Textron 6.5 showcased at Modern Day Marine

[nml]

Good points pinzgauer thanks. As you said Grendel was optimized for the AR-15 action. Not the cartridge. If clean state, (imo) 123gr is too light to replace Mk316, whether or not you reduce caliber.

[Koshinn]

It's no accident creedmore and 260 is starting to dominate bolt gun stuff where the 308 and 708 used to rule

Starting? 6.5mm has already dominated bolt gun competitions, then fell in popularity to about even with 6mm. 6mm is just faster, which makes it better at like 1200m and in, where competitions take place. But 6.5 is close and has better barrel life.

In any bolt gun competition where a 6.5mm or 6mm round is allowed, .308/7.62x54 is not competitive at all. I can't remember the last time a 30 cal user was in the top 50 in the PRS.

[Clint]

If clean state, (imo) 123gr is too light to replace Mk316, whether or not you reduce caliber.

M855 ball has a BC of ~.294 (G1), while Mk262 (77SMK) has a BC of .362 (G1).

M80 ball has a BC of ~.380-.390 (G1),

The 175 SMK used in the M118LR and Mk316 loads has a BC of .496 (G1).

The 175 TMK bumps that to .530 (G1).


Compare that to 6.5mm projectiles available in weights from 95-140 grains, with BC's ranging from .365 up to .625 (G1).

The Hornady 123 A-Max and Sierra 123 Match King both have a BC of .510 (G1).


Even middle weight 6.5mm projectiles match the BCs of long range 30 caliber projectiles.

This is clearly a long range advantage.

[CanineCombatives]

"I dont have to kill him, I just have to stop him from doing what he's doing"

[nml]

Clint good stuff. I think we're on the same page. Why am I going to replace 175 gr SMK with a tipped 123 gr instead a tipped 175 gr?

(Like you said it is only G1) but the 175 does over 2400 fps.

[pinzgauer]

Missing the point with the 175 30 cal discussions... Even if decent BC it does meet the mission they are solving for

If they could use 7.62 NATO in carbines+SAW+LMG they would do so. They can't, due to recoil & weight in the carbine. (and to a certain extent, the SAW). Ammo weight is a big deal.

So if you drop it to tolerable recoil & carbine weight envelope, you end up with 7.62x39 in 30 cal, which has bad downrange ballistics due to stubby bullets. Use a 162-175g bullet at mid-power and you have horrible trajectory. So not good for SAW/LMG usage.

5.56 is fine for carbine and to a certain extent, SAW usage. Flat trajectory in current weights, though starts dropping in heavier weights. But is running out of steam for what they'd like to have SAW be able to do at longer ranges. And at a real disadvantage for LMG.

6.5 splits that difference, uses a bullet weight much more penetration than 5.56, with much improved downrange ballistics over the same weight 30 cal.

The textron 123g at 3000 fps is close to 270 performance at short ranges and beats it long ranges (due to high BC bullet). My bet is recoil will be close to 260/creedmore/708, so may not be usable for carbine stuff.

The whole reason to change is to go lighter weight ammo, and improve ballistics across carbine/SAW/LMG. It's a big challenge. And likely will never happen anyway.

If they could tolerate an AR-10 type carbine/ammo loadout, they would could do it in 260/creedmore and be done. But they can't for rank & file usage. And not a big enough GI difference in shooting capability to use the advantage of the longer range ballistics of the 6.5. IE: they are training limited, not range limited even with 5.56.

Grendel is pretty much 7.62x39 with significantly better downrange ballistics, a bit more steam, and slightly reduced case taper to work better in AR's. Yet still work in AK's and SAW's. It was designed for sustained full auto and steel case usage. And inherently accurate due to some of it's design factors (PPC lineage and the great 6.5 bullets available). Easiest cartridge I've seen to find accurate load/gun combos.

Where it's limited is in COAL to fit in AK/AR-15 platforms. And pressure limited to deal with bolt thrust limits of the AR-15. Load it to bolt gun pressures and it's 100-150 fps closer to the textron mythical cartridge. Stretch it another .1-.2 and you'd be very close. But have not addressed the weight reduction by going to plastic case.

I love grendel in AR's, very balanced cartridge. Would be an improvement in SAW's. But would not be enough for LMG usage. And if you don't fix that, they might as well stay with 5.56 carbine+saw and 7.62 NATO for LMG. And there is a compromise in # rounds for given weight & mag loadout. (25 vs 30 per mag)

[Clint]

Clint good stuff. I think we're on the same page. Why am I going to replace 175 gr SMK with a tipped 123 gr instead a tipped 175 gr?

(Like you said it is only G1) but the 175 does over 2400 fps.

You might do it for three reasons.
1) lighter cartridge weight, regardless of format ( conventional brass, polymer, telescoped case)
2) better downrange ballistics and MER for the same recoil
3) equivalent downrange ballistics at reduced recoil


For the same recoil and BC, the 123gr can be sent downrange at 3000 fps vs 2500 for the 175gr.

Which one is easier to make long range hits with?