So I noticed on Macon Armory’s website, in regards to their guaranteed to feed barrels, they have a disclaimer against the Spikes Glock Lowers. They state their is an inherent design flaw which causes certain 9mm rounds to feed improperly. Does anybody have more info on this or details of the design flaw?

I have a 2019 Spikes Glock lower and it works perfectly with a 5.5" Macon barrel. Tested with a box of 147 HST.  All ran OK.

As I understand it, the mag catch may not hold the mag at the proper height in some (older?) lowers.

Rudy (Macon's owner) is working on a catch that solves the problem for people that encounter it.

Need some help!  I have a Nordic Comp 9mm lower for M&P that I am building.  I am using an upper from a Glock configuration and finding that the bolt binds with the lips of the M&P mag.  The width of the bottom feature of the bolt is wider than the distance of the mag lips.  Who makes a bolt that works with M&P mags?

Hi Billk77.  If you post your question as a brand new topic in this forum, you'll get a lot of responses.

Edit - did it for you!  

link to post in main forum

Ditto- A great post to sticky....

Wondering about anti-rotation pins and quality.  I've read several places that the AR9 cause trigger pins to rotate.  I have a set of KNS pins but wanted to
know if they were the same or higher quality than stock pins.  Any experience with them?

I'm not sure why 9mm, more than any other caliber, should cause trigger, and not hammer pin or both trigger and hammer pins to rotate.  The trigger and hammer pins should not rotate; rather, the trigger and hammer should rotate on the their respective pins. So said Mr. Eugene Stoner:
https://pdfpiw.uspto.gov/.piw?PageNum=0&docid=03045555&IDKey=EC76F808724E%0D%0A&HomeUrl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526­d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25­252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D3­045555.PN.%2526OS%3DPN%2F3045555%2526RS%3DPN%2F3045555
I use anti-rotation pins from various vendors for most ARs regardless of caliber if I expect that they will get shot a lot.
Best of luck with whatever you pursue.

MHO, YMMV, etc.  Be powerful; be well.

Wanted to give a quick update on my AR9 build.  I was using a brand name AR lower with a FoxtrotMike upper.  Had problems with failure to eject and went back and forth with FM and the mag block manufacturer.  Finally decided to quit messing around and just buy the complete FoxtrotMike lower.  Once it came in, I cleaned it up and lubed the buffer and spring.  First thing I noticed that the buffer retaining pin was beefier than normal which makes perfect sense for a blowback AR.  I also noticed that it had an ambi safety and the hammer seemed a little heavier than normal.  Cleaned and lubed it and took it to the range.  All ammo ran without any hiccups.  I ran factory 115 grain as well as my own reloaded 124 ghp and fp 147 grain.  Not a problem with any of them.  Also ran it suppressed without any problems whatsoever.  

Lesson is that buying a stripped lower, lpk, buffer tube, spring, heavier buffer, and a mag well adapter can easily cost more than buying the factory lower that matches the upper.  The guys at FoxtrotMike worked with me all the way through.  I know there are other brands out there and they could very well be just as good.  Just wanted to say that these guys have tested their product and know what works.  Save some time, effort, money, trips to the range, and aggravation by getting the proven product.

Building your own is always an exercise in "trial and error", with "error" being a significant part of it.  I'm not a fan of FM but I'm glad it all worked out for you.

Minor updates...

Great writeup Droppoint. I appreciate the time you put into all of that, and I will reference it whenever I have troubles. I will point out that one notable exception to the rule regarding polymer lowers breaking in PCCs is the Cavarms lowers. They hold up exceptionally well to 9mm or .45 conversions.