Yesterday, I ran the XCR through a series of tests to see how it does against severe conditions. The testing was caught on video by an area pro and I should have it back from editing by the end of the week. Prior to testing, the gun was cleaned and oiled. Ammo was M193 out of Pmags. I did switch to my other lower with a fixed CTR as I did not want to get the foam pad on the folder soaked with water and mud. I figured the CTR would be easier to clean afterwards. The scope and light were stripped as there was no need to expose them to the sand and mud.
The first test was a sand test in which the gun was laid ejection port side down and sand poured over the gun covering everything from the gas block to the rear of the receiver. I wanted to see if the charging handle would let in enough grit to cause a problem. I picked the gun up as smooth as I could trying not to shake off any sand and fired the gun. In doing so, the upper receiver popped up. I slapped it back down, chambered a new round, and fired again. The chamber popped open again.
As I continued testing, I found that the rear pin was not locking fully into the lower receiver. This had not happened on the lower normally run with the XCR-SF configuration so I did not check for it. I seated the pin gently with a hammer and had no further problems. I checked my various lowers and pins today with calipers and all are within .002 inches. It looks like acceptable tolerances stacked up in a bad combination for me. I doubt you need to worry about this with a factory gun, but if you have BRD like I do and swap uppers and lowers, check to make sure the rear pin locks fully. It did not hurt anything, but is a surprise when it pops open during shooting. It has loosened up enough now that I can seat it by hand, but still doesn’t seat by itself.
Back to the testing. I laid the gun in the sand from the first test with the ejection port up and again covered it from just in front of the gas block to the end of the receiver. Sand filling the ejection port did not slow it down a bit.
Next was the submersion test. The gun was taken straight from the sand test and submerged. If there was sand on the gun, so be it. The gun worked fine. The gun was submerged a second time with no problems.
Following the submersion test was the mud test. I mixed up mud slightly thicker than a milk shake. The gun was laid on the ground with the ejection port up. Mud was poured over the gun from front to back, more than an inch thick. The gun was pulled from the mud and fired. It fired and the empty cleared the ejection port, but did not have enough energy to fully chamber the new round. The gun was cleared and a round chambered and fired with the same results. The gun was then submerged in the water trying to get it clean enough to fire. It would fire, eject, and start to chamber but could not fully seat a round.
I broke the gun down, cleaned it and oiled it in preparation for the final test. With the exposed gas tube of the SF configuration, some people have expressed a concern over the gas tube being fragile. The tube was hit with a hammer hard enough and repeatedly to dimple the tube. The gun still functioned fine. The tube was struck in a second location creating a second dimple and functioned fine. In inspecting the gun later in the day, I found that I had actually bent a portion of the rear of the gas block. It did not seem to matter.
As a note, the sand test was repeated after cleaning (not sure if it was before or after the hammer test) with the pin fully locked and performed as expected. The sand did not make a difference.
All in all, I came away really impressed with the XCR. No matter how dirty I got it, it would always fire and eject the spent shell. I am not sure other designs would have always cleared the empty. I don’t know if I expected the gun to pass the mud test or not. That was a lot to throw at it, especially after being buried in sand and submersed.
An ejection port cover may have helped if it was closed before getting covered in mud. Can one always be sure that you will dive into the mud before the firing and not during? Would the ejection port cover hang up due to the mud and block the ejection port?
I should have the video by the end of the week and will be sure to post it.
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