Tank Guns – The Bulge

Among things I didn’t know but kind of suspected was, ‘what purpose does the funny bulge in tank barrels serve?’

I figured it had to do something with the gases during firing but I didn’t know if it was some sort of “accelerator” that created a back pressure the recoil system needed or if it wasn’t gas related at all and had something to do with barrel harmonics, ease of maintenance, or some other such item.

Turns out guess one, gas system, was right on the mark. But my meandering thoughts that it was an accelerator that helped the recoil mechanism in some way was far more complicated a thought than the actual purpose.

Bore Evacuator

Cool title. What does it do?

Creates a pocket of slightly lower pressure behind the gun’s round so that it pulls the gases out of the barrel instead of dumping them into the turret. I’m sure some of you reading this have been ‘gassed’ by rapid firing a rifle or machine gun where the air wasn’t taking the expelled gases away quick enough and you got a facefull, especially on a suppressed gun that doesn’t use a flow through system like an OSS. Now imagine that with a round the size of a tank and the chamber is in the enclosed with you just scant inches from the chamber…

Yep, lovely. So in turrets where the gas would harm personnel or machinery they add the bore evacuator which creates that slightly lower pressure behind the round and helps pull the gases out instead of having them linger in the barrel and clear equally at the muzzle and into the turret.

Guns like the M777 155mm field artillery piece have no need for it because they’re an open air system. The gases have plenty of space to vent and not choke their personnel. On mobile systems that don’t have them, the turrets are either unmanned or the pressure generated by the cannon doesn’t expel into the compartment in enough volume to matter. On any system that you can avoid using them, it is best to do so. Just like adding a suppressor to the end of a rifle barrel increases and alters maintenance requirements, adding a bore evacuator makes the gun barrels more complex and maintenance intensive.

And now that we’re down the tank rabbit hole.

Big thanks to Scottish Koala for producing content to entertain us while we’re still in quarantine and avoiding murder hornets.

Keith Finch
Keith is the Editor-in-Chief of GAT Marketing Group editor@gatdaily.com A USMC Infantry Veteran and Small Arms and Artillery Technician, Keith covers the evolving training and technology from across the shooting industry. A Certified Instructor since 2009 he has taught concealed weapons courses in the West Michigan area in the years since and continues to pursue training and teaching opportunities as they arise.