OK, I own one, and before that a “normal” 243, the WSSM is giving me about 150fps more than the standard 243 Win’ with 100gn bullets, as already been highlighted this gives similar performance to a 243AI or a 6mm Remington.
The WSSM case is massively constructed, and needs some handloading tricks to get the best from it, because the necks are so thick this c leads to inconsistent neck tension with the potential for accuracy issues, this can be over come in two ways; the easy one and the expensive one. The easy one is to use a Lee neck crimp, see posts else were, (the method I use) or you can have a your barrel rechambered for a tight neck chamber, this would mean that you have to turn all your necks down to about 0.015” thickness.
The standard US brass, Winchester, seems to be quite hard and brittle, to get a reasonable amount of reloads from this brass it is wise to anneal it after a couple of reloads else you will start to get split necks. If you are running loads away from the max’ pressure you will get sooted necks, this is because the thick brass is not expanding fully in the chamber, so you really have to push them bullets on a bit.
Because of the short fat case some rifle owner have reported feeding problems from the magazines, although I have not had any issues from my Browning but the bolt operation does fell more “cluncky” with this cartridge than a longer 308 or 30-06 biased cartridge.
There are a couple of small advantages with the WSSM over a standard 243, you can run 2 to 3 inches less barrel and still remain big deer legal, also the WSSM rifle actions are normally based on a 223 length action/mini Mauser. So you can build the ultimate compact rifle on this case. Despite what Muir’s says the WSSM has found a niche in the USA, a couple of companies are building “new upper receivers” for M16/AR15 rifles that use a standard WSSM or a wildcat with the WSSM case being necked up to 6.5/7mm or 30 cal’ this allows a AR15 based rifle to have a ballistically superior cartridge than the bigger and heavier AR10. The bigger 7mm WSM is the one cartridge to have in F class at the minute.
Although my own 243 WSSM shots 5/8” groups from a skinny stalking barrel and has been very effective on everything from roe kids to red stags it is hard to recommend the cartridge to a beginner, if the rifle in that calibre is very cheap or a model that you really want for some reason then now you know what you are letting yourself in for, if you are just looking to build a fast 6mm then a 243AI would be a lot easier way forward.
ATB
Tahr