7mm Spitfire guns

[The Basket]

Had the Enfield P13 gone into production and the .303 replaced by the .276 or 7mm round, would the Spitfire fired 7mm rounds instead?

 

[Shortround6]

Only if you want crappy incendiary and tracer ammunition. And much more rapid wear on the gun barrels.

Edit, British would have figured out pretty quick in WW I that whatever advantage the .276 Enfield cartridge may have had as a rifle round it was a lousy machine gun cartridge.

It advantage as a rifle round for average conscript troops vs the .303 is debatable as it is.

 

[The Basket]

I would have assumed that the British would have perfected the .276 so it didn't burn out the barrels. Certainly was an issue with the P13.
It's interesting to think that the Vickers and Lewis and later Bren used the 303 so would have to assume that they would have been 7 mm as well.
I'm sure the .276 would have been fine as a machine gun round. Not got a huge rim like the 303 or 8mm Lebel.

 

[Shortround6]

You can't repeal the laws of physics with development/perfection.

A .303 used 37 grains of cordite as a propelling charge. a few types of .303 ammo used up to 40 grains. the .276 Enfield used a charge of 49.3 grains of cordite. You are releasing 33% more heat with every shot into a smaller diameter barrel.
Even if you switch to nitrocellulose powder with a lower flame temperature you still need much more powder than the .303 in order to reach the advertised velocity. The .276 has more powder capacity than a .30-06 or a .280 Remington (.30-06 necked down to 7mm).
The .276 was about 3 1/2 mm longer (both case and complete cartridge) than the .303. This extra size was one reason the P13/P17 action was desired for sporting rifles in the 1920s and 30s. It was much easier to convert to .300 H&H and .375 H&H than other military or commercial actions.
The rear end of the case is about the size of a standard belted magnum, the belt that is. The .276 did have a fair amount of taper.
The back end of the .276 was about .008 in smaller than the rim on the .303.

and you still have the smaller diameter barrel.

A .243 Win will burn out it's barrel quicker than a .308win. Same case and powder capacity, just necked from .308 to .243. They tried making some .224s on the .308 case but barrel life was truly horrendous, not a surprise after the .220 swift.

Going to a case using 33% more powder and having the hot gases go out through a smaller bore and then trying to do it hundreds of times per minute is not going to end well.

 

[parsifal]

The Spitfire adopted the 0.303 caliber because it was cheap , and ammunition was in virtually unlimited supply. if significant dollars had to be invested in a revised armament, I think it far more likely the british would have been looking at increased caliber, probably to 0.5" caliber, but perhaps even to the intractable 20mm cannon fits.

 

[Shortround6]

I think he is asking what would have happened if the UK had adopted the .276 just before WW I, how would that have affected the choice of guns for the Spitfire (and Hurricane and everything else) in the 1930s, no huge stock of .303 ammo to deal with.

I believe, much like the Italians did in the late 30s with the 7.35mm, the British would have switched back to the .303 not long after the shooting started in WW I and the .276 would have been consigned to the rubbish bin and no lasting change would have to be dealt with.

As it was the British manufactured about 7,000,000,000 rounds of .303 in British factories during WW I. Factories in other countries added considerably to this total but just for the British switching to the .276 would have needed 6000 short tons more cordite ( or equivalent amount of nitro cellulose) and thousands of tons more brass to make the cartridge cases.
The .276 was simply not a practical cartridge at the time with the available propellants, either cordite or nitro cellulose.

 

[Barrett]

Firearms designer John C. Garand (of Canadian origin) developed his famous M-1 semi-auto rifle for a .276, which offered superior ballistics over the .30-06 round. But Big Army had tons of 06 ammo and did not want to convert. The decision to stick with .30 cal came in the early 30s, I believe. (Similar situation exists today. Near the start of the GWOT some special forces guys actually got 6.8mm (.277 cal.) rifles built and apparently deployed with them satisfactorily but there's no way billions of rounds and millions of weapons will be ditched.)

 

[Shortround6]

The American .276 was a much smaller cartridge than the .276 Enfield. ans would have offered some savings in materials over millions of rounds produced. It also would have had much less barrel wear than the .276 Enfield.
But yes, existing stocks of ammo and existing production facilities can make changing over a very difficult thing to do. Nobody wants to spend the money in peace time and nobody wants the delay/disruption in a full scale war.

 

[drewwizard]

First off, the smaller and faster cartridge do not burn out barrels. They do cause some accelerated throat erosion requiring a chamber reaming after 10,000 rounds down the barrel. The solution in production done with the M-16 was chrome plate in the chamber area. In long range target shooting it's usually stainless steel barrels. The smaller faster cartridge is lighter which is great for an infantry as they can carry more bullets, and the cost is lower to manufacture.

For an aircraft it's a really bad idea. The smaller cartridges have more limited range. When you are talking about shooting at another aircraft at 600 yards, the smaller round loses so much energy that minimal damage results. Might as well throw stones. The 30 caliber aircraft rounds quickly changed to 50 caliber, then to 20mm (25mm and 37mm).

 

[Shortround6]

Key here is smaller and faster cartridge.
The .276 was NOT smaller. It was fatter and longer than the .303 and used around 30% more propellant behind a similar weight but skinnier bullet.

That is a recipe for burning out barrels, especially with the propellants of the time. Nitrocellulose got a lot better in the 1930s than it was before WW I and it got even better after WW II.

The 5.56 uses around 1/2 to 5/8ths the amount of propellant as a .308/7.62 Nato. and a bullet that started out almost 1/3 the weight.The bullets got heavier.

.220 Swift inbetween .223/5.56 and a .308/7.62 Nato.

Swift got a reputation as a barrel burner pretty quick. Part of the problem was actually jacket fouling and hand loaders could back off the powder charges 5-10% and still get high velocity (not quite as high) and much better barrel life. Swifts were the first factory rifles to come with stainless steel barrels.

 

[The Basket]

The British 7mm never reached maturity so what it's final form would have been is debatable. Obviously burning out barrels after 1000 rounds is bad form so I would expect the round to have been altered or underpowered or something.
Oddly the rifle was excellent out of the box although it was a Mauser copy.
The idea of the 7mm was to have a flatter trajectory which would give it better accuracy over distance. One must also remember that 8 303 machine guns in a fighter was Revolutionary and I would expect 8 7mm would have been equally novel. The Italians and Japanese were happy with less.

 

[Shortround6]

The British 7mm was as mature as it was going to get in 1913-14, It had already been through a number of variations.

Altering the shape of the case does little or nothing despite some peoples claim to the contrary. It may make the cases harder to form.

Lowering the powder charge does work, but then "underpowering" the cartridge seems to be defeating the purpose. Making the velocity difference between the .303 and the .276 closer means a closer trajectory path and less difference to justify the change.

The difference in trajectory for long range rifle shooting has little application in air to air combat where the effective distances are much shorter. A few inches difference in impact on an aircraft fuselage?

The Japanese may have been happy with much less than eight .303s, the Italians were not, shifting to a pair of 12.7mm machine guns in the early/mid 30s, before the Hurricane and Spitfire first flew. The 12.7 was roughly 3 times more powerful on a round to round comparison.
The Italians failed to increase the rate of fire as time went on, although they did try using HE ammunition. The pair of synchronized machine guns might be equal to 3-4 synchronized .303. When mounted in the wing one 12.7 might be equal to two .303s. Yes less than eight .303s but the Itialians weren't happy" about it, they simply didn't have the engine power to carry any more. Their primary fighter engine, the Fiat AR 74, made roughly the same amount of power as the Bristol Mercury in the Gloster Gladiator.

They also tried fitting additional 7.7 machine guns at times.

Here is a bit of internal ballistics (what happens inside the gun) information. It is a bit simplified but bullet velocity is dependent on the pressure applied to the base of the bullet vs the weight of the bullet per unit of area (sectional density).

What this means is that using similar powders (to keep the burning curve the same) is that, due to the difference in diameter, you can accelerate a 145 grain 7mm bullet to the same speed as a 174 grain .303 bullet using the same pressure. If you want to use a 165 grain bullet in the 7mm you need more pressure, if you want higher velocity you need more pressure.

The smaller diameter bullet will have less room inside for incendiary materiel and it's AP qualities may be suspect, especially at anything other than a 90 degree impact. Long skinny bullets not doing so well at oblique impacts or penetrating after intermediate barriers. The US .50 having trouble with that one for instance.

The British, after the BoB, moving to a mix of 50% AP and 50% incendiary ammunition as fast as production would allow.

 

[The Basket]

The change to 7mm and the P13 was to rid the rimmed 303 and the SMLE which was considered flawed.
Only for them to survive until the FAL.
8 X 7mm machine guns would have been considered powerful in 1930s speak as even the Bf109 had 2 machine guns in its first guise.

 

[Shortround6]

Turns out the SMLE wasn't as flawed as they thought. A better back sight and bit heavier barrel could make up a good part of the difference in practical accuracy. At least as far as you were going to be able to train 98% of the recruits to. It also tolerated mud a bit better, even if not close to flawless in that regard.
AS shown above the 7mm needed more resources in brass and propellant to manufacture. That is without considering the barrel wear problem. Barrels with little or no rifling in the first few inches of the barrel ( or even the first 1/2 to 3/4 of inch) have lower velocity and poor accuracy.

Sure eight 7mm guns would have been better than two or four rifle caliber machineguns used by other countries but since they show no real advantage over .303 machineguns at 300-400yds range and more than few disadvantages what is the point?

They won't be any lighter, the barrels won't last as long, the trajectory against an aircraft sized target shows no advantage, time of flight difference is marginal at 300-400yds but does get better with longer range but 99% of the pilots have no business firing at over 400yds.

Armour piercing will range from slightly better to slightly worse depending on range and impact angle. Incendiary ammunition won't hold as much incendiary material.

Guns may fire slightly slower (heavier bolt and or heavier recoil spring), bolt may have slightly longer travel. Ammo weighs more per 100 rounds, larger heavier links. Gun has to pull more weight of belt.

I am failing to see any advantage for the 7mm for aircraft use.

And darn little for rifle use from 1914 on.

BTW these are two of the rifles I own.

The bottom one is a converted No 4 Enfield and will make anybody who claims that "rear locking lug rifles won't shoot" a liar.

What works on the range may be totally impractical in combat.

 

[The Basket]

The SMLE was far from perfect.
And if the British had got a 7mm rifle and was in full production and was the standard weapon in a ww1 that started in 1920 then bit late to go all misty eyed for the 303. Considering the P14 was better....in my view....than the SMLE then common sense has no real place in arms procurement.
If the 7mm round had become workable then if the Browning machine gun was in 7mm then I would say that is a done deal

 

[Shortround6]

The P13/14 may very well have been a better rifle.
However the .276 was a lousy cartridge in 1913/14 and would have been a lousy cartridge in 1920 or in 1930.
It would take until the late 30s or post WW II for powders to be developed that would make the .276 at least usable.

I have pointed out several reasons why the .276 Enfield was a lousy cartridge, please point out how I am wrong.

And even if, through the repeal of the laws of physics, the .276 Enfield had been adopted as an aircraft machine gun cartridge,
what advantage in terminal effectiveness (target damage) does it have to warrant it's adoption?

The whole thing, cartridge and rifle, was an exercise in misidentifying the problem and then trying for a jeewhiz technical solution instead of the practical one.

The Boers out shot the British in South Africa using the 7mm Mauser cartridge. There is no question about this. However the conclusion or lesson seems to be in error. The 7mm Mauser as used by the Boers had no great advantage (or end a moderate one) over the .303 round in use at the time. Both rounds used round nosed bullets of very similar velocity, unless the Boers were using hunting bullets. However the Military Mauser sights do not take kindly to changes of bullets/trajectories of different ammo. And firing at long ranges (600 yds and over) requires both accurate range estimation and observation of fire and bullets that go where the sights are aimed. The 7mm round as used by a varity of countries changed to a lighter spitzer bullet at higher velocities in the early 1900s but these rounds were not the one used by the Boers.

British .303 trajectory chart.

The MK VI (the one in black) was the round used in the Boer war. The MK VII (in red) was adopted in 1910/1911 and as can be seen, added around 100 yds to the effective range of the rifle (new sights would have to be fitted). The .276 would still be superior but a large amount of it's superiority over the MK VI round had disappeared.

Now we get into the other aspect of the problem the British had in South Africa. Lack of training or lack of proper training. Trying to hit man sized targets at 600 yds and beyond take both skill and training. Post Boer war and Pre-WW I the British army did devote a fair amount of time to rifle training and got quite good. However the reduced time available for wartime training meant that standard of Marksmanship disappeared and perhaps never returned, certainly not for the duration of the war. The .276 Enfield had the twin problems of increase recoil (approximately 15%) and increased muzzle blast that made training recruits that much harder. Yes the P13/14 had better sights (and perhaps a better trigger?) but it's higher velocity is not going come into play until long ranges are used. And then you run into target identification, wind drift, poor lighting and the biggest problem, just holding the gun steady enough to keep the sights on the target at those ranges.

The SMLE may have been a long way from perfect but it was good enough for the vast majority of troops it was issued to (and in the No 4 version, it fixed the worst of the No 3s problems). I can give an Olympic quality rifle to a new shooter and until he/she conquers the basics they won't do any better than the person next to them with a rifle costing 1/10 as much.

The idea of average troops making 1000yd shots is almost absurd. At one time I was on a 1000yd range with the gun in the top picture and had 14 minutes of windage on the gun. The bullets were being blown 140 inches (just over 3.5 meters at that distance) and the wind wasn't really that bad, shooters that routinely use that range told me they had seen days when 23-24 minutes of windage where needed (over 5.8 meters). Using a cartridge with an extra few hundred fps of MV or that shoots a couple of feet flatter a isn't going to help much.
That rifle when sighted dead on at 900 yds ( almost all rounds landing in the highest scoring ring) is 5 feet low at 1000 yds. How many people can tell the difference between 900 and 1000yds without either an optical or electronic range finder?

 

[The Basket]

Remember this is the British military making these decisions...not I.
The arguments you are putting forward are what they believed at the time. So the decision to focus on long range or a new Mauser style rifle or a 7mm cartridge is fact. This is the British military! They accepted the SA80! Common sense or facts don't apply. If they said we are accepting the P13 then that would have happened.
I have said that the 7mm Enfield round was trouble but given time they would have fixed it or fudged it or even faked it.
The SMLE did have issues real or imagined and the so did the 303 and the Mauser action is considered the holy grail of bolt actions. So a copy makes sense. The P13/P14 or even Enfield M1917 was superb out of the box which is very rare for a new rifle.
You need to chat to the Small Arms Committee in 1911 if you feel the .276 cartridge is a bad egg.

 

[Shortround6]

You need to chat to the Small Arms Committee in 1911 if you feel the .276 cartridge is a bad egg.

It is not that I feel the .276 was a bad egg. I have shown the the .276 was a bad egg.

I have said that the 7mm Enfield round was trouble but given time they would have fixed it or fudged it or even faked it.

Ok I could be wrong, why don't you tell me HOW they would have fixed it or fudged it or even faked it.
No waving the hand in the air and saying they would have done it if they wanted.
HOW would they have fixed it?
HOW would they have cut the recoil?
How would they have fixed the muzzle blast?
How would they have fixed the barrel wear?
How would they have fixed the need for extra materials to make the cartridges?
How would they have trained the soldiers to use the extra range?

BTW the P-13 rear sight is NOT adjustable for windage so in the conditions I mentioned above our intrepid 1000yd shooter would have to hold his front sight 3.5 meters to the side of his intended target. Now how he knows what bush or window corresponds to to 3.5 meters I have no idea. So many front sight blade widths? and that changes for every distance.

As far as the materials consumed goes, just filling a Spitfire with 300 rounds per gun and eight guns would use over 4 pounds more cordite and even more than 4lbs of brass.

You have yet to point out any advantage the .276 would have had for air to air use. Perhaps a bit less lead needed on a turning target? A bit less deflection? How much less? you only need to aim 6 plane lengths ahead instead of 7?

It's fine to use up materials if you are getting something (and if you have them), The amount of powder and Brass needed to fill P-47s ammo bays is enormous but then Eight .50s do a lot more damage than eight light machine guns. I am also not a big fan of the .50, It used a lot of material for what they got out of it.

The .276 was a bad answer to the wrong question. As a machine gun round it would have been worse.

During the last 30 or more years there have been a number of super sniper rifle rounds put on the market and some used in combat.
Nobody has been dumb enough to buy machine guns chambered for them.

 

[The Basket]

Eh? I am not saying the 7mm would be better. The Small arms committee is.
Since the ww1 started the 7mm was dropped so what the British would have done is pure speculation. What the British would have actually done, I have no idea. But the clue is that it was dropped. It was not revisited. Maybe that is the clue what the British would have done. They would have cancelled it.

 

[Shortround6]

They did cancel it and the cancellation, as such, seems to have been the result of a burst rifle at Aldershot. A round cooked off in a hot chamber. A number of experiments were done to determine the pressure and several experiments were also done with Nitro cellulose powder from Kynoch which showed even higher pressures under such circumstances. to quote from the report;
" it became clear that until a suitable propellant had been developed, the new .276 inch rifle and cartridge could not be passed into service."
This has little or nothing to do with the War breaking out. The ammunition was unsafe for general issue as it existed. The blown caps and hard extraction are also signs (put not proof positive) of excessive pressures. Some propellants are very temperature sensitive and what works at 60-70 degrees F can result in having to hammer the bolt open and/or blown primers at 90-100 degrees F. You can solve this by backing off on the powder charge by a few percent but then you don't get the desired velocity.

At the same time they were working on reducing barrel wear. Now they did learn a lot and they were fumbling around in the dark compared to what is known now but the bullet designs tried were many and varied and did little to actually change the results.

Throat erosion is a complicated subject and some requirements are in conflict with each other. For example getting the bore sealed by the bullet as fast as possible helps with throat erosion, there is less high pressure gas passing by the sides of bullet as the bullet starts moving.
However some designs of high speed cartridges depend on a loose fit of the bullet in the first few millimeters of travel and the resulting blowby to keep the pressures within safe limits.

Jacket fouling is a whole different subject (depositing unwanted material in the barrel instead of removal of barrel material).