www.dcra.ca. Click on the rules button and all in one spot.
You are right, there are no limitations on stock dimensions in the Canadian rules. However, given the use of 76mm in the US rules, some Euro or Commenwealth county must be implementing this. So Canada will likely follow. No new rules on this yet.
Definitely there is no rule from anyone on the width of the buttstock

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On the 223 VS 308 wind drift issue, I think there will be more parity even in the real world as new bullets come out in 22cal.
Up until now, the main market has been service rifles with stubby bullets the norm. Berger, Hornady, JLK are pushing forward with some very nice 80gr. I am sure Sierra and Lapua will follow suit.
There is little reason why 0.46 to 0.49 type 22 cal bullets can't be made if the market is there. Velocity in the 223 are also likely to move up. Almost all development has been for the AR and shorter barrel tactical/varmint rifles.
I see some post where shooters are pushing 75gr Amax to 3150fps accurately in 30" bolt rifles. Now we are getting to a more level playing field with the 308. Maybe even surpassing.
155gr at 2950/3000fps is already 'BR' toasty in a 308 and there will be little room to increase performance. Personally, I have never gotten over 2850fps accurately. Most posts on F class 308 shooters talk about using 175g MK or 178gr Amax at elevated velocities. That will soon change.
There is little doubt the 223 will come to equal if not dominate the F,T/R) class. With its reduced recoil and costs, what better way to attract new shooters and those recoil shy.
Burning 1/2 the powder per bang will also show benefits in the heat of summer and these long relays.
Jerry