BTW did you use the stock rail or the CROM?
Oh, thanks that you asked, that's indeed an important detail! I do use the CROM mount, which really gets the optic into a really nice plane (with respect to the bore and front sight). The only hard part is that there is VERY little clearance between the front of the HE503 and the front hex screw. You are best off buying a spare hex key or two and grinding it carefully down to just barely fit into the hex slot under the front of the optic. Even then it's hellishly tight, but doable.
A few pictures for reference:
A normal hex bit won't even fit here:
So you need to modify a hex key by shortening the driving end:
Bonus tip: If you're struggling to mount a light in a sensible manner, and have the Aridus Zhukov-style forearm with the M-Lok slots, you can mount most Surefire Scout and Streamlight Rail Mount family lights to a MAG935 (that's the part number) extended cantilever M-Lok mount from Magpul (
https://magpul.com/m-lok-extended-cantilever-light-mount.html?mp_global_color=118).
NOTE: This doesn't fit the SureFire DS00 Dual Activation Switch or M600DF Scout Light!
My gun runs a Streamlight HL-X, and thereby you eliminate almost all barrel shadow (just a tiny bit in the far corner). I decided to run the pressure pad remote they include, and that with their "automotive grade" double-sided tape, and an extra zip-tie thrown around the Zhukov's insides hold it in place with a high degree of confidence.