The M1A rifle pictured at the top had a significant problem right out of the box.

My customer reported that every time he fired the rifle, the bolt jammed tightly. It was extremely difficult to pull the bolt out of battery. The jam description normally would focus my diagnosis on the bolt and its complex linkages, necessitating some disassembly. On the other hand, this is a brand new, robust rifle. Why would a new gun already fail so dramatically?

I decided to fire the rifle to recreate the problem, verify the customer’s problem description, and see what else might be going on.

I decided to use my test firing procedure normally applied at the end of the repair to gather symptoms of the bolt jamming at the beginning of the repair. That decision paid off in a quicker, more specific diagnosis of the cause which avoided the need for any rifle disassembly.

I discovered that by firing just one round (early step in my test firing sequence) that the bolt did not jam in battery as reported by my customer. The rifle fired but the empty case was not ejected. It was still in the chamber. I easily pulled the bolt back and eject the empty case. The bolt jam did not occur.

The plot thickens. I put two rounds in the magazine and test fired the rifle again (next step in my test firing sequence). As expected from the single shot test, the first round fired but was not ejected. When I tried to manually eject the first round, I couldn’t budge the bolt out of battery! When I released the magazine with the second round still in it, I could again easily pull the bolt back and eject the first round.

This rifle is gas operated, that is, the bolt is recycled by gas pressure from the bore against a piston as the bullet exits. The test results thus far strongly suggested that the gas pressure from the bore against the piston was too low to cycle the bolt.

The repair strategy became focused on adjusting the gas pressure higher against the piston till the bolt would eject a single round AND lock back if the last round in the magazine. Only then would I attempt to fire two rounds from the magazine to see if the gas pressure adjustment also solved the original bolt jam problem.

At the shooting range, it took 4 single shots with gas pressure adjustment in between each shot to create enough gas pressure on the piston for the bolt to eject the empty case. It took 5 more single shots with adjustment for the bolt to lock back after ejection.

Once the gas pressure was high enough for the bolt to eject AND lock back on firing one round, two rounds were loaded in the magazine. Firing the first round, the first empty case was ejected, and the second round was placed in battery by the bolt. Firing the second round, the second empty case was ejected, and the bolt locked back. The rifle was cycling normally now.

 This conclusion led me to investigate at the gas pressure assembly instead of the bolt assembly. The bolt assembly jam was a symptom, but not the cause. At the end of the assignment, adjusting the bore gas pressure back to the bolt made the bolt eject empty cases once again. Using the test firing procedure, I was able to confirm that once the bolt was cycling again correctly, the magazine with additional rounds had no jamming effect on the bolt. Successfully loading and firing three rounds from the magazine verified that the rifle was restored to full operation. The rifle was repaired.

During the repair discussion I talked about my test firing procedure. Here is a summary of that procedure:

a)      Confirm no obstructions and clean the barrel

b)      Fire one round to verify bolt operation, i.e., firing pin, extractor, ejector

c)      Fire two rounds to verify receiver operation, i.e., magazine feed, new round into battery

d)      Fire three rounds to verify magazine feed, i.e., shell stops for single feed, magazine spring strength

This test firing approach gives you progressively more details about what works and what doesn’t with the gun. If the test firing identifies a problem and the problem is taken back to the workbench and the problem is thought to be solved, always start the test firing procedure from the beginning. The solution may have affected something that previously tested ok and starting in the middle of the procedure will miss that sleeper problem.

Caution: Notice that I do not load up the magazine and do the 1-2-3 round testing from a full magazine. That would be the quickest, easiest way to complete the test, but it represents a significant safety risk that I personally discovered a several years ago.

I needed to test a pistol that I had repaired. I was convinced that the repairs were correct. As a testing shortcut, I loaded a full magazine to save time reloading. When I pulled the trigger, I got the surprise of my life: the pistol went full auto and emptied the 10 shot magazine in 3 seconds !! My repair had corrected an extraction problem, nothing to do with the fire control assembly (trigger, hammer, firing pin); hence, I did not notice that the customer had “customized” the sear.

The takeaway is that if you start testing with only one round, the gun can’t go full-auto. If the gun somehow can go full-auto, the worst situation is full-auto with two rounds, not a full magazine, a significantly reduced safety risk.