Headspace, friend, is the single biggest (and most misunderstood) bugaboo you can think of regarding Lee-Enfield rifles.

For one thing, the .303 is a RIMMED cartridge and the rules are completely different. The big threat regading headspace is with RIMLESS cartridges because it is possible for the cartridge to go too far forward, be fired, expand in the chamber and then the base move backwards, pulling the casing in two and allowing massive amounts of gas to blast back in your face. With RIMMED cartridge this is not possible, simply because the RIM stops the casing from going too far forward. Oh, you might have a BIT of excess space and you might even crack off the odd casing, but this is very seldom dangerous; most of the time it is a nuisance (and expensive, which is why I'm fairly careful) but it is not the "lurking killer in disguise" that it has been made out to be. For more information, there is an excellent article right on this forum, called HEADSPACING 101, which sets it all out.

Military specifications for the SMLE Mark III and Mark III* are as follows:
Minimum: .064"
Maximum: .074"
There is also a FIELD gauge at .070"; if the rifle will accept this one, it is time to go to the Armourer..... and there are at least FOUR of these gentlemen on this forum as regulars. They know MUCH more than I do.

Military AMMUNITION was held as close as possible to the maximum .063" rim thickness. This is where you could find problems; I have seen and measured commercial ammunition with rims MUCH thinner than this. If you are shooting ammo with .050" rims, then you are trying to work with an EXTRA .013" of effective headspace with every cartridge.

You are in Detroit. Last time I was in Detroit, it was just across the bridge from Windsor and I don't think they have moved it. The BEST single brass I have ever encountered for handloading is the Canadianicon Defence Industries brass from the 1942 - 1945 period. Headstamp was just "DI 19XX Z". It was noncorrosive/nonmercuric primed, it takes standard American primers and it was amazingly consistent: every specimen I have measured over the years has been either right on .063" rim thickness, or so close to it as makes no difference. In my opinion, it is the best reloading brass ever made. That said, it IS getting a bit long in the tooth, but it responds very well to a mild annealing. I have one box of this stuff that has been through one of my rifles (a Ross) 15 times and still does not need trimming..... but that is in a very tight rifle, mild loads and LUBING the INSIDES of the necks. But this brass is out there and quite likely there is an adequate supply just on the other side of that big bridge from you. Likely somebody will be willing to hep out; sorry, but I'm just over 1,000 miles away!

BTW, my load for the SMLE is with this brass, any good primer, 37 to 38 grains of IMR-4895 (depending on what the rifle wants) and a Sierra 180 Pro-Hunter flatbase bullet seated out to the OAL of a Mark VII Ball round. Enfield rifling always responds best to flatbase bullets. This is a fairly mild load but it is very accurate in my rifles.

London Small Arms (LSACo) was actualy a co-operative effort among all the "best" London gunmakers and their rifles were excellent quality. They were also only FIVE percent of the rifles made during the First World War and the company made NONE during the Second World War. They are NOT common.

Now that you are on here, you can download a MANUAL for your rifle and a bunch of the technical articles; there is a whole LIBRARY here and it's all free!

Your rifle should be able to shoot into a 3-inch circle at 100 yards, possibly even less. I hav a couple here which will shoot into ONE inch. If the rifle doesn't shoot this well, you have a problem..... so you come back on here and somebody will help. If your rifle shoots wildly erratically, or if it suddenly starts to shoot wildly erratically, the problem likely is what the old-time Imperial match types called "The Damned Crack": a crack in the fore-end of the rifle, just ahead of the butt-socket strap. This can be repaired with Acra-Glas and accuracy will be restored to an amazing degree.

By the way, I notice that ths is your first post. Welcome aboard! It's a fun ride and the more the merrier!

Download some manuals and articles, read carefuly... and come back again.

BTW, I am sure that some of the guys would really like to see photos of a good London rifle.

Hope this helps.
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