You assumed correctly what I meant about "charge 3" (an estimate, but should work with other types, too.) A different sized and shaped rocket nozzle can give different performances with the same amount of fuel, as does an internal combustion engine. So why wouldn't it work with a gun breech/chamber also? About the bagged charges: each of the "pellets" (they don't use powder like in bullets, but rather pre-shaped pieces) in those charges are composed of a certain weight and shape of composition to offer the most ideal performances when the propellant burns. The concept here is to use those same propellant "pieces" (but in bags sized for the 105 breech instead?), but maybe they DO mean using the very same actual bagged charges: but that would require considerably more strength being engineered into the breech area of the gun..

interrested 2, I was looking a little more at the United Defense site and noticed that they claim 30 km range "assisted". I believe that means with a rocket assisted projectile. What little I am understanding of this technology based on some comments I think doggtagg made it would appear that the variable volume thing might have advantages in any sized gun. Maybe it would allow you to get longer ranges and perhaps even allow one to use other propellants in a 155 gun. Not sure why you would want to do that but I'm no artillery expert.

doggtagg, in reading more on the United Defense site they talk about using "modular" charges. Then later I see some reference to them as "MACS" charges which they say are different from bags in that there is not waste. It appears they use some charge that they claim is fielded but it is not a bag charge. Anyone know what this is?

I had some thought about the "odd" marketing idea. Just like other companies perhaps UDLP is making a big deal out of using existing propellant because perhaps current 105 cannons or something another company is offering does not. Does anyone know if there are currently 105mm in the field and what kind of propellant they shoot. Also, anyone know if another company is marketing a cannon that does not shoot existing propellant. The UDLP web site talks about there not being a need to develop new propellant with their system which leads me to believe someone elses cannon required new propellant.

the UK's M118/M119 field gun, and the french 105 LG1 are in service, as is older model US types and Italian pack howitzers with second- and third-world nations. Several countries also deploy 105mm SPGs. Few of these use fixed ammo (propellant case and shell in "one piece"), many do use the bagged charges. And I do agree that UDLP's concept may just be all marketing scheme... I would suggest emailing the company rep and asking his/her input on the subject. The MACS propellant system can be checked out over at ATK: http://www.atk.com/ProductSheets/Category/PropellantsandEnergetics/2012797.htm It was, for a time, suggested for the Crusader SPG, and would have incorporated a laser ignition system. It may be possible to design the 105mm gun to use a chamber designed to hold these same charges. Perhaps UDLP's "variable volume chamber" is a marketing scheme to sell a gun system that can be rapidly configured to use either MACS or bagged charges? Try asking them: the worst that happens is they say no..

The main advantage of this over semi-fixed or cased rounds is the ability for one gun to do a TOT barrage. This is where the first shot is loaded w/ the maximum # of bags and fired at a high trajectory (Think hang time) and subsequent shots use less powder and lower trajectories, resulting in all rounds landing at the same time and the point - guarranteed to mes up the bad guys day. This is old school arty pratice. A good crew of gunbunnies can do this w/ towed or SP arty, as long as it uses separate charges. McDuck

mcduck, Very interesting concept. Sounds scary if your onthe wrong end of that. This for sure should be able to be done with any artillery that has more than one muzzle velocity made available by the number of bags used. So what would be the advantage with a variable volume gun? Perhaps as someone said earlier they can get even more variations on velocity by changing not just the amount of powder but also the volume. That would allow for more possible combinations of velocity and gun elevation to hit a target and thus more possibility to do this TOT thing. I wonder what value this variable volume would be to propellant designers. Any of you guys into that end of things and see any value as a laboratory gun?

The variable volume concept minimizes headspace. That is the volume between the charge and projectile. Minimizing headspace improves muzzle velocity uniformity and accuracy. McDuck