Early magazine

[RCS]

I believe this is the second variation magazine case (left side in photos) and used in the Mark 1* and
any other magazine Lee Enfield with sights for the Mark VI cartridge. Are these magazines common
to find ?464544645546456

[Sunray]

What you have is a No. 4 Rifle mag with one locking lug on the left. And a No. 1 Rifle(the SMLE) with 2 lugs on the right. Neither has anything whatever to do with the cartridge used in 'em. Nor is there a 'variation' involved.
A No. 4 mag can be used in a No. 1 Rifle, but not the reverse without grinding off the lower lug.
They're fairly easy to come by, but usually not cheap. Gunparts, for example, wants $54.75 each for an original No. 1 Mag. Aftermarket No. 1 mags run $43.75 each but are on sale at $220. Same $54.75 for a No. 4 mag(also used in the No. 5 Rifle) but are currently on sale at $39.99 and are new aftermarket mags. Both are less money at Sarcoinc. No. 1 mags are on sale there at $29.95. $40 for a No. 4 mag.
No idea why they say they're manufactured by "SMLE". Or why they list the No. 4 under SMLE. Been yelling at em for years about that. A No. 4 Rifle is not an SMLE.

[RCS]

I should have posted on milsurps !