As a mechanical engineer, I am curious as to how choke tubes can blow out without, in some cases, at least, shearing off the threads of either the tube or the barrel.
It seems as if the barrel must expand outward enough to permit the tube to pass forward without thread shearing. One way that comes to mind might be substantial pressure leakage into the volume in-between the tube and the barrel around it. This pressure would cause the barrel to expand radially, while the tube would not expand, since it would experience approximately equal internal pressure (as usual) and external pressure due to the leakage. If the barrel expanded enough, radial clearance between the tube and barrel threads could occur. This would allow tube threads to slip past the barrel threads and the tube to blow out.
With information on the thickness of the barrel wall remaining after the threads were cut, tube and barrel thread dimensions, and an estimate of pressure, some simple calculations could determine if my guess as to how, and why, tubes sometimes blow out is reasonable.
If it is, keeping tubes tightly seated to prevent leakage would be particularly important. Without leakage, choke tubes are forced outward against the inner barrel wall, forcing tube and barrel threads firmly into contact and making slippage impossible.
In any of the cases observed, did shearing of the threads permit the blow out to occur? It certainly seems to have not been the case with the Mossberg in which the tube was re-installed and continued to function.
Unfortunately, as with many educated guesses, calculations using some typical dimensions do not seem to support mine. Anyone have any better ideas as to what might be physically happening?
Last edited by vangulil; 05/28/07 11:13 PM.
