I took my New 26 gen 4 out to the range today along with 4 (10) round mags, 7 (15) round mags and 3 (33) round mags. I shot through all of the 10 and 15 rounders without a hitch. I was relieved everything wen't so smooth. I then popped in the first 33 rounder(all 33 rounders are new). Fired the first shot, the slide locks due to a failure to feed. I dropped the mag, cleared the round and set the round on the bench. I then re inserted the mag, took the first shot and the slide locked again. cleared and re inserted the mag. Every single round in the mag failed to feed. The last two 33 rounders fed flawlessly. I ended up shooting about 350 rounds through the 26 and besides the one 33 rounder everything was flawless. I set the faulty 33 rounder aside and fired it through my 19 later and it fed flawlessly. The 19 had close to 1,000 rounds through it. What can cause a magazine to fail so badly? assuming it is the magazine... The mag spring tension felt similar to the other 33's. The 33's were purchased from midway and I'm returning the mag I had the issue's with tomorrow.