A tube gun is a barreled action that is fit into a solid tube that completely supports the action.  From what I have seen, they don't seem to have as many weak points like a typical bolt rifle.  The tube gun only has one joint where the barrel is threaded into the receiver,  unlike conventional bolt guns that have recoil lugs, non-symetrical holes drilled, cutouts etc.  Other than one joint, inside the whole setup is a fully supported, high-strength tube.  Another advantage of the tube gun is that it is very easy to make a switch barrel system with minimal tools or skills to switch out barrels.  In less than 5 minutes you can go from a 300WSM to a 22-250 by switching the barrel and putting a different bolt in. This makes it a very versatile system.

Coming Soon is the Elisio Tube gun that I am excited to show.

Below:

MAK Tube Gun: 26" ABS Satern 5R barrel chambered in 6.5 creedmoor, .700 fluted PTG bolt with Sako Extractor, speedlock firing pin with a timney tactical trigger set at 12oz, AICS 10 round magazine, completely blueprinted Rem 700 receiver with a .703 raceway, Seekins 30mm rings with an 8x32x56 Nightforce NPR-2 benchrest scope, fully adjustable Magpul stock with hogue grip.  

This rifle was broke in by fire/clean for the first 15 rounds removing all copper traces each time.  Upon the break in, I fired the middle group then completely cleaned the rifle.  The bottom target was the second 5 shot group to be printed out of the rifle, then completely cleaned.  The last group I fired consisted of a fouling round, then a 3 shot group.  I don't have load data for these targets just some info as follows.  These 3 different loads consisted of Hornady brass (match prepped), 130 gr Berger VLD's and 39, 39.5 and 40 grains of RL-17.  I forgot my tripod, so I couldn't chronograph these loads to get any data.  I completely pulled this load out of the air, but there were no signs of pressure.  These were seated at different depths, but I think with a little time you could get a load to do what you want.