Yes, the upper had previously been on a BCM lower and exhibted the boring reliability you’d expect from a DD or BCM product.
Also, what exactly do you mean by a lock back check?
I would call Anderson and see if they will replace it.
Lock Back Check- Place a single round in a mag and load it into the rifle and fire it to see if the bolt locks back.
Has the lower been tested with other uppers?
Sorry, I was unfamiliar with the nomenclature for this. Yes, this has been checked and the bolt does lock back after the weapon fires the last round.
I have not tested the lower with a different URG. In fact, in my concern over the lower, this did not occur to me. I’m off work the next two days so I will try this as well.
Also, I saw somewhere where someone mentioned polishing the feed ramps on the URG. How would I go about doing this if I needed to?
So I decided to take the advice of IG and a few others and went ahead and ordered another lower. I’ve got a Rainier stripped lower on the way, to build on. Like a couple of you mentioned, I don’t want a gun that I may need some day to have such a major issue and I could’ve avoided that by not ordering a cheap lower, but live and learn. I appreciate the help you guys have given me. I may continue to experiment with the Anderson lower just for my own educational purposes and if I find out anything new I’ll post it here, but from what I can tell, like ETSGroup posted, the mag doesn’t sit high enough in the lower due to the lower being out of spec.
Ok, so the Rainier lower came in last week. I got it assembled and mated with the URG went out yesterday before work and put a 20 round box through it for a function check. I had one of the similar problem as last time, but this was out of the same GI mag I had used before. I then switched to a D&H mag and it fed, fired, extracted, ejected, and fed again every time without issue.
Today, I had a little more time and put another 40 rounds through the carbine. I fired ten rounds each through two different PMAGs, ten through a D&H mag, and ten through the same GI mag. The PMAGs were flawless, the D&H was as well, and the GI mag only had one feeding issue (same as the previous ones, only less severe), which was quickly cleared and firing resumed.
After the lower was finished and mated with the URG I took a lot of time riding the charging handle and watching the rounds feed from the mag, up the feed ramps, and into the chamber. Unlike with the Anderson lower the mag sits higher causing the point of the bullet to contact the feed ramp above the lip where the feed ramps in the barrel and the feed ramps in the upper meet. The feeding was very smooth and the carbine worked as intended. I tried this with multiple mags, including the aforementioned and problematic GI mag and it even worked as it was supposed to.
The best I can figure out is that particular mag may have more issues which may cause an occasional problem that is unrelated to the carbine. As someone posted earlier, those mags aren’t known for their great feeding geometry and I think that is manifesting itself here. It’s an old GI mag and I don’t believe it’s of any real quality, it’s just what I happened to grab when I was trying the carbine with the previous lower and noticed the problem (which I’m glad I did since it brought to my attention the much bigger problem with the Anderson lower).
All that said, I certainly believe the problem, like many of you said, was the low quality lower being out of spec. When comparing the gun as it’s configured now to my all BCM carbine, the mag sits where it’s supposed to, and the rounds contact the feed ramps where they’re supposed to. I will certainly continue to shoot the carbine to make sure there are no further problems, but without the problematic mag.
Thanks again for all the help and info that you guys gave me.
We just had an Anderson lower in my class last weekend in San Antonio that was (wait for it) out of spec. Something was off with the geometry of the hammer and trigger pin holes and the trigger/hammer wouldn’t release properly. It wasn’t the fire control groups fault.