expanding foam guns

Yes

Also yes if using again in the near future.

or just blow cleaner through the gun & then leave it open?

Only if planning to leave unused for a long time.

One more thing - I advise paying extra for the pink fire rated foam. The ordinary stuff is a tad more flammable than I'm happy with having used both.

I can't say I have tried all the brands, but they seem to be interchangeable.

It varies... they tend to seal slightly better than the non "gun" cans, but not always perfectly - they will still lose pressure if you leave them long enough IME

I normally rinse through with the cleaner from a can of cleaner, then leave dry. Unless its going to be more than a couple of weeks, I just leave the foam can on the gun.

Yes.

Err, usually!

If I'm not leaving a can of foam on it, then I tend to leave some cleaner in it instead, it's difficult to say how long is "too long" to leave a part used can of foam on it, days is fine, weeks is fine, months usually causes [me] problems.

Looks like that VT320 came to a sticky end!

AFAIK, the 'gun grade' foams are standard.

I've kept the same can of foam on for more than 6 months. I find it a really useful source of sticky expanding stuff on tap. In fact, I wouldn't fancy taking the can off in case the foam set right inside the nozzle. That said, the gun I got from screwfix has started to leak around the trigger/pin. Doesn't impair use, yet.

I squirt through with cleaner each time I change cans - seems worthwhile.

Were you the one who posted some test results here recently?

Thanks (to everyone else too).

Yes...

Thought so. Interesting stuff.

Well, for some definition of "interesting". Personally I was a tad pissed off that at least one brand of foam was insanely flammable after curing, especially as another brand of non fire rated stuff appeared to be a lot less so.