Jason4x4, do you have access to a trigger pull scale? The pull weight for the double action trigger gives a very approximate estimate of the mainspring strength, so it would be useful to know the double action trigger weight. For example, if the weight is below 7.5lb, then you probably need a longer strain screw, and if the weight is above 10 lb, then there probably is another problem. If the double action is between those weights, knowing it still might give some hints.

You can also use the trigger scale to directly measure the strength of the mainspring as shown in post #2 of this thread:

question about testing hammer spring weight

If you need a longer screw, you should try the advice above from MajorD. Use the cup from a spent small primer as a shim on the end of the strain screw. This will give a good indication whether a longer screw will help.

If you have trouble finding a new strain screw for a square butt, there is a seller on ebay called "gun garage" who usually has them. I have no connection to this seller, and I have not tried their strain screws, but I know they often have hard to find screws in stock.