Project Vulcan: T45 and M61

[pyro-manic]

What about the actual timeline makes you think it could have been done more quickly?

[KJ_Lesnick]

1. Because the gun was designed around a 0.60 calibur and test fired in 1949 and improved through the early 1950's; then later redeveloped for 20mm and 27mm (20mm was selected) based on a desire for more hitting power.  Basically a certain amount of time would be shaved off, but some developments take time (it's harder to shoot a 20mm round than a 0.60 at a high rate)

2. I should have made my questions more detailed: I'll amend that.

With the engineering extant in the timetables...

• If the USAAF had been willing to pursue 20mm right from the start of Project Vulcan
  
• If the USAF had from 1947 or 1948 decided to rededicate the gun to 20mm
  

How much quicker would it be online?

[pyro-manic]

The project started in 1946, the first prototypes were fired in 1949. So that's how long it took to design and build. Changing the calibre would not alter that. The 20 and 27mm versions were tested in 1952. Not much scope for improvement there.

[wuzak]

I don't know what the alterations were, but they were not necessary as the original gun worked very well!

If I recall, it's accuracy wasn't as good, but it didn't matter for ranges used.

Perhaps you could find some data to back that assessment up?

Also, accuracy depended on what rounds were being used, as they could have different shapes.

One mentioned was a longer chamber.

That seems like an attempt to fix that

To fix what? Accuracy? I'm not sure, but I don't think the chamber has all that much to do with accuracy. That is more to do with the barrel, its rifling and length, and the size, shape and weight of the projectile.

What lengthening the chamber did do, in practice, was to make the firing pin strike less reliable.

Before that they stuck with .50s because it was the only working option.

20mm had more hitting power, if an improved projectile or cannon design were used it would work...

The Hispano was said to have 3x the hitting power of the 0.50" Browning. So, in effect, the Spitfire with 2 x 20mm and 4 x 0.303" had more hitting power than teh P-51B/C with 4 x 0.50" or the P-51D/K with 6 x 0.50". And a Spitfire with 2 x 20mm + 2 x 0.50" had the equivalent firepower as the P-47 with 8 x 0.50", but without as much ammo.

[KJ_Lesnick]

Perhaps you could find some data to back that assessment up?

Perhaps you're mistaking my quote... my statement was derived from a link.

Also, accuracy depended on what rounds were being used, as they could have different shapes.

Ballisitcs

To fix what? Accuracy? I'm not sure, but I don't think the chamber has all that much to do with accuracy.

I misread it, I thought they lengthened the barrel...

What lengthening the chamber did do, in practice, was to make the firing pin strike less reliable.

Why did they do that then?

And a Spitfire with 2 x 20mm + 2 x 0.50" had the equivalent firepower as the P-47 with 8 x 0.50", but without as much ammo.

Impressive...

[Weaver]

The USAF had an institutional bias towards accuracy over firepower, derived from the fact that they were mostly fighting fighters rather than trying to tear huge bombers apart, which made them value the higher velocity of the .50 cal over the higher terminal effects of the 20mm. This was shown up as incorrect in Korea, so although Project Vulcan had already been going a while, it didn't really gain momentum until after about 1950/51.

European countries, having had the experience of trying to shoot down large numbers of bombers quickly, seized on the lessons learnt by the Luftwaffe and adopted low-velocity/high-capacity 30mm rounds fired by MG-213-inspired revolver cannons.

Eventually, the 20×102 mm cartridge was determined to have the desired balance of projectile and explosive weight and muzzle velocity.

So the 20x102 was designed specific for the gun?

Yes and no: the 20 x 102mm round was the .60 cal cartridge opened out to take a 20mm shell, so that they didn't have to redesign the whole mechanism. Ironically, it's one of the lowest-powered 20mm rounds ever made.

Fun fact: GE made a prototype gatling that fired the 30mm ADEN/DEFA round: now wouldn't that have been tasty...

[KJ_Lesnick]

The USAF had an institutional bias towards accuracy over firepower, derived from the fact that they were mostly fighting fighters rather than trying to tear huge bombers apart, which made them value the higher velocity of the .50 cal over the higher terminal effects of the 20mm.

It's kind of ironic when you think about it: The USAAF believed in strategic bombing and using large heavy bombers, yet didn't seem to value the weapons needed to bring such planes down; the USN was mostly interested in tactical bombing and most tactical bombers were small.

Despite the accuracy issues, the USN managed to bag a healthy number of planes (well healthy for them!)

Yes and no: the 20 x 102mm round was the .60 cal cartridge opened out to take a 20mm shell, so that they didn't have to redesign the whole mechanism.

That's fascinating!  It would have likely been a modified 20x110 if a 20mm was chosen from the outset, and 20x110 if the modification was made after 1947?

Ironically, it's one of the lowest-powered 20mm rounds ever made.

Still wouldn't want to be hit by it!

Fun fact: GE made a prototype gatling that fired the 30mm ADEN/DEFA round: now wouldn't that have been tasty...

It would have been one hard hitting beast!

[Mr.Creak]

which made them value the higher velocity of the .50 cal over the higher terminal effects of the 20mm.

IIRC it wasn't the velocity they favoured so much as the rate of fire.

[wuzak]

which made them value the higher velocity of the .50 cal over the higher terminal effects of the 20mm.

IIRC it wasn't the velocity they favoured so much as the rate of fire.

The muzzle velocity of the 0.50" was only slightly more than that of the Hispano.

The RoF was a bigger advantage - around 100rpm more for the 0.50" (M2) than the Hispano.

[KJ_Lesnick]

I figure if you have 3 times the hitting power, the fact that it fired rapidly enough would still allow a horrifying amount of damage to be done.

[rickshaw]

I figure if you have 3 times the hitting power, the fact that it fired rapidly enough would still allow a horrifying amount of damage to be done.

That is, if you hit.  A lower RoF would prevent that in a fleeting air combat.

[KJ_Lesnick]

That is, if you hit.

True enough, but if the RoF was close enough (500-600 vs 600-700) you'd still be likely to hit right?

[wuzak]

That is, if you hit.

True enough, but if the RoF was close enough (500-600 vs 600-700) you'd still be likely to hit right?

Having two 20mm cannons may have had the same hitting power as 6 x 0.50", but not nearly as much ammo. The ammo would be gone very quickly.

Thats why the RAF maintained the additional 4 x 0.303"s in Spitfires. To give them additional firing time.

Later in the war they had developed a better gun sight which gave better accuracy for the average pilot, so they took out the 4 x 0.303" and replaced them with 2 x 0.50".

[KJ_Lesnick]

Having two 20mm cannons may have had the same hitting power as 6 x 0.50"

Well, IMHO a more appropriate armament would be 4 x 20mm: I did a wikipedia check and got my numbers mixed

• HS404 refire: 600-700 rpm
  
• 0.50 BMG: 750-850
  

You'd pump out 2400 to 2800 rpm with 4 x 20mm, vs 4500 to 5100 rpm with 6 x 12.7mm

The F-86E had total ammo of 6 x 12.7 with 300 rpg (1800 rds); the FJ-2 had 4 x 20mm with 150 rpg (600 rpg) and the F2H-3 had 4 x 20mm with 220 rpg (upper pair), and 250 rpg (lower pair), or 940 rounds

• F-86E: 21-24 seconds to expend ammunition
  
• F2H-3: 20 to 23.5 to expend ammunition
  
• FJ-2: 12-15 seconds to expend ammunition
  

While your assessment is correct in that the plane would burn through ammo faster, the lead-computing gunsight helped improve accuracy.

Opinions?

[pyro-manic]

I'll take a Hunter with four ADENs, please!