303 to 7.62 mag conversions.
You can try and get a spare mag, they come up occasionally, but are getting rarer by the minute. If you end up with a choice (very unlikely) go for the Stirling mag, it is the best.
One conversion done here by a guy in Queensland is an inner straight stack mag contained within the original mag. Holds 5 rounds in a vertical column. Utilises the standard spring. works ok, straight line feeding. I have never seen one and have gone down this route a few times, but sold off the rifles each time because it got too hard.
I recently bought a Lithgow 7.62 conversion which was absolutely mint. It is very rare apparently and my friend who owns a gunshop here started offering huge sums of money for it. I will be able to but a new MK10 7.62 and still walk away with a $1000 or there abouts. Gotta get a win sometimes.
I forgot to mention there are a lot of 7.62 conversions around and as they were used for single shot long range shooting did not benefit from the mag conversion. The old mag was left in place to fill up the hole.
Mick.