Lessons Learned: Troubleshooting Shortstroking
I broke the restriction screw on a 1st Gen SLR that I had couple thousand trouble-free rounds through on my Wolf Pup, my shorty AR. When I contacted Rifle Works, instead of sending me the replacements parts I requested, they had me send in my old gasblock and sent me a brand new SLR-7 with all the latest improvements. Rifle Works was fast and courteous and answered all my questions promptly. I am very happy with their customer service and how they backed their product.
Trouble is, as soon as I installed the new gasblock, the Wolf Pup started short stroking, even with the gasblock WFO. When I started troubleshooting this problem, I fully expected it to be the new gasblock. The AR didn't start short stroking until the replacement was installed Imagine my surprise to discover the source of the problem was the carrier instead. (I was also relieved because it meant Rifle Works did it right.) Bolt travel in the carrier was gritty leading me to believe the expansion chamber is leaking. It's not the gas rings because the bolt tested in another carrier and it functions perfectly. I do plan to replace the rings as soon as possible, just in case.
I learned and relearned some valuable lessons-
- When a problem is intermittent, take a moment to figure out why. Intermittent problems can be very confusing because they can come and go during the troubleshooting process. But they are a valuable clue. Intermittent problems are usually due to a part that's failing due to gradual wear. In this case, I though maybe there was a chip stuck in the gasblock, but a quick inspection eliminated that possibility. My second thought was the gasblock was venting too much gas, but as it turns out, that wasn't the case either.
- Take notes. Write out the problem and note step by step what you've done to isolate the problem. This forces the brain to organize the problem and outlines step by step the problem and the troubleshooting process. It also lets you go back and remind yourself what you tried and what the results were. It's also a record of the problem in case it or something similar ever comes up again.
- Make one change at a time. This is of particular importance if the troubleshooting process is taking time and you start to get fatigued or frustrated. Making more than one change at a time will only confuse troubleshooting and muddy the results.
-Visual inspections are not always enough. Always check your findings with a function test. The BCG passed the gas ring test. But it wasn't until double checked my findings with a test firing that it became clear the problem was with the carrier, not the gasblock as I originally thought. Fortunately, I found I could feel grittiness while moving the bolt inside the carrier and investigated this further. This helped me narrow the problem down the the carrier.
- Be thorough and assume nothing. The first thing I did was replace the SLR-7 with a gasblock I knew worked. Once I had narrowed the problem down to the carrier, I re-installed the SLR-7 and tested it with the suspect carrier. The AR shortstroked. I tested the SLR-7 with a good carrier and the problem was eliminated.
- Listen to hunches. At the start, I had a thought to test the upper with another BCG. But I was too focused on the SLR-7 as a potential problem, then got distracted with other anomalies. The carbine action spring was an inch longer than my other carbine action springs. The hammer in the lower was harder to reset than the hammer in other lowers. If I had followed my hunch and replaced the BCG, I would have saved time and rounds in test firing. The upside is, I eliminated the anomalies as the source of my problem and I gained knowledge.
- Good spare parts are worth their weight in gold. If I didn't have a spare BCG that I knew was good, my AR would still be down.
- The lockback test is an essential tool in troubleshooting. It immediately identified the problem as short stroking. The lockback made it possible to isolate the actual cause of the shortstroking as each change was made.
The solution to the short stroking problem in the Wolf Pup was s simple one. It took some work to perform a thorough troubleshooting from changing parts and coming across anomalies I had no experience with, but I'm satisfied that I have, with certainty, isolated the problem to the carrier and was able to fix it.
There are many who will tell you how easy it is to build an AR, that they snap together as easy as Legos. I have been guilty of the same thing. But, as simple as an AR is, it still continues to surprise me
