“There lives more faith in honest doubt… than in half the creeds.”
Tennyson
Developments!
Some ammunition companies are now making high-strength, steel cartridge cases that can supposedly handle 80k psi. Some are monolithic. Others are two-piece (“bi-metal,” with the cartridge base of steel, while the forward portion is traditional brass). Bullets mounted on these high-pressure rifle cases will go 200-300 f/s faster than the equivalent from an all-brass (conventional pressure) case.
With bolt-action hunting rifles (maybe sniper-rifles also), this significant increase in chamber pressure may require an increase in barrel and chamber thickness, will generate colossal muzzle blast (which may be dampened by a suppressor-can), and will certainly diminish barrel-life. But, otherwise these new cartridges are probably doable and may gain some traction.
However, with autoloading rifles and machineguns, this new high-pressure technology has become straightaway mired in durability issues!
With our new bi-metal 6.8×51 (277 Sig Fury) cartridge, and SIG’s new rifle designed to shoot it, we’re already on our second version of the rifle, and significant durability problems have not gone away. This system may eventually “work,” but not without a lot of barrel and suppressor replacements (not to mention bolts, extractors) being readily available. A military rifle must be reliable and have a reasonable service life. Temperamental, high-maintenance rifles represent a unmistakable liability, but during recent conflicts we in the USA have become accustomed to adequate resupply and equipment maintenance. During a future sustained, desperate, multi-front conflict, availability of spare parts and maintenance will certainly suffer, maybe fatefully!
To address these durability issues, a “normal pressure” all-brass version of this 6.8×51 ammunition is consumed during training, while the bi-metal, high-pressure version will be issued when real fighting starts. Interesting theory, but that proposed switch has issues all its own, not the least of which are mandatory re-zeroing and the fact that the high-pressure version of the 6.8×51 round currently cannot be manufactured fast enough to keep-up with demand during significant contact. Adequate supplies may never become available.
“Gain-twist rifling” represents yet another way of addressing the barrel-wear issue. It’s been around for many decades, mostly with artillery pieces. The rate of rifling twist actually increases as the projectile moves toward the muzzle. There is reduced throat erosion and pressure-spikes when rifling is essentially parallel with the bore just in front of the chamber, increasing only as the bullet moves forward.
In any event, the rest of the Western World’s armies, particularly our NATO allies, have expressed not the slightest interest in this dubious American high-pressure cartridge. Even our own USMC has decided to pass. The whole project may ultimately succeed, but it’s getting off to a really rocky start. Even its formally-ardent promoters are jumping ship!
A parallel development is the 5.56×45 “HICAR Project” Using high-pressure, steel cases, chamber-pressures of 85k-100k psi are deemed necessary to convert our current M4s from 300m rifles to 600m rifles. Again, I see deal-busting durability issues rearing their ugly heads almost immediately. Current rifles will never stand-up to these high pressures, and many voices will thus suggest simply moving to another “normal pressure” caliber (6mm ARC, 6mm Creedmoor) instead, since current M4s would all have to be replaced anyway.
Reasonable durability and extreme performance are mutually antagonistic. For our Army, any army, a rush to either extreme is probably a bad idea. We can’t have it both ways, but we may find a workable compromise
No joy yet!
Meanwhile, I’m not trading-in my M4, nor my supply of “conventional” 223 ammunition!
/John
