What required the use of a rubber mallet? I think maybe you bent the hammer strut on your hammer when you removed the mainspring housing, but you might just not be making sure that it fall rearward when you close the mainspring housing.
Here is how it should be taken apart.:
Cock the gun and pull the trigger which will allow the hammer to fall forward. Lift the mainspring housing lock and bring it up and then remove it from the gun by pulling downward on it. Now the receiver can be pulled forward, but you could use a rubber mallet the first time that you try this because at times they are very tight and require either bumping it forward by a mallet or bumping it downward onto a padded bench on the back end.
Now, pull the bolt out of the back and you should have the receiver and barrel, the bolt, and the lower grip frame. I use a spray cleaner from here to remove anything that the factory put on it for rust protection. I then will apply a drop of oil to the hammer where the pins go through and wipe my finger over the bolt as well.
Now place the bolt back into the receiver. Place the receiver back onto the gun and slide it rearward to make the lug in the receiver slide back under the lcoking part on the barrel. It should just slide right back in place for you and it shouldn't be as hard the next time to remove the receiver either. Now, look into the gun at the rear and lean the gun downward, you may have to reach in with something to push the hammer forward out of the way. Next, put the mainspring housing back into the gun with the lock still out. Tip the gun backwards to you with the barrel up in the air and allow the hammer strut to come back to you and then lower the locking mechanism and close the housing. Pull the bolt back and the fire the gun to check to see that you have it right.
If it still won't work right, take a look at the hammer strut and see if it is bent. If it is, you need to contact Ruger and get a new one and then follwo the directions. Hope this helps you out. If you cannot get it figured out, box it up and send back to Ruger, they should take care of it for you and most likely won't charge you anything for it this time.