M&P 15 Sport question regarding ammo

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gmhiggins
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M&P 15 Sport question regarding ammo

Post by gmhiggins » Tue Sep 13, 2011 12:23 am

I recently picked up a M&P 15 with the 5.56NATO 1/8 5R barrel on it.

As I understand it, 5.56NATO barrels can fire .223 Rem, but not the other way around. S&W's site says most of the 5.56 barrels can use either ammo, but under the sport only 5.56 is listed.

Can an M&P 15 sport with the 5.56 1/8 5R barrel fire .223 (55gr if it matters) ammo safely, or should I try to trade the .223 ammo I picked up for 5.56 NATO?
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Re: M&P 15 Sport question regarding ammo

Post by WileyCoyote » Tue Sep 13, 2011 12:43 am

5.56 barrels (should be stamped as such on the barrel somewhere), should be good to go for .223. i shoot 55gr .223 out of mine no problem. one of them is a 1/7 twist, the other is a 1/9 twist.. not sure what the "sport" designation means for S&W??
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Re: M&P 15 Sport question regarding ammo

Post by gmhiggins » Tue Sep 13, 2011 1:31 am

WileyCoyote wrote:5.56 barrels (should be stamped as such on the barrel somewhere), should be good to go for .223. i shoot 55gr .223 out of mine no problem. one of them is a 1/7 twist, the other is a 1/9 twist.. not sure what the "sport" designation means for S&W??
Sport = super base model, basically. It is well made with good quality parts, but has zero frills. The barrel is stamped 5.56 1/8 5R.
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Re: M&P 15 Sport question regarding ammo

Post by WileyCoyote » Tue Sep 13, 2011 10:38 pm

the 5R is just some kind of rifling designation.... but if it's 5.56NATO chamber, i'd be pretty certain it's ok for .223, even though they weren't that specific on the webpage... though, for the ultimate peace of mind, wouldn't hurt to call S&W up and flat out ask them...
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Re: M&P 15 Sport question regarding ammo

Post by Rich 2.0 » Wed Sep 14, 2011 5:54 am

hey higgins ...................

223 in a 556 chamber ... thats ok ...

556 in a 223 . no no no no .. sami pressures way higher on 556 then 223....


now a 1/8 twist ... it will loooove heaver bullits... 69-75-77 it will do some major nice grouping ( yea i know alot on dis stuff)...

the lighter bullits 55-62 .. eh ... 4 moa ( thats 4 inch square at 100 yards) is all it may do .. even worse at longer ranges....
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Re: M&P 15 Sport question regarding ammo

Post by bruceg » Sat Nov 12, 2011 6:01 am

Is the same true for 7.62 x 51 and .308?
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Re: M&P 15 Sport question regarding ammo

Post by Rich 2.0 » Sat Nov 12, 2011 10:56 am

bruceg wrote:Is the same true for 7.62 x 51 and .308?

send me a pm brother............

a rifle thats chambered for 762x51 can fire 308 .. a fifle thats chambered for 308 .. welll you shouldnt fire 762x51 because of head pressures 762 has more pressure than 308 .. sometimes as much as 15,000 psi depending on the load .. even the bullit is the same its the necking and pressure on the case thats diffrent .....

rich the 223/308 master of da fourm ....
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Re: M&P 15 Sport question regarding ammo

Post by bruceg » Sat Nov 12, 2011 4:15 pm

Thanks
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Re: M&P 15 Sport question regarding ammo

Post by pps_dad » Sun Nov 13, 2011 8:39 pm

WileyCoyote wrote:the 5R is just some kind of rifling designation.... but if it's 5.56NATO chamber, i'd be pretty certain it's ok for .223, even though they weren't that specific on the webpage... though, for the ultimate peace of mind, wouldn't hurt to call S&W up and flat out ask them...
5R rifling just means that there is 5 lands and 5 grooves instead of the common 6 and 6, same rifling that Thompson Center uses.
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Re: M&P 15 Sport question regarding ammo

Post by Rick » Sun Dec 18, 2011 9:19 pm

Rich 2.0 wrote:
bruceg wrote:Is the same true for 7.62 x 51 and .308?

send me a pm brother............

a rifle thats chambered for 762x51 can fire 308 .. a fifle thats chambered for 308 .. welll you shouldnt fire 762x51 because of head pressures 762 has more pressure than 308 .. sometimes as much as 15,000 psi depending on the load .. even the bullit is the same its the necking and pressure on the case thats diffrent .....

rich the 223/308 master of da fourm ....
I bow to your wisdom ohh metric minded master... :egrin:
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Re: M&P 15 Sport question regarding ammo

Post by willbird » Mon Dec 19, 2011 1:29 pm

pps_dad wrote:
WileyCoyote wrote:the 5R is just some kind of rifling designation.... but if it's 5.56NATO chamber, i'd be pretty certain it's ok for .223, even though they weren't that specific on the webpage... though, for the ultimate peace of mind, wouldn't hurt to call S&W up and flat out ask them...
5R rifling just means that there is 5 lands and 5 grooves instead of the common 6 and 6, same rifling that Thompson Center uses.
The first I ever heard of the 5R profile was Boots Obermeyer. IMHO there is a lot more going on with it than just the number of lands/grooves.

http://www.kriegerbarrels.com/5_R_Rifli ... wp6676.htm
The Obermeyer 5-R™ style rifling is simply a different style of rifling that has a more 'ramped', or angled transition from the groove to the land and back down from the land to the next groove. Our conventional 4 groove rifling has nearly parallel sides to the groove. The internet is full of information describing perceived benefits to the 5-R™ rifling over conventional styles, but most of this is comparing "apples to oranges" as they are usually comparing one manufacturer's "non 5-R™" to a different manufacturer's "5-R™" barrels. We have honestly seen no significant differences between the two styles of rifling when comparing our barrels.
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Re: M&P 15 Sport question regarding ammo

Post by gmhiggins » Fri Dec 23, 2011 1:55 am

I nearly forgot about this thread. In case anyone was looking for a definite answer, it is yes.

The M&P 15 sport handles .223 and 5.56 just fine.
To ignore your rights is a giant slap in the face to our Constitution, our freedom, and every single man and woman who has died protecting them.
We didn't lose our rights overnight. To think we'll get them back overnight is simply foolish.

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