More then anything 7 1/2 shot is fine since most shoot 8s for normal trap shooting. So you are already throwing a little larger shot. Some use 7 1/2s depending what their gun likes. BUT, many shooters are using a Improved modified choke maybe a full choke for normal trap shooting. Let's consider, on a trap range the closest shooting positions are 16 yards behind the trap house. OK, got it ? So if you are REAL quick add another 15 yards so right there is 31 yards, right ? So shooters at the back end of the trap field are shooting from 27 yards behind the trap house. Just any normal trap field, so being REAL quick add that 15 yards, and now those targets are being broken at 42 yards. See ? And that is nothing the least bit unusual.
At many clubs, when you enter one of the games for money, ties are broken by stepping out to areas another 10 yards or more behind the normal firing range on the trap field. It is not unusual to fire another entire box of shells from that distance before breaking the tie, and your opponents have each missed one. So that would be at least 52 yards. NO problem with clay targets. BUT, you can be certain, first those are NOT out of the box field guns, they are in the least a specially made Trap Guns. In the extreme, a highly modified, specially made Trap Gun.
So, at the greater distance, be certain to use a FULL choke. AND be sure to break the target as it is rising, not when it begins to fall from the high point of it's trajectory. 30-40 yards is no problem absolutely doable. And no 3" shells may well blow the pattern, and produce holes in the pattern you could throw your hat through. The modified choke is your problem, you are likely hitting several more targets then just the ones that break, because they are only getting hit with a few pellets, and only getting dusted. Stick a full choke in and that will change everything.