I am on this... I have just been sorting out some mags for projects.
There are several variations that you might encounter in the older rifles. They all can be tweaked to work, but some are more correct to have in a particular rifle. There is an amount of interchangeability between models mags and their components. It can get confusing. Different number designated springs, platforms, cases.
So I will confuse myself again with some nomenclature. I try to keep it simple so that I can understand wot I am trying to say.
These early mags have a model number to the styles, No.1 mag, No.2 mag, 3 & 4. They came along with the evolution of the rifle. Mainly concerning the changing ammo, and provision for charger loading the mag with charger clips.
No.1 case is as used in Long Lee Metfords and Enfields.
No.2 is used in the early Sht.LE.
No.3 case is a conversion to handle Mk.VII (pointy bullet) ammo and is converted from either a No.1 or 2 case. Often found on Charger Loading uprgrades.
No.4 case is new made and is as found in No.1 Mk.III rifle.
The one in your pic on the left has indeed had work done to its feed lips, but at the factory. It is one of the earlier mag cases No.2, reworked with the right stop clip and riveted on left feed lip. It was modified in this way to accept both Mk.VI (round nose) and Mk.VII (pointed) ammo. This conversion mag then becomes a No.3 mag.
No.3 mag would be correct for an early Sht.LE or Charger Loading Lee Enfield/Metford rifle conversion.
The one in your pic on the right is a No.4 mag (No.4 mag case, not same term as a mag for a No.4 rifle) and is correct for 1907 onwards (I think) SMLE rifle.
Look on the cases' spine for the number 3 or 4.
The rivet on the stop clip sticks out a wee bit and will bind in a rifle that does not have clearance made for it in the trigger guard and mag well. So I betcha the one marked '3' was the one you found to be 'sticky'? The rivet was jamin on something up inside.
You mention "I am not sure if it is a genuine No 1 Mk III magazine or a No 4 magazine which has been swapped."
Neither of your mags are designed to fit the No.4 (WWII) rifle, although the No.4 mag case can be made to work with tweaking.
All four versions of the mag had a narrower front face. That is why a No.1 rifle mag will fit in a No.4 rifle, but usually not the other way around. I say usually cos sometimes the darn things will just fit (different contractor variations).
Some No.4 case mags were modified to fit the No.4 rifle to augment supply in WWII. The spine was ground down to produce a single latch the same config as that of the standard No.4 rifle mags.
Not confused yet? Dig this.........No.3 mag takes a No.3 body, No.2 platform, No.1 spring and a No.3 auxilliary spring. No.4 mag takes No.4 body, No.3 platform, No.2 spring and a No.4 auxillary spring....help!
This was a looooong post just to say, you need to fit the one on the right that is marked with a 4 on the spine.





























