This may be a bit late but here is a link regarding the confusion on thermal expansion.
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html#c2
An Aluminum 7075-T6 tube is fired from a gun with a mass on the front end. Total weight is 10.132 lbs. Yield stress (compressive) taken from MIL-HDBK-5H is 68 kpsi. The peak acceleration is about 18,000 g's.
Here are the specs.
Tube
dinner= 2.225 in.
douter= 2.736 in.
length = 16.55 in
Gun...