.277 Fury vs 6.8 SPC: The Best of the Best of the Best? Sure

Defiant America ^ | January 28, 2024 | By Sam Jacobs

[Paal Gulli]

A note for you .30-cal devotees.

John Garand built the prototypes for what would become the M1 battle rifle in .276 Pedersen. He chose that round because in the 1920's the Army's ordnance bureau had conducted a study concluding the the "Goldilocks" caliber was .27-.28 -- the best compromise of lethality, recoil and ammunition weight -- and the Pedersen was a decent round that fit that bill.

When Garand's design won the competition (over, ironically, John Pedersen's own rifle), Secretary of the Army Douglas MacArthur made acceptance of Garand's rifle contingent on it being converted to use the .30-06 Springfield round on account of he had more than 3 billion rounds of the stuff left over from The Great War sitting in munitions depots.

So the .30-cal wasn't the first choice but it was forced on them by economics.

Garand also prototyped it with "primer actuation," which probably would have been a disaster in a military rifle, so not everything he did was brilliant.

Garand's first prototype also had a detachable box magazine because Garand had seen what a combat multiplier Browning's M1918 BAR was, and it had 20-rd detachable box magazines. But Army OB put the kibosh on that, too, insisting that all submissions use a fixed internal magazine of no more than ten rounds capacity. Garand sometimes gets "blamed" for that oversight but it wasn't his choice.

And RE: the .30-06, the first production models of the M1903 Springfield rifle had iron sights calibrated and marked to 2800 yards (image below), almost 1.6 miles. On later versions it was reduced to 2400 yards. And in the hands of a competent marksman, they could in fact hit an "area target" at those ranges. But it was always a waste of resources to give every grunt a rifle with that sort of potential.

[NorthMountain]

I’m squishy. So is a rubber butt-pad. Metal, not so much.

I think we’re largely on the same page.

[saleman]

Isn’t bullet velocity the culprit in barrel degradation? I see a listed muzzle velocity of 2830 fps. That’s not excessive

-——————————————————————————————It’s not that simple.

Generally “overbore” cartridges will have a shorter barrel life than none overbore? cartridges. Someone can tell me if right or wrong but I believe shot out barrels are more shot out chambers. Heat at ingnition and such...Plus unburned powder down the bore. Anyway, heat is the problem, not velocity. Which is not to say that velocity has nothing to do with heat. Or something....

Although, I don’t have any experience at 80,000 psi. Doubt anyone much has any either.

[Magnum44]

A gas-operated semiauto should be very different from a bolt-action.

Agreed, but...

The bolt/BCG being driven forward introduces a new impulsive force

using the stored energy from taken from the recoil before it could be transferred to the operator, thus reduced recoil at the operators shoulder.

[NorthMountain]

Again, energy and momentum are not the same thing. Recoil is a conservation of momentum phenomenon.

[Paal Gulli]

"Isn’t bullet velocity the culprit in barrel degradation?..."

No.

Barrels wear out from the breech, where bullet velocity is lowest, not at the muzzle, where it's highest. The culprit is the high temperatures in the firing chamber, which creates a blowtorch effect on the leade and near riflings. And while it's in this superheated state, it gets bombarded with granules of flying gunpowder, like a sand blaster.

[smokingfrog]

Seems like a solution in search of a problem that doesn’t exist.

[Paal Gulli]

"...But Army OB put the kibosh on that, too, insisting that all submissions use a fixed internal magazine of no more than ten rounds capacity...."

I left out out "clip-loaded" fixed internal magazine of no more than ten rounds capacity. They didn't specify stripper clip or en-bloc and JG chose the latter.

[Magnum44]

We may be talking past each other.

The force applied to the bullet at ignition causes a equal and opposite force on the bolt face, which initially is held in place by the bolt lugs. The mass of a 55-77 grain bullet is trivial to the mass of the 5-7 lb rifle. The expanding gas is channeled to unlock the bolt and drive the BCG back. The BCG as it is accelerated by the gas has momentum, which is transferred to the spring and stored as energy in the compressed spring, which in return imparts that on the BCG as it is driven forward to load the next round.

All of that action is ‘powered’ by the cartridge you just fired, so the force applied to your shoulder (or body if you dont shoulder the gun) is less than what would have been applied by the amount used to cycle the action. In a bolt action, none of this energy is subtracted from the process, thus more ‘slam’.

I can see where I may have used the term energy in a confusing fashion, but all the energy originated from the firing of the cartridge and it is expended kinetically through these components.

[exnavy]

I agree. And more powder also increases CUP. With 80,000 cup in play, that is 454 casul range. I fired one revolver in 454. To say recoil is stiff is understating it.

[gundog]

I understand the throat erosion thing. I’m curious about the pressure curve of whatever propellant is being used. To generate the kind of pressure they’re getting, wouldn’t a relatively slow powder be used?

[Paal Gulli]

"Energy and momentum are not the same thing...."

Energy is a scalar value, not a vector value. And energy is only conserved in a perfectly elastic collision, which the impact of a bullet never is.

I think it was Roy Whetherby, the first evangelist of Kinetic Energy, who put that bee in everybody's bonnet. KE/ME is exactly the wrong tool for assessing the lethality of a cartridge, but that doesn't stop gazillions from using it.

And old acquaintance of mine (who obviously was well more more science-literate that your average shooter) used to say, "The Gospel of Kinetic Energy: proposed by the ignorant, parroted by the unknowing, evangelized by those who failed high school physics.

It bears mention that none of the more credible lethality calculators (Hatcher's relative stopping power, Taylor's knock-out factor, Thorniley stopping power, etc) used velocity factored exponentially, yet KE does.

In the world of science, this is what's known as "a clue."

To put a point on it, kinetic energy never killed nobody.

[exnavy]

Good analysis, but what a sweet caliber that 30-06 is. Powerful, accurate, especially in the O3A3. And just fun to shoot.

[ETCM]

It’s a 10 lb rifle, probably more with the fancy XM-157 optic/fire control system. A reviewer noted:

“The recoil is actually smoother, better controlled than that of the A4 but powerful enough to momentarily shift your weight backward. If standing, you need, as always, to have the right body mechanics but you lean more into the XM-7.”

[Myrddin]

The 6.8 SPC maintained the 2.26" COL that fits in an AR-15 magazine well. The 277 Fury is too long to use the standard AR-15 lower and the 80,000 PSI chamber pressure is too high for a stock AR-15 barrel (typically 55,000 PSI). The bigger, higher pressure 277 Fury has no place to go without a new line of lower/uppers/barrels.

I never purchased any 6.8 SPC or SPCII uppers. There was a difference in the bolt face and chamber between SPC/SPCII. I think the 6.5 Grendel had a similar problem on barrels and bolt faces. I did build/buy 6.5 Grendel rifles.

[Red Badger]

It’s all about the Benjamins......................

[NorthMountain]

all the energy originated from the firing of the cartridge and it is expended kinetically through these components.

Energy is indeed conserved, but most of the chemical potential energy in the propellant (and primer ...) is immediately converted to heat. The remainder, of course, transferred to KE of various things including the bullet, powder gases, BCG, rifle itself, etc. No argument there.

But conservation of energy doesn't govern the relationship of the recoil impulse to the velocity of the bullet. That's conservation of momentum.

[Magnum44]

Ok, I see what your point was now. Yes, in a closed system, momentum is conserved just as energy is conserved. No argument there either. Have to be careful that its a closed system and not a squishy one. :)

[NorthMountain]

Have to be careful that its a closed system and not a squishy one. :)

A closed system can be squishy; that's part of the reason I'd like to see the high speed video of a rifle being shot by a human AND a rifle shot while hanging freely. When we humans pick up a rifle and shoot it we're part of the squishy closed system. I'm not particularly large; I've seen video of "Kentucky Ballistics" (he's big ...) shooting ridiculously large rifles that I wouldn't want to mess with. Shoulder a rifle and you become part of "m2" (the mass of the rifle).

FWIW:

A friend bought a .44Mag revolver, S&W Model 29, and was initially frustrated with it. The factory scales are wood, checkered but still slick, and very chunky. He felt that the recoil was unmanageable; it rotated in his hand and the cylinder latch cut him every time he fired it. When he voiced his concern, someone recommended that he swap the factory scales for Pachmayr (rubber) scales, which are also much thinner. He did, and immediately was able to control the thing. "Perceived recoil" is a very complicated thing.

[Magnum44]

"Perceived recoil" is a very complicated thing.

But its easily measured by the bruise marks left. :)