Its a bit off track but on the subject of blow-by it is only fractional in the scheme of firing a round in this clip we can see the blow-by exit first and has almost dispersed when the projectile exits followed by the longer lasting jet of gases from the ignition of the powder also visible are un-burnt powder grains/flakes.
Furthermore, Gale McMillan of McMillan barrels fame, made the valuable point that forming a boat-tail actually added another potential source of static eccentricity and thus a potential source of greater precession, especially at shorter ranges.
For decades, pretty much every bench-rest record was shot with very carefully formed, flat-based bullets. The nano-seconds of exposure of a boat-tail, to erupting muzzle-blast, has the potential to induce "wobble" and greater precession. The gyroscopic spin of the bullet will iron that out in a few hundred yards, as long as the boat-tail is PERFECTLY concentric to the rest of the bullet.
The Mk8 .303 was not introduced so the average Tommy / Digger could head-shoot the Hun at 1000 yards with a bog-standard SMLE / No.4. It was to extend the effective beaten zone capability of the Vickers (on a tripod) and Bren guns. Getting caught in a shower of subsonic Mk8 bullets at 2000 yards would not be a pleasant experience.
As for increased throat erosion, swapping a barrel on a Vickers or Bren is a "user" task, performed during brief halts in firing, as opposed to the field workshop nature of a rifle re-barreling.
With Vickers being deployed in "teams" drawn from a specialist Platoon,or even a machine-gun battalion, a "solo" gun is an aberration. With six or more guns on a fire task, one could always be "off-line" for a barrel swap, stoppage clearance, parts replacement, a quick clean and re-oil, re-laying, or whatever.
The Mk8 .303 was not introduced so the average Tommy / Digger could head-shoot the Hun at 1000 yards with a bog-standard SMLE / No.4. It was to extend the effective beaten zone capability of the Vickers (on a tripod) and Bren guns. Getting caught in a shower of subsonic Mk8 bullets at 2000 yards would not be a pleasant experience.
As for increased throat erosion, swapping a barrel on a Vickers or Bren is a "user" task, performed during brief halts in firing, as opposed to the field workshop nature of a rifle re-barreling.
With Vickers being deployed in "teams" drawn from a specialist Platoon,or even a machine-gun battalion, a "solo" gun is an aberration. With six or more guns on a fire task, one could always be "off-line" for a barrel swap, stoppage clearance, parts replacement, a quick clean and re-oil, re-laying, or whatever.
G'day Bruce..
Wholly agree with your post, although swapping out barrels on a Vickers and a Bren were really for different reasons.. The Vickers barrel reciprocates through a stuffing box gland on the water jacket that needs to be repacked after continual shooting. This I would think is the main reason for breaking down a gun, which was, as you say, a crew responsibility. The reason for swapping barrels on the Bren was to allow them to cool, which was not an issue with the water cooled Vickers. In both cases, barrels were subject to Periodic REME/RAEME Inspection when they would be guaged and condemned if out of limits... I'm sure Peter Laidler could confirm..!
Throat erosion is a real problem in high velocity guns and is mainly caused by the peak gas flows just as the projectile seats in the rifling.. the original MAG/GPMG had a sustained fire barrel with a stellite liner at the end of the chamber to counter this, but they had great problems getting it to stay in place...
Only saw a Vickers barrel swap in a workshop, once; long ago and far away.
I spent a lot of time both firing and fixing the good-old M-60, which also had / has a "Stellite" insert. The REALLY flogged out ones that were used to make "Blank Firing" barrels, usually had quite good-looking throats / leades, (Stellite), but were often virtual smooth-bores beyond that; NOT to be used for overhead live fire. Talk about getting your money's worth out of a barrel!
Never saw a liner come loose. There is a small gap between the stellite bit and the nominally hard-chromed remainder of the bore. I figured that this was to allow for a difference in the expansion characteristics of the two materials.
When we had to "de-mil" M-60 barrels, the liner was a challenge; the gas-axe just bounced off and the "drop-saw" with the nastiest abrasive wheel was not terrible effective. One trick was to cut around the circumference, down to the liner, and then attempt to shatter it by bashing it with a BIG hammer. Eventually, it was decided that if the locking collar was destroyed and the barrel forward of the stellite cut into short pieces, it could be considered "innocuous" enough to go in the "controlled scrap" bin. If that stuff ever went near a smelter, the stellite could have been a cause of annoyance to the operator.
Stellite is interesting stuff. It is primarily an alloy of cobalt and chromium and usually contains tungsten and / or molybdenum and a small amount of carbon.
Stellite drill bits are often used for drilling materials with a hardness above 50RC.
The trick is that the drill bit is used "lightly" at first, to HEAT the material surface and disrupt the hard crystal structure, then more pressure is applied to cut to depth.
Set-up must be absolutely rigid, just as for Carbide tooling.
These are not your Grand-dad's high-carbon twist drills, though they have been around for decades.
The subsequent tapping of threads into Stellite-drilled holes in those hard Eddystone breech-rings, is another matter.
Given the physical characteristics of Stellite, forming the barrel "inserts" would be an interesting process.
I'd been aware of it for decades too, I was issued an M60 back in '77 and therefore heard things when they were spoken about it. The Russians had used nickel liners, about indestructible but the cost was prohibitive. I'd also heard the corrosion around the liner was a problem...
The Russians had used nickel liners, about indestructible but the cost was prohibitive.
I know Ivan is deeply into chroming barrels, but never heard of nickel lining... not pure nickel surely? Usually the problem is getting the nickel from jackets off the bore..!
The problem with Stellite is getting it to stick to things...! It will be interesting to see if there are any new developments in this area with quite a number of now materials such as cubic boron coming on the scene.. forming/machining is always a problem..
Ivan is deeply into chroming barrels, but never heard of nickel lining... not pure nickel surely
I can only relate what was told. You probably have a better suggestion, I knew about their chroming everything, bolt face, piston head, barrels... But at the time we were told nickel. Could be far fetched...story probably had no substance.
The chrome isn't magic though, one young soldier of mine returned from Afghanistan and told me he'd examined AKs that you couldn't see through the barrel because of rust...I'd have loved to seen that. Must have been Mujahideen leftovers...
I wonder what improvements they made to the making of the barrel as the presenter says it is good for 15,000 rounds before changing, still an 850 round single pull continuous burst from the M-60 E-4 is not bad without a single hicup!
PM
Originally Posted by Bruce_in_Oz
