turret blast colours?

What do you mean?  The turret doesn't change color when the cannon is fired.  

I suspect you're referring to the blackened end of the gun tube? Unless you're building a Napoleonic or Civil War cannon -- omit it.  It's a modeler's myth that has nothing to do with WW2 era cannon whose shells used smokeless propellent -- therefore no blackening of the muzzle ends.  Soiling would often occur but it was due to the crews swabbing out impurities left behind in the gun tube -- whatever solvent would dribble the dirt/muck out the end.  But whenever you see a tank model that looks like the builder dipped its cannon into an inkwell -- you can be sure that guy never saw a real tank in action.

T26E4

I suspect you're referring to the blackened end of the gun tube? Unless you're building a Napoleonic or Civil War cannon -- omit it.  It's a modeler's myth that has nothing to do with WW2 era cannon whose shells used smokeless propellent -- therefore no blackening of the muzzle ends.  Soiling would often occur but it was due to the crews swabbing out impurities left behind in the gun tube -- whatever solvent would dribble the dirt/muck out the end.  But whenever you see a tank model that looks like the builder dipped its cannon into an inkwell -- you can be sure that guy never saw a real tank in action.

Would prolonged use/firing of the gun tube cause some paint discoloration especially around the muzzle possibly due to excessive heat?

Thanks. 

sorry barrel end I mean.

Would prolonged use/firing of the gun tube cause some paint discoloration especially around the muzzle possibly due to excessive heat?

Not really, the muzzle does not get so hot as to discolor paint.

Ahem! Discolored on an Abrams barrel:

TomZ2, I wonder if that is just the paint on the barrel and not weathering. To me, the over all scheme on that Abrams suggests it is just black from the camouflage, not carbon. Much like the barrel of this tank here....

I'm no expert but I've always thought blackening the barrels was a bit of fiction when it comes to armor. I also do not like to blacken wing surfaces on aircraft around their gun ports. It just doesn't strike me as accurate, especially not in the heavy handed way most people do it.

On the other hand, a slight bit of weathering on the barrel does imply its recent use which may benefit the viewer. This is all "art" in any event...model how you like it.

...the over all scheme on that Abrams suggests it is just black from the camouflage, not carbon.

You are correct.  The camo scheme on NATO camo Abrams does have black at the front of the barrel. 

As to your, "This is all "art" in any event...model how you like it," comment.  Some of us actually strive for accuracy, not artistic BS that isn't how the vehicle really looks. 

Gino, I understand completely and I'm not going to debate it. Every one has their own motivation in this hobby, some accuracy, some art. We all participate in the hobby at different levels of interest. But over all, that is why I lead with the evidence rather than the opinion...I prefer accuracy.

FYI The actual detritus at the end of an Abrams barrel would be whitish powder, not black soot.  In the photo, I believe you have a black camo painted barrel end that has had the dust rubbed off, revealing it to be darker than the dust remainder of the tube.  The tube was often a convenient hand hold.

I think it is just paint. Challengers have the muzzle painted black. Some Challys also have the barrels in black except for the extractor.

Very informative discussion. Thanks.

That 3-tone jobbie looks like an Aussie Abrams..

In the Aussie scheme, much of the front end of the barrel, back to the bore evacuator, is painted black.