K, looking at the bayonet you'll see a plunger and a pin holding the plunger in.
Looking at the plunger you'll see it "bottoms out" when you push it in. Pushing it in is suppose to allow you to put the bayonet on the rifle, and as you have reported, it don't always work the way it is suppose to.
Punch out the pin being careful not to loose the sping. What you need to do is file or grind the inside (closest to the bayonet proper) of the plunger which will allow it to be pushed in farther.
That should give you more clearence. If the spring guide is too long to allow your plunger to be pushed in enough, then shorten' it a bit.
Now put it back together and you should be good to go.