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.

stancrist said:

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

In general, at velocities well below the speed of sound, gentle rounded curves at the nose have lower drag.  This is largely because it is important to keep the boundary layer attached, and rapid changes in the rate of curvature, especially where the ogive meets the shank, can cause flow separation.   The attached photo WWII droptanks are good examples.   The bottom example shows one elongated with a cylindrical center section. 

A longer elliptical nose shape can reduce drag vs a half sphere as long as the projectile only flies directly into the oncoming air and not at any significant angle.   The longer elliptical noses are more sensitive to angle of attack and would not do as well with the level of wobble and pitch change experienced with current LV grenades as noted by MR T.  Longer projectiles are also more difficult to stabilize and require more spin.

The transition from the shank to the boat tail also needs to be rounded, although the length of the boattail is not as critical.    There is a certain amount of diminishing returns for drag reduction as the boat tail gets longer.   As you observed, the back portion of the boat tail can add a lot of length for the amount of payload it would carry.   That is why it is common to see a truncated boat tail.  

P-51 Drop Tanks:

The longer projectile length of most 40mm MV should give you room to improve aerodynamics but it would be at the altar of both potential HE fill and optimal fragmentation pattern. Time of flight is already better than 40mm LV by virtue of higher starting MV, so it's not clear the tradeoff is worth it over better effects on target IMO. It's an optimization problem of course, so you can have a bit of both, or a lot of one or the other

Thanks for the briefing.  Very enlightening.