DIY Takedown 9mm AR (Tool-less upper!)

Is making a 9mm AR into a “takedown model” easier than everyone thinks it is? Takedown models allow a rifle to be stored and transported in a very small package. Here’s my 16″ 9mm AR takedown upper, and how it works. This information is intended solely for entertainment purposes only. Do not perform any action

New 9mm AR Mistake: Snap Caps

While great for dry fire and manipulation practice, snap caps are not a conclusive test for feeding and ejection. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to

FM Hybrid Lower: Bolt Hold Open Fix

The Foxtrot Mike (FM) 9mm polymer hybrid lower (Glock mag) may come with an ambidextrous bolt hold open. If used with a non-FM upper, or even some FM uppers, the bolt catch may not work at all without some modifications. This information is intended solely for entertainment purposes only. Do not perform any action based

Adjusting the FM-9 Ejector

2 methods to adjust the FM-9 ejector into proper relation to the bolt. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified gunsmith for repair. All

The Clever S&W “Response” Recall Fix

The bolt face design used by S&W in the 9mm Response is known to allow out-of-battery (OOB) discharges. Did they come up with a fix without changing the bolt face? This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this

Matador Arms Mat-9 Bufferless Upper

The Mat-9 can transform an AR lower into a very compact PDW that can fire when folded. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified

Stepping away for a while (Update: I’m back, baby!)

[January 2024] Due to the unexpected loss of a very close family member, I will be unable to reply to any inquiries for a while. I will be back. Please be patient as my family tries to heal and move forward. Thank you. UPDATE: It’s now March and we’re still going though a lot here, but we’re starting

Last Round Feed Failure

Detailed Root Cause Analysis Experiencing a feed failure only on the last round in a magazine? The magazine may be activating the last round bolt hold open (LRBHO) too soon. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information

9mm Compatible AR Triggers

Which triggers work, and which ones don’t? Here’s what people have reported on the forums. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified gunsmith for repair.

Taccom 3 Stage Adjustable Recoil System + Cushioned Buffer Spacer

How does Taccom’s “3 Stage” PCC Adjustable Recoil System compare? Let’s find out! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified gunsmith for repair. All copyrights

Replacement 9mm Firing Pins

Sometimes a firing pin will simply snap. It happens. Finding a replacement isn’t always that easy. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified gunsmith

Which 9mm Bolt Should I Get?

The bolt is one of the core critical parts of a 9mm build. Choosing the right one can make a big difference in how the build performs. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not

A $54 9mm AR Bolt? Does it work?

Who doesn’t like a great deal? But is it worth it? Let’s take a look and find out. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a

KAK Industries K-SPEC PCC Buffer

KAK Industries has just come out with a new buffer design that includes a cushioning system in the head, similar to the way a hydraulic buffer works.  Will this be a winner or just another snake-oil gadget? This information is intended solely for entertainment purposes only. Do not perform any action based on any of

Maxim Roller (Bearing) Delayed Buffer System [Sep 2023 updates]

Could this be a drop-in CMMG RDB killer? TL;DR: Almost, but not quite. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a qualified gunsmith for repair. All

Advanced Primer Ignition (API) Blowback

No, Advanced Primer Ignition (API) blowback is NOT used in open bolt submachine guns (SMG). Let’s look at what API blowback is, and why so many people are confused about what it is and why they believe it’s part of SMG operation. This information is intended solely for entertainment purposes only. Do not perform any

9mm AR Gentle Recoil Buffer System: Final Configurations

April 2024: 9mm AR with Gentle Recoil System WINS IPSC NATIONALS in Brazil! Link Short stroked configuration with carbine tube, Kynshot RB5015HD buffer, 1 Kynshot spacer weight, Wilson Combat flat wire carbine spring. See below. May 2024: New Wilson Combat Springs ALERT! I have received 4 reports that new Wilson Combat AR-15 flatwire springs bought

Kynshot Hydraulic Buffers Comparison

This is a comparison of 6 different Kynshot hydraulic buffers. I purchased most of these for experimentation with the “Gentle Recoil” project. Model PistonPressure** Length Weight BodyDia. PistonShaft PistonThrow IntendedCaliber RB5007 ~5 lbs. 4″ 6.0oz. .76″ .2″ .41″ 9mm RB5015HD * ~10 lbs. 4″ 6.0oz. .76″ .2″ .41″ 9mm RB5000 ~10 lbs. 3.25″ 4.1oz. .69″

Geissele Super 42: “Get It” or “Gadget”?

A braided AR recoil spring based on a “Machine Gun” spring? Is it quieter? Better? Real innovation? Marketing nonsense? Let’s do some testing! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always

Your first range trip: Is this normal? What is and what isn’t.

For new shooters or someone who is not familiar with a blowback gun, some of the quirky behaviors can be concerning.  It can be tough to know what’s normal and what isn’t.  Here’s some of the things users have reported that you should and should not expect. This information is intended solely for entertainment purposes

A no-frills $276 upper: Does it run? Can it feed HST hollow points?

$276 INCLUDING bolt and charging handle! Was it worth it? Let’s take a look at an assemble-it-yourself bargain upper and see! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning

Aero EPC 9mm – the 3 parts I would avoid

Most Aero Precision EPC 9mm parts seem like a good value for 9mm AR builders.  However, I would avoid 3 of the parts, substituting with different options. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not

Flat Wire Spring Comparison

Flat wire recoil springs are quieter and provide more consistent spring pressure than a standard mil-spec recoil spring. I purchased 7 of the more popular AR flat wire recoil springs and compared them for buffer fit. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the

Fixing the TNW Aero Survival Rifle

Swapping a few parts made charging the ASR easier, and recoil more managable, while still maintaining caliber-conversion compatability. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a

Gentle Recoil Part 2: Hydraulic buffers, A5 and Carbine buffer tubes

The Gentle Recoil System (GRS) for 9mm blowback has proven to be a success based on the feedback I’ve received. Can we make it smaller and still have good results? This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this

Tested: Aero EPC Buffer Kit Slow-Mo

Does the Aero Precision EPC 9mm buffer kit prevent bolt bounce? Let’s see how it performs in the real world. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. All copyrights and trademarks

The Original 9mm AR Deadblow Buffer

I managed to get one of the few brand new original Colt R0635 9mm submachine gun (SMG) buffers still available. Let’s see how it works! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or

A Case FOR Solid Buffers???

A Colt “enthusiast” recently proposed that Colt’s 9mm AR guns “…all have solid buffers, which are absolutely necessary to prevent bulged case heads and eventual case failure.” This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not

BCA Bufferless 9mm Upper – is a 13.5oz bolt safe?

A 13.5oz 9mm blowback bolt (bufferless!) in an aluminum upper receiver?  What could possibly go wrong? This is going to be interesting! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. All copyrights

“Gentle Recoil” 9mm AR Project (with updates and testimonials)

I didn’t think it was possible, but I was blown away by the results. Smooth, “gentle” recoil from a 9mm AR simple blowback with off-the shelf parts. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not

Hydraulic buffer spring testing – slow-motion video

High speed slow-motion video is very revealing, and what I found needs to be seen to be believed. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning firearms to a

Using a Colt mag adapter. Slip fix, FM9 bolt fix.

An R&D Precision Colt magazine magwell adapter is an inexpensive and reversable way to convert an AR lower to 9mm. Here’s what they are, how they work, and a few fixes to common problems. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information.

Still getting failures to eject? Check the extractor.

If after adjusting the ejector you find you are still getting a failure to eject, there’s one more thing to check. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning

Do I need a last round bolt hold open (LRBHO)?

A LRBHO device is very convenient.  It lets you know that your firearm is out of ammunition instead of suffering from some sort of malfunction or failure.  However, it isn’t necessary. What is a Last Round Bolt Hold Open (LRBHO)? The LRBHO mechanism works by letting you know that your gun is out of ammunition.

Tech analysis: FM-9 bolt. Light strikes, slam-fire concern?

I was sent an FM-9 bolt for root-cause analysis by the owner who was having some problems with light strikes and a concern about reported slam-fires. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed

OOB warning – missing bolt face bottom lug

In September, 2022, I had an out of battery detonation with a particular bolt that I own. I’m convinced that the missing bottom lug on the bolt face was a major contributing factor to this OOB, and I’d avoid any simple blowback AR bolts made this way. This information is intended solely for entertainment purposes

The Overmass Project: World’s heaviest 9mm blowback action? (with videos)

[UPDATED Dec 2022] This is my biggest experiment project so far. How much mass can we put into a 9mm blowback before it stops cycling? This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or

A2 rifle buffer tube on 9mm AR pistol?

Yes, it can work just fine. It’s just a matter of making sure there isn’t too much or too little space for the buffer, bolt, and spring. It also needs a retaining kit for the takedown pin detent and spring. This information is intended solely for entertainment purposes only. Do not perform any action based

Feed fix: Bevel sharp edges on bolt face

Another feed fix for AR9 builds! As a cartridge is pushed forward toward the chamber, the cartridge base can catch on sharp edges on the bolt face, stopping the feed. Two small bevels with a file may resolve the problem completely without the need for expensive barrel cone machining. This information is intended solely for

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

If you just want to get a simple blowback 9mm AR running reliably with minimal explanation and details, this is for you. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring

Video analysis: “The Perpetual Agony of the AR-9”

About 9 months ago “Hop” (YT user: Hoplopfheil), who is also a contributor to The Firearm Blog, posted a video about all the problems he is having with his AR9.  He swaps mags, barrel, and other parts trying to fix his persistent problems, but the gun keeps giving him problems. This information is intended solely

EPC Feed Fix Part 2 – magazine height fix

The another piece of what seems to be the never-ending Aero EPC feeding problem saga: the mag catch and magazine height. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Always bring malfunctioning

Case head separation in a 9mm AR

This one is interesting. I’m going to try to stick to the facts, then get to how this could happen in a blowback 9mm. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted.

Do I need to headspace my 9mm AR?

Headspace is defined as the distance measured from a closed chamber’s breech face to the chamber feature that limits the insertion depth of the cartridge. Headspace in 9mm AR’s is usually affected most by how deep the chamber is cut into the barrel. A chamber cut too short could result in a cartridge sticking too far out

Aero EPC Barrel Feeding Fix Update! (feed cone picture added)

Aero is apparently replacing the original EPC/Ballistic Advantage barrels for their customers with feeding issues! They claim to have developed a new feed cone solution that has been “rigorously tested” with “tens of thousands of rounds”. We shall see… I’ll post pictures as soon as I can. This information is intended solely for entertainment purposes

Buying Cheap Glock (and Colt) Mags

Once again, someone has posted online that they are having problems with a cheaper brand of Glock-compatible magazines. I understand the temptation to buy cheap mags – why should you pay the exorbinant manufacturer’s price when you can get a cheaper brand that works just as good! The problem is, they don’t. Really. You can

Mossberg 590S Shockwave 12 Gauge

And now for something completely different… This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. I am not a lawyer. This is not legal advice. The Mossberg 590 Shockwave is an unusual firearm

Building a Competition PCC

A guest article by Reddit user ZChaosFactor for Blowback9.com. If you have any questions, please contact ZChaosFactor on Reddit. [I don’t build competition PCCs, so I can’t be much help here.] This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of

Which defensive ammo should I use?

Most defensive ammo uses a large hollow point bullet. Unfortunately, most 9mm AR barrels are not designed to feed hollow point ammo.  Just because a barrel feeds FMJ ball ammo reliably, doesn’t mean it will feed hollow point defensive ammo. This information is intended solely for entertainment purposes only. Do not perform any action based

SB HBPDW 9mm buffer weight

For those interested, the new SB Tactical HBPDW 9mm buffer is only 2-5/8″ long and weighs 7.95 oz. That’s a lot of mass in a small package! Optimal bolt+buffer mass for 9mm is around 22-24oz. This buffer should get the reciprocating mass right where it should be, despite having such a short buffer tube. 9mm

Another Improved Feed Cone Supplier? (Grid Defense/Ghost Elite upper)

***Sep 2023 update: It appears that some time between Feb and August 2023 they changed their feed cones again and not it’s not as wide as it was after the last update. This may result in feeding problems again. I would not use them now until we see reports of how this more narrow feed

Glock mag or Colt mag?

Traditionally one of the most controversial topics for PCC, similar to the 9mm vs .45 AARP debate. (Two world wars! …OK, boomer.) This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Pros and

Another Success Story! (plus build list)

Congratulations to Redditor u/Mildblueberry for a successful home build 9mm AR that runs 100% even with large-cavity hollowpoints! This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. MBB went into the build process

The Mean Arms EndoMag Insert

The Mean Arms EndoMag inserts allow you to use your standard AR lower with a 9mm upper, without the need for a magwell adapter. Although a clever idea, the EndoMag has, in my opinion, a potentially dangerous design flaw. This information is intended solely for entertainment purposes only. Do not perform any action based on

The 9mm AR: A flawed design

The 9mm AR can be a fun and effective firearm, but there are a lot of things inherently wrong with the design. No one would design a brand new 9mm rifle from scratch and somehow end up with a clone of the 9mm AR. Despite this, the 9mm AR is a very popular platform and

Vltor A5 parts and 9mm blowback

Twice in the last week someone has asked about using a Vltor A5 buffer tube with their 9mm blowback AR setup. A 9mm blowback setup can use an A5 buffer, but should not use an A5 buffer tube….here’s why… This information is intended solely for entertainment purposes only. Do not perform any action based on

Building a 9mm AR: what to expect.

Talking with fellow AR9 builders, I have come to realize that many people new to building a 9mm AR platform expect all these random parts will simply fit and function together perfectly the first try like an AR-15. Be prepared to be disappointed. 9mm AR’s are significantly more complicated than an AR-15 to get running

Brigade Firearms New Feed Cone?

One of the biggest problems with the 9mm AR surrounds feeding issues. The 1980’s feed cone everyone still uses is almost always to blame. Brigade appears to be the latest to join the growing number of barrel makers to improve this relic of the 80’s! Redditor “vogie563” has reported that Brigade Firearms is now machining

Suppressor series #2: First round pop fix

The first shot out of a suppressor may be noticeably louder than the following shots. This is because of a phenomenon known as “first round pop” (FRP). This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not

.308 spring revisit: Is spring resonance the real issue?

This weekend I went out and did some more experiments with springs. What I found was very interesting. Is the .308 spring popular because it doesn’t vibrate? This weekend I tried swapping weights and springs again, this time to see its effect on suppressor gas blowback. The effect was minimal. However, when I used a

Suppressing the 9mm AR

Blowback 9mm is a good host for a suppressor (silencer).  The barrel is fixed, so you never have to worry about the weight of the suppressor affecting cycling like with a tilting-barrel pistol. Subsonic ammo is necessary for best performance, but most common 147 gr. 9mm loads are subsonic so they tend to be easy

Aero EPC-9 – what the heck is going on? [Updated: replacing barrels!]

Aero Precision makes some fantastic lowers. I have one on my home built AR-15.  However, it looks like the EPC-9, their entry into the budget AR9 arena, has fallen prey to some of the same “budget AR9” issues as all the rest. Fortunately they are following up and fixing some of the issues their customers

Captured spring systems – a bad idea for PCC?

Captured spring systems were originally designed/intended for the 5.56mm locked-breech AR-15. Two popular ones are the JP Silent Capture and the Armaspec Stealth. These systems have demonstrated themselves effective and reliable in the locked-breech 5.56mm AR platform, but may not be a good idea for the average person’s 9mm blowback. This information is intended solely

9mm AR Troubleshooting Guide (simple blowback)

This guide includes some of the more common malfunctions, probable causes, and some possible resolutions for a semi-auto simple blowback 9mm AR. This list is not comprehensive. It is work in progress and will be updated as time allows. This information is intended solely for entertainment purposes only. Do not perform any action based on

Blowback 9mm AR: Steps of operation

Understanding all the individual steps of 9mm blowback operation can be important to troubleshooting problems and ensuring proper operation. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Geek alert! We’re going to

Installing or replacing your barrel. Here’s what you need to know.

There are plenty of barrel options out there.  Picking the right one can make the difference between a reliable gun and a nightmare. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. All

Franklin Armory® BFSIII® binary trigger in a 9mm AR

Getting the Franklin Armory® BFSIII® AR binary trigger to work in a 9mm AR can be a bit tricky. With some trial, error, and patience, I found it can run reliably and is a whole lot of fun. This information is intended solely for entertainment purposes only. Do not perform any action based on any

The Strike Industries [and KAK Industries] short buffer tube on 9mm blowback?

So you want make a short 9mm AR. How about using a really short buffer tube? Can we get away with a tube 2″ shorter than usual in a simple blowback operated 9mm? This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The

Aluminum case ammo – Can I use it in my blowback 9mm?

Aluminum cased ammo is often less expensive and lighter weight than brass cased ammo, which makes it an attractive option. Some blowback guns can run aluminum ammo without any problems, but many won’t, which is why many manufacturers don’t recommend it. This information is intended solely for entertainment purposes only. Do not perform any action

Pistol Caliber Carbines (PCC): Why bother?

Some people really get upset (I mean REALLY upset) over the popularity of pistol caliber carbines (PCC) and “large format” pistol caliber pistols. This includes AR-platform pistols and the like. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this

What hammer do I need for my 9mm AR? (hammer/bolt compatibility)

The idea that a 9mm-specific hammer is NECESSARY for a 9mm AR is a myth. There are four common hammers out there, and hammer selection depends on the bolt profile. This is the information I have been able to find from my research into the topic. This information is intended solely for entertainment purposes only.

FM Products 9mm AR: the 2 parts I would change if I bought one.

Foxtrot Mike Products (link: https://fm-products.com) manufactures competitively priced AR platform blowback 9mm guns and parts. For the price, their products appear to be good quality. However, I would swap out two specific parts if I were to purchase one of their 9mm ARs. This information is intended solely for entertainment purposes only. Do not perform

What 9mm buffer do I need??? (and spring)

Let’s look at a little quick history and then get to what works best for most typical 9mm ARs. NOTE: None of this applies to the CMMG Banshee. It uses a different operating system. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information.

Beware of obsolete parts

Many well-meaning people continue to recommend parts that were only meant to be used in the original 1985 Colt 9mm AR SMG. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy of this information is not guaranteed or warranted. Many of

M&P 15-22 & ejection fix

How this all started: We were looking to brush up on our manipulation and handling skills with the AR-15 platform without burning through our .223 ammo, so we decided to go with a CMMG .22 LR conversion kit for our AR. The idea was to maintain the same manual-of-arms. This information is intended solely for

Improving the MP5 trigger

(Semi-auto only MP5 trigger job) The HK MP5 is one of the most iconic sub-machine gun (SMG) platforms in the world, often recognized by anyone who has watched movies or played first-person shooter style games. Known for their gentle recoil impulse and controlability, the MP5 comes to us from an age of firearm design when

Upgrading your 9mm AR trigger? Read this! (Foxtrot Mike Products FM9 out-of-battery detonation)

Almost all 9mm simple blowback AR platform factory guns have a shortcoming that should be addressed when upgrading the trigger. If your 9mm AR came with a “mil-spec” style trigger and a solid buffer, this is important! This information is intended solely for entertainment purposes only. Do not perform any action based on any of

The old-school pistol non-“brace” options

The US Dept. of Justice has recently proposed regulating pistol stabilizing braces essentially out of existence. Before pistol braces ever came on the scene, there was another way to “enhance” a pistol buffer tube on an AR pistol. The following is for entertainment purposes only. I am not a lawyer. This is not legal advice.

David Tubb’s spring video numbers wrong?

Simple and easy testing you can do yourself suggests the measurement apparatus in David Tubb’s “Everything You Should Know About AR Buffer Springs” video may have been providing readings that were around 10-20% too high. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following

Carbine spring testing results [Updated 2023]

In need of a way to measure the compressive strength of an AR-15 carbine recoil spring, I developed a simple test apparatus for AR-15 carbine springs based on 1911 recoil spring testers. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy

The case against .308 (XP, etc.) recoil springs in a 9mm AR

“The fact that an opinion has been widely held is no evidence whatever that it is not utterly absurd…” ― Bertrand Russell The idea that 9mm ARs need a .308 recoil spring is a myth that has become quite popular and is being perpetuated by (mostly) well-meaning people. Some manufacturers of “budget” AR9s recommend .308

9mm AR build parts list (with links and examples)

My first build took months to get it running 100%. If I could do it all over again, these are the parts and suppliers I would have used for a basic build. This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The accuracy

The 2 most common blowback problems

The two biggest problems that have plagued the 9mm AR platform ever since it’s introduction are failure to eject (FTE), which can cause all sorts of crazy jams, and failure to feed (FTF). This information is intended solely for entertainment purposes only. Do not perform any action based on any of the following information. The

Reducing 9mm blowback perceived recoil

For many people who are familiar with the 5.56mm AR-15, blowback recoil from a 9mm feels “harsh”, “sharp”, “abrupt”, “excessive”, etc. Simple blowback pistol caliber firearms will tend to have greater perceived (felt) recoil than a gas operated 5.56 rifle. This is the nature of the operating system. 1/2 of the energy of the cartridge

PCC Blowback mass: Orion’s Hammer revisited

Orion’s Hammer has been referenced by many different sites as a source of information for calculating blowback mass. I intended to use these calculations to find bolt velocities in the blowback 9mm AR and compare them to the bolt velocity of 5.56mm AR gas operated bolt. If the 9mm has a higher bolt velocity, it

Everything about the “AR9”

There are a lot of myths, speculation, and just plain BS about the 9mm AR. Between obsolete “9mm hammers”, un-ramped bolts, too-light “9mm buffers”, and all the horrible advice, it’s amazing anyone can get them to work right. The first 9mm AR that I assembled had many issues, requiring months of research and experimentation. It