piercing problems

[fab3]

The machine is an old 1500 watt mazak laser path. Recently when cutting .25 mild steel I encounter problems piercing. The machine pierces through just fine within the time designated but when it switches over to cutting power the material blows out so bad that any small holes are out of the question. All thinner materials pierce and cut fine so I am puzzled. Any help is appreciated

 

[Foostrap]

Sometimes if the diameter of the piercing hole is too small, you won't have enough room to evacuate the material when the cut starts, and you'll have a blow off (kind of like pouring too much water in a funnel that is too small; the water overflows). So, if you can do so, add a little circle after the piercing, to increase the piercing diameter (0.050" for example).
Other reason could be the material getting too hot. Maybe try to separate pierce as a test, to see if that helps. If it helps, and you don't want to separate pierce, then try to lower the power for your lead-in.