I went to see if your review was on Midway's site but I don't see it. There were several other people who reported blown primers in the 55gr ammo. They all seem to be in the last couple of months.
Here is a review one guy posted.
Looks like quality control issues
By Mike
from Minnesota
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I am also having some pressure issues with this batch. After seeing all the reviews and having some issues myself, I did some basic testing. My lot is #00218/G and after blowing a few primers and seeing other obvious signs of high pressure (primer cratering, witness marks on case left by the ejector hole in bolt and extreme "scrubbing" of head stamps), set up the chronograph. On several 20 round strings, the extreme spread was 119 to 140 fps. I checked each round after firing and found that the rounds that had blown primers (or gas leakage due to stretched primer pockets - primers fell out after tapping the case on a bench) were running about 80fps faster than the average of rounds that did not show issues. After editing strings taking out the 2-3 hot rounds, the strings ran pretty consistent with an average velocity of 3168fps with extreme spread in strings of 39 to 53fps, which is typical out of this rifle - a stock 5.56x45 M&P15. The cartridges with blown primers were all running around 3240fps with one as high as 3280fps. Some 30 round boxes had no issues, while others had two or three of these "hot" rounds. There is no way to tell which ones are bad until you drop the hammer. This seems like an obvious quality control issue. I like IMI ammo and have been very happy with it up to this point. While they do group quite well, I can't recommend this ammunition until this issue is worked out - at least not this lot number.