ShVAK muzzle velocity

[Hooligan]

FYI Pyro in case you don't already know this.

Various sources I have seen claim MVs of 750m/s, 800m/s and 860m/s for the ShVAK and I used to believe 800m/s was probably the correct velocity due to similarities between the mine round/mg151 muzzle and the ShVAK round/ShVAK muzzle.

Just yesterday I discovered that ShVAKs were made with at least 2 and possibly more barrel lengths.  Engine mounted ShVAKs are equipped with a longer muzzle so that the muzzle extends entirely through the engine.

Note that the following measurements are approximate based in part on my measurements of pictures or scale drawings with a ruler.

From pg. 82 “The Machine Gun, Volume II, Part VII”, George Chinn

Basic ShVAK

Weight 40kg
Length 1.76m
Muzzle Length 1.15m

Long Barrel ShVAK

Weight 68kg
Length 2.12m
Muzzle Length 1.51m

MV 808 m/sec
Projectile weight is unspecified.
It is not clear whether this MV is for the basic or long barrel but based upon similarity to the 151/Mine, I assume it is for the short barrel.

From pg. 157 “Rapid Fire” by Anthony G Williams

There is a picture of a long-barreled ShVAK

Length 2.65m
Muzzle Length 2.04m

Note that he 90cm additional barrel length from the basic ShVAK

Just for comparison, the Hispano Mk V lost about 30m/s muzzle velocity when the muzzle length was reduced 30cm from that of the HS Mk II.

Hooligan

[Pyro]

Hi Hooligan,

Nice observation.  This is a somewhat perplexing problem because even the better sources are contradictory.  The Germans spec'd it out to a lower MV as can be seen in the back cover of Chinn's volume II and there's a similar corraborating charts in German Aircraft Guns and Cannons.  However I did not use these lower ~750 m/s velocity in AH.  How I rationalized the differences and where I believe the confusion comes in is in the different types of mounts and designations.  Page 15 of your Chinn reference shows the longer barrel Shvak to be used in the engine mount(MP).  I believe this to account for the differences in references and I believe that the longer barrel was also used in the sync mount.  On page 74, you'll see this to be applicable to the Shkas, on which the Shvak is based, with a longer barrel for the synchronized version.



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Doug "Pyro" Balmos
HiTech Creations

[Hooligan]

Yes this is perplexing.

I originally looked into this because I noticed that the ShVAK cartridge and muzzle length were similar to the Mg151/Mine combination but that I had seen sources that listed the ShVAK at 860m/sec.  From cut-away drawings of the 2 cartridges I determined that the volume of propellant in the 92g Mine and 96g ShVAK rounds is very close so I THINK that the ShVAK which has a similar muzzle length to the Mg151 probably has a MV around 800.

That picture in "Rapid Fire" of the very long muzzled ShVAK is now making me wonder if this wasn't an engine mount in one of the Yaks or an La-7, and if that particular mounting had a MV of about 860m/s.

But it looks like you already knew this stuff anyway....  And since this is why you make the big bucks, I'm happy to let you figure it all out  .

Hooligan

[juzz]

La-7 didn't have an engine-mounted cannon afaik. The third cannon was assymetrically mounted on the right side of the nose.

[-lynx-]

Juzz - almost all soviet fighters had all their weapons engine mounted. Either firing through the spinner or synched. La5-7 were not exceptions to the rule with 2 ShVAKs sitting on top of ASh82.

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lynx
13 Sqn RAF

[juzz]

I take "engine-mounted" to mean mounted in the engine, firing through the prop spinner - like the Yak-9U, or Me 109G cannon are. The La-7 didn't have it's third cannon mounted in such a way, afaik.

[senna]

With all due respect, how does this add up to the fact that I can never HO a La5 and get away with it  

BTW: I can Ho F4uc just fine.

-- senna (p-38 jock)

 

Originally posted by Hooligan:
Yes this is perplexing.

I originally looked into this because I noticed that the ShVAK cartridge and muzzle length were similar to the Mg151/Mine combination but that I had seen sources that listed the ShVAK at 860m/sec.  From cut-away drawings of the 2 cartridges I determined that the volume of propellant in the 92g Mine and 96g ShVAK rounds is very close so I THINK that the ShVAK which has a similar muzzle length to the Mg151 probably has a MV around 800.

That picture in "Rapid Fire" of the very long muzzled ShVAK is now making me wonder if this wasn't an engine mount in one of the Yaks or an La-7, and if that particular mounting had a MV of about 860m/s.

But it looks like you already knew this stuff anyway....  And since this is why you make the big bucks, I'm happy to let you figure it all out   .

Hooligan

[juzz]

Pilot quality.  

[This message has been edited by juzz (edited 11-10-2000).]

[-lynx-]

 

I take "engine-mounted" to mean mounted in the engine, firing through the prop spinner - like the Yak-9U, or Me 109G cannon are. The La-7 didn't have it's third cannon mounted in such a way, afaik.

They're not actually mounted in the engine, just between cylinder banks where there's space.

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lynx
13 Sqn RAF

[juzz]

Which is why it would be pretty damn hard to fit a cannon firing through the prop hub on a radial engined fighter...

[Pyro]

I had a few assorted 20mm rounds on display at the con including Hispano, 151, and a ShVAK.  I'll have to pull the ShVAK round apart one of these days.



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Doug "Pyro" Balmos
HiTech Creations

[-lynx-]

 

Which is why it would be pretty damn hard to fit a cannon firing through the prop hub on a radial engined fighter...

I must have been brain dead when I wrote what I wrote here earlier . I'd say it's impossible with conventional un-geared radials

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lynx
13 Sqn RAF

[This message has been edited by -lynx- (edited 11-21-2000).]

[Wisk-=VF-101=-]

The Soviet sources I read consistently indicate the following data for Shpitalny-Vladimirov Aviation Highcaliber (ShVAK):

Entered service: 1936
First combat use: 1939, Khalkhin-Gol operation against Japanese on I-16s

Caliber: 20mm
Weight of the projectile: 96 grams
Initial muzzle velocity: 800 m/s
Rounds per minute: 800
Weight of the cannon: 42 kg
Weight of a 1 second burst: 1.28 kg

BTW, only very early models of La-7 were armed with ShVAKs (and they had two of them, not three). Only one regiment got these La-7s.

Since late 1944 ShVAK was replaced by Berezin's B-20 on all Soviet fighters still in production (Yaks, Las etc.). The sources claim that while B-20 had the same ballistics as ShVAK it was almost two times lighter and simpler to manufacture. Here are the data for B-20:

Entered service: October 1944
Caliber: 20mm
Weight of the projectile: 96 grams
Initial muzzle velocity: 800 m/s
Rounds per minute: 800
Weight of the cannon: 25 kg
Weight of a one second burst: 1.28

Sources:

1. "Soviet firing arms" by D.N. Bolotin published by "Voenizdat" (USSR ministry of defense publishing house), 2nd edition, 1986
ID Nr: BBK68.512-B79-UDK623.44 (this is like western ISBN)

2. "Weapons of Victory" by:
Sr. editor V.N.Novikov (and 12 authors, among them designers and chief designers of Soviet weaponry, for example A.E. Nudelman (NS-23)) published by "Mashinostroyeniye" ("Machinebuilding"), 1985
ID Nr: BBK63.3(2)722-2-0-70-UDK623

3. "History of Aircraft Construction in the USSR" by V.B. Shavrov published by "Mashinostroyeniye" ("Machinebuilding", 3rd, corrected, edition, 1994
ISBN 5-217-00477-0

[brady]

  The us army ordnance museum/the Aberdeen Proving ground has a wonderful display on aircraft cannon rounds and they are cross sectioned so u can see the wall thickness. I just wish i had taken better pictures when i was their

       Brady