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.

Thanks! I'll add that to the post.

Added a section to try to clear up confusion on handguard length:

Handguard length

- 9mm barrel length is measured by MOST manufacturers as the actual barrel length, chamber face to muzzle, since there is no barrel extension like with 5.56.
- The barrel sits about 9/16″ inside the receiver from the rear of the handguard.

Generally:

- Handguard length = barrel length: Muzzle is 9/16″ inside the handguard.
- Handguard is 1/2″ shorter than barrel: Barrel covered by handguard, Muzzle will be about 1/16″ inside.
- Handguard is 1″ shorter than barrel: Muzzle outside handguard, threads partially exposed (7/16″ total), but thread shoulder is under the handguard.
- Handguard is 1 1/2″ shorter than barrel: Muzzle, threads, shoulder, and a little extra barrel exposed (15/16″ total).

OP, I have a little feedback for your excellent post(s).  I have run both Colt-style and Glock-style lowers - with the same uppers - and I’ve had a blast with them.

I have had good results with a regular carbine buffer running Winchester White Box 9mm.  Keeping in mind that WWB is loaded on the mild side, I had good feeding and ejection magazine after magazine.

On the other hand, with that same standard buffer, aluminum cased Blazer 9mm would shred on ejection.  Not bulge, but really self destruct.  I haven’t had a chance to mess around with that setup using a heavier buffer, but I’m sure that it was the buffer.  A light buffer would allow the bolt to start opening too soon, and the remaining pressure would destroy the case.

As for “what to do about the gas tube hole,” I’ve ignored in on the 9mm uppers I’ve built.  Except for the one I needed “something” in that hole to help center the hand guard I was using.

Thanks for your input!

Using a 3 oz buffer in an AR 9mm blowback is not recommended. ARs were never originally designed for harsh blowback forces. Lighter mass = shorter parts life & risk of case ruptures on extraction. AR 9mm simple blowbacks tend to run well with around 22 oz reciprocating mass. 22 oz is typical for other types of 9mm blowbacks as well.

More mass results in softer recoil and is more gentle on the system. I run one of mine with 27 oz and it feeds/functions all ammo perfectly, suppressed or not. Even weak factory range ammo.

Aluminum cased ammo is not recommended in blowbacks for exactly the reasons you stated. Use at your own risk.

I just ignore the gas tube hole. Never saw why some folks think it's a problem.

This is an excellent resource!  Something else not designed for harsh 9mm blowback recoil forces are Geissele triggers.  The hammer will deform and flatten over time as they are not hardened.

Yikes! Good to know.  

Thanks!

The first time I ran with the basic carbine buffer was because that’s what was in my SBR’d lower, and I wanted to run my (then new) 10” 9mm upper.  As I said, with that 115grain WWB, it worked fine.

I think this actually demonstrates something that some 9mm users just don’t get.  A gas AR can handle a wide range of different loads because the gas system meters the gas.  A blowback system can’t do that, so those hot loads are going to shake you up a bit while the wimpy loads may not always cycle - all because the balance of spring, bolt mass and buffer mass really only works for a fairly small range of loads.  Fortunately, decent-powered 9mm rounds, with between 115 and 130 grain bullets, fit into that range pretty well.

Maybe I missed it, but what differences are there between a colt style and a glock style?
I have a YHM colt 9mm lower and a barrel to build a pistol.  What specific parts are different between the two?

Usually it's the magwell, mag catch, LRBHO mechanism, and the bolt. Specifically, the cut of the "feed lug" [not sure if that's the right term) at the bottom of the bolt that pushes the next round in the magazine into the chamber. The Glock/hybrid bolts have a more narrow feed lug.

If you're building a Colt mag setup with a Colt mag lower, you'll just need a Colt compatible or Hybrid (Colt and Glock) compatible bolt. My two identical Brownells 9mm bolts are hybrid style. One's in a Colt mag, the other in a Glock mag.

Any Glock-compatible bolt should also be Colt compatible.  The difference is a very small difference in the width of the feed rib on the bottom; Glock magazines have a smaller area for the feed rib.  I’ve used Glock -compatible bolts with converted Uzi and various Colt magazines without issue.

The REAL issue is that Colt-style systems use straight, Uzi-style magazines, while Glock uses angled pistol magazines.  So whatever is holding your magazine in has to hold the right kind of mag in the right position and location for feeding.  My only Glock-compatible lower is a QC-10 billet lower.  It works great, though it really doesn’t like KCI magazines.  Magpull’s mags seem to work ok.

I just got a Christensen AR9CA and took it out to the range today.  Would rarely feed the first round from a mag.  tried about 5 different mags.  Got home, re-cleaned and oiled everything and tried it with snap-caps.  Same thing.  Anyone else have this issue or suggestion?

I ran a test on a full auto colt 6991 (10.5 inch) and a Colt DOE.  Using a stock bolt with moving weights 5.5 oz and Kynshot hydraulic buffer 5015HD. Stock colt carbine spring, 115gn Federal FMJ.  Stock buffer gave us 1050 Rounds per min.  Kynshot buffer gave us 860 rounds per min.   The kynshot shot noticeably softer and more controllable.  We also shot Vltor H4A4 7.1 oz buffer which gave us 910 Rounds per min.  The DOE was pretty much the same as the 6991 RPM wise.  

The originator of this post is awesome. The guy knows his stuff. I have found that the Colt 6951 9mm AR is a very solid platform.  About 1k price. Colt worked out the bugs in this platform. They invented it.

I also found that the LaRue MBT and Schmidt 2 stage triggers work very well in Colt 9mm lowers (Simi auto).  This is with thousands of rounds shooting. No issues at all.

Thank you!  I'm glad you found some of the info I put together helpful.  The website has all the latest. There have been a lot of updates.

This is the most popular article now on my site and is the culmination of my research into what needs to be done to make a 9mm AR run correctly.  These steps work to get almost every 9mm AR functioning like it should.  

4-step guide to make (almost) any AR9 run 100%

Here are some 9mm (AE 115 gr. round nose ammo) Rate Of Fire (ROF) numbers (in Rounds Per Minute) yielded by several AR pattern recoil buffers.  The firearm used: Colt M16A1 with a Gibbz side charge upper and Colt 16 in. bbl., standard unknown brand 9mm direct blowback bolt (approx. weight 15.4 oz.), standard stainless steel carbine length recoil spring in a standard carbine length buffer tube.  The only thing changed between test runs (10 rounds each) was the buffer.  Not all tests were performed on the same day. Buffer approximate weight is given in ounces in parentheses, ROF value is after the colon.

H3 (5.6): 971;
Steel shell carbine length buffer with three tungsten anti-bounce weights (7.6): 886;
Standard “9mm two-piece mechanical” (5.6): ave. ~875;
KynSHOT RB5015HD (6.1): 765; and
B & T AR9 AR15 (6.1): ave. ~700

Disclaimer:  I have no affiliation with or financial interest in any vendor or manufacturer.  I am not a competitive shooter or a blogger who receives any form of compensation or sponsorship for endorsements, or favorable public or private comments.  I do not have a website, podcasts, webinars, or online videos; or books/magazine articles.  Use of vendor and/or product brand names, if any, is for informational purposes only; and products or services were purchased by me from regular commercial sources.

Best of luck.
MHO, YMMV, etc.  Be well.

ETA: I forgot to mention, the B & T hydraulic buffer, with the shroud that covers a portion of the recoil spring, has much less of the "sprong" recoil spring noise than any other buffer that I have tried.