British .303 vs 50 Cal M2

[David Fred]

besides using wikipedia, what was the difference in weight between a Mk.5 Hispano and M2 Browning?

Here's the comparison between the 20mm Hispano and the Mk108 30 x 99.Note that only 1/3 of the 30mm is propellant. Muzzle velocity is only 550 m/s, which means a 5 meter drop at 550 meters. Plus, the plane had 100 rounds per gun firvthe bottom two, and 80 founds per gun for the top two.

This is an interesting (if crappy) cannon. In order to increase rate of fire from about 410 rpm to 600, instead of mounting the recoil spring around the barrel like a Bofors, they put it behind the bolt. To prevent a release of explosive gases in the fuselage, it had a very short barrel, (44cm) hence the lower muzzle velocity.

 

[David Fred]

View attachment 490423

Here's the comparison between the 20mm Hispano and the Mk108 30 x 99.Note that only 1/3 of the 30mm is propellant. Muzzle velocity is only 550 m/s, which means a 5 meter drop at 550 meters. Plus, the plane had 100 rounds per gun firvthe bottom two, and 80 founds per gun for the top two.

This is an interesting (if crappy) cannon. In order to increase rate of fire from about 410 rpm to 600, instead of mounting the recoil spring around the barrel like a Bofors, they put it behind the bolt. To prevent a release of explosive gases in the fuselage, it had a very short barrel, (44cm) hence the lower muzzle velocity.

One other thing I did, using the book I mentioned, and another called "Who Won the Battle of Britain" by Wing Commander H.R. Allen. I put it in a spreadsheet, because in 40 years I still can't build a table in Microsoft Word.
It's in the top table.
Below is the cartridge photos of the 20mm and the 30mm. Sorry, I'm new at this.

 

[pbehn]

View attachment 490424 View attachment 490424



One other thing I did, using the book I mentioned, and another called "Who Won the Battle of Britain" by Wing Commander H.R. Allen. I put it in a spreadsheet, because in 40 years I still can't build a table in Microsoft Word.
It's in the top table.
Below is the cartridge photos of the 20mm and the 30mm. Sorry, I'm new at this.

Great post David, basically it shows why the RAF switched from 8 x rifle (sometimes 12) 0.303 calibre mgs to 20mm cannon in 1940/41, and why the P-51 upped from 4 to 6 guns between the B/C and the D version.

BTW I always used to construct tables in Exel and paste them into Word.

 

[Shortround6]

I am not understanding some of the tables.
Rate of fire isn't making sense as labeled. rate of fire for the number of guns over how many seconds?
Energy at impact at what range or impact velocity?
Energy at impact for how many projectiles?

BTW the velocity for the .303 is incorrect, Velocity was between 2400 and 2500fps for most service rounds used in WW II.

 

[tomo pauk]

Here's the comparison between the 20mm Hispano and the Mk108 30 x 99.Note that only 1/3 of the 30mm is propellant. Muzzle velocity is only 550 m/s, which means a 5 meter drop at 550 meters. Plus, the plane had 100 rounds per gun firvthe bottom two, and 80 founds per gun for the top two.

This is an interesting (if crappy) cannon. In order to increase rate of fire from about 410 rpm to 600, instead of mounting the recoil spring around the barrel like a Bofors, they put it behind the bolt. To prevent a release of explosive gases in the fuselage, it had a very short barrel, (44cm) hence the lower muzzle velocity.

MK 108 was a very good cannon, throwing good-sized HE shells at good rate of fire, while being lightweight for all or that.
A reason why the MK 108 have had low MV was that propellant charge was of light weight when compared with weight of the shell. What version of the MK 108 was with 410 rds/min?

 

[David Fred]

Great post Fred, basically it shows why the RAF switched from 8 x rifle (sometimes 12) 0.303 calibre mgs to 20mm cannon in 1940/41, and why the P-51 upped from 4 to 6 guns between the B/C and the D version.

BTW I always used to construct tables in Exel and paste them into Word.

Thanks. Now that I am getting on a bit, I find the time to buy and read these specialist books, and this is a good one, not cheap, and supposedly in "layman's terms" (layman what I can't imagine).

 

[pbehn]

Thanks. Now that I am getting on a bit, I find the time to buy and read these specialist books, and this is a good one, not cheap, and supposedly in "layman's terms" (layman what I can't imagine).

It just seems an odd comparison because they are different eras. If there were any 8 x 0.303 armed Spitfires or Hurricanes flying in 1944 they weren't being used as fighters. You could also compare the firepower of the Mustang Mk I with 4 x 20mm cannon ordered in 1940 with P-51B/C with 4 x 0.5" mgs since these were operational in the same era.

 

[David Fred]

MK 108 was a very good cannon, throwing good-sized HE shells at good rate of fire, while being lightweight for all or that.
A reason why the MK 108 have had low MV was that propellant charge was of light weight when compared with weight of the shell. What version of the MK 108 was with 410 rds/min?

There was none. The author points out that a longer barreled version with a conventional Bofors type recoil spring and without Advanced Primer Ignition would have had higher MV but lower rate of fire. The projectile had 83 grams of explosive in Mk 108, a substantial load, useful against slow moving bombers, but a fighter speeds, withe the trajectory of a drop of 1.225 meters at 250 meters, and 4.9 meters at 550 meters, adjusting aim in fast moving combat against maneuvering fighters would have been nearly impossible. In fact, I can find no record of a fighter being downed by this weapon, and on hit would have been enough.
The Germans called it the "pneumatic hammer", because of the the "thunk, thunk, thunk" it made when fired.

 

[David Fred]

It just seems an odd comparison because they are different eras. If there were any 8 x 0.303 armed Spitfires or Hurricanes flying in 1944 they weren't being used as fighters. You could also compare the firepower of the Mustang Mk I with 4 x 20mm cannon ordered in 1940 with P-51B/C with 4 x 0.5" mgs since these were operational in the same era.

I built the table years ago when someone asked, not on this forum, what if the MkI Spitfire had used M2's instead of 1919's

 

[Graeme]

Part of an article by Roy Braybrook. Air International September 1985...

 

[Greyman]

Part of an article by Roy Braybrook. Air International September 1985...

"It was cheap, readily available, fully developed ..."
In the mid 30s when they would have needed to make a decision? I would argue no.

"It is a fair bet that the Air Staff rejected this option on the ground that 'If this is what the Americans are doing, it is almost certainly wrong'.
Citation needed on that one. Where's that eyeroll emoji?

"The irony of the situation was that Luftwaffe aircraft never were armoured against 0.50-in ammunition."
I think he would be surprised at the effect of passing through several feet of aircraft structure would have on a .50 bullet.

 

[Shortround6]

Well,
1. in error on fully developed.
2. in error on weight
3. in error on rate of fire in time for the BoB
4. Early ammo and in fact early WW II British ammo, used a lower velocity than the the Newly introduced US M2 loadings. British were buying ammo with 1500fps velocity in 1940 and after instead of getting the 2800-2900fps loadings.
Once again see : .50 inch Browning - British Military Small Arms Ammo

"
Britain was aware of this development and first considered use of the Browning in late 1918 to counter German ground attack aircraft that were fitted with armour too thick for the .303 inch Armour piercing ammunition to defeat. As the war ended, British interest in the .50 inch Browning lapsed for several years.

Further trials took place in 1923 and 1924 with ammunition supplied by Kynoch to compare performance with the newly developed .5 inch Vickers ammunition and in the period 1924 - 26 Woolwich both reloaded American cases with their own design of bullet and manufactured complete rounds. Kynoch also supplied flame tracer ammunition."

and
""Cartridge S.A. Armour Piercing .50 inch Browning W Mark Iz" was the American M1 AP round and included the Remington made contract ammunition. Britain purchased .50 inch ammunition both from the American government (via the U.S. Steel Corporation) and on contract from Remington for the RAF, some of which was specially marked to British requirements. Large quantities were also supplied under Lend Lease."
"The bullet had a gilding metal envelope with a hardened steel core and a lead tip filler with no sleeve. Weight was about 750 grains."
"Muzzle velocity was 2,500 fps with a charge of about 240 grains of nitrocellulose propellant and penetration was 1/2 inch of armour at 1,000 yards."

 

[tomo pauk]

There was none. The author points out that a longer barreled version with a conventional Bofors type recoil spring and without Advanced Primer Ignition would have had higher MV but lower rate of fire.

Hmm - then why specifying the rate of fire of 410 rds/min at the 1st place? How much higher the MV would've been if the working principe was not the API blowback? Since when the API blowback is equivalent of high RoF and low MV anyway?
The MK 108 have had 30g of propellant, the MK 101/103 112g, both for the Mine shell. So unless the ammo for the MK 108 is helped by fairy dust or unicorn breath, the MV will still remain as it was with the 330 g M-shell.

The projectile had 83 grams of explosive in Mk 108, a substantial load, useful against slow moving bombers, but a fighter speeds, withe the trajectory of a drop of 1.225 meters at 250 meters, and 4.9 meters at 550 meters, adjusting aim in fast moving combat against maneuvering fighters would have been nearly impossible. In fact, I can find no record of a fighter being downed by this weapon, and on hit would have been enough.

Re. no record found on MK 108 downing a fighter - how many late-war German records have you read?
That drop on distance - is it for sea level, 10000 ft, 25000 ft?
Interestingly enough, Germans themselves were of opinion that MK 108 is a viable weapon even for the targets doing 700 km/h.

The Germans called it the "pneumatic hammer", because of the the "thunk, thunk, thunk" it made when fired.

That is probably how the Allied crews called it.

 

[swampyankee]

Hmm - then why specifying the rate of fire of 410 rds/min at the 1st place? How much higher the MV would've been if the working principe was not the API blowback? Since when the API blowback is equivalent of high RoF and low MV anyway?
The MK 108 have had 30g of propellant, the MK 101/103 112g, both for the Mine shell. So unless the ammo for the MK 108 is helped by fairy dust or unicorn breath, the MV will still remain as it was with the 330 g M-shell.



Re. no record found on MK 108 downing a fighter - how many late-war German records have you read?
That drop on distance - is it for sea level, 10000 ft, 25000 ft?
Interestingly enough, Germans themselves were of opinion that MK 108 is a viable weapon even for the targets doing 700 km/h.



That is probably how the Allied crews called it.

With a muzzle velocity of 550 m/s, a drop of 5 m in 550 m horizontal distance assumes vacuum.

 

[Shortround6]

The "drop" is a rather overused and almost useless way of comparing aircraft guns.

Drop is dependent on time of flight. Whatever distance your projectile covers in 1 second, that is the distance at which it will "drop" 4.78 meters.
Distance covered in 1 second goes increases with altitude as the air gets thinner.

Now as to why it is near useless, fighter guns were not set dead level in the plane. sighting chart for a P-47

Guns were pointed slightly upwards to cross the line of sight and then fall back down to the line of sight.
Now this is good example of one extreme, guns almost 4 feet below the line of sight/sight line and guns with a high velocity/slow velocity decay.

The German 20mm mine shell and the 30mm mine shell are the other extreme but the 30mm is not quite as bad as portrayed in many online accounts as it is seldom compared to the other common German guns/projectiles

A 109 has the guns much closer to the line of sight but then it doesn't really matter if the projectiles go 10-15 inches above the line of sight instead of only 6-9 inches. You can get the downward crossing of the line of sight out to a useful distance. The idea that the poor pilot was having to compute "drop" at combat ranges of 200-500 meters is rubbish. Once the bank goes past 45 degrees then drop may enter into it but trying to figure a few feet of drop compared to how many plane lengths ahead you need to be shooting in minor.

They were trying to compute lead on the moving target and in this short flight times was definite advantage.
However, Flight time for a 30mm HEI 330gram projectile with a MV of 500m/s to 600 meters was 1.66 seconds. The 92gram 20mm mine shell from a MG/FFM took 1.428 seconds. These are at ground level.

AS to Tomo's question;

Since when the API blowback is equivalent of high RoF and low MV anyway?

It all depends on how the gun was set up. You could get decent rate of fire (but not great) and high velocity as the Japanese showed with the Type 99-2.

But API blowback guns are rather sensitive to ammo and especially so if you are trying for light weight.
In order to get the rate of fire up (and the weight down) on the MK 108 they used a light breechblock which meant the breechblock started moving to the rear quickly, more quickly than a heavier a breech block. SO quickly that the base of the cartridge was coming out of the chamber before the projectile left the muzzle and the unsupported sidewall of the case would blow out letting high pressure gas into the action and gun compartment. With a short barrel the projectile cleared the barrel, the gas pressure vented through the open muzzle and no more blown cases.
guns like the Hispano use a combination action. They use a mechanical lock to hold the bolt closed until the projectile reaches a certain point in the barrel at which point the mechanism unlocks and the residual pressure in the chamber/cartridge cases, pushes the breech block back and extracts/ejects the case.
At the cost of some weight/complication this allows for a much lighter breech block/mainspring to be used to get the rate of fire up.

On the MK 108, once they got to a certain point in the design/development they were stuck. They can't make the barrel longer without suffering from the blown out cases, unless they use a heavier breechbock and/or main spring. Heavier breech block means heavier gun and lower rate of fire. Stronger mainspring/buffer might mean slower opening but faster closing, effect on rate of fire is????? however faster closing means more battering on the gun parts and for a gun designed to be built of stampings and lower grade steel that may not be a good option.

As I said, the API method of action is not mutually exclusive from high rate of fire and high MV (look at 20mm Oerlikon guns as used by the Americans and British, ballistic twin to the Hispano but it sure isn't lighter

 

[tomo pauk]

Thanks for the feedback, people.

This is how the Germans rated two weapon options for the Me 262 - one comprises from 2 x MK 103 and 2 x MG 151/15 (= migh MV), other is the historical set-up with 4 x MK 108 (= 'low' MV). The effect on target of 10 HE shells of the MG 151/15 is judged to be equal to one hit of the 3 cm M-shell. Hit percentages and time-to-hit with 'normal' Revi, with EZ 42 sight and conclusion:

 

[David Fred]

"It was cheap, readily available, fully developed ..."
In the mid 30s when they would have needed to make a decision? I would argue no.

"It is a fair bet that the Air Staff rejected this option on the ground that 'If this is what the Americans are doing, it is almost certainly wrong'.
Citation needed on that one. Where's that eyeroll emoji?

"The irony of the situation was that Luftwaffe aircraft never were armoured against 0.50-in ammunition."
I think he would be surprised at the effect of passing through several feet of aircraft structure would have on a .50 bullet.

Thanks. I think the cannon was well suited for bomber work, but I like the .50 "hail of lead" against inline engines or the light Japanese aircraft

 

[Barrett]

Sidebar:
Long (long) ago when I didn't have a lot to do, I crunched the numbers on AAF fighter armament effectiveness, deriving the credited kills as a % of all claims (probables-damaged.)
Guess what?

Four .50s was optimum for WW II fighters; anything more was excess baggage.
The P-51D had 50% more firepower than the B/C at a gain of only 10% in lethality.

Little known: the upgunned F4F-4 was done at request of the Brits who wanted more punch against German/Italian aeroplanes. But the extra "throw weight" was offset by reduced ammo & therefore trigger time. I asked some Wildcat exponents about that, and got the same response from most (Joe Foss, Swede Vejtasa, George Wrenn, etc): "I saved two guns as get me home insurance."

The FM-2 "Wilder Wildcat" reverted to four guns and did extremely well--in fact, it had by far & away the best kill-loss ratio of any WW II fighter I know of, on the order of 30-1. (Largely reflective of the CVE mission.)

 

[Shortround6]

Four .50s was optimum for WW II fighters; anything more was excess baggage.
The P-51D had 50% more firepower than the B/C at a gain of only 10% in lethality.

Little known: the upgunned F4F-4 was done at request of the Brits who wanted more punch against German/Italian aeroplanes. But the extra "throw weight" was offset by reduced ammo & therefore trigger time. I asked some Wildcat exponents about that, and got the same response from most (Joe Foss, Swede Vejtasa, George Wrenn, etc): "I saved two guns as get me home insurance."

The FM-2 "Wilder Wildcat" reverted to four guns and did extremely well--in fact, it had by far & away the best kill-loss ratio of any WW II fighter I know of, on the order of 30-1. (Largely reflective of the CVE mission.)

And again we are back to who was ordering what, when.

IF the British were ordering Wildcats before the US got the rate of fire of the M-2 up to 800rpm then the six gun armament certainly makes sense.
60 rounds per second vs the 40 rounds per second of the four guns. Once the M-2 got to 800 rpm you had about 53-54 bullets per second but didn't have the extra weight.

IF the British were ordering in 1940 they were planning on ammo having a MV of 2500fps. I don't know exactly when the US changed to the M2 loading over the M1 but the British were ordering M1 equivalent ammo in 1940-41, The US had changed a bit earlier but I don't know when.

The Mustang "B"s and the FM-2 used M8API ammo (as did just about everything else from 1943 on) Almost the entire belt was the M8 armor piercing incendiary round. In 1941-42 the belts used various mixtures of AP and Incendiary ammo at best, at worst there was a certain amount of ball ammo included. Add tracer to suit

What I don't know (aside from the M8 ammo which was too late) is how much the rate of fire and the change in MV may have affected (or not affected) the British choice to go with six guns.

 

[Shortround6]

Getting back to the original subject a British 8 gun fighter in 1940 could put out about 150-160 bullets per second.
If we assume 1140 rounds per per barrel (19 rounds per second) and a weight of 174 grains per bullet we get a weight of 3.77lb per second of metal being put in the air. Adjust rate of fire as you see fit.

For the .50 cal option we have 4 guns firing at 600rpm or 40 bullets a second total, each bullet (ball or AP) is 750 grains (British spec) so we get a weight of
4.28lb of metal in the air per second.

Now the British .303 ammo was about 2440fps for Ball (which was fired out of about 3 guns of the eight in the BoB) and 2500fps for the AP with the tracer and incendiary pretty much falling right in line. British spec for .50 cal ammo in 1940 was for 2500fps muzzle velocity.

This means at close range down low or even a few hundred yds range at altitude there wasn't much to choose in velocity of impact between the two and therefore the impact energy will pretty much follow the weight of metal. Granted each hit will penetrate deeper or cause more damage on substantial parts. Hitson skin over voids will call for pretty much the same fabric or metal patch.

The .50 cal in British service will not show a big difference in deflection shooting either with the initial velocities being so close.
Granted as the range opens the Advantage will show up more but as the range opens the deflection problem gets considerable worse for both guns.

Please note this is for 1940 and the BOB. By 1942 things were changing for both guns, greater scale of issue of AP and incendiary for the. 303
Slightly lighter but much higher velocity bullets for the .50 and the higher rate of fire.