Enfield 7.62x39 barrel

Awhile back, I bought a barrel labeled "Enfield sporter" online, sight unseen, thinking it would be nice to have a spare and that it was a shortened 303 that had been taken off a No 4. When it got to me it turned out to be something completely different. It has no markings and uses a Savage style barrel nut for attachment and headspacing, but it does thread into a No 4 receiver with no problems. It's not 303 though - after some testing with different headspace gauges, it appears to be 7.62x39.

I'd love to actually use this on a rifle, even if it's only a single shot with no magazine. I know No 1 and No 4 barrels can thread onto either receiver, although there are some minor differences in the threads. The front sight on this barrel ends up at 2:00 when properly headspaced in the No 4 receiver that I have. Is there any way to tell if this was meant for a No 1 or a No 4 or doesn't it matter?

Attachment 95421

Careful with those threads.

Both No1 and No4 barrels have the same pitch; 14 TPI, but have very different thread forms.

No4s are pretty much pure "Whitworth" (55 degree) form, whereas No1 (and earlier) breech threads are "Enfield Special" form, 49 degrees 40 minutes, with radiused roots and crests like a BA thread form. Full spec of a No1 thread is:

Outside Dia. .99555" (Dia. across radiused crests)
Root Dia. .9024"
Eff. Dia. .9574"
Pitch .0714"
TPI 14
Angle 49deg 40min
Crest radius .01411"
Root radius .00804"

One of these days I will stuff that data into AutoCad or similar and see if the numbers actually work to five decimal places like it shows on parts of the original paper drawings.

If you want to try a magazine version, have a close look at either Mini-30 mags, or the odd "single-stack" mags that came with the strange "compliance" AK sporters a decade or so back. They appear to have been made in both 5 and 10 round capacity. The trick is to use a mag that seats close to the chamber and is narrow enough to not require machining out of the sides of the receiver / body magazine well, especially at the thin, forward section.

Reliable extraction and ejection are the next challenges.

Didn't AIA make, or at least plan to make, modernized Enfields in various calibres including 7.62*39? If they actually did it before things went bush I wonder if they kept the threads the same as the Enfields they were replicating. Or this could just be some custom request someone had for a barrel maker. Interesting piece anyway.

Think its from Special Interest Arms, they did the .45 ACP conversions after Rhineland arms and were producing a 7.62x 39 kits too, but don't recall the savage type locking ring on the 7.62.

SIA was my guess as well since I'm in the US and I don't think any random AIA parts made it over here. I've seen the SIA kits on both No 4 and No 1 actions, although not with that specific locking ring. That's mostly what I'm wondering - can I use the No 4 receiver I have or go hunting for a No 1?

They will go into either. I know the threads are not the same, but that is an SIA barrel, and it will go into no1 or a no4 without a drama. With that breeching collar it’s meant for no4.
If you get in touch with SIA, Richard might be nice enough to send you modified bolt head and ejector to suit too, for a very reasonable cost.