Here’s a thread in ARFcom’s Build It Yourself forum where the consequences of gorilla (no, not “guerrilla”) gunsmithing come home to roost.
The modular nature of the AR let Our Hero (who just joined ARFcom, and thus dwells in Baby Duck World) assemble a working one first shot:
I built my first AR, took it to the range and it shot great. No malfunctions and great groupings.
Since he titled his thread, “Shouldn’t have messed with [it]” we have already had some foreshadowing of the fact that he did not leave well enough alone, and he didn’t:
I didn’t like the compensator I had though so I bought the standard A2 style flash hider. Put my upper in the action block and into my vise.
Anybody see what’s about to go wrong here? Class? Bueller? Anyone?
We’ll explain. The action block is for protecting the receiver, which although forged 7075 is still only a thin-walled alloy forging, while removing, installing, and especially torquing a barrel. We’re going to emphasize what’s next: action blocks are not for removing muzzle devices. Why not? Well, consider the following as a crude illustration of an AR barrel, with the letter E being the chamber and barrel [E]xtension, the letter A being the gas block or FSB, and the letter D in brackets being the muzzle [D]evice:
So what our novice protagonist did was secure “E” and apply torque at about “D” — 16 or 20″ distant. The barrel is fairly stiff and acts more like a torque tube than a torsion bar, delivering most of that torsion efficiently to the interface between the barrel extension and the upper receiver — where nothing resists that torque but the barrel nut, a little, and the locating pin on the extension which fits into a matching groove in the upper receiver. The locating pin is just for lining the barrel up consistently; it’s not made to bear torque loads, but it is steel and the aluminum alloy slot it rides in is even less able to resist. The pin can bend, but it’s steel. What usually happens is that it springs the upper receiver or cuts the metal of the upper.
What happened here:
The comp came off no problem but the crush washer did not so I got a screw driver gave it a few taps and it came off but damaged the threads on the barrel a little.
Repeat after WeaponsMan, please: “The right tool for the right job.” In fact, write that down. There will be a test. Because all of life is a test — an IQ test.
If you have a crush washer that will not come off, you can thread it off. Don’t worry if you have to mark up its perimeter with pliers or even grind flats on it to get purchase with a wrench, because then you’re going to throw it away. Many fasteners, from the rod bolts on your 350 Chevy to the crush washers on muzzle-devices, are made for one use only.
If you gouge the threads, the right thing to do is to chase them with the right size die. WWBD, though — What Will Bubba Do?
It didn’t look too bad so I put on the new flash hider and it wasn’t too hard to get on I attributed it to the damaged threads but when it got down to the crush washer I had to put some serious torque on it to get it to line up but it went on.
Yeah, ’cause nothin’ fixes threads like cross-threading something else over them. Note also the calibrated Bubba torque wrench, with its precsion torque meter:
- Faint city-boy torque;
- Some torque;
- Some serious torque;
- King-hell torque.
Well, “some serious torque” may not be what the -50 says but the proof of the pudding, etc., so how did Our Hero Bubba do at the range?
at 25 yards it was shooting 8 inches high and 6 inches to the left I knew it would change my POI a little but I had to adjust my sights as far as they would go to zero it again and I know that is not right and I am not okay with that since I didn’t have to adjust the sights at all the first time I went out.
He didn’t say anything about the size of the group changing yet, just point of impact (POI) shift. any muzzle device causes a point of impact shift. Ceteris Paribus asymmetrical devices cause more of a shift than symmetrical ones. The M16A2 flash suppressor is asymmetrical — two “slots” are not milled out, so that no gas escapes in that direction. Those slots should be oriented down, to reduce the amount of dust that’s kicked up when the gun is fired. And so you do have to expect
Quick rule of thumb: a fresh AR upper should work with the windage and elevation near the center of their travel. (A few clicks off absolute center is OK. Most of the way to the end of travel, is not OK). If it doesn’t, Bubba is In Da House.
He’s also violated the Golden Law of Troubleshooting: change only one thing at a time. But for a Bubba, he wises up quickly, and makes one change:
So I took of the muzzle device off and found out I cross threaded it and thought that was the issue so I shot it again with no muzzle device and same thing 8 inches high 6 inches left but still a great grouping its just not where I want it to be.
He found the POI change was the same with the A2 flash suppressor and without it:
i dont think its anything with the muzzle because I shot it with the cross threaded flash hider and with no muzzle device just exposed threads and it shot in the exact same spot for both
Ergo, it wasn’t the A2 cage per se that changed his point of aim. But something did it. Without examining the bubba’d upper, we can’t diagnose it, but our guess is that it was a consequence of either damaging the muzzle crown in his enthusiastic attack on the crush washer, or of torque damage to the barrel assembly or its seating in the upper receiver.
Amazingly — it is ARFCom, after all — he got good advice about what his problem might be, and he began to take it. His responses:
[D]oes this mean I need a new barrel or upper receiver or just take it all apart and re torque everything down to specs?
…I will take it apart as soon as I get home from work and see what she looks like. And my die to re thread the muzzle is supposed to come in today….
Barrel is a gov profile barrel. I learned my lesson and ordered all the correct equipment for my next build….
Ok took it all apart and everything looked fine except for the feed ramps but I could hardly tell they didn’t line up its barely noticeable. Put it back together torqued it all to specs and took it to the range. its shooting in the same exact spot maybe just an inch lower this time but still way off. So I have no idea whats going on
The bit about the feed ramps not lining up tells us he did torque the barrel out of its place in the upper receiver, and the consistent and continuing shooting to a point of impact eight inches out from the point of aim strongly suggests the receiver is hosed, probably where the barrel alignment pin sits.
In the end, he (with a lot of help from the board) came to the understanding that he needed to try a new upper. He lacks the tools, information and skills to inspect his present upper.
Update: I can zero the rifle but I have to adjust the front and rear sights to their extremes which I am not ok with. It is to the point that when I shoulder the rifle I need to remove my cheek from the stock to get a clear sight picture (sure optics would work) but the poi is out of my comfort zone. So I ordered a new upper from Anderson and just my luck the upper is botched and my bcg hangs up about halfway in and my charging handle won’t fit either. So I’m calling them on my lunch break to see what they can do for me.
One suspects that he’ll learn a lot, and in the end have a shootable rifle, but right now he doesn’t. Contrary to what is said in the thread, a displacement of point of aim can come from a damaged crown (without necessarily opening up the groups) but his problem is almost certainly a bubba’d upper receiver.
Eight inches is rather badly out of spec. He can’t even use this thing as a burglar defense gun now, unless the burglars where he’s at are broader in the chest than the skinny meth heads we have around here.
What he should have done, and the things he did right
So, what should Bubba have done, and his rifle would be good and accurate?
He should (as he undoubtedly knows now), have clamped the barrel forward of the FSB (or, with an FSB block, at the FSB) before R&R’ing the flash hider. He definitely should have gotten some advice before putting his back into the wrench on the flash suppressor.
But he did some things right. He asked for help, and most of the comments in his thread gave it to him. He didn’t act on his first impulse, which was to reef on the barrel again, clamping it with a Reaction Rod instead of an action block. (A Reaction Rod is the cat’s ass, but doesn’t address the problem of applying force 15-20″ away from where the barrel’s anchored). Few things can produce more expensive scrap metal faster than impatience at the armorer’s bench.
And a Final Warning
One last warning. Many people take on a flash suppressor replacement as a first attempt at customization. There are a million different kinds to try out. And it’s so tiny, it’s trivial, right?
No, not right. This guy’s results explain why that’s not necessarily a good idea: Just because of part is small, doesn’t mean it’s easily handled, or susceptible to trivial customization. Make your first experiments in AR-smithing on some part of the firearm that is not critical to accuracy and reliability. (That means, not the barrel).