Since I mostly shoot a 6mm, I try to clean mine about every ~200-300rds, but I've gone as long as ~500-600rds quite a few times without anything getting wonky (mostly).
I have had my barrel speed up and throw my dope off a couple of times when running it into that 500rds+ range (most likely due to carbon building up), so now I try to stay more on top of it, just more so for keeping my speed/dope from getting wonky, not so much for any sort of accuracy fall-off reasons.
For a larger bore/caliber cartridge like 6.5CM, I'd probably go longer between cleanings.
That said, compared to some around here who're pulling out the abrasives and borescopes: by their standards, my barrel has probably never been clean lol! I just stick to Boretech Eliminator, using patches and nylon bore brush, and I don't spend longer than ~10-15mins cleaning.
The only thing I do that is maybe somewhat out of the norm is half way through cleaning I pull the bore guide, then I use a 10" chamber rod with a nylon chamber brush to get my chamber/throat while I let some of the Boretech marinate in my barrel. This is for peace of mind and/or added comfort that I won't have to go up against the dreaded carbon ring, and helps get any carbon junk out of the receiver/feed-ramp area. I finish the chamber with a chamber mop, pop the bore guide back in, and finish cleaning the barrel. Think I use maybe ~20-25 patches total.
If you don't already have one, I recommend this thing:
Amazon product ASIN B00LCT9WCK
Before a match I usually will clean it... but I also try to send a few downrange if there's a "zero range open" period before the match... it probably doesn't matter, but no reason to be firing foulers on the clock if I don't have to.