Sub frames can have the serial number on them, not the grip portion, making the gun much more convertible to different frame length and grip sizes. SIG makes one like that which converts to varying combinations of long slide hi cap to short slide short mag near pocket gun. One serial number, two or three slides and grips, different magazines, etc.
Why polymer? Costs. A single steel or aluminum alloy frame has to be formed by forging or rolling billet, then machined to final dimensions with it's unique serial number. A polymer lower is hot molded in a die with it's unique serial number put on the sub frame or integrated metal panel. The much smaller and less expensive metal bits in the polymer framed version aren't expensive, and the polymer itself is literally pennies in material costs. The cost of the die is much more but properly used it can make thousands if not tens of thousands of them which averages that cost down to literal dollars - and not many.
Polymer is a lot less expensive - case in point, how much for an LCP these days? $200 - Ruger dropped the price significantly. Part because the molds were paid for, part because of competition against guns at their previous street price of $275-300. The other makers aren't taking the battle to them. Yet.
Compare that to the Glock 19 which is still pretty close to what it was 20 years ago - meaning Glock has been slowly dropping the price, not raising it. The HK P7 went from $800 to $1400, the Glock 19, not at all.
So, if a LCP only retails for $200 now, how much does that frame really cost? A few bucks for the stamped formed metal bits, pennies for the FRN hot molded into the die, and the cost of the die for it's individual use. I will go out on a limb and say that most of the lower polymer frames "cost" less than $20. But we still have to add back overhead, initial design, etc. A steel or alloy frame would go 2-3X that. The price difference between metal and polymer frames on the market seems to top out at about $200 for the privilege of metal and it's costly manufacture and machining. A SIG P238 seems to have a $550 retail, the Kahr CW380 about $350. Rough apples and oranges comparison.
The Glock Blue price tho? $350. Hmm. I'd suggest if they wanted to turn the screws on the price they could volume bid it under a massive contract as low as $275. About the same as what the LCP sold for initially.
You can see the same difference in the M4 contract bid price when the base gun bids for $650 to the .Gov with KAC rail another $250. About what they sell for now. Two years ago, it was $1200 but Colt has a lot of cash flow issues and so they are doing the same as Ruger, selling lower to improve volume.
Polymer can really improve the bottom line with a much higher markup and still net a highly competitive price against alloy. As far as performance alloy and polymer are both on the same footing - either will crack under extensive shooting. In that light they are somewhat limited in lifespan but the lower cost means the few that do break will be covered when replaced. The overall cost of the fleet works better and that is what taxpayers demand.
Can polymer stand up, sure. Examples: first, a lot of modern V8 engines use polymer intake manifolds. Of course that's a static no moving parts component. Ok - small engines are moving to polymer carburetors, and they have been using polymer camshafts which endure a lot more stress and wear. No issues yet. I had one and when it broke it was a metal valve that failed.
As for shooting them the polymer guns are noted for being a bit more forgiving in recoil - either because the designers were forced to slow down the hammering, or because they are a bit more squishy compared to rigid metal. I give the latter more significance but both could be in play. In long term shooting a rental range in Vegas notes the metal slide cracks FIRST, not the polymer frame. Some Ruger LCP owners note their guns crack at the extreme rear of the frame near a pin hole first. LCP's aren't known for soft recoil. YMMV.
I choose polymer for deep conceal and summer wear as its definitely getting more humidity and exposed to corrosion more frequently. I have a compact alloy gun for belt wear. Planning a trip to the beach? Polymer. Extreme use outdoors over a long period of time with limited maintenance, like the Army's new pistol? I don't see alloy being the better choice, but it's a political dog and pony show in terms of arms acquisitions. Pistols aren't a major combat weapon, those assigned them get M4's in the box. Pistols are green zone off duty wear. Still yet the Army has to come up with a decision, who saw the M9 coming?
