just take whatever lenght of the barrel of 9/16" brass, and stick a 2-3 inch piece of 17/32" brass in the back. The tighter brass at the back of the barrel keeps the dart in, while pressure builds up behind it. when enough pressure builds up...Bam!
just epoxy it back together wrapped in E-tape for 4 days. then use a small metal rod to enforce the plunger, thats what i did, and its almost perfect, just a little more heavy