Hey guys, just wanted to see if anyone had any advice on what direction I needed to head in.
As the title states the slide doesn't lock back, on empty, when I use Wilson Combat 7-rd mags in my STI Guardian, .45acp version. When I use the factory 6-rd mag everything works as it should.
Something else I've noticed is that when inserting the WC mags there is a little resistance on the mag at about 3/4 of the way in. A hair bit more of a push and it seats just fine. The factory 6-rd goes in smooth.
Both mags work great when firing, chambering and extracting.

What I want is a 7-rd capability and for the slide to lock back on empty.
Any ideas?

Sounds like maybe weak springs in your Wilson Magazines.

The resistance probably is the mag catch. Mag bodies may be different in size by a little.

I'll be home in a few days and will remove the slide and try to assess the situation a little better.
I'm still learning when it comes to trouble shooting the 1911 platform.
I'll break out the calipers on the mag bodies as well and see what I get.
I'll report back on that sometime Wednesday.

With an EMPTY mag inserted, slide forward, slowly pull the slide all the way to the rear. Watch the mag follower and see if it engages the slide stop.
Is the gun new?
is the mag new?

A new gun can have very tight tolerances and a weaker spring could keep the slide stop from engaging.

The first thing I would do is remove the SS and using FLITZ or another quality metal polish, polish all contact areas on the SS and the hole it goes in. You can use flitz on a q-tip to polish the hole.
I personally have never had any issues with WC mags and I used a lot of them shooting competition. However you can replace the springs with WOLFF EXTRA POWER springs. They are a little more stout than the stock WC springs.
If you have problems finding ones for the officers mags you can cut a couple of coils from a full size spring.

Springs

ALSO.....look at your grip while you are shooting the gun and mage sure you are not holding the SS down with your thumb keeping it from being activated.

sounds like 2 different problems if the mag sticks on the way in or out it is probably close to time for a new mag as they are used the top will start to spread and take a look at the follower it may be warn as well

Getting resistance 3/4 of the way in is typical in a 1911. The mags dont have much of a taper like a double stack mag. This can me more noticeable with a newer gun as the mag catch spring can be pretty stout in a factory gun.