Has anyone compared whether Gold Dot 124 or 115 work best in these R9s or is there no real difference?
I little less perceived recoil with the 115's, but I would use the 124's if available and they function in your R9. Remember, you're launching the bullet from a VERY short barrel, as a general rule of thumb the heavier projectile will penetrate deeper with all other things being equal.
That is my view as well. However, as Tracker has noted, buy whichever one you can wherever you can find it.
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And by the way, I've taken my own advice and ordered a supply of the 115s. Thank you for the link, JB.
For a number of reasons of which we are all aware, such reasonable prices may soon disappear.