Thanks for the reply, MikeD. See my answers below each of your questions:
I am not very familiar with the plinkster but the first thing I would look for are any burs or rough edges that the follower might be catching on, check the follower itself as well. If you find any, sand them smooth.
-I will try to disassemble the mag to see what I can find. I typically try to stay away from trying my hand at this sorta stuff because I can' ever seem to get things to go back the way they were originally. I guess there's not really a loss if it happens this time, since the mag is pretty useless at this point anyway.
Does the spring appear to sit straight or is it applying uneven pressure on the follower causing it to tilt and bind?
-From what I can tell, the follower is sitting straight. Since the first 3 bullets seem to feed fine, maybe it isn't sitting straight once it drops lower in the mag, beyond the point where it seems to catch.
Is this a metal bodied magazine? If so does it appear to have any dents, etc thet should not be there?
-yes, it is the original 10-round metal mag that came with the gun when I purchased it. I don't see any visible signs of dents.. but if I keep using it that will likely change because I have to tap the mag on the side of the shooting table to get the spring to pop back up and push the bullets up that are close to the bottom. Of course, the "tapping" seems to get a little harder the more aggravated I get with it.
It should be clean but not lubed heavily as oil will attract dust which will affect performance. Use just enough oil to prevent rust on metal parts, you dont need any more as most mags run best when dry.
-the first time it started catching, I sprayed a little WD-40 in it just to see if that would help. I was afraid to put oil in it simply because, like you said, it would puddle at the bottom and catch dust... eventually getting sticky. The WD-40 was no help.
Thanks again for the suggestions. I will carefully disassemble the mag and maybe hit it with a real fine sandpaper on all sides, and lightly lube all the walls and spring with oil. Hopefully this will help. I priced a replacement 10-round mag yesterday at Academy and it is $24.99 + tax. Wow - I only paid $109 for the gun when it was brand new. Hard to believe that the cost of a tiny, 10-round mag was almost 25% of the total cost of the gun. An aftermarket 25-round mag was $28 + tax, but it was all plastic, and the online reviews for it weren't too kind so I left it alone.