What bullet weight is the correct one for a Model 59? I believe my Model 39 should use a 147 grain bullet, I do know 115 grain shoots low in it. Thanks for your help

Both the 39 and 59 were designed around the standard 115 gr FMJ 9MM round.
The 124s and 147 came much later.

Don't forget that early 39's and 59's had a higher twist rate than the rest. I believe the change came around A250000. I personally find the older barrels to be more accurate than the lower twist rate barrels, but both are combat accurate or better with 115 gr or 124 gr bullets for me. Of course your results may vary.

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J.D. Roy