450Bushmaster.net

I am new to the AR, and just put one together with an Anderson lower and Bear Creek 18” complete upper. I’m using an AR Stoner magazine. I am having feeding problems while using Winchester XP. The gun is lubricated. I also adjusted and lubricated the feeding lips on the magazine, and still having the same issue. I’m trying to figure out my next step. Has anyone else with an Anderson lower had the same problem? I’m wondering if it needs a different buffer spring and buffer tube. Or should I just change up the Ammo? I would hope a brand new upper wouldn’t have low gas pressure, but maybe I should give Bear Creek a call and see what they suggest. I’m trying to rule everything out before I need to send the upper back to them.

I am using an Andersen lower and a stoner 5 round magazine with a bushmaster upper. I did clean up the feed lips on the magazine with a sharpening stone before I tried using it. When loaded the rounds it felt like it was digging into the brass. I have fired about 120 rounds and had only a couple failures to feed but those were with non factory rounds (300 grain speed flat lead nosed).

I just tried the Hornady Blacks this morning. No more issues. I’m glad it was something simple.

I'd also recommend tweaking your feedlips up a touch and trying the Winchester again. You might want to grind out a half circle in the front of the mag, sometimes a round can catch there during feeding.

Also, do not lubricate your feedlips, and make sure you clean all the oil out of the chamber before firing. getting oil in the chamber when shooting increases bolt thrust, which we really don't want in this cartridge.

The unfortunate thing about building a lower is that they are like potato chips, you can’t just build one! I built one for a 6.5 Grendel and a couple more that are still to be determined!