Firing a German Pak-40 75mm Anti Tank Gun
 

https://www.youtube.com/watch?v=T7fhBm1ouSU

Notice how very tiny the gun shield is...

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

I am tempted to believe that the tiny gun shield is there to protect the small pieces of the gun: "We can always get more crew".
Alternatively: "this shield will be of some assistance as long as the barrel is pointing directly (I said Directly) at the enemy."
Either way, clearly a design feature designed by designers not planning on doing the firing.

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

I guess it protected the layer, behind his sights, quite well, against accidental shots, and even not precisely aimed MG bursts. Of course, it won't be sufficient against snipers and well-aimed MG fire, but I don't think it's a purpose of the shield. They're not meant to protect in a long duel. Even if the layer and loader are cramped and hidden behind the shield, a precise rifle fire would make impossible delivering ammo and would pick the rest of a crew. Note BTW, that Pak-40 has spaced twin layer shield, pretty good against rifle bullets.

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

If you have the cash to spend, this is the place where they filmed this:

http://www.drivetanks.com/

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

By my understanding, also mobility and conceability were rather important design criteria for anti-tank guns, and having a huge and heavy gun shield does not really help either.

That said, there is also the late war German 88 mm PaK 41/43 where the design criteria seem to have been something entirely different..

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

Probably just a matter of size. Once anti-tank guns grew to 75mm and beyond, concealment was a one-shot affair. Size and firing signature (debris and muzzle flash) would probably rule out any chance of concealment beyond the first shot or two - as the video posted earlier shows quite clearly.

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

This shield might give some protection....

http://i1327.photobucket.com/albums/...ps4mhewxpx.jpg

http://i1327.photobucket.com/albums/...ps4691578f.jpg

The 88mm Gun Equipment X5E1 (the "Garrington Gun"): an experimental gun developed to replace the British 25 pounder of WW2 fame. This prototype was produced by Garringtons Ltd (part of the GKN group) was one of the most innovative of its time. A new gun was needed to fire shells made of higher grade steel and containing more explosive than the 25 pounder. The guns carriage had an upswept trail with a large overhead shield to protect the gun crew from shell splinters and the flash effects of nuclear explosions. To compensate for the weight, hydraulics were used for traversing the gun in action. For fine traversing the trail end was slid hydraulically from side to side across a rear plate. For larger switches, the whole gun was tilted forward, lifting the trail end and allowing the gun to be rotated on its platform.

Unfortunately firing trials at the Royal School of Artillery in 1958 revealed serious flaws in the design. The guns sights and elevating arrangements were defective and its excessive weight made it almost impossible to manhandle. Propellant fumes built up under the protective dome like shield so only thirty minutes of continuous firing were possible. Later in 1958, NATO adopted 105mm as the standard calibre for close support weapons and the project was cancelled.

Re: Firing a German Pak-40 75mm Anti Tank Gun
 

The shield on that Garrington Gun looks indeed like it would protect the upper bodies reasonably, though if I were to crew one I would still want to build a sandbad emplacement around to also protect my legs and groin area.

Also, the weight must have been quite considerable.