Does it also do this when the magazine is empty, in battery or slide locked? Is the magazine also difficult to insert, in battery or slide locked? You might have to dress the magazine catch channel. My Garrison came with a raised horizontal ridge in the channel, probably stainless casting or MIM. Easy to sand the channel down with 600grit, then finely polish with finer black oxide sandpaper or metal polish. Mine needed dressing on the button side which didn't take much effort. Here's two from an accomplished 1911 smith:
The question of why magazine catches don't function smoothly and easily is not uncommon. So, I thought I'd put together a simple pictorial guide to help folks out. It's the little things that make a difference and elevate your pistol above the ordinary. The magazine catch consists of three...
www.1911addicts.com
The normal operation of locking any fully loaded magazine into a 1911 pistol with the slide forward should require no more force than that which can be applied by pushing it into place using one thumb. If a ball peen hammer is needed to lock it into the pistol, you’re going to be at a serious...
www.1911addicts.com
Another thought SA uses a strong magazine catch spring. I couldn't get a magazine to drop freely w/o changing my grip and making sure I was fully pressing the button. I bought an assortment of Wolff springs which made the SA mag catch much easier to press w/o changing my grip.
Wilson does make good magazines (heavy gauge metal), but it could be out of spec. Contact Wilson for their suggestions.