bernard MIG gun: ID and nozzle/tips mysteries: nozzles offered in brass AND copper, + OLD bernard MIG gun 'bonus question'

nozzles for my 'ancient' K&K (bernard) MIG gun are offered in brass, and, for more money, copper (apparently, they're otherwise the excat
same, dimensionally, and otherwise). I assume there must be a reason they're offered in TWO metals, but, what *IS* the reason? does copper last longer? steel mig wire stick to it less? or maybe not at all?
see the MIG gun itself here:
nozzle "inner parts" closeups and stuff here:
also, this bernard MIG gun came on (with) my (possibly even MORE ancient) airco dip-pak 200 MIG welder. I called bernard with these questions, but a young 'college age' sounding chick answered my questions - at least one of the answers later proved wrong. SO, I'm going to ask here:
is this K&K MIG gun called an "E-Z feed" gun? or called a "Q-200" gun, or, possibly "neither of the two", but something else again. what is it? I do know this gun (as received) uses Bernard eccentric tips - it came with ONE tiny, short one in it...
re K&K: on this page, it says "BERNARD is also responsible for the sales and distribution of K&K Welding Products." so, it seems K&K isn't simply a 'bernard clone brand'. but what do I know?
anybody know what era, or year, my particular MIG gun was MADE? it also doesn't use the (so-called, short) "gun-end liners" ("jump liners", I think they're called)
also, MY gun came with one diffuser, the one in the gun, which has no printing or ID marks on it whatsoever (so I assume it's some clone brand part). it's a damn UGLY, scratched-up UGLY-looking thing: the -outer nozzle DOES say bernard on it, and has the number of the nozzle,
so I assume 'real' bernard. the diffuser (that came in it) held the one 'short' eccentric tip.
on ebay, I bought, and hope to use with this, new bernard diffuser 4235, and some 'long, 1500 series' tips. these ARE useable with, or "in" this gun, correct?
"golden plus points" to anyone who call sell me some of the feed rollers for this MIG. you can see images of the (poor, lonely, still single after all these years) feed roll I have for it HERE:
thanks for any and ALL info you guys can provide for me, and for any help identifying this gun 'trade name' or 'model type', what I can and can't 'use with" it, nozzles and eccentric-tips wise, that sort of thing.
much appreciated, thanks.
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