I just upgraded from a cheap Bushnell to a Vortex Ranger 1500 and would recommend it.
First one I got was defective though. Wouldn't range shit. Sent it back to Vortex and they replaced it. New one works well so far but I haven't had much time to use it.
The Sig was on also one I considered.
I had my slide work done by Fire 4 Effect and the quality of the machining and refinishing was excellent. I wouldn't hesitate to use them again. I also like that they have dozens different options so you can get the features that work best for you. For me I wanted truly functional and aggressive forward cocking serrations.
You might also look at Way of the Gun and Primary Machine.
I agree that machining a factory slide is the way to go rather than aftermarket. YMMV.
Had the same question so I tested all the popular mags - fully loaded. On MY lower, a Troy mag was the easiest to seat.
I didn't try a metal GI mag though.
I was going to say it isn't getting enough gas. Open up the GB a couple clicks. Happened to me over the weekend at Regional.
Then you said it wouldn't even feed when using charging handle. Can you try a stronger spring on your JP SCS?
I've got 2 guns with SLR gasblocks (set screw) and KMR rails.
No clearance issues.
Fantastic combination of one of the best gasblocks out there plus THE lightest handguard.
I got a Bar-Sto barrel for my M&P. Had them fit it also. Very disappointed. POI was off and accuracy was no better than KKM or Stormlake.
I will never buy another Bar-Sto product. I will, however, buy other aftermarket barrels.