I think hes asking why rather than what if.

 

Because that's what the regs say.  The reasoning behind it has to do with the fact that the SGL shooting ranges primarily exist to support the hunting community, and allow hunters to sight in.  In my best Cuomo-esqe voice, "Nobody needs 30 bullets to kill a dee-ah".  So the "only load 3 rounds" is intended to keep the semi-auto crowd (which you can't use to hunt in PA anyway" inconvenienced enough, that they don't want to use an SGL range for just recreational shooting.

Like I said, go closer to dusk

Gotta be careful there...  buddy and I almost got cited for shooting after hours.  Apparently, "sunset" is whenever they decide, regardless of whether or not the big ball of hydrogen is still just above the horizon.  His active duty status bought us just enough good will that we received warnings instead.

the game comish doesnt play or take shit, they have more powers then the PASP.
the three round shit is because the cry baby Fudds back in the day. i use Private land only these days for the  most part.
Susquahanna and Bradford counties on any given weekend.

It's public ranges run by the state game commission They use to be free, now they are free if you have a hunting license.  If not you can buy a permit to use them.

Since the ranges are run by the game commission and paid for with hunting license fees, they are intended to be there as a service for hunters to shoot.  So they instituted the 3 rounds in a magazine at a time to dissuade AR and AK shooters from target practicing, and "shooting up the ranges"   I'm actually surprised they even allow semi-autos at the range, since they are illegal to hunt with in PA.  

Our laws for owning guns are great, but the FUDD runs deep in our hunting laws and Game Commission policies.


ETA:  The official reason is so that people can ask for a cease fire to check/change targets without having to wait for a long string of shooting to finish.