50 cal (high rate of fire) vs 20mm cannon (hitting power)

[pbehn]

As ever good points, but the P51 development went from 4 x 0.5 to 6 x 0.5 they would have done it for a reason, presumably because 4 x 0.5 was lacking. I am not aware of any significant complaints about a lack of 'trigger time' (I do like that phrase) of the P51

Possibly because even before the P-51B was introduced strafing aircraft on the ground was part of many mission profiles and in that only the number of bullets per second matters because a ground target is only in the gunsight for a fraction of a second.

 

[Deleted member 68059]

This may help. From USAAF microfilm report.

 

[jmcalli2]

You certainly have a point in particular on long distance escort missions. That said, the Tempest gave you about 16 seconds of fire which isn't bad and not that many pilots used all their ammunition. You could also point out that a burst from the 4 x 20 would do far more damage than from the 6 x 0.50 so less ammunition would be needed

Good points, but weren't most Tempest missions strafing/ground attack? A different issue from air to air; again, it depends upon your mission.

 

[jmcalli2]

This may help. From USAAF microfilm report.

View attachment 600945
View attachment 600946

Cool!

One thing to keep in mind: not all 20mm were created equal. The Hispano fired a bigger shell at a higher muzzle velocity and faster or similar rate of fire than the smaller and lighter Mg151/20; The WWII Fighter Gun Debate: Gun Tables

 

[pbehn]

Good points, but weren't most Tempest missions strafing/ground attack? A different issue from air to air; again, it depends upon your mission.

from wiki for the HS MkV … Ammunition types available included Semi-Armour Piercing, Incendiary (SAPI) and High Explosive, Incendiary (HEI).[10] Around 42,500 Hispano cannon of various marks were manufactured by Birmingham Small Arms (BSA).

 

[jmcalli2]

from wiki for the HS MkV … Ammunition types available included Semi-Armour Piercing, Incendiary (SAPI) and High Explosive, Incendiary (HEI).[10] Around 42,500 Hispano cannon of various marks were manufactured by Birmingham Small Arms (BSA).

Now, just to add more powder to the charge, consider the US M9 37mm cannon. This was used on late model P-63. It differed from the M4/M10 37mm in that it was a completely different design, being developed from the US Army 37mm AA gun. While it had the same low rate of fire as the M4, it fired a 10% larger shell at 2800 ft/s. The down side was it was really heavy. With that big shell at that high muzzle velocity heavy bombers could be attacked outside the range of defensive fire with a one round kill weapon.
Good thing B-17s, B-24s, and Lancasters didn't have to deal with that!

 

[The Basket]

I British.
I want my 303.

Moving to Korean War and it was quickly apparent that 20mm cannon was the way.

Fast firing 20mm cannon. The Zero in service quickly found out the Wildcat was a tough old bird. The machine guns were just scratching the paint work. The Tempest didn't carry 303s. So the proof is in that pudding.

 

[Koopernic]

I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a "it depends". Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. I would take reliability as my number one choice, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber.

Food for thought.

Cheers,
Biff

The most important variable is that 50 caliber gun has less drag in certain circumstances.

 

[Shortround6]

consider the US M9 37mm cannon. This was used on A late model P-63

Fixed it

The M9 cannon was used on one P-63 aircraft, as in one plane, not one model or version.
P-63s from the A-9 on got the US M10 37mm cannon which used the same ammo as the M4 cannon. It fired just a bit faster but used a real belt (disintegrating link) for feeding and held a lot more rounds than the M4 set up.

Confusion comes from the M10 cannon being called the T9 when in development.

 

[Shortround6]

I don't think I have seen a mention, except in passing, of one of the big reasons the US chose the M2. Production and logistics standardization

During the 30s the .50 cal (not yet the M2 ?) was used by the air corp, the ground army, the Navy (and naval aviation) and the Marines.
Using the same receiver and interior parts it was possible to build an aircraft gun or a water cooled AA gun or any other version. The M2 was also possible to convert from left hand to right hand feed with s few parts. Later it was possible to convert the slow firing ground guns to higher rate of fire aircraft guns by changing barrels and a few other parts. not often done.
The .50 was a barrel burner and light weight aircraft barrels and fast firing guns without 200-300mph cooling breeze was not a good idea. PT boats may have been the only users of high rate of fire guns in surface combat?

This gave quite an advantage in logistics. The advantage tended to fade during the war with the sheer quantity of war material but the light Navy AA gun (before the 20mm Oerlikon) used the same ammo as some of the Navy aircraft guns (the others were .30 cal) , and the Army aircraft guns and the army ground anti-armor gun (up until about 1940) and AA guns. There may have been different kinds of ammo but each and every one could be fired out of any of the "different" guns should the need arise. Likewise bolts, firing pins, springs, extractors, ejectors and feed parts were all 100% interchangeable.
The advantage in manufacturing and supply was considerable.

This may have helped outweigh the disadvantages of the .50 cal.

 

[PAT303]

The most important variable is that 50 caliber gun has less drag in certain circumstances.

That is true but two Hispano's weighed 100kg yet had the on target effect of 6 Brownings that combined weighed 230kgs, so pluses and minuses for both.

 

[pbehn]

Now, just to add more powder to the charge, consider the US M9 37mm cannon. This was used on late model P-63. It differed from the M4/M10 37mm in that it was a completely different design, being developed from the US Army 37mm AA gun. While it had the same low rate of fire as the M4, it fired a 10% larger shell at 2800 ft/s. The down side was it was really heavy. With that big shell at that high muzzle velocity heavy bombers could be attacked outside the range of defensive fire with a one round kill weapon.
Good thing B-17s, B-24s, and Lancasters didn't have to deal with that!

That was the first job of the escorts, make sure there is no easy shot. They may not have been able to do much about an attacking Me262s speed, other than make sure they had to use all of it and its hard to hit a moving target when you are doing 500MPH yourself.

 

[tomo pauk]

Cool!

One thing to keep in mind: not all 20mm were created equal. The Hispano fired a bigger shell at a higher muzzle velocity and faster or similar rate of fire than the smaller and lighter Mg151/20; The WWII Fighter Gun Debate: Gun Tables

The Hispano II fired at lower RoF than the MG 151/20. In ww2, Hispano V saw serivce in Tempest.
US Hispano was equivalent of the Hispano II (when worked).

 

[jmcalli2]

I British.
I want my 303.

Moving to Korean War and it was quickly apparent that 20mm cannon was the way.

Fast firing 20mm cannon. The Zero in service quickly found out the Wildcat was a tough old bird. The machine guns were just scratching the paint work. The Tempest didn't carry 303s. So the proof is in that pudding.

Wan't the original Typhoon design to have 12 .303s, or have I had too much Balvenie Doublewood tonight?

 

[jmcalli2]

Fixed it

The M9 cannon was used on one P-63 aircraft, as in one plane, not one model or version.
P-63s from the A-9 on got the US M10 37mm cannon which used the same ammo as the M4 cannon. It fired just a bit faster but used a real belt (disintegrating link) for feeding and held a lot more rounds than the M4 set up.

Confusion comes from the M10 cannon being called the T9 when in development.

My bad; I know the M9 was used on the P-63D (the bubble top), but I thought it was on the E and F also.
Thanks for the correction!

 

[jmcalli2]

That was the first job of the escorts, make sure there is no easy shot. They may not have been able to do much about an attacking Me262s speed, other than make sure they had to use all of it and its hard to hit a moving target when you are doing 500MPH yourself.

The Me-262s carried Mk 108 30mm. These had a relatively low muzzle velocity, so you'd have to get closer. The shell was about 40% the size of the M9 37mm, but the rate of fire was 4 times faster and the gun weighed 1/3 as much, so you trade off was heavy shell at long range vs more shells at closer range.
Just a thought: missiles are essentially very big shells at very long range.

 

[jmcalli2]

The most important variable is that 50 caliber gun has less drag in certain circumstances.

Now, that's an interesting take! Tell me more!

 

[jmcalli2]

The Hispano II fired at lower RoF than the MG 151/20. In ww2, Hispano V saw serivce in Tempest.
US Hispano was equivalent of the Hispano II (when worked).

 

[PAT303]

Now, that's an interesting take! Tell me more!

In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.

 

[wuzak]

The most important variable is that 50 caliber gun has less drag in certain circumstances.

Now, that's an interesting take! Tell me more!

In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.

I thought Koopernic was referring to the aerodynamics of the shell for improved ballistics.