I'm a 72 year old newbie. I bought the M&P15 1/9 16" 5.56/.223. This is my first AR and I'm a bit confused. I've been into shooting and reloading for more than 50 years, but I didn't think that the ARs would would be so ammo sensitive. I needed some ammo for it and I ran across some at Walmart, Winchester 5.56 45gr. So I thought it should work, I sure was surprised when I shot some. I was sighting in the scope but was having a heck of a time. I changed targets and tried again. Out of 40 rounds I got 8 in the center ring at 100yds. but the rest of the rounds were spattered all over the target. I quit shooting. I went to a good gun store and asked for someone who knew a lot about ARs I met the young fella and he said that what I had been shooting would not perform well in the 5.56 chamber, he said that a 68gr would shoot a lot better, he said it was in the lead of the rifling for the 5.56 that causes all the problem. Haven't gotten out and got heavier ammo yet, the store that has heavier ammo is 50 miles away one way. Can anyone else shed any light on the proper ammo to use. Thanks Wagoosh.