Easiest way to find out is to perform a swing test.
load the model up flight ready, less the igniter. tie a slip knot in a length of heavy thread of light twine. balance the model at the CG with the slip knot. in an open field or someplace where you can swing the model over your head in circle. start the model out they let out about 6 to 8 feet of line swinging the model fast enough to keep it straight out on the end of the string.
Observe the flight. If the model flys forward in the direction of your swing..... That's great the model will be stable. If the model turns over flying backwards, Stays sideways or rolls around on the string.. You'll need to add some nose weight.
I keep a blob of clay with me, during swing tests. add a little clay to the side of the nosecone and try again. if that wasn't enough add more, if you think you added to much take a little off and re-swing.
At some point the model will fly nose first and level. Now you can remove the clay for the nose cone. and either insert it inside a hollow plastic cone securing with a (LITTLE) epoxy. or trade the clay for bb's, fishing split shot or #9 lead shot. helds with a little epoxy or glue. After permanent installation I like to swing the model one more time just to ensure I got the nose weight right.
If it's a balsa nose you may have to drill it out to add the weight, Usually the extra weight of the glue or epoxy used to secure the noseweight will offset any weight lost by the drilling
Hope this helps.
PS: You can see this technique better in ANY additions of G.Harry Stines book "The Handbook of Rocketry". I strongly recommend every model rocketeer own at least one copy