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What XCR Caliber and Chasis are you?

  • XCR-L in 6.8x51

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  • XCR-M in 6.8x51

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  • Nay! XCR-L in 5.56!

    Votes: 2 20.0%
  • Nyet! XCR-M in .308 is fine!

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  • I don't care, give me my damn rifle already.

    Votes: 1 10.0%
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Discussion Starter · #1 ·
I have a thousand bucks that says Sig Sauer is going to win the Next Generation Squad Weapon competition (whether that means the MCX Spear is going to be a standard military rifle or a SecOps weapon is a different discussion). Sig's 6.8x51 round is what's being fired from that beast and the LMG that they are going to go with it.



My question is, can this new caliber be adapted to existing multicaliber rifles like the XCR (or the AR-15 for that matter)? The new round isn't 6.8 SPC, it's a new cartridge that generates internal pressures of 80-100K PSI (FYI, 5.56 pressures are at 55K PSI). Making a new barrel or bolt isn't that big of a deal and civilian rifles don't have to be limited to bullpup lengths, but does anyone know if the XCR's upper can handle that kind of pressure? Can any commercially made upper do that or do we have to wait for Sig to deliver to the civ market? And last, which version of the XCR would the barrel conversion be for, the -L or -M?
 

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Discussion Starter · #14 · (Edited)
Boils down to dimensions of the bolt and whether it can fit in the existing -M upper. Also, are the magazine dimensions the same as LR/SR25?
Of course, a 51mm bullet won't fit into a gun with a magwell built for 45mm long bullets. Missed that detail.

What's bbl life like with that kind of chamber pressure?
From what I understand that the barrel handles most of the bullet's combustion. Does the receiver need any particular reinforcment to handle 80-100K PSI of pressure from the cartridge going off? I don't know what the MCX Spear or the other NGSW guns are made of but would an aluminum upper suffice to deal with that kind of chamber pressure and recoil?
 

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Discussion Starter · #18 ·

This is news to me, but to those not in the know, the MCX-Spear and the 277 Fury have been announced to be sold commercially. As much as I have held off on getting the MCX, I'm just about dead set to get the Spear (when the gun isn't a limited edition price and when Sig stops holding a monopoly on 277 Fury, I ain't paying $8000 for a damn rifle).



It makes me kinda sad see that the Spear seems to be eating the lunch of what the XCR could be having, if Robinson Arms had the will to hunt for it. The Spear has some of the same features as the XCR (it now has a folding side charging handle!) while firing a badass round. I hope the -M can be made to chamber the 277 Fury to at least keep the platform relevant, or that RA does something in the near future to dissuade me from getting a Spear.
 

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Discussion Starter · #21 ·
M is more relevant in 308 than the SPEAR is going to be for decades, if ever.
Are you saying that because of Sig's track record of abandoning or obsoleting platforms/generations? Because I honestly think they are going to get the contract, even if they have to evolve the Spear later on down the line. 277 Fury seems like an expensive and complicated round, but it seems to be doing well in the trials as far as I can see.

I know right? No way I can hide that kind of expense from the missus! I'd rather save for a Barrett M82 or M107 at that rate. I just hope Sig can bring it down to $2K in a couple years or so (probably $3K considering how much the vanilla MCX Virtus is going for these days).
 

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Discussion Starter · #26 ·
If the 80k pressure is a cost driver for manufacturing the platform couldn't someone develop a lighter brass cased load? That would enable reloading as well. Course there may be too much of a trade-off in performance.
From what I understand from the Sig representative, the stainless steel section of the case was added so that the internal walls of the case were a consistent thickness, so they would have as much internal space for powder as possible to reach the pressures they were going for. Very thoughtfully designed.

With that in mind, I still wonder if the -M can adapted to shoot 227 Fury at this rate, or if the gun needs to be upgraded to contain the pressures. The Spear looks a lot beefier than the regular MCX, beyond the wider mag well.
 

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Discussion Starter · #28 ·
What about the 277 are you after?
It's nothing really, just trying to say on top of technology; if the military is looking to replace their main battle rifle caliber I want to be in on it. However, time will tell if that really comes to pass or if there are any changes to the availability of 5.56 or .308 when 227 Fury hits.
 
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