.223 Rem v.s. 5.56 NATO preference on Smith & Wesson M&P 15 Sport II

R

raoufhakam

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Just ordered a Smith & Wesson M&P 15 Sport II from Tend Canada last Friday and i know the Smith & Wesson website states its compatible with both calibers, but is there any preference to one over the other being more/less reliable, accurate, cleaner,....etc. ?

also, anybody had issues with Barnaul steel cased .223 ammo on this rifle?

just a brief background, i've never owned/used a civilian AR-15, but have been using the C7 in the Army for years so i'm pretty familiar with it. And i've been looking for a while for a .223/5.56 rifle, initially was looking for a Non Restricted only, and my searched funnelled down to one of three: Ruger Mini 14, KelTec SU-16, Norinco T97, but i honestly couldn't justify buying any of these when they're few hundreds more than a AR-15 so i got a gun club membership and ordered the M&P 15 Sport II on the same day.
 
The Barrel is 1/9, so it "should" prefer 55 gr ammo over heavier ammo like 75 or 77 gr. (Accuracy wise) Most guys just shoot 55 gr at targets anyways. 5.56 or .223 are both fine.
 
1/9 was actually designed to stabilize heavier bullets than 55grn, 61.5 in fact. 1/7 was designed to stabilize the longer, heavier tracer bullet. Bearing in mind that the original twist was 1/12 and it worked just fine with 55grn, going to 1/9 will allow you to stabilize just about anything. Twist rate is not only determined by weight of bullet but also by length of bullet.

I'm not going to get in to the .223/5.56 debate, I'm tired of arguing it. LOL Suffice it to say that in your rifle, they are interchangeable.

Scott
 
m39a2 said:
1/9 was actually designed to stabilize heavier bullets than 55grn, 61.5 in fact. 1/7 was designed to stabilize the longer, heavier tracer bullet. Bearing in mind that the original twist was 1/12 and it worked just fine with 55grn, going to 1/9 will allow you to stabilize just about anything. Twist rate is not only determined by weight of bullet but also by length of bullet.

I'm not going to get in to the .223/5.56 debate, I'm tired of arguing it. LOL Suffice it to say that in your rifle, they are interchangeable.

Scott
Click to expand...

The groups will open up a lot if you shoot 75 or 77 gr out of a 1/9. Not a big deal for plinking at the range, but it will be significant. It should be fine for 55-62 gr, but 1/9 starts to have stability degradation after 60 gr.

1:9 is okay all around if you can't decide what loads you want to shoot
 
55gr FMJ is your cheapest option. I had an M&P Sport and it loved 55gr V-Max. As for the 1 in 9 twist, 55gr-60gr will work regardless of the conditions. 69gr Match from Sierra, or Nosler will likely also work year round, but not 68gr Hornady match. 75gr Hornady match, and 77gr Sierra MK's will likely shoot well in hot humid weather, but may not be stabile in cold weather. You may also find that your new M&P won't stabilize 62gr FMJBT's. It's not the bullet weight, but how long it is in relation to its weight. An example is the 68gr, and 75gr Hornady Match. The 75gr is actually easier to stabilize than the 68gr.
 
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