Newly built open gun failed to feed, here's what I did to fix it..

[Whoops!]

Hi all, I finally got around to having Doug Jones put together a previously Accu-Railed Limcat upper I purchased by itself about a year ago. It was advertised to only have 1500 rounds through it and I believe it. No breech face wear. The person had obviously shot lead ammo through it and leaded the comp . . . I'm ok with this since I was planning on having the whole thing bead blasted anyway since it was an ugly blue color and it's hard to find a Limcat top end by itself, especially this generation in all of it's glory.

I didn't think it would work at first, the recoil spring was approximately 10 lbs and I always use 19 lb mainsprings which in many cases cause fully built open guns to be too heavily sprung. As a result, I had told Doug not to worry about the gun if it didn't work. Doug does good work in a quick time period and I highly recommend him, he had nothing to do with the issue this gun had. That being said, after lightening the springs it still didn't work. It would normally fail to feed, sometimes so excessively that I couldn't force the slide shut on the ammunition halfway into the chamber. There were long scracthes along the side of the brass after shooting. At first I thought ejector, this gun was using an extra long ejector that hadn't been cut for magazine clearance and so it was rubbing along the brass as it fed. Cutting the ejector for clearance may have made some difference, but didn't fix the main issue. Then I thought a burr in the barrel . . . there wasn't one. Then I thought extractor. The upper had an Aftec extractor already installed and it was almost like it had too much tension. Alas, that was not the issue and the firing pin stop was properly fitted.

I noticed the barrel ramp wasn't completely uniform. The barrel hadn't been throated, but it was possible someone incorrectly cut the base of the ramp as one side was higher than the other and unevenly cut. I straightened it out and repolished the ramp, along with the breech face, and pretty much every other internal of the gun while I was at it (I like the slide to feel super smooth). It still didn't work.

While hand-cycling the gun without the extractor installed, I noticed the bullet at the top of the magazine was not the one causing the failure to feed. It was actually the bullet beneath the top one. I knew it wasn't a magazine issue, as I had tuned the mags myself and they had worked well on another gun. In this case, someone put a very small angle cut on the bottom of the breech face. As the slide was feeding the top round, the straight cut on the bottom of the breech face would dig into the next round in the magazine and force it into the lower section of the feed ramp, jamming the slide. This explains the long scratches along the brass (which prior to seeing this I was beginning to think had nothing to do with the issue) I radiused the cut so it wouldn't dig into the next round in the magazine and polished the underside of the slide and breech face again. . . fixed. Total time to diagnose and fix, including range time, 6 hours.

Edited October 31, 2013 by Whoops!

[kneelingatlas]

Nice work!

[Whoops!]

Also, on a side note, I really like this generation of Limcat upper. He didn't tri top all the way through like he does with his new ones, decreasing the integrity of the slide where it's most likely to crack (near the ejection port). He utilized a full square cut for the compensator, further reducing the recoiling mass. He used a big compensator with diagonel porting, an ideal in my opinion, although I wish the last chamber in the compensator was longer, more similar to Akai or Dawson's compensator. The only part that leaves me leary are the cuts at the front, I wish there was more metal between them. It shoots well, but then all modern open guns do with the right shooter .

Thanks.

Edited October 31, 2013 by Whoops!