As an RSO I have seen lots of folks show up with brand new guns just out of the box that have never even seen light of day since the store. While some may run OK, it is more likely the case that it will have some of the typical break-in woes of any firearm. You don't want to have those when you are trying to shoot for score. Also, many people who bring these new guns have never shot THAT TYPE of gun before. For example, they only have shot revolvers and now bought a Semi Auto so they can qualify to carry both. Or, they own a DA only gun with trigger safety, but bring their brand new gun to show off and shoot and have no idea that how the external safety works. These are bad combinations to try and deal with when you are under the timer.
Just as bad is having a supposedly good quality firearm that has been poorly maintained or shot to death. We actually had one class where a student brought a little Browning BDA 380 (Beretta 84BB) and when they racked the slide and it slid forward, the slide went flying about half-way to the target and the other internal parts fell onto the table.
So, to reinforce, make sure to take a good quality, well maintained firearm that you are familiar with and know operates well for you and you should have no problems if you can hit the target with it.
