I think we're kinda not on the same page. I'm talking about keeping 5.56 until LSAT comes. 

My argument was against switching to 6.5 Grendel or 6.8 SPC as a cartridge.

I think me and the other guy were talking about the 6.5/6.8 equivalences in the LSAT program, not switching from 5.56 to either of those right now.  I don't know where the confusion came from.

Not really.

The 6.5 LSAT weighs practically the same as the current M249.

If you replace metallic 7.62 NATO with a 6.5mm, you just force-multiplied rather than divide.

7.62 NATO is the inherent problem with our small arms mix, not 5.56 NATO.

A 6.5mm LSAT that has lighter ammo than 7.62 NATO with better hit potential, better armor defeat, and more retained energy with farther effective range than the PKM and SVD, but with an LMG that weighs less than a SAW by 8 lbs, and allows the LMG gunner to carry more rounds in less space.

Now you just augmented the units disproportionately to the extent that resupply can be pushed even farther if needed, weapon life is much longer in the maintenance picture, and even the guys with DShKas are within reach.

We need to place a big, fat target on 7.62 NATO, blast through it and purge it from the system, while phasing in 6.5mm LSAT.

Why would that be odd?

In what metrics are you relating assault rifle purchases to light machine gun purchases?

This is really hard for me to understand how someone with experience in these matters would conflate the 2.

Because I believe the LSAT was supposed to be adopted in an assault rifle version too. I may be wrong though.

And 7.62 NATO blows fucking dick. I'd be all in favor of going from 7.62 NATO to a 6.5 right now.

More cartridges > case diameter
More cartridges > case length
Smaller nut sack pouches > fatter nut sack pouches
LSAT > Minimi/SAW
6.5mm CT > metallic linked 5.56
PKM/SVD overmatch > PKM/SVD reins lead down on you

Anyone have handy the comparative weights of the various proposed LSAT cartridges in 5.56, 6.5, 7.62, etc?

Without all of the brass, I would think there would be less of a weight penalty between bullet diameters with LSAT.

Don't get my started on 7.62 NATO

I make it my life's work to shit on every "7.62 NATO is great" thread in GD. 

Do the smaller LSAT with 6.5 CT inside smaller CT cases than the 7.62 LSAT, with lower working pressure, much higher BC in the .290 G7 range/.580 G1.

Any Army that purposely chambers machine-guns and rifles in 7.62 in the 21st Century deserves the consequences.

There might be a good reason for the current 6.5 CT example, enemy body armor being the biggest factor to consider.

You could achieve the same defeat with a 6mm version in a smaller case though. He who shows up to the next skirmish without armor defeat capability combined with restrictive ROE is going to face very motivated insurgents in the close fight.

The LSAT LMG is right around the corner. The LSAT carbine/rifle is still a few years out. I figure it's because the focus for that has been caseless ammo, not cased telescoping. Hell, they might be waiting to see which version of the LMG gets in before they bust ass making a rifle for cased and another for caseless. Who knows.

Remember how many M9's the Army and Marines bought just a few years back? And now they're replacing them with the P320's. And that's just a recent example. I wouldn't count on gov't procurement making sense.

almost 3 times as heavy as 5.56, with barely any advantages. Heavier weapon, heavier ammo, hardly any increase in range. I don't like it at all, as a infantry cartridge.

Shit..... there is data that suggests mk262 establishes parity with 7.62 NATO, as far as range is considered. Which is fucking pathetic for a cartridge that weights that much. And also shows how far we've come since the 50s.

M249 - 40lbs
5.56 LSAT - 20lbs
6.5 LSAT - 40lbs
M240 - 70lbs
7.62 LSAT - 45lbs.

I can see doing 5.56 and 6.5 LSAT as being a huge advancement, but 6.5 across the board doesn't help much to the majority in the weight category.

The 6.5 carbine is also pushing 10lbs with 2 round magazine capacity.

The Marines always get screwed, I am glad they are getting new rifles.

Nobody is talking about switching to metallic cartridges for LMGs moving forward, nobody that is up-to-speed anyway with where the technology is at least.

We're talking about capabilities that can be duplicated or exceeded by LSAT when contrasted against existing metallic cartridges, not stuffing more metallic cartridges into 1950s designs for LMGs.

If someone is still fixated on 20th Century Technology in 2017, they need retraining and education.

7.62x51 NATO is 12.5 pounds for 200 belted cartridges.

7.62 LSAT is 7.5 pounds for 200 belted cartridges.

6.5 LSAT (Same polymer case as 7.62) is about a couple ounces lighter than the 7.62 for the same number of belted rounds, but has superior ballistics. Like another poster said, it's 6.5 Creedmore on steroids.

5.56 LSAT is 3.8 pounds for 200 belted rounds.

No idea how much the links weigh, but it isn't much.

Got weights for CT belt links, and CT individual rounds.

Weight of 1 round of 6.5mm CT: 237 grains / 15.4 grams
Weight of 1 belt link for 7.62mm/6.5mm CT: 22.5 grains / 1.46 grams

Weight of 1 round of 5.56mm CT: 127 grains / 8.2 grams
Weight of 1 belt link for 5.56mm CT: 13 grains / 0.84 grams*

*Plastic belt link figures given in various LSAT/CTSAS presentations are all over the place, from 6 grains to 21 grains, so I am using a guesstimated figure of 13 grains for this exercise, which I arrived at simply by scaling down the 22.5 grain figure for the 7.62mm belt link. If there’s an error here, it shouldn’t significantly affect the end result, and using these figures should at least be fair to both calibers.

Weight of 1 round of 5.56mm NATO (M855, M855A1, Mk. 318, or SS109): 185 grains / 12.0 grams
Weight of 1 M27 belt link: 30.9 grains / 2.00 grams
Weight of 1 30-round USGI magazine: 1,750 grains / 113 grams

Weight of 1 round of 7.62mm M80A1 Ball: 356 grains / 23.1 grams
Weight of 1 M13 belt link: 65.1 grains / 4.22 grams
Weight of 1 20-round M14 magazine: 3,580 grains / 232 grams

Estimated weight of a 20-round 6.5 CT Pmag is around 150 grams, the math on TFB is fairly close to my own estimates. (Mechanical HVAC guy, here)

The more I look into the weight per cartridge, I'd figure an M855A1-style 6.5 projectile in the 5.56 LSAT case would be about the perfect balance between weight, size and effective range as a general-purpose cartridge. Depending on the load, it looks like it would surpass the 6.5 Grendel, though I'm not sure how close it would get to the Creedmore.

ETA: Whoops, meant to say a 6.5 projectile in the 5.56 CT case.

ETA2: Got some info from TFB LSAT Should be accurate enough for our purposes.

Roger. I'm tracking

Sounds like they need to stop worring about 7.62 LSAT and focus on 6.5 and 5.56, see how far they can take them.

Short story:

It's substantially lighter.
Weapon reliability is increased dramatically.
Heat transfer into the barrel is significantly reduced.
There is no mechanical ejector or extractor, because the cased ammo themselves feed and eject through new case push and rotation of the rotating chamber.
It's the next true evolutionary step from the Stoner system, which set an engineering feat in reducing moving parts that was not addressed until LSAT, but for an LMG in this case.

What LSAT does is start to make the guys at the Squad Level consider carrying more of them as an Assault/Multi-purpose LMG, where you have technology creating the reality of a new duty position, just like it has done with the rifleman, machine gunner, grenadier, sniper, RTO, FO, etc.

The maneuverability and firepower provided by the LSAT will enable a Rifle Squad to unleash some serious whoop, and you will see a fundamental change in infantry tactics because of it.  It allows you to switch back and forth from base of fire to assault without relying on one guy in the Fire Team for the bulk of fire like the SAW currently enables/restricts.

This is what I think the Marines are seeing a little with the IAR, since it is lighter and more maneuverable.

LSAT steps it up with a similar weight weapon, but with linked ammunition that weighs almost half as much, in a smaller profile due to case length.

You could have 2 or 3 LSAT gunners per Fire Team, with a DM and Grenadier supporting them, just bounding and slaying dismounted insurgents or infantry that was dumb enough to go toe-to-toe with US logistics, for a force that handles both irregular and regular enemy forces unlike any in history.

If one understands the dynamics of dismounted warfare, as well as materials science and applied physics, you can form a better picture of how the LSAT will revolutionize dismounted combat.

That sounds fucking awesome.

This is why I think the LSAT in 5.56 excells. The weight of the LSAT LMG + 800 rounds of linked 5.56 weighs 20lbs.

Imagine giving everyone a 20lb combat load that consists of 800 rounds of belted ammo, and giving one guy a 6.5 LSAT LMG + 800 rounds linked 6.5 CTA weighing 40lbs.

Maybe they want 6.5 for all, but I can see a huge reason to use 5.56 and 6.5.

A 5.56 / 6.5mm mix makes a lot more sense for dismounts than 5.56 linked, 7.62 linked.

I don't see the advantage for assault rifles yet due to the structure of the mechanism and the diameter of the cases, unless you go with a drum magazine versus stick/box.

We're basically seeing reality imitate art when looking at some of the concepts that have been put to the screen with older movies even.

Would the price of the 5.56 LSAT LMG be cheap enough to push it through as a standard issue weapon?

Seems like they could use polymer in a lot of places we haven't been able to prior to reduce price.

Actually, I'm wondering if a type of quad stack magazine would be feasible in cased telescoping ammunition, since it's pretty much a straight wall type of cartridge.

Or maybe something similar to what was in Gears of War... Two double-stack round stacks, one in front of the other. It makes for a fairly wide magazine that isn't extremely thick or long. Hell, in a bullpup type rifle with a magwell similar to that of the Halo assault rifle, the magazine's bulk wouldn't be a problem, so long as it carries a sufficient number of rounds and the feeding mechanism is reliable.

Could always use a P90-style magazine, as well. Lower handguard pivots down,(Or is set lower with a cutout in the rear for the magwell) magazine pops right out of the magwell and slides out of the handguard. With that kind of setup, you can use less material in the receivers and have the magazine produce the round right in front of the chamber. It does produce some engineering challenges as far as handguard size/bulk, and heat shielding.

For a bullpup design, a side or top loading P90-type magazine would work.

ETA: If it can be done with a 12 gauge shotgun, you can make CT rifle rounds work from a P90-type magazine.

Life does indeed imitate art, at times.

All I know... If I have to maneuver, with a squad/fire team... and I have a choice of a Belt fed or a M27 for the SBF element


I'll take the Belt fed.

And they bought people to make the barrel shoot 24K rounds, and have a mean time before failure of 15K rounds too?

HK was nearly bankrupt six months ago.  They didn't have enough money to pay attention.  The G36 fiasco and unbelievable rape of the company and investors by the executives.   They bought planes, boats, helicopters, mansions, cars...  

Direct impingement isn't exactly on a winning streak.  It's in survival mode as far as large military contracts are concerned.  

The next combat rifle of the US armed forces will be something different than the stoner gas system.  

It doesn't matter if anyone likes it or doesn't.   The simple truth is - that's what's coming.   What we got from this announcement is even more writing on the wall.

Explain to me how barrel life has anything to do with the action of the weapon itself.

I can't wait to hear your reasoning.

You won't get it done, because you'll be bound by the same hurdles the guys doing the job are right now.  

Sorry to bust your bubble.  (note, this is not my guess, or opinion it was pretty well explained by SME's and you're not saying anything they have not heard before)  

Not disagreeing with what you've said, but more of a question for my own edification to learn from those who know:

Same problems with the long stroke piston PWS system as you described above?  What about with things like the Tavor, BREN 805, and other non-AR piston rifles that take some design influence from the AR?  What about piston op-rod designs like the M1 Carbine, M1 Garand, or Mini-14?

If you'd rather reply to me in an IM so as to not derail this thread, that's fine too; same goes for anyone else willing to answer the above.  

IMO, because those designs aren't attempting to directly substitute/replace an internal piston with an external one.
They're clean(er) sheet designs compared to the 416.
FFS, despite being designed to function on an AR15 lower, the Faxon upper is a better design (in some regards) than the 416.

German engineering!

I don't see where I claimed that it did.  Asking me to defend a  conclusion I never made is a straw man.  

The barrel life and the mean time before failure are plainly written in the specs.  It's the USMC that is demanding those, not me.

Did you read the document?  

From M67854-17-I-1218_RFI_for_IAR_021017.pdf

 Well, in addition to the rifle mechanisms I inquired about before, what about the Taiwanese T91 system?  Shouldn't it exhibit the same problematic areas as the M27?

Yep

They just want something new, the M16/M4 has been around since 1960(57yrs).

Change is coming, and its not a M4A1