Why the fad for 25mm grenades?

They lack the HE capacity of 40mm grenades in the UBGL role, while in the direct fire support role they lack the large beating zone of a 7.62mm GPMG, while they lack the long range flat trajectory of the .50 cal HMG.

Why the fad?

Because that's what the US Army dictated the OCSW Objective Crew Served Weapon was going to be.

Sure beats me why they didn't opt for improving on the 40mm versions.

My guess is they wanted something with a higher muzzle velocity that didn't rely on lobbing its shells to maximum ranges, wasn't as susceptible to high cross winds,

something that could incorporate a built-in fire control computer that could lase distances to targets and program a round to detonate near enough where intended yet not be so heavy and cumbersome between the gun and its ammo that it took 3+ men to carry it all around.

 

So in the end, this is what we (US Army) look to be getting, the XM307/XM312 convertible machine gun, adaptable to fire the 25mm grenades or 12.7mm bullets.

 

http://youtube.com/watch?v=U4_pnRM_UCI (Yes, it's a cheesy YouTube video, taken from that show Future Weapons)

 

 

 

...and anytime you see pics of the various FCS vehicles, they most often have the 307/312 in some manner of RWS/pintle mount up top acting as secondary weapon.

 

 

 

 

  However it doesn't look like a replacement for UGL's, GPMG's or .50 cals to me.

I kind of agree there.
In some instances, weight of shot (lead or HE) downrange in a given time is what determines kill power.

The OCSW's 250 rpm as either 25mm or 50 cal almost pales in comparison to the Mk 19's 375 or so rpm, and the 50 cal's 450 or whatever rpm.
But I guess more people in the Army's procurement departments are towing the party line more to the fact that fewer but more precise (better aimed) rounds are better in enough situations rather than higher rates of fire which have a greater downrange dispersal pattern.

 

Does a few well-aimed fuzed 25mm rounds equate to greater anti personnel potential than a few 40mm grenades which scatter around the intended target?

Or do half a dozen 25mm High Explosive Armor Piercing rounds, better placed due to their flatter trajectories, give a better anti-armor (or anti materiel) perfomance than half a dozen 40mm HEDP grenades?

Does the 25mm have enough future growth potential (lethality improvements), or is its smallish caliber destined to make it more or less a one trick pony?

starting a grenade launcher thread