When a trigger group is loose in the stock, there are 2 reasons why. First, the stock wood on the bottom where the trigger group bears, may have been compressed after 50+ years of use. You can add shims of wood to correct that situation. Second, the lugs (the little 'pins' on the forward end of the trigger guard ) that cam into the receiver may be worn (flattened). The easiest way to correct this is to peen those pins with a ball peen hammer being careful to support the trigger guard. Remove the guard to do this. All you want to do is 'fatten 'em up' a little or create an edge on the pin. When mounting the trigger group in the stock, it should be a very tight fit. Most correctly fitting groups will have to be rapped with the palm of your hand to click the guard in place. Some are so tight, guys use a small rubber mallet. To open a really tight fitting trigger group, you can use a section of a G.I. cleaning rod or screwdriver to pull the guard out. You pull slightly forward and down. If you have the milled guard with the hole behinf the trigger, that is where you put the cleaning rod or screwdriver.