I think you should use magnum primers with IMR 4227. However, that load is way below Hodgdon's 18.0 gr minimum.
If you want a softer load, try my favorite of 6.0 gr SR4756, which I discovered as suitable for my SP101 with 125 gr XTPs.
I use heavier bullets with serious magnum loads that I shoot in the GP100 5". There I might try full up IMR 4227.
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