The USP 9 all polymer 15rd magazine concerns me since it isn't steel lined. Even Glock added steel FULL lining to their mags in the early 1990s (The earlier NFML mags had steel on three of the four sides). HK now sells a 18rd USP9 magazine that is steel lined so this calls to question is there a functional or durability issue that necessitated the change (the earlier translucent 18rd are non-lined)?
The "all plastic" USP9 mag is the reason I have generally avoided the model.
*Before someone says anything ... I know HK polymer is different than Glock polymer (I have owned and used both since 1994). However, Glock is the Chevy Impala of the gun world while the USP is more akin to a H1 Hummer so I believe drawing a comparison between the cheap gun's lined mag and the superior gun's unlined magazine is warranted.*
Thus we arrive at my questions:
1) Who here has a lot of experience (e.g. duty use, high round count gun gaming, etc) with the unlined magazines? Any problems?
2) What about leaving them loaded for extended periods of time?
3) Any concerns about leaving them in a hot car or other "extreme temperature conditions" like sub-zero winters?