Elbonia is looking for a new rifle. Should pierce personal armour to Lvl 4 ideally and be able to reach 600m combat distance in an LMG / SAW / DMR. Should be capable of trench clearing / house to house and fit an (integrated) suppressor by default. Magazines should hold at least 30 round, preferably 40. Elbonia is undecided on cartridge, but is not a fan of 5.56x45.

Gentlemen, please make your proposals.

Ohio Ordnance Works HCAR. The old "Black Tip" AP loading with higher velocities thanks to powder improvements.

And of course, MagPul needs to develop an improved magazine.

1-6 LPVO with BDC reticle, illuminated dot at center of crosshairs, have a setting where it's large enough to use as a regular red dot at lower powers.

Sounds like a case for Colonel Sabot!

7.62×42mm TV polymer cartridge case with a 6.8 SPC case head, loaded to 64mm OAL with a saboted saboted L/D=6 4.8g 5.56mm .26 G7 VLD EPR, charged with 25gr of Vectan SP3, fired at 1000m/s through a 420mm 1-in-5.5" progressive twist barrel. 

The guns firing this cartridge would be F90MBRs, Ultimaxes, and KAC LAMGs, lengthened and strengthened around the chamber to accomodate the +80KPSI cartridge.

The guns come with a threadded compact lightweight flow-through suppressor that supports the sabot all the way to the end.

Rifles are equiped with a fixed 6x and piggyback reddot, LMGs with reddots and magnifiers (same for night fighting carbines) DMRs with 3-15x scopes

Alternatively, if you dislike Colonel Sabot's solution;

Also a 6.8 SPC-baes TV polymer case, necked down to 6mm, loaded with a 4.8g L/D=5 6mm EPR (.23 G7), launched at 1000 m/s from a 500mm barrel.

Despite being less impressive ballistically this cartridge would actually be useful in a DMR, on account of not having to deal with sabot separation. Still, at that BC and MV you can have a 600m fragmentation range in a reasonably sized cartridge.

Due to the need for a full length barrel, i recomend fielding Elbonian troops with 20" barreled F90MBRs and 24" barrled HBARs exclusively. No Carbines Allowed.

VPMudde said:

The guns come with a threadded compact lightweight flow-through suppressor that supports the sabot all the way to the end.

Then maybe it's time to resurrect the Gerlich concept and the "littleJohn" adaptator.

You could fire a "full calibre" 110 gr 7.62 mm long-nose, flat-base bullet (C7 = 0.18) at 880 m/s, or the "squeeze bore" version with a solid core at 1250 m/s, and don't care about sabot separation.

graylion said:

Gentlemen, please make your proposals.

Since we talk about Elbonia i suggest the Gepard GM6 Lynx.
Penetrates Lvl 4 at 600 m easily and much further. Will not need exotic ammo for this Can do the LMG/SAW and DMR role as well with minimal modification. With proper ammo can even work in the light anti armor and anit air role.
Can fit a supressor. Sweeps trenches if you shoot along the trench axis. Will sweep trough several occupants with high reliability. Its on the far end to the other side of the spectrum compared to 5,56x44.
The round cound will be more tricky. But a modification to use belt feeding and use 30 rds belt drums might work. As well as a beltless feeding device. Even a 30rds drum magazine could work.
Since there is no weight and size limit in the tender the GM6 IMHO is the most effective solution since 12,7x99 has no problems what so ever with Lvl 4 body armor.

P.S.: Should the GM6 approach be to conventiona for Elbonia brass I suggest the PAW-20. Everything above applies to this one as well in addition the bullets are shells and go boom.
There even is a "machine gun" using the same ammo as support weapon awailable: the Strike.

schnuersi said:

the GM6 IMHO is the most effective solution since 12,7x99 has no problems what so ever with Lvl 4 body armor.

The old generation (around 2000) British "lvl IV" plates were able to stop the 12.7 mm steel core AP at 650 m...

EmericD said:

The old generation (around 2000) British "lvl IV" plates were able to stop the 12.7 mm steel core AP at 650 m...

That is still 50 m more than required.

BTW what lvl 4 has not been specified. So it can be assumed its Elbonian lvl 4 with most likely means "flak jacket" level of protection. ;)

schnuersi said:

That is still 50 m more than required.

Yes, but with plates that are now 20 years old... 

schnuersi said:

BTW what lvl 4 has not been specified. So it can be assumed its Elbonian lvl 4 with most likely means "flak jacket" level of protection. ;)

Could be.

It seems that a US company could provide 5.56 mm AP ammo that could defeat NIJ Lvl IV plates at 200 m, I'm really curious to try those ammo.

Squeeze bore adapters tend to wear out fast, whereas only shooting either saboted VLDs or heavy subsonics lessens wear and tear on your barrels. A replacable adaptor is prone to malfunctions such as not being replaced for cost savings, not being used in training for cost savings, etc. But a gun that never wears out? What could possibly go wrong with that?

Though in order to fire a reasonably sized projectile at mach 4, you're looking at .30-06 energy levels. At that point you can do as the Swedish snipers did, and accept the accuracy penalty for having miniscule time of flights. Perhaps an HCAR isn't such a bad idea after all.