Mossberg 320BA .22 question with pictures

I recently got a Mossberg 320BA from my dad. The gun is in really good shape for being so old. I took it to the range today and the thing is a tack puncher.

My question for you is why are there 2 screws on the back of the rifle? The open screw hole is the screw in question. The first one obviously holds the receiver cap on, but the one in front of that if i put the screw in wont allow the bolt to go back far enough to reset the safety or eject the empty shell casing. Is that the purpose of the screw or is there something I am missing. Below are some pictures of the area in question:

image of the 2 screw holes, the empty one is the one in question.
http://gimpedguild.org/forum/imagehosting/404d2a4859b12a7.jpg

more zoomed out for reference.
http://gimpedguild.org/forum/imagehosting/404d2a46830373d.jpg

Likely it had a short blind screw that did not go deeper than the receiver wall. These screws holes were also very likely the mounting points for a set of target peep sights :)

These screws were for a peep sight. They can be had from Gunparts.com or any hardware store. The missing screw, however, will not affect operation at all.

Yep, those models were drilled and tapped for receiver sights, as well as grooved for scope mounts. The rear cap on the receiver is released by a lever, which is revealed when you undo the screw holding the receiver to the stock and lift it out. After you take off the rear cap, you can pull the bolt out, and clean the barrel from the rear.

so those screws are just place holders. Thanks guys, looks like i just need a shorter screw to plug the hole to prevent dirt getting in behind the bolt.

Thanks again!