Any shot is safe providing your fuel and Nitrous system is high quality and working properly. When you say "safe" I can only summize that you are reffering to the bottom end. There are plenty of l owners running a 4 lb pulley with 150 shot and have no adverse effects. Frankly I am a big fan of the 100 shot and the 75 shot.I have a brother in Virginia who runs a 4 lb pulley with a 150 shot and the truck has no problems in the last 16,000 miles.Some engines cannot handle it while a majority can. My personal suggestion if your concerned is to go with a 75 shot or 100. But you decide .BTW, I am an NX dealer and I have discussed this in detail with the engineers at NX.Just my .02.