First of all remember that if you have only 'dry' mounted the gun in a shop, you will NOT mount it in the same way when you actually come to shoot it. Secondly, each and every gun of the same make and model, can all feel different to each other. I went with a newcomer to buy his first gun. Against all my advice, he wanted a new gun. He is left handed and we tried around 5 different guns, all of the same make and model, eventually deciding on a RIGHT handed model, which was the best fit. (although right handed, there was no cast or the stock was dead straight, giving the best eye/rib relationship.).
Whilst shooting yesterday on a 100 bird practice, I was using my new 20 bore, my Grandson was using my 725. At lunch (after 50 targets), I spotted a small red mark on his right cheek, just as you experienced when shooting a similar gun. I felt that as my Grandson has a longer neck than me, he was probably lifting his head in order to see the target. As the gun has an adjustable comb, I raised it by around 3/8". After the next stand, he said it was smacking him a bit. I dropped the comb by 1/8", He went on to straight the next 3 stands without any further problems. He ended up on a 58/100, not bad for his first 100 birder and his first shoot since last September. I was well pleased anyway.
It is ALWAYS worthwhile trying a gun before you buy it, if at all possible, or try to negotiate a full refund towards another gun, if the current gun is unsuitable.
adj comb can be fitted , I think they should be standard on all competition shotguns ! we gain and lose weight , summer/winter clothing . etc .
OR get the stock fitted correctly in the first place. For some people, the adjustable comb is the WORST thing they could possibly have ! :???: