Having some problems with my RIA 1911 A1 CS when using 7 round Metalform magazines. I have two of these mags. Both have problems with last round hold open. The mag that came with the gun occasionally has this problem, but the Metalform mags fail to lock open every time. All the mags lock when manually cycled. I am wondering if it's a gun problem since the factory mag sometimes fails to lock. Any ideas? Gun and magazines are less than 6 months old and I have only fired about 400 to 500 rounds through the gun total.