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I really don't know why the flat is on the right on the Lanchester BAR. I would just assume that it is because that's how it was on the MP28-II. Why was it on the 28-II? I can only assume that because the 28-II extractor extended to the full diameter of the tube (can anyone put a photo of one up?) and protruded out of the front of the breech block the flat would allow any rubbish to clear. Otherwise it'd prevent the BB from going forward fully
A good modification to a standard Lanchester is to insert a grub screw into the side of the BB top hold the floating firing pin assembly fully forwards. This eliminates the original inertia firing pin. Not as good as a Sterling breech block though. The even better news is that you can still use the Sterling BB in a Sterling!
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05-30-2018 11:49 AM
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Why was it on the 28-II? I can only assume that because the 28-II extractor extended to the full diameter of the tube (can anyone put a photo of one up?)
A good modification to a standard Lanchester is to insert a grub screw into the side of the BB top hold the floating firing pin assembly fully forwards. This eliminates the original inertia firing pin. Not as good as a Sterling breech block though. The even better news is that you can still use the Sterling BB in a Sterling!
Here's an image of the '28 BB with extractor ...
That's a fine idea for modifying the firing pin on a full-auto Lanchester. Unfortunately most of us in the US can only fool around with semi-auto, closed-bolt guns without the fixed firing pin.
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I would just assume that it is because that's how it was on the MP28-II.
Lots of stuff was that way, just because...
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Originally Posted by
ProLibertate
In looking at all the pictures of original barrels that I can find, on the chamber end, eject side, there is a flat machined. I've been looking at my receiver tube and semi-auto bolt assembly. I juts don't see why there is a flat. There is no feature in the tube that needs be cleared and no feature on my bolt that needs that space either.
Why is the flat there? What am I missing?
There is a feature inside the tube that needs to be cleared. It’s the front sight.
The Lanchester front sight sits in a dovetail that’s cut into the tube. The bottom of the front sight is flat. The flat on the barrel allows it to clear the bottom of the front sight.
Attachment 93743
Last edited by Vincent; 06-02-2018 at 06:36 PM.
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Originally Posted by
Vincent
There is a feature inside the tube that needs to be cleared. It’s the front sight.
Well dang - I went and installed my front sight after the barrel. And now I learn what that flat is for!
Thanks for the information. Off to my shop to drive out the front sight and cut that flat.
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This little gap also caused a bit of a problem when Patchett (and a major part by Bert LIST don't forget...) were formulating the Mk5/L34. High pressure gas venting from the ported barrel was leeching through this gap and into the mechanism. Something you definitely DON'T want!. So they solved this by re-designing the rear barrel stop/support to accommodate a small locator. Now, the Mk5/L34 barrel flat seats/locates on this locator flat which also seals the gap. All a reminder of its Lanchester ancestry.
Another bit of useless Lanchester and Sterling history
Interesting, Peter. I hadn’t thought about gas venting through there.
When they designed the closed-bolt semi-auto guns, they made the blocking bar that prevents a full-auto bolt from being used just low enough to allow the flat on the Mk4 barrel to clear. Do you know why they did that? I don’t think it’s a coincidence.
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Looks like 0.059” from the inside of mag well to barrel breech face.
That's 1.5mm. So, probably taken directly from the MP28.
Last edited by Vincent; 06-03-2018 at 06:30 PM.
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Originally Posted by
Vincent
There is a feature inside the tube that needs to be cleared. It’s the front sight. The Lanchester front sight sits in a dovetail that’s cut into the tube. The bottom of the front sight is flat. The flat on the barrel allows it to clear the bottom of the front sight.
Attachment 93743
Just a bit of an update. I had left the flat off on my build, and have now found that the flat is not needed if the receiver tube is of a reduced inside diameter. The added wall thickness means the bottom of the sight does not protrude into the tube.
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How you gonna modify the trigger?
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The original Lanchester had a modified MP28 fire control mechanism. The tripping lever has a hinged extension that trips the trigger bar for semi-auto fire.
Some pictures here MP28 II Torch Cut Receiver Tube Section with Fire Control Parts, 9mm, *Good* - MP28 II Schmeisser - More - Submachine Guns - Machine Guns
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