I can only echo Ryans comments.
Predominately the top Service Rifle Shooters in the country where CF members using C7A1 rifles.
I've won the 300m and 500m deliberate with a 16" and 14.5" barreled carbine (respectively on different years) using a TA31 and TA01NSN ACOG (respectively).
To shoot Cdn Service Rifle - all you need is a service type rifle.
Since in Canada you can monopod your rifle usign the mag - do it -- it gives and additional point of contact - and common sense shows us that that will make your position more stable.
I will agree with Scott that pressure on the bolt carrier can alter the way the bolt locks up -- but the changes are miniscule compared to the benifits.
You cannot rest the mag in the US (either HighPower or LEG matches for DR) [and as some here can attest - they get really pissy at Kevin when they catch him

- I was using a M4A1 at 600m what the hell did they want - still got DR ]
Service Rifle is not benchrest -- its a mix of things --- I dont think it is as relative to cbt shooting as it could be -- but it does a decent job of teaching an intro to shooting - as people learn mirage, wind and external ballistics -- its a good building block for future sniper candidates.
1:7 pretty much the only barrel I use these days -- it has been proven that they are just as accurate with 55gr as a 1:9 -- and you can use the 75/77gr gr bullets as well -- which anyone who has shot 400,500 with 55gr can attest that the heavier rounds are much better at that distance.
I've shot Service Rifle from back when I was issued a FN C1A1, I've shot it with 14.5, 16", 18", 20" and even a suppressed rifle.
Ryan is a better shooter than I.