7mm Spitfire guns

[drewwizard]

I keep hearing these arguments on barrel wear and have to wonder why someone thinks this would be a real factor in the decision. For one, aircraft machine guns have their barrels burned out all the time and are replaced. Very long bursts are far worse for a barrel than high velocity cartridges. You are putting $25 dollar barrels x 6 on a $50,000 airplane, using 150 gallons of Gasoline on a mission, 4 quarts of oil and a large souped up engine. The machine will be piloted by a very highly trained and expensive pilot and have two full time ground crew to service the aircraft between twice daily missions. All this expense to damage the enemy's very expensive equivalent. The better you can damage the other guy as compared to him damaging you is the decision. If you think barral wear figures into this equation, then you should not be designing combat aircraft. Barrels especially in combat aircraft are simply an expendable. A 5 second burst, and the barrels are done anyway.

 

[Shortround6]

For one thing the .276 Enfield round was burning out rifle barrels during the Pre-WW I tests.
The costs-problems this involved counted against it's adoption.
Likewise increase wear on ground machine guns would not be looked on with favor.
A water cooled Vickers gun in .303 needed a new barrel in about 10,000 rounds if fired according to the manual (200rpm). Needing more spare barrels was an expense/complication not wanted.
One of the Vickers guns more famous actions involved 10 guns firing just under 1 million rounds in 12 hours. they used up 100 spare barrels.
Provision of spare barrels is not a trivial matter.

The American .50 cal was a notorious barrel burner and pilots were "supposed" to limit the initial burst to 75 rounds. which is about 5 3/4 seconds and they did NOT replace the barrel after that, they did if the pilot abused the barrels with long , hosing fire. 300mph winds over the barrel with low temperature air offers pretty good cooling if the trigger is not held down.

However the .276 Enfield is pushing the envelope for very little return. Whatever extra power it has over the .303 ( and please note it will carry less incendiary material due to smaller bullet) is minimal compared to going to bigger guns.

 

[The Basket]

The ,276 was burning barrels out on a bolt action rifle! Not a machine gun.

 

[Shortround6]

And if it burns out barrels on a rifle what miracle of physics is going to stop it from burning out barrels on a machine gun?
Machine gun barrels require less labor to change but they require the same labor/machine time to make.
Machine gun barrels can be ruined in 500 rounds or less or they can last 5000 rounds or more even with the same cartridge, depending on rate of fire and cooling provided (often time between bursts).
on the cartridge side it is pretty much governed by the flame temperature of the propellant, the amount of propellent and the bore size. The .276 used much more propellent in a smaller bore.

 

[drewwizard]

The point is, gun barrels on a fighter plane would be a minor expendable in the cost of operating such an expensive machine.
Cooling with cold air at altitude is a nice thought, but the slowness of heat transfer does not keep the inside of the barrel cool in a long burst. Even if it was immersed in liquid nitrogen you would still burn out the barrel.
The criteria is different for an infantry weapon where cost matters. Now would you make a special aircraft weapon in a different caliber? Probably if it had an advantage that the accounting department would recognize. Saving the expensive plane is easier to justify.

 

[Shortround6]

While individual pilots certainly varied they were NOT supposed to fly around with their finger on the trigger (or thumb on the button) until the ammo ran out. They were supposed to fire in bursts and it was generally thought (before the war) that 2-3 seconds was as long as they cold could keep the target in the sight. If the there is no target in the sight they were supposed to stop shooting. Most of these guns fired open bolt and a 300mph wind blowing well below zero air through the barrel has some pretty good cooling properties.
BTW, this air cooled effect was noticed in WW I when they took the water jackets off the guns

Notice the louvers in the jacket, which could not be done away with as it supported the front barrel bushing/gland.

and these guys flew a lot slower than WW II planes

Supplying barrels at a much higher rate than needed for a minor change in effectiveness just doesn't make sense.

 

[J.A.W.]

@ S-R 6, ta for the most informative posts, & ta for showing us your own pieces.

I've fairly recently inherited a slightly interesting .303 rifle, from my late father.

It is a quality-built BSA of Boer War vintage, a 'Long Tom' ( as they are known downunder)
that was uprated to 'match spec' by fitment of a Aussie made 'Lithgow Armoury: Heavy' barrel.

These custom-modified rifles drew 'tut-tutting' from the haughty Englanders when presented for use
in 'Inter-Empire Service Shooting Competition' or somesuch - according to my old man.

I do recall being impressed by that ol' banger, as a kid - when told "Have a go son",
& later found out he'd slotted in a number of 'naughty' Vickers MG cartridges - to feel the "extra kick"!

Those were the days, eh..

 

[Alicatt]

As a young whipper-snapper in the local Air Training Corps we had the luxury of having an outdoor full-bore range that we shared with the territorials.

As a 12 year old heading out to the range with a Rifle No.3, the rifle that was almost as big as my self it was quite a daunting excursion. We got put through the paces in stripping and cleaning the rifles before heading out to the butts to mark the fall of shot. Lunchtime and we swapped ends and I go my turn behind the sights, being shown how to hold the rifle prone and got to fire my first round and I had moved back off the firing point, even digging in my heavy tackety boots the recoil was still lifting me up off the ground, I ended up having one of the officers sitting on my back to keep me in place.
Many years later I was a proud owner of a Rifle No.4 Mk1*, great rifle and quite accurate, I sold it on in 2010.

My father, when in the RAF, shot at Bisley for RAF Tangmere just after WW2, during the war he said one of his duties was to shoot unexploded ordnance and before that after leaving school and going into the local shipyard he was in the home guard and there he had a Lee Enfield that had been all wrapped up with wire so that it could be used to fire rifle grenades.
The only target shooting I do now is with a bow and I have been shooting arrows for over 50 years now

 

[Clayton Magnet]

Can you currently own a center fire rifle in the UK? I was under the impression that it was shotguns and rimfire only

 

[Glider]

With the average life expectancy of an aircraft and the chances of it firing enough rounds to wear the barrels out. The UK decided to lower the manufacturing standards and increase the production. A decision that seems to have been correct as I have never heard of issues of this nature

 

[The Basket]

The British person can own a bolt action rifle. Even an AR-15 if converted to bolt action only. Self loading rifles are verboten and full auto is double verboten.

An interesting thing I saw on the P-13 spoken by an internet gun expert was that it was a dead duck and the cartridge killed it off. The army wanted the rifle to match the numbers specced and since it couldn't then it was ducked. But the guy also said the P-14 was USA only and this wasn't the case as UK production was tried but there was no spare capacity so it became USA made as the P-14 was an easier build than the SMLE. Just copy 7mm Mauser! If the P-13 was a political decision then it would have gone through somehow.

It was the Enfield 280 that was eating barrels not 303.

 

[Shortround6]

With the average life expectancy of an aircraft and the chances of it firing enough rounds to wear the barrels out. The UK decided to lower the manufacturing standards and increase the production. A decision that seems to have been correct as I have never heard of issues of this nature

Depends on the gun, the ammo and length of burst/fire discipline.
If you read the 1942 US manual for the .50 cal aircraft gun it has a host of restrictions on long you should fire it (75 rounds for the first burst) , how long you should let it cool off and how many rounds per minute you should fire after the initial burst (25 rounds per minute each minute after the initial 75 round burst and cool off period) that nobody in combat was going to pay any attention to. The US usually had a good supply of spare barrels and the gun body and internal parts would outlast quite a few barrel. Around 1944 they started chrome plating the bores and barrel life went up significantly.
The US .50 used around 15-16 grams of propellent with each shot compared to the 2.5-3.3 grams of a rifle caliber gun. Not all powders have the same heat value per gram of weight (or the same flame temperature) but you get the idea, If you want the high performance round you better be prepared to pay for it, including increase logistics difficulties.