would the bolt remain held by the locking shoulder during firing or would it ride over the ledge and boom

That was a question we often contemplated decades back but never had the parts to actually test.

[Peter Laidler]

It WILL unlock and the BB will go into orbit probably followed by large chunks of the brass case. This is due to the relative inclined angles of the BB and the locking shoulders. You must have inclined angles in a tilting lock locking situation like this albeit very slightly inclined. This is because - and I am going to keep it VERY simple now - the BB rotates (downwards) into the locked position

[mrclark303]

So does the Bolt Carrier actually take any pressure during the firing cycle, or does it simply ensure the Bolt is held in battery and all the forces are directed rearward at the locking shoulder?

[Peter Laidler]

Now you're asking......... Taking me back to my teaching Physics days..... Nope, it's a bit more than that...... But the rearward loading on the BB will mechanically force it rearwards of course but a part of that rearward force will attempt to lift the rear of the BB by virtue of the (relatively small) inclined angles of the locking bent of the BB against the same inclined angle of the l/shoulder. However, this mechanical inclination of the BB to lift - due to the two inclined angles mentioned - is thwarted by the more substantial area of metal to the rear of the locking bent in/at the inside rear top of the BBcarrier. In turn, the BBcarrier is held downwards against this upwardly directed loading by the sliding ribs

Are we all still here - or have we all gone into a deep slumber? Right, while the BBcarrier if out of the rifle, I want you to have a look inside at something more interesting. It's sounding more like a school physics lesson now......... Look at that LOCKING BENT ramp thing at the rear of the inside of the BBcarrier. Got it? Notice the approx 1/2" distance it extends to the rear from the ramp part. This is the locking shelf (or locking medium in technical terms) and is a VERY important feature of the mechanism. As the BBcarrier is pushed rearwards by the piston, this long 'shelf' ensures that while the piston and BBcarrier is pushed rearwards, the BB remains positively locked downwards ahead of the locking shoulder. for a further 1/2" or so This one part of the inbuilt mechanical safety.

But there's more. You'll now see that the BB can't start to LIFT out of LOCK (called commencement to unlock - which isn't the same as 'unlocked' of course) until the BBcarrier has moved rearwards by approx 1/2". And by then, the rear of the striker is shielded. The same thing but sort-of in reverse happens when the BB and BBcarrier goes into lock down. But now, the rear of the striker is not accessible to the hammer until the BB is locked AND the BBcarrier is almost fully forwards.......... But there's more.......... If by your quick action of the trigger (or in the auto role) you do release the hammer before the BBcarrier is FULLY forwards, the hammer will cam forwards more slowly............... anyway, you'll get a misfire due to what is called 'diminished force of blow of the striker'

Wake up at the rear of the class...............

[mrclark303]

As ever Peter, a very concise and interesting lesson regarding the mechanical function and forces involved.

I've just gone through the function check with my cut away to follow your post, facinating stuff.

Many thanks John.