^ I agree, the "metal" ones will typically be closer in overall weight - but the weight distribution can still be quite different.
I'm actually not sure if you can use a "real-steel" (i.e. designed to go in an actual firearm) tungsten or other heavyweight guide-rod in the airsoft replicas, but this might help shift the balance forward a little. Airsoft replicas of the gas-blow-back (GBB) genre - ones that use the magazines as the pressurized propellant gas container - are typically pretty decent at simulating the full weight of a loaded magazine, however, that weight never changes, and what's more, without the magazine, even in models with heavy metallic weight-plates hidden under their grip panels (such as the Western Arms 1911 replicas), the barrel, which typically contributes significantly to an actual pistol's weight, as well as the slide's masses are quite a bit off.
Airsoft "metals" are typically what we Americans would consider "pot metal." Yes, there are aftermarket components available that are made out of "aircraft-grade" aluminum, but as you can imagine, it's not going to weigh the same as steel. In some cases, some of the better (in terms of aesthetics [which likely will -NOT- matter to someone using the replicas specifically for Force-on-Force training] as well as functionality) replicas come with a "heavyweight" ABS-plastic slide, which can weigh as much as - if not more - than a "metal" counterpart.
Depending on the replica, a "metal barrel" - which is actually an outer, cosmetic barrel replica that shrouds an inner 6.0x mm barrel through which the BB travels (as you can imagine, this gets pretty hilarious when you're looking at airsoft M4/AR15 replicas :lol
- can also help forward-shift that weight balance. But in many cases, it's still to little/no avail, as the materials are so different.
Sitting on a table, my KSC Glock 18C, with authentic Glock trademarks (hey, I'm a collector
), outfitted with a metal slide and barrel looks just my real G32.
But pick them up, and it's very clear that the weight distribution is quite different.
From Glocks to Berettas to 1911s/2011s (and I have a few of the latter that are completely decked-out, built by top "airsmiths" overseas like Clarence Lai; my shooting friends make fun of me because for as much as I love 1911s, I still don't have a real one, yet I have several airsoft 1911s/2011s that cost just as much as a real Wilson, STI, or SVI would), they all show this trait, regardless of how much has been done to them or what make/model (OK, that's not completely fair - some of the airsoft revolver replicas are pretty spot-on in terms of weight and weight distribution).
This is indeed one of those training issues that you'll have to work through.
Airsoft is only one of many different training tools - choose what is appropriate for your