gatnerd said:

I think incremental improvement absolutely would have prevented OICW/XM29. Namely as starting with 40mm as the first increment would have likely prevented the pursuit of 20-25mm...

I agree it would likely have prevented 20-25mm ammo, but I doubt it would have prevented OICW. 

I think it would just have resulted in the OICW HE component being developed for 40mm ammo.

gatnerd said:

Likewise, incremental experience with early giant FCU's paired with a M16/M4+M203 would have likely disabused any fantasy of a semi auto grenade launcher+assault rifle+fcu combo...

I agree.  I think that a 40mm/5.56mm XM29 combo weapon would certainly have been dropped, and superseded by something like the XM25 in 40mm.

gatnerd said:

Incrementally, if the FCU and AB were really nice, it also could have negated the pursuit of a multi shot grenade launcher, as the FCU+AB shell may have been found effective enough to not warrant a dedicated large launcher. 

I very much doubt that.  The OICW concept was formed primarily for HIC.  Planning for operations against (near) peer opponents, I think the Army would have considered a multi-shot, semi-auto weapon necessary even in 40mm caliber.

gatnerd said:

Kind of further supporting this, after OICW/XM29 failed, we saw private industry basically replicate steps 1-6 on their own via incremental improvement. First a FCU for the MK47, then STK and Rheinmetall developing AB 40x53 and their own FCU's, then development of 40x51MV and 40X46ER with pre-fragmented casings, and now here we are with SSW as the dedicated multi shot 40x51mm ab launcher.

Yup.  Give the SSW the XM25's FCU and we'll be right where would've been had the OICW been developed in 40mm.

gatnerd said:

How would the shape of 40mm be improved for subsonic aerodynamics?

Like was done with 25mm?

Refleks said:

A decent intermediate step would have been giving up fantasies of taking out BRDM and BMP with your blooper and replaced the LV HEDP with  40mm MV firing bounding HE...

How much more effective is bounding HE versus HEDP? 

Way back at the beginning, the Army fielded bounding HE.

YouTube

M79 40mm Grenade Launcher

The M79 grenade launcher is a single-shot, shoulder-fired, break-action grenade launcher which fires a 40x46mm grenade which used what the US Army called the...

The other way 'round.  More like an extended teardrop shape with the round part aiming foreword.  A long, gently tapered ogive mainly helps with supersonic projectiles.

stancrist said:

I very much doubt that.  The OICW concept was formed primarily for HIC.  Planning for operations against (near) peer opponents, I think the Army would have considered a multi-shot, semi-auto weapon necessary even in 40mm caliber

Thats possible.

The other option for HIC would be a 'OICW Lite' similar to FN's concept with the F2000 + Smart Grenade launcher, where 'volume of fire' is achieved by having all the riflemen in the squad issued an OICW. 

Its now possible to make an "OICW Lite" thats slightly lighter then the proposed NGSW Rifle once accessories are factored in:

Thales F90 MBR 16” w/ SL40 Grenade launcher = 9.44lbs 

Multi Ray 800 FCU= 1.54lbs

ACOG TA33+RMR+Mount = 0.875lbs

= 11.86lbs

Whether this is a validation of the OICW Lite concept, or an alarming note on the weight of the NGSW, is hard to say. 

gatnerd said:

The other option for HIC would be a 'OICW Lite' similar to FN's concept with the F2000 + Smart Grenade launcher, where 'volume of fire' is achieved by having all the riflemen in the squad issued an OICW. 

Its now possible to make an "OICW Lite" thats slightly lighter then the proposed NGSW Rifle once accessories are factored in:

Thales F90 MBR 16” w/ SL40 Grenade launcher = 9.44lbs 

Multi Ray 800 FCU= 1.54lbs

ACOG TA33+RMR+Mount = 0.875lbs

= 11.86lbs

Whether this is a validation of the OICW Lite concept, or an alarming note on the weight of the NGSW, is hard to say.

I have to say that I see no logical basis for validation of the "OICW Lite" concept.

First, a multi-shot, semi-auto grenade launcher was central to the OICW concept.

Second, all of the riflemen in the squad were supposed to be equipped with the OICW, so giving each of them an "OICW Lite" with a single-shot grenade launcher would not allow the squad to achieve but a small fraction of the volume of fire versus being equipped with the full-fledged OICW with multi-shot, semi-auto grenade launcher.

Third, both the F2000 and F90 are bullpup rifles.  At no point in time would they have had a snowball's chance in Hell of being adopted by the US Army.

nincomp said:

A long, gently tapered ogive mainly helps with supersonic projectiles.

So a pointed grenade would not have better ballistics than with a round nose?

nincomp said:

The other way 'round.  More like an extended teardrop shape with the round part aiming foreword.

Some mortar rounds have such a teardrop shape. 

It seems very impractical for a grenade round, though. 

Imagine how long the cartridge case would need to be.

stancrist said:

It seems very impractical for a grenade round, though.

It doesn't have to be that extreme.

More like this one only flying backwards:

This shape would allow for good placement of fragments, has room for a fuse, minimum frontal area and good sub sonic aerodynamics.

Given the extreme low velocity of the 40mm LV rounds, the aerodynamic shape is less important than the stability of the said round imparted by relatively lose bore riding projectile with a single thin drive band that might or not fully engrave into the rifling

Having a grenade bonded into the case also seems like a sub-optimal solution.

For estimating possible aerodynamic improvements, we can use the 40 x 53 MK 19 grenade launcher firing table, published in FM 23-27. It has a column for an "XM918 reduced time-of-flight experimental ammunition", different from the ordinary M918.  

When the distance/elevation data for 400-1500 m are used for a back-of-the-envelope calculation, it shows that the XM918 projectile has about only 57 percent air drag compared to M430 HEDP data. 40 x 46 projectiles seem to suffer considerably larger air drag (150 percent relative to M430). There is obviously ample room for improvement. 

Hopefully, some forum reader can show us the shape of the "XM918 reduced-time-of-flight" projectile. Again, this is not the ordinary M918 TP, which has a separate column in the firing table. 

Disclosure: the XM918 muzzle velocity is given as 335.3 m/s, compared to 240.8 m/s for the M430. The latter mass is estimated as 240 g. The drag computation is based on the assumption of identical muzzle impulse for both cartridges, resulting in 172.4 g for the XM918 projectile mass, using distances 400 to 1500 m.