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If you are referring to the original Squad Automatic Weapon project from many years ago, I am not sure. The original 6mm SAW used the existing 5.56mm (.223 Rem) case.

Around the same time many folks were experimenting with wildcating the same case for use in Thompson Center pistols and they were used in .257, .264, .277 .284 and .30 diameter with the .264 and .284 becoming actual calibers, 6.5 and 7mm TCU. There is also the little .25 Wooters which is the same thing in .257 but it remains a wildcat. Actually the .300 Whisper is a quasi-factory round, I think Cor-Bon actually ran some.

Of late on Special Forces Group has experimented with bigger cases from the .30 Rem to the .220 PPC in a wide variety of cases. Their recommendation ended up with the experimental adoption and actual issue of M4s in 6.8 SPC.

Indepentendly, Alexander Arms has been floating the "6.5 Grendel" which is a modified 6mm PPC case pushing .264 bullets.

Lots of stuff out there!

Onward,
Jim H.
 

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Crash;

I see. If you note the 1st type (on the left) has a case about as long as the 5.56X45 but the shoulder is set back making the neck longer. This round, when loaded was too long to fit in m-16 mags and was dropped pretty early I think. Same with the Aluminum cased ammo that had a slightly longer case and an even longer O.A.L.

A lot of this had to do with the fact that the platform for the Squad Automatic Weapon (SAW) had not been selected. When it was finally settled that the FN-249 (MINIMI) was to be it and that it should take M-16 mags as an emergency issue then it was all over for the 6mm but one last try was to just make both M-16 & SAW in 6X45MM.

It never really took off.

The factory ammo I have wasn't too impressive (a 75gr bullet at 2550 fps) but safe handloads pushed the 85gr BTSP to around 2750 in a 20" barrel.

Jim
 

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Crash,
This is a wild guess but the round looks kind of similar to the 6.5 Grendel. I suspect with a 140 you would be getting around 2400 to 2500 from a 20". I think the Grendel is set up for a 120 (which is not really all that bad sectional density wise) at about 2700+ from a 20". A 140 6.5 is *very* long.

It certainly has some merit for long range stuff in a carbine. Tactical penetration is not bad either.

Jim
 
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