(While most readers will know this, on the off-chance someone doesn't)

 

52-calibre refers to the barrel length, so it is slightly more than 1 meter longer than at 45-calibre barrel (155mm x 7 for the difference in length between the two, roughly). All else being equal, this means the propellant has more space and thus more time to combust and for the resulting gas to expand before the projectile leaves the tube, imparting more energy to the projectile, resulting in longer range. (Depending on a variety of factors, you could say an additional 10 to 20km, though I am sure someone will chime in with exact figures for specific projectile/charge combinations.)

 

The disadvantages?  There aren't many, in my opinion, but apparently they are significant enough that the US can't manage to adopt a 52-calibre weapon... or even a 45-calibre one, for that matter (IIRC, both the M109A6 and M777 are 39 calibres, and currently the NLOS-C will be 30).  A longer tube can be more difficult to manuever and transport, it adds a significant amount of weight to the system (since you also need a more robust carriage /mount, recoil system, etc, to cope with the more powerful recoil).  Depending on your design, and what propellant you fire, the tube may wear out and need to be replaced sooner, if you make a habit of firing the higher charges used to attain that extra range (I've read of experimental designs that needed to be replaced after as few as a thousand rounds, which a tube of artillery in a high-tempo war could fire in less than 48 hours).

Chucking a shell further doesn't really help if you can't get it suitably close to the target.

 Thanks for your views.  But could the increase in range in 52 caliber be so significant as to overcome the disadvantages of weight, a longer barrel and difficulty in moving the gun.  how does the 45 caliber gun score on these counts when compared to a 52 caliber 155 mm gun

For the USMC transportation has become a major consideration.  The M198 compensated with vastly more area covered that its predecessors.  Unfortunatly the deck space available has decreased since the 1980s & the deck space & cube requirements for other items also increased.  Doubling the area covered by the cannon  ceases to be helpfull if the weight of metal or ammo available to hit any particular target is significantly reduced.

The much weaker signal from the MVsets we strapped to the barrels could also be usefully detected by the sigintel folks.  At least thats what they claimed, & they had the our locations for MV calibration shots as their evidence.   I'm skeptical they could pick up many of those transmissions, but it wasnt my specialty.  

Elsewhere I've been told any future enemy would not have the smarts to use the radar emissions & other US Forces signals.  We are just too superior.  I suspect most of us here would find that attitude more than a bit arrogant and blatantly stupid. 

It's also harder to maintain accuracy with a long barrel. Longer barrels are more susceptible to bending, differential heating, manufacturing flaws etc.

Ooooh yeah - FK is right - I almost forgot about mechanical wear and "thermal droop".  At least with tank cannon, those factors would cause errors prmarily in the range/elevation, and much less so in deflection.  I assume it is similar for howitzer tubes, which fire much slower shells, although (theoretically, in combat) many, many more rounds in an average 24-hour period than a tank does.

It depends on what ammo you want to fire.  52-cal was designed to be compatible with existing stocks including the shell form agreed in 1963 (basically M549 shape).  Obviously to achieve the full max range it need a new charge as well.

 

45-cal barrels were designed to perform best with S African ammo design.  No serious army is going to put themselves in their hands.  To achieve its range with a shorter barrel may mean hotter burning propellant that increases barrel wear.  The shell is also high streamlined and so has payload space, of course you can use a standard shell but you won't get the best range.  However, a shorter barrel may have other advantages in terms of its tactical utility.

 

It's true that area of influence increases exponentially with range, and range is a good thing.  However, the nature of arty ops is changing, multi-bty concentrations are becoming less necessary due to improved ammo effectiness, rate of fire and dispersion.  Electronic sights are also making guns more mobile because they are much quicker to deploy, this too is having an effect. 

 

For strategic transport weight and volume isn't generally a problem with towed guns, but lane length definitely is (although that's really a special form of volume).

 

The british Army planned to upgrade to a 52 cal gun on thre AS90 which would have offered a significantly increased range, the programe is currently on hold or cancelled -something to do with the propellant not meeting the british requirements not to go bang if the vehicle was hit i believe.

 

More on point the South africans 155mm 52 cal gun is im sure capable of firing in excess of 40 KM in comparison to the 39 cal gun  m109's 20-24KM (ish) Range