Hi all, wow, and thanks for all this info.
Sorry for delay in my reply, work has been keeping me very busy lately.

VAnimrod, thanks. Steve Redgwell's books look great, and very informative. They've made my list of gotta gets.

Rocky, I've no doubt that somebody has probably tried the conversion I've alluded to, but they have been quite secretive about it, as I still can't find any reference to it.

DigitalDan, thanks for checking your reference, looks like another book has made "the list".
You are quite right, the 303-22 and 303-25 are quite well heard of over here,with the 303-25 being quite popular.
A lot of converted SMLE's and M17's turn up for sale with this conversion having been done. They are often quite cheap too.

Lonerider, try doing a search on the web for either 303-25 or 303/25. this is how us Aussies tend to list the cartridge. Make sure your search engine isn't just looking within the USA.Hopefully you find what you are looking for.

To all interested in SMLE's, have you seen a book by Ian Skennerton on the history of the Lee Metford and Lee Enfield rifles. It looks like another good read, and I've been hanging out to get my mitts on a copy.

My main reason for these enquiries is due to me inheriting my late Father-in-laws (miss ya John) SMLE No.1 MkIII*.
I'm a bit loathe to actually do anything major to this rifle, as I'm led to believe that it was John's father (Harold) service rifle. Harold was posted in Papua New Guinea during World War Two. The rifle bears the marks of being "sold out of service" on it's stock. Even if it wasn't Harold's actual service rifle, I'm certain it did belong to him, and was passed down to John when Harold passed away, and has now made it's way to me with John's recent passing.

I have taken it up to the range, and the old girl still functions as intended, but time has taken it's toll, and a past lack of maintenance or hard use means that the barrel is very dark and the crown quite pitted. No amount of scrubbing so far seems to be able to remove the crud from the barrel, and Hoppes #9 through the bore will see the patches come out brown, whilst Sweets 7.62 will have them coming out black.
Hopefull with time, TLC, and probably a re-crowning, I can get some sort of accuracy back out of her. Enough to allow me to shoot the service rifle comps at the range anyway.
Last resort though is to have her re-barrelled, as I think the bore may be a bit oversize (haven't slugged it yet) for competitive use with .311/.312 projectiles. Not that I'm expecting to be a major threat for any wins in the comp, but it would be nice to know that the rifle is at least up to par for the job!
It's all probably a moot point, as in order to shoot service rifle, it probably has to be chambered for the original cartridge.

Sorry for the ramble guys, and thanks once again for your input.

Cheers,
Aussielad.