Gap between barrel and receiver

[Peter Laidler]

Yep, got that now Son. Well done the Armourers! I only had a SKN action here to browse at, that's why I asked JM (sorry to wake you up JM.....) for an inside view. Problem solved. Thanks again. Arte et Marte

[muffett.2008]

JM, did you check the undercut on the barrel's? to my way of thinking, if the undercut is inadaquate, the barrel will lock up where the thread ends, sufficient torque can be applied to get the barrel to clock correctly.
As the twist is LH, this would ensure the barrel is not likely to unscrew on firing.
I have noticed this problem a few times over the years, but never associated it with the factories, I always assumed some *** had done it post assembly, they say you should never assume.

[Ridolpho]

Pardon the ramblings of a non-engineer (geologist) but the "inclined plane" of the threads is at a very low angle relative to the axis of the bore and the force directed along the bore by the shell head pushing on the body through the bolt will generate a huge amount of friction along the inclined plane- perhaps enough to overcome the torque generated by the bullet hitting the rifling?? All those actions displayed by Jmoore would tend to suggest losening by shooting doesn't happen. In any case fascinating stuff and highly educational.

Ridolpho

[Peter Laidler]

I have actually seen this slight rotating of a barrel before my very eyes.

I was stood behind a few soldiers zeroing in their SA80 rifles, just glancing occasionally while oooking through my binos..... only to see one group of shots gradually walking off the target so I walked over to the shooter and kicked his feet - as you do - and asked him why he was continuing to shoot off the target (I was a tad more forthright than that if you please.....). He told me that he was aiming at the bull and so far as he was concerned, that's where they were!

As I looked down at his rifle as he was shooting and could actually see the foresight cranked over to the left (or was it the right.....?). He couldn't see that the barrel or gas block seemed to be loose to point of unscrewing. I stopped him shooting and lo and behold, the barrel was just over hand tight but unscrewed using a spanner with no vice clamps.

Anyway, a barrel will unscrew if it's not tight!

There was a sequel............ He asked me how I could tell that the barrel was loose
Me: I could see the sight block over to one side
He: Well, I was still using the foresight and it was shooting OK
Me: I could see the shots getting further away from the target
He: How come..........? I was aiming at the bull
I thought about a technical answer but instead, just told him to get another rifle from someone else!

[jmoore]

JM, did you check the undercut on the barrel's? to my way of thinking, if the undercut is inadaquate, the barrel will lock up where the thread ends, sufficient torque can be applied to get the barrel to clock correctly.

You got it! As you were about to drift onto the subject after viewing 5thBatt's photos, but managed to restrain yourself. But barrl photos will not be forthcoming today. Mostly because i haven't found them.

More details coming.

[Homer]

Bruce is that right that a mauser 98 is also breeched up internally? The same individual that persistently suggest that any gap present between action and barrel shoulder is a case of laziness and poor workmanship also suggest that the mauser is breeched up on the external face of the action.

SMLE breeching data:

According to drawing No. A.I.D. 1318. to accompany S.A. 435A, the pertinent dimensions are thus:

From receiver front face to forward face of inner breech ring: 0.681" Accept, 0.689" Reject.

From absolute end of barrel to shoulder of Knox form: 0.6911".

Thus, under any acceptable gauging, there should be a SMALL gap between the front of the receiver / body (or "shoe" if you prefer REALLY old Snider-vintage parlance) and the rear of the Knox Form. Therefore, SMLEs are INTERNALLY breeched, like a Mauser 98.

When I get a few hours spare, I will dive into the crypt and dig out the relevant numbers for the No4.

[jmoore]

Bruce is that right that a mauser 98 is also breeched up internally? The same individual that persistently suggest that any gap present between action and barrel shoulder is a case of laziness and poor workmanship also suggest that the mauser is breeched up on the external face of the action.

The Gew98 and following should have the rear face as the primary datum. The barrel reinforce at the front face should not be the primary locating feature, so, no, that other unnamed fellow is incorrect from a design standpoint. I'm not really a Mauser guy, but it shows up in print often enough and with references to German documentation...

For a good breakdown of many turnbolt action designs in great detail try The Bolt Action: A Design Analysis, Vol. 1 by Stuart Otteson. No Lees, unfortunately!

Which, to continue with the tangential nature of the subject, leads to Lee's last design, the 1899. In which, much to the consternation of most anybody interested in design and manufacture, has locking lugs both toward the rear and front of the bolt! Imagine trying to get all four lugs to bear in a production environment. The horror...


Not to mention that the bolt head is a separate piece, AND that the lugs are at 90 degrees to each other.



The horror...

[Homer]

This makes perfect sense and why would they complicate the procedure if it wasn't completely unnecessary.




=Peter Laidler;237253]Surely.................. It's a case of what I call in mechanical engineering terms, the bleedin' obvious! If there's NO gap between the front face of the body and rear face of the nocks form, how will you know whether the rear face of the barrel is breeched up against the corresponding face of the body? I say, let's cut out the crap and stick with the facts![/QUOTE]

[Homer]

Sorry I've been replying to post as I've been reading through the entire post and just got to jm's post. Fascinating really. I would have thought surely one face must be bedding down in order to torque up the barrel unless the thread is bottoming out.


Edit. And now I've just got to muffers post mentioning the thread. I'll try to keep up from now on.

[5thBatt]

Here is another in my collection with a gap, this time a 1893 MLM MkII with its original Metford barrel