Barrel threads for MKlll No1

[d43p]

Need help with rebarreling a MH. Putting a MKlll barrel on and need to know the threads per inch so I caan time it. Also, will a reamer cut the rim and case, or do I have to rebate the barrel first?

[Multigunner]

First off the Enfields used a "Whitworth thread" rounded at top and bottom.
Threads are 14 TPI.
Shank is .687 long
Threaded portion of Shank is .997 Dia.
The SMLE barrel has a relief cut around the breech end .10 long and diameter reduced there to .90.

So far every No.4 barrel I've examined had the threads off set by nearly half a rotation from those of the SMLE.
A No.4 barrel can be fitted to a SMLE action, but so far as I can tell requires some careful hand fitting ( removing metal from breech and shoulder areas)and would require cleaning up the chamber with a finishing reamer.

The case headspaces directly on the rim to breech interface, theres no counter sink.

The rimmed case means the headspace is controlled by just how well the barrel fits into the receiver ring, and the length of the bolt from locking lugs to bolt face.
The detachable threaded bolt heads were hand ground to achieve the proper headspace.
To some extent wear could be rectified by replacing the bolthead with one that was longer from the shoulder of its shank to the bolt face.

Bolt heads for the No.4 rifles were numbered. Size 0 being the shortest and size 3 being the longest.
SMLE boltheads were not numbered. Bolt heads taken from previously repaired or scrapped rifles were kept in the armorers parts bins and used whenever possible in rectifying headspace of rifles brought in for repair.
An un issued replacement SMLE bolthead that had not previously been fitted to another rifle would have a small S stamped on it.

[jmh54738]

The Whitworth thread also has a 55 degree included angle.

[Multigunner]

I hadn't commented on the MH by which I expect he means a Martini Henry action.

Barrel shank is a bit different but an SMLE barrel might be altered to fit, though it will take some work.
Shank of the Martini Henry and Martini Enfield is .70 long. Outside OD of threads is 1" even, so an SMLE shank may be a hair loose.
Threads are 14 TPI.

The machinist drawings I have don't show the counter sink for the rim, you'd have to check the old barrel if you still have it to cut the extractor opening properly.

I'd suggest sleeving the old barrel shank, and would also suggest a less powerful cartridge.
The Martini Enfields were in use when the BP cartridge was still in use, and while probably strong enough for the Smokeless .303 up to the MkVI ( I don't know if they were ever proofed for the MkVII) many of those Martini actioned rifles, if in carbine form at least,were used with a reduced power Carbine load.
Don't know that much about these, but they are a Black Powder era design, and probably should be used with BP level pressures.