<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by mcook
[br]...The 6" screw caps are schedule 40. The manufacturer is Spears... If you go to there website, you can review the specs of all their pipe and fittings....Believe me, those caps are heavy<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Yes, that type of cap is heavy. After a quick look at the spears website, I found that their 6" sch40 caps weigh 1.5 lbs for a female plug (FIPT) and 1.7 lbs for a male (MIPT) plug.
If, as you say, you were able to hurl these heavy endcaps across a street at high velocity, then I have no doubt they could easily crash through a window and a layer of drywall. Heavy plus fast often equals damage.
On the other hand, everyone (myself included) seems to agree with the part where you say...<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">There was a loose rag in the barrel opening. This would have been the path of least resistance.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

My final 2 questions:
1. what were the barrel dimensions?
2. How many times did you fire this launcher before the "accident"?
If your story is true and complete, then one explanation I could potentially accept would involve the barrel being too restrictive for the massive chamber volume of >61 liters. However, even if flow were choked by a small diameter barrel, this possibility still seems unlikely considering the pressure expected from combustion. I wonder if you could be leaving out some other key detail, like oxygen enrichment, launching before the solvent welds have fully cured, etc.