TFB Behind the Gun #134: Pondering the XM7 and the 6.8x51mm w/ Darwin

by Luke C.

Published: September 26th, 2024

tfb behind the gun 134 pondering the xm7 and the 6 8x51mm w darwin

Today fellow writer Darwin and I dig into the U.S. Army’s new rifle and its strange hybrid-cased ammunition. The NGSW program and the resultant firearms that were selected have been met with both praise and disdain for several reasons. However, today the aim is to discuss some of the positives and the negatives of this platform and its cartridge, from the perspective of civilians, reloaders, and of course, guys who just love guns. We’d also like to hear your thoughts on the XM7 and its new cartridge. Thanks as always for listening!

More TFB Behind the Gun Podcast Episodes:

TFB Behind the gun #134: Pondering the XM7 and the 6.8x51mm with Darwin

“In today's episode of TFB's Behind the Gun Podcast, we're bringing back TFB Writer Darwin to talk about the new SIG MCX-SPEAR otherwise known by its military designation - the XM7. The XM7 is the result of the NGSW program and I've recently had the opportunity to start digging into one of their Civilian versions of the rifle chambered in the new 6.8x51mm hybrid cased ammunition. Darwin is quite a fan of not only SIG's new rifle but also battle rifles in general. Today he and I will discuss some of the history of the XM7, and talk in depth about the new 6.8x51mm cartridge and some of the potential it might have even outside of combat. Please welcome back TFB Writer Darwin to the Show!”

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Luke C.

Reloader SCSA Competitor Certified Pilot Currently able to pass himself off as the second cousin twice removed of Joe Flanigan. Instagram: https://www.instagram.com/ballisticaviation/

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7 of 8 comments

Dstev98141 on Sep 26, 2024

Overkill is far better than underkill!

2 Reply
- See 1 previous
- HemngwaysBeard on Sep 26, 2024
  
  Honest question: What does the term “overkill/overmatch” mean in this circumstance?
  Because ammo availability for suppressive fire could be considered as “overkill.” Using a lighter rifle/ammo that enables soldiers to carry other gear like drones could contribute to “overkill/overmatch.”
  
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- Lcon on Sep 27, 2024
  
  @HemngwaysBeard it’s overmatch due to potential AP and range. The Army is basing its assumptions on a numerical inferiority. So they want to engage the adversary before he can close to engage.
  
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Longbow on Sep 27, 2024

I still think the “partnering” that kept them from adopting the polymer case ammo with the XM7 was a mistake. It would have somewhat offset the additional weight of the ammo and rifle

1 Reply
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- Lcon on Sep 27, 2024
  
  The polymer ammunition that was offered was optimized for the Bullpup rifles. It was designed for a long barrel. To get it to work in the XM250 and XM7 as selected would have required increasing lengths of the respective barrels from 17.5 and 13 inches respectively to 22 and 20 inches which would have put them both over the Army’s weight and size maximums. The only other way would have been to send TV back to the drawing board to redevelop their cartridge to Sig’s pressures which would have delayed the production and program.
  
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- Mig1NC on Sep 29, 2024
  
  100% agree. Also, I would mention, the ability to simply re-barrel aircraft mounted guns on the UH60, AH-6, etc, from 7.62 to 6.8 would have saved a lot of weight on helicopters which is critical.
  
  If the ammo design had come first, TV could have optimized the poly cased round for whatever parameters were desired. Then the LMG and assault rifle could have been competed separately based on the winning ammo design.
  Although, having said that, the Sig MMG338 would be a good replacement for aircraft mounted M240s, saving weight and giving standoff vs ground based heavy weapons fire.
  
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- Lcon on Sep 29, 2024
  
  @Mig1NC this assumes that M240 conversion is only possible with TV’s ammo.
  The problem with this line is if the Army had laid out requirements for the cartridge to perform like the finalized version then it would still have the Awesome chamber pressures. Had they laid out requirements that were what TV offered in its bid then the XM250 would have been the RM277 AR. Well many critics go after the XM7 few question the selection of the XM250. The RM277 as a rifle doesn’t seem that bad but as an Automatic Rifle… if you think the reduction in magazine size for the XM7 from 30 to 20 was dramatic imagine if the Automatic gunner went from 100 round belts to 20 round boxes.
  
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