Hello everyone this is my first post

I recently purchased a M&P 15 OR from a gun show, but now I have a few questions.

I am trying to confirm that 5.56 will shoot without a problem however I can't find a stamp anywhere marking the barrel. I actually have not been able to find any markings on the upper receiver at all. The lower receiver does show the S&W logo with a serial number SP 74xxx and states Model M&P-15.

I plan on calling S&W tomorrow, but is it common for the barrels to be unmarked?

I am aware that since this was purchased from a gun show it could have been pieced together, will S&W be able to give me much info solely based on the serial number on the lower receiver?

If its an m&p-15 im pretty sure its a 5.56 lower which means it will shoot both 5.56/.223. From my knowledge s&w never made a lower that was for .223 only. So you should be good to go with whichever round u prefer.

I would have to say S&W cs. might not be able to help you with your issue. As uppers and lowers are so interchangable, You could have a upper that isn't the same one the lower left the factory with. If it was me, I would go over that barrel with fine toothed comb looking for caliber size. The only place you are going to find what the barrel is chambered for is on the barrel. This is because these guns are so interchangable. Me, I'm working on building a .300 blackout and all I have to do is swap out the barrel, same lower, same upper receiver, same mags, way different bullet, Just a different barrel.
As a word of caution, till you know for 100% what your barrel is chambered in, avoid shooting 5.56 in it. A 5.56 can shoot both 5.56 and .223 with no problems, but a barrel chambered in .223 can be dangerous if loaded with 5.56 ammo. 5.56 ammo is loaded to a higher pressure. The .223's high pressures are around 55,000 and the 5.56 is somewhere around 65,000. So be careful.

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15T,15-22,5946 & some not S&W

Thanks Argonnakid I don't plan on shooting any 5.56 since I am not 100% sure, I just don't like being uncertain. I removed the handguard and replaced it with a quadrail and did not see any markings under that area.

I haven't had a problem with .223 at all and hopefully I can start some reloading soon so the 5.56 won't be a factor anyway. This is just more for my curiosity I guess.

Thanks again for the advice.

Medic I be wary to shoot it period if the barrel is unmarked. I even go as far as having a gunsmith check it out. I was talking to a friend yesterday about AR's and he has his gun setup so he can go from 300black out to 223/5.56 just by switching out the barrel's. I have never heard of any decent quality barrel not being marked. Racking my brain all my barrels have caliber markings. Maybe your just missing the markings I know on my AR the barrel markings are extremely hard to see and read there pretty small.

Just to add I found this video on Brownells on how to change out a barrel http://www.brownells.com/aspx/learn/...aspx?lid=10339 does not look to be overly complicated.

I bought a barrel for cheap and it was very lightly stamped around the muzzle, right behind where the threading is. It was like they rolled the barrel across the stamp. But it was lightly stamped

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Grover Oathkeeper

To provide an update for anyone reading this, I checked with S&W customer service with the serial number. They were very friendly and told me that the lower receiver was sold as a stripped lower.

I guess now if i want to know more about the barrel I need to visit a gunsmith. I removed the handguard and the gas block just to double check for any markings and there are none.

It may sound like bad news but at least now I am more familiar with the rifle I have.

Can we get a picture? Please

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Grover Oathkeeper

I agree with Mr Grover. We like pictures around here.

A good gunsmith should be able to tell you pretty fast what your barrel is chambered for. Just make sure they measure the "leade or throat" of the chamber. That is where the difference between the two calibers is at. The throat on a barrel chambered in 5.56 is a little longer than one in.223 is. The throat is the distance between the bullet while still in the case and where it first contacts the rifling of the barrel.

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15T,15-22,5946 & some not S&W

Unstamped barrel bad, stamped barrel good. IMO I would put the money toward a good barrel rather then spend time and money at the gunsmiths unless of corse you know him well. A good barrel is everything even if your shooting 223's if it's not top notch I feel everything else will suffer.. Any barrel maker worth anything at all will make sure that his barrel is well marked..Again IMO George

I have to agree, it is industry standard to mark a barrel, so to have one that is unmarked at all is an iffy deal.

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Grover Oathkeeper

I was kinda hoping the op would come back and update us on the status of everything. I am a tad curious to how it worked out.