My exploding “.223” Pistol Build

By Bill Paradis
Gun Club of America SilverPLUS Member

With high expectations, and the anticipation of adding a new pistol to my brother’s collection, he and I set out to build an AR15 pistol from an 80% lower from Genesis CNC, and a complete pistol upper from SOTA. He was on vacation and stopped by here to build his new pistol. He knew I had the tools, the range, and, thanks to AGI, the knowledge to build out a stripped lower. He had all the parts shipped to me and brought his milled 80% lower with him.

I watched him build it as I told him where all the little parts went and how they were installed. This did not go without issues as the lower did not use a standard bolt for the pistol grip and the bolt they included was not long enough. I found him a bolt and, of course, it was too long. Naturally I volunteered to shorten it and promptly closed the cutter on my finger. After many colorful words were uttered and bandages applied, we were able to attach the pistol grip and complete the gun.

As you can see the pistol looks very good and we were anxious to test fire our new creation. We were rightly proud of ourselves but did not yet know the horrors in store for us.

We quickly loaded a magazine with .223 ammo and headed down to the range. When we got there and tried to load the pistol the round did not fully chamber. No problem we thought, new bolt carrier group and probably just a bit stiff. So we ejected that shell and tried to chamber the next round with the same results. I quickly asked him if he was sure that the upper he ordered was a .223 upper and he assured me he had indeed ordered a .223 upper. So, after ejecting the second round and attempting to load a third, with the same results, I reminded him of the definition of idiocy, trying the exact same thing changing nothing, and expecting different results. He of course said it was probably my ammo.

We took the pistol back to the shop to see if we could discover what might be wrong with it. I was sure I could diagnose it, after all I am a “gunsmith” and fully certified. We removed the upper, and then the bolt carrier group (bcg) from the upper. I tried to put a single round in the chamber. Naturally it did not chamber. So I asked him again if he had ordered a .223 and he assured me he had. Belatedly, I asked him to look at the barrel and see what caliber it said it was. Of course it was a .300BLK barrel. He had ordered a .223 but what he got was a .300BLK. Naturally he blamed me for not checking this as I was the “gunsmith” and should have known better.

Fortunately I had some .300BLK ammo, so we reloaded the magazine and merrily went about our way to test fire this new pistol, knowing we had worked out all the kinks. When we got to the range we inserted the magazine and released the bolt. Amazingly the round chambered; funny how that works. The first shot was fired and I retrieved the brass, I have to check the brass and reload of course, and everything looked good. The brass did not show any marks or a bulging primer. So we fired again and heard the sickening sound of the hammer hitting the lower. No problem, pulled the charging handle and saw that the round had failed to feed. We tried again and the round fired and extracted perfectly. Bingo, now we started shooting to sight in the pistol.

Pulling the trigger the third time, we got much more than we bargained for. I was watching for the brass so I could recover it, when I noticed my brother was now laying on the ground. I thought this was odd until I noticed the buffer tube, buffer and spring also laying on the ground where he had been standing. After assuring me he was ok and only got punched in the jaw, he said something about a mule kicking him. We collected all the pieces, and yes, I found the brass, and returned to the shop to try to determine what had gone wrong.

While looking at the parts we noticed that the brass molded into the rear of the lower for the buffer tube extension was still on the buffer tube but no longer in the lower. As you can see in the following photos, this is not how it should look.

Lower with bcg still in place.

Buffer tube with the brass insert still attached.

I was sure there was a brass insert there before we went to the range

Rear ring of lower split when the insert filed for divorce.

Remember this is a polymer lower and the insert was apparently not able to stay “inserted” with the forces involved in catching the bcg and returning it to battery. Fortunately for my brother, the bcg did return and did not join the buffer tube in punching him the face.

Lessons learned: Never take for granted that a malfunction won’t happen. Always wear safety glasses. Maybe don’t worry so much about the brass and watch what is happening. Maybe we should have used a heavy buffer in a poly lower, shooting .300 blk in a pistol length barrel. The pictures here show the damaged parts. We were LUCKY!

9 Responses to My exploding “.223” Pistol Build

    • I agree. Being a certified gunsmith should of told him to either return the barrel or order the proper one.

  1. She certainly departed controlled flight! Lucky indeed. No polymers for me . Maybe there’s a reason Stoner used what he did where he did?!

  2. The good news, nobody died. Also a new lower that is quality and not a cheap plastic part and the other parts will all be usable.
    Maybe a carbon reinforced polymer or just a 7075 billet machined.

  3. I have shot thousands of rounds through polymer receivers and never had a problem. I have not and will not shoot any that are made from an 80% and machined by any individuals who are not in the manufacturing business. I also do not shoot any aluminum lowers/receivers made by an individual. I too am a gunsmith and wish to thank Bill for sharing his experience with this group.

  4. I to had a similar event although it was a ar15 rifle.I just got it assembled and my brother went to try it out.I fired the first round and it ejected.We checked the brass and it looked good.The second the same but on the third,my brother like you was watching for the brass.But when he looked up I was holding the front half in my left hand and the rear in my right hand.This was not a 80% lower it was a factory lower.I called the company and they sent a new one.This one had a steal liner.By the time I received,I had milled an aluminum 80% and was using it so I gave it to my son.Who used it for about a year and it broke again.NO more polymer lowers for me thank you.

  5. I have two polymer lowers from a company endorsed by no less than Frank Proctor. I have had zero malfunctions from either of these, only some minor alignment and fitment issues that resolved themselves with use. The company is Tennessee Arms, and they have both finished and 80% offerings. So there are acceptable alternatives and Variations in quality. Check out their website, especially the videos showing the ruggedness of their lowers, including an extreme motaring procedure!

  6. no plastic nor 80 percent lowers for my builds. What difference does it make if one more of my guns has a serial number?