So I went to the Indy 1500 gun show and saw a 4.5" MPX K pistol with the collapsing brace and finally decided to get one since the price was the best I've seen so far.

Of course, no iron sights. Sig website doesn't sell the MPX specific sights, and I've heard normal AR sights might not have enough front post adjustment to zero on the MPX. Filing down the front post is an option, but really?

Is there something that works off the shelf on an MPX? I'm thinking zeroing it at 25 yards makes the most sense. Centurian Arms HK style diopter sights might be nice...

You could go the other way, put a quality RDS on it and skip the irons.

Troy HK style micro buis set The Troy HK style micro set may be what you are looking for. I haven’t seen any buis sets that sit lower than these. I’m planning on getting a set for my 8” MPX for the same reasons.

I'll probably put a red dot on it, but irons are always a good idea, especially on a PDW.

Height above the rail isn't the issue. It's the ballistics of a 9mm from a pistol length barrel versus the 5.56 aftermarket iron sights are designed for and running out of height adjustment when zeroing. Or so some people have reported.

My 8" Gen2 MPX braced pistol came with irons from SIG, back when the company was still including them with the guns. I read a review someplace that said they were originally made by Samson Manufacturing for SIG NH. I'm not sure how true that is since Samson really doesn't have any of their own current branded sights that look anything close to the "SIG" set. They're true AR sights since they're the exact same irons that my early Gen2 FDE 516 came with a few years earlier. Certainly Samson could've made a huge run of these and SIG was merely providing them on the MPX and MCX until they finally ran out. Physically and visually they're a bit of a wart when collapsed on the rail. Usable but kind of homely, which of course had me on the lookout for a more discreetly folded pair when not in use.

The lowest profile iron sights I came across are the Bobro Lowriders. If you want 'flat' these are about as low as they come. These too are AR (5.56) sights, and are just as limiting in adjustment if not more so as any other 5.56 iron sight. I bought a set for my MPX when Primary Arms had a sale going on; Folded down they're great but flipped up for use...not that great. On a MPX or any braced/shouldered pistol caliber gun they're probably fine given the sorts of closer-in distances someone using these would be shooting to. My set doesn't solidly lock when in the upright position. If they're indicative of the type, it likely won't matter 100m and in but I'd never choose to use them when shooting with a longer distance rifle.

The rear Lowrider folded down over my MPX's Raptor charging handle:



I don't have a pic of either of the sights in an upright position. And I haven't had a chance to shoot with them outdoors since the state mandated the outdoor shooting ban over the concern of possibly sparking wildfires.