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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.
 

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I don't know but the 1/9 twist should work great with 55-62gr and the M&P should be quite accurate with any decent ammo. Maybe it just doesn't like Winchester but I think 45gr is a little light for a 1/9 twist. it maybe spinning it just a little too fast for that light a round.
 

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Woodstock is right, 45gr is too light in a 1/9 twist barrel. 45gr ammo is meant for varmint hunting and looser twist barrels in the AR platform such as 1/12 twists. The 1/9 barrels should do well with most ammo in the 55-69gr range. The trick is finding what your rifle likes the best. You will most likely have to spend some money and buy a few different types of ammo, (HP, FMJ etc., depending on your purpose for the rifle) in a variety of weights to see what you rifle likes the best. I recommend doing this online to avoid your long drive, and you have a better chance of finding a good variety of ammo. Also, your rifle won't really come into its own until you have a few hundred rounds down the barrel and it is broken in well enough to start showing great groups.
 

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I have an M&P -15 Sport. Did a few modifications. I'm hitting bulls eyes at 50 yards. Will be taking it to the farm and trying to sight it in at 200 yards. 55 grain .223 is what I have been shooting, mostly cheapest stuff on sale at Cabelas.

Can use the Magpul sight, the UAG red/blue dot, my Buckmaster 3-9x40 scope or the laser. The bi-pod for a bit more stability for a shakey old man. Just got some Federal 193 in 5.56 to try and some Remington .223 SP. Adding the ATI rail was a pain. It was .25 too long. Got it done and its is a really great tight fit. Scope and laser are holding well.







 

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M&P 15OR 1/9 Ammo help

OP,
45 gr might be a tad light for optimum performance, but it should shoot much better than that. I've shot 40 gr out of 1:7 with better results than that. IMO, the cause is more likely to be the scope/mounts (defective or loose) or operator error. Since you have plenty of accumulated trigger time, my bet is on a scope problem.
FWIW
YMMV
 

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That 45 grain Winchester is frangible ammo used for close in combat. I'm surprised it made it to 100 yards. You need 55 grain ammo. You can use the Tula but don't expect great accuracy. You will have to bite the bullet and get some good stuff. 55 or 62 grain stuff. kwg
 
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