To add a few more details:
For their lowers I've always had some trouble getting the pins in/out with the uppers I've used. With their uppers it's a little tight but can be done by hand. The fit between the "matching" (meaning both mag) lowers and uppers is quite good. It seems a little tight in front, the gap in the back is as far as it'll go down without force, but it's easy to get everything lined up. I'd rather have everything a little tight than a little loose.
How they sit unpinned:


How they sit pinned:
For their lowers I've always had some trouble getting the pins in/out with the uppers I've used. With their uppers it's a little tight but can be done by hand. The fit between the "matching" (meaning both mag) lowers and uppers is quite good. It seems a little tight in front, the gap in the back is as far as it'll go down without force, but it's easy to get everything lined up. I'd rather have everything a little tight than a little loose.
How they sit unpinned:


How they sit pinned:

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