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So if the U.S. Military adopts the XM5 Rifle and switches to the 6.8mm cartridge, will all the 5.56 ammunition become Available? Inquiring minds want to know?

They'll bury it in a landfill before they let the CMP sell it to citizens for a fair to all price.

US Military will still be shooting 5.56 for quite a while. Articles I have seen say this new rifle will be issued to infantry and special ops personnel and others will retain the current M-4. Plus, the other services are not yet on board with the 6.8 and 5.56 is still the NATO round and our Pacific allies also use 5.56.

What I’ve heard is that the M4 (in 5.56) will continue to be the issued weapon for support troops and those manning crew served weapons…much like the M1 Carbine's early role in WW2…while the new M5 will be issued to the infantry and to SOCOM. Given the cost of converting the entire infantry over to this weapon system, I suspect we'll see them first issued at the squad level to a single squad-member, to be used in a DMR role, and then gradually issuing them out to the rest of the troops as production ramps up. Also from what I’ve heard, the special Vortex optic that’s supposed to be issued with it hasn’t even finished development yet.

Another factor is this: the astronomically high pressure developed by this new 6.8x51 ammo that enables it to drive a 140 grain bullet at 3,000 fps is likely to make it a real barrel burner. That’s similar bullet weight/velocity to the old .264 Winchester Magnum, a cartridge that’s famous for burning out barrels in not much more than 1,000 rounds. A regular hammer forged chrome lined M4 barrel is typically good for 30,000 rounds or more. If the M5 burns up barrels in just a few thousand rounds, then it’s not a good value for the cost, even with the suppressor included.

And then there’s the ammo cost. It’s significant that Sig is offering the civilian version in both 6.5x51 (AKA 2.77 Fury), and in .308 Winchester. It seems very likely that, in order to keep the retail price closer to sea-level, ammo manufacturers will offer a version of the .277 cartridge that uses a standard case instead of the hybrid case used by the milspec cartridge. That would mean that the cheaper cartridge would develop pressures closer to .308 or 6.5 Creedmore…meaning that customers' Ballistics expectations will have to be adjusted.

MSRP from Sig for the rifle is $8,000, and that doesn’t even include BUIS, let alone an optic. There’s no way it’s actually worth double the price of something like a SCAR17 for instance…other than maybe that’s maybe what the market will bear right now because it’s "the latest and greatest". But intrinsically, it’s way overpriced. Add to that the fact that it is very likely to burn through barrels at quite an accelerated rate using the (very expensive) ammo designed for it, and this is strictly a rich man's gun. The Sig MCX Virtus Patrol rifle…the roughly equivalent 5.56 version of the Spear…sells for $1,999.99 at Sportman's Warehouse. That’s a $4,000 price differential. Compare that to the $380 price difference between a SCAR16 and a SCAR17. (In this comparison, both of the SCARs are overpriced, given that the Virtus is $1,600 less than the SCAR16, but the point remains that the Spear isn’t worth 4 times what the Virtus costs.)

The design is a good design, for the same reasons that the Virtus is a good design. But in my personal opinion, the Pentagon would have been FAR better served to have developed the rifle in something like 6.5 Creedmore, or 6.8 SPC, if they were looking for something with more pop than 5.56 but less weight than .308. And then, you could later swap out the 5.56 barrels on the M4s for one chambered in 6.8 SPC, or alternately swap out the .308 barrels on the various iterations of M110s, Mk17s, and M240s for barrels chambered in 6”5 Creedmore.

I think that would be more cost effective.

(EDITED TO CORRECT 2ND PARAGRAPH, TO READ ".264 WINCHESTER MAGNUM" INSTEAD OF "6.5 WINCHESTER MAGNUM".)

Hah, but when does the Pentagon do the intelligent thing. They'd rather buy one F-35 which can theoretically offer cover and protection to one ground troop action until it has to leave station to refuel/reload when they could buy a dozen A-10's that could protect several ground troop actions at the same time while rotating so one is on station while another is returning to refuel/reload. Because it's always better to spend exponentially more money on something less capable and useful for the specific job.

This will involve a TO&E change and training for those units getting the new rifle, and for their support units. Someone has to be able to fix them when they break/wear out. And it's not just the rifles: magazines, magazine cases, spare parts, special tools and gauges, manuals, blank firing adapters, arms room storage, vehicle racks, gun cases, maybe slings ... Lots of gear is involved in a changeover.
The equipment changes I was involved in were done as Battalion sets, whether it was vehicles weapons, or whatever. The project manager builds up stockage at one of the arsenals until they have enough for the new TO&E, then does a mass swap-out with the unit at the top of the list. Oh, and the unit has to make the old equipment meet issue standards before the swap-out. That's because the gear may be issued to other units down the line, or provided to allies.
The order is somewhat complicated and possibly political: The regular-army FORSCOM unit I deployed with didn't trade in our M1911A1's until well after Desert Storm. Our counterpart Army Reserve units had already had them for some time.

threoh8 wrote: Mon May 16, 2022 8:59 am Someone has to be able to fix them when they break/wear out.

This rifle is going to really keep unit armorers busy. As I pointed out above, barrel life is going to be a real problem. Sig's .277 Fury (AKA 6.8X51MM), the round around which the Spear is designed, has nearly identical ballistics to the old .264 Winchester Magnum…a notorious barrel burner which commonly destroyed barrels in as little as 1,000 rounds...and that was with longer hunting/target barrels. The .277 Fury SAAMI Maximum Average Pressure chamber pressure is 80,000 psi—compared to .308 (62,000 psi) or to 5.56 (62,366 psi)—in order to offset the effect of a 16" barrel length on velocity. It therefore cannot avoid burning barrels at an accelerated rate. Science. Barrel burnout can be somewhat attenuated with chrome or QPQ linings, but it will never be able to equal the roughly 30,000 round barrel life of an M4. This is going to be an expensive rifle for American taxpayers to procure, feed, and maintain.

I still say that our tax money would be better spent on rebarreling M4s for 6mm ARC or 6.8 SPC, and rebarreling existing and/or issuing new M110s in 6.5 Creedmore. There HAS to be a better solution than .277 Fury in an $8000 rifle.

I believe the point of going with this cartridge is to defeat body armour at least thats what I read

patterson wrote: Mon May 16, 2022 3:42 pm I believe the point of going with this cartridge is to defeat body armour at least thats what I read

I read that too … but whose armor? Russia's "thoroughly modern army(tm)" ( ) is using body armor in Ukraine that isn’t any better than cardboard.

I have a theory about that. It may be nonsense, but it feels true to me. The way Russia is expending its soldiers lives in Ukraine communicates that their leaders hold those lives of their soldiers very cheaply. It’s a cultural thing. We, OTH, are anxious to avoid casualties to the extent possible, and we give our combat troops higher quality body armor, helmets, etc., because we don’t want the domestic political fallout. Totalitarian societies don’t have to worry about rising casualties. They can always blame it on the savagery of their inhuman foes, and their people will believe it. Russia IS a totalitarian society. They sold their illegal invasion of Ukraine to their people as a holy mission to stamp out the Nazi threat against Mother Russia; and the Russian people, being deprived of other sources of information, are swallowing it. If their boys get shot dead because they wore inferior body armor, that’s just another generation of sacrifice in their nation's long history of sacrifice, for which their leaders never pay a political price.

ANY WHO…

Maybe against Chinese body armor? Do their troops even wear armor? ¯\_(ツ)_/¯