To add to the discussion, if this were a modern day setting it would be much more likely to have a pistol or revolver than a sawed-off shot gun. If it is a pistol gripped double barrel like you see in the movies, it is going to be hard to conceal. If it is a warmer climate even harder to conceal. I live in FL and when I carry sometimes I only carry a very small semi auto (kel-tec p32) my glock 30 is much harder to conceal in summer clothes and I have a medium build. Even harder if you are thin. (.32 compared to a .45) If your a big guy it is easier to conceal a larger sidearm. A sawed-off shot gun is going to be hard to conceal in anything other than a trench coat.
Not sure how CoC handles firearms, never played it, but the effective range is going to be very short and accuracy is a joke. I do IDPA and it is hard enough to hit stationary targets at upto 50 yards with a semiauto pistol. If you want to nix him do it on range, reload time, rounds (2 rounds in the example) gun vs 15 for a Glock 17 9mm (30 round magaznes are available but are long, you can see them in T3 and Transporter 2 in full auto glock 18's) or 13 in a Glock 21 (.45) or 8 in a Colt (1911 .45) (Punisher Movie). Or even 5-7 rounds in a revolver, you can load fast with speed loaders but they are bulky. Even with a revolver or small auto you will have 6 shots to the sawed off's 2. And a longer effective range.
You can also nix him in ammo choice. If he is using birdshot it will do nothing but piss someone off past a foot or two IT DOES NOT PENETRATE. Buck shot will do better (8-9 .30 calliber balls) but the veliocity will be much less for such a short gun. The shot shells are designed to burn in 18-24 inches of barrel and lots of the powder will just blow out the end and not make the projectile get upto normal speed. Plus the muzzle flash will be significant and could blind you like a flash bulb for a short time if it is dark. If you want to see how wimpy birdshot is for self defense see this link:
http://www.theboxotruth.com/docs/bot3.htm There are lots of other real world tests on here as well.
And for a final nix if this is present day USA that this CoC took place in sawed off shotguns are illegal in most states. For shotguns under 26 inches over all and a barrel under 18 inches you have to have a federal tax stamp for $200. To get it you have to get fingerprinted, get the chief law enforcement officer to sign off on your paperwork, submit it to the ATF and wait 2-6 months for approval, and background check. Then you can purchase said shotgun which will run at least $600 not including the tax whereas a mossberg 500 with pistol grip 8 shot pump action with 18" barrel will run $250.
You can bypass this process by just taking a hacksaw and going to town. If you are caught with such a firearm you will have a nice stay at Club Fed simply for possesion. It is looked at as a criminals tool not a self defense item, let alone being a sub-par firearm. I don't recall what the exact penalties are but it is significant. More anti self defense states have even stiffer penalties, with minimum sentences. In NY for instance I think it is 5 years minimum state charges and then federal. This law was not enforced much until after the 60's, and rarely enforced before that. But is aggressively enforced now.
In regards to carrying in church, if I went to church I would (agnostic). There are a number of cases where a psycho went into a church and started mowing people down. There is a real good chance that most people are unarmed there so it is a target rich enviornment with little chance of opposition till the cops show up. You can trust the police, I trust my glock and the hours I put in at the range. So for the same reason I have life insurance I carry a sidearm for protection. If your morals take a differant path that is your choice you are welcome to it. But there are lots of fine people who carry firearms in church and you will never know it, these are moral upstanding people who have had background checks, and passed various test issued by the state to get a permit. If they carry you KNOW they are not a felon, have no abuse/battery charges, do not have a restraining order on them etc. They have to pass the background checks be finger printed and pass competency tests. What do you know about the other church goers?
So if you want to nix it you have clothing and concealment issues related to body size, climate and dress. Laws, and effectiveness of the firearm. I'll take my 10-13 rounds of .45 over 2 rounds of 00 buckshot any day. So there are ALOT of ways to nix this issue if you so desire. If you have firearm questions feel free to email or IM me and I can answer them