Ruskie- don't worry about others, just go and have a fun time.
I always shoot at Raahauges, and AFAIK there is no rule on what type of gun you can use, the only rules on their website are regarding the ammo you can use.
As a matter of fact, two months ago my buddy (a calgunner) wanted to go along and another calgunner said he had an extra shotgun for him to use. It turned out to be a converted saiga 12 with a skeleton stock, short barrel, and a big muzzle brake.
There was only one person (an old rich white guy) who looked at it and scowled, nobody else cared. My buddy couldn't hit anything with it and ended up borrowing a different gun from another member of our group, and he had a great time.
Just last month, another calgunner went with me- he took the 20" barrel off of his mossberg HD gun and installed the 28" barrel for the first time. It was still a black synthetic pump mossberg, if any of the purists were sneering at it, none of us cared enough to notice. We had a great time and he's hooked and wanting to return next month.
Basically, focus on the target, and shoot it by instinctively pointing the gun. Don't worry about the sights, and ignore all of the other shooters.