Question abount M&P15 Sports's Non-Chrome Lines Barrel

[saddlerocker]

Does anyone know the specifics about the M&P15 Sports barrel?

I understand that Chome lined might be overkill for a semi-auto, and that the M&P15 Sport has 5R rifling and is not chrome lined so It should have better accuracy,
BUT
Is it basically just a standard Rifle barrel or is it somehow more durable than a normal bolt action rifles barrel?
I wouldnt dream of putting 30 rounds in under 1min through my 223 bolt action for frear of serious barrel wear.

How could this normal barrel in the M&P15 Sport handle casual Semi-Auto firing?

 

[Z-Michigan]

It is "Melonite" treated (nitrocarburizing) which greatly increases surface hardness, corrosion resistance, and wear resistance. It is very close to the durability of hard chrome, but it costs less and has no effect on accuracy. It will be fine for just about anything you could do with it other than trying to shoot it to failure (i.e. continuous mag dumps for over 10 minutes). Since it's 4140 steel it probably would fail at a slightly lower temperature than a 4150 or CMV barrel, but that's only relevant if you intend to do 10+ minutes of continuous mag dumps.

It appears to be an excellent set of features for a budget AR, and really the 5R rifling, 1/8 twist and Melonite would not look out of place on a high dollar AR. On paper it's a better barrel than the Bushmaster ACR has.

 

[saddlerocker]

I wish it cost like $650 with Chrome Lined, Id be all over it.

I have a M&P9 with the melonite, the slide and rails wear pretty easily on metal to metal surfaces, and I have heard the slide wears easily from holsters, but Dont know about the bore.

Im considering building an AR kit or purchasing upper/lower to save some cash, but the M&P15 Sport is tempting for the price

 

[Z-Michigan]

I wish it cost like $650 with Chrome Lined, Id be all over it.

IMHO that wouldn't make it any better. If I'm stuck with 4140 barrel steel (which is what S&W uses) I would rather have nitrocarburizing than chrome.

I have a M&P9 with the melonite, the slide and rails wear pretty easily on metal to metal surfaces, and I have heard the slide wears easily from holsters, but Dont know about the bore.

I have an M&P9 also. And Glock's "Tenifer" is basically the same process. The one issue for the M&P pistol is that all the metal is stainless, and Melonite is actually less beneficial on stainless steel than on regular carbon or alloy steels. It's a bit of an odd decision for S&W, and of course Glock uses non-stainless steel for the barrel and slide. Both pistols have outstanding reputations for durability, however.

Im considering building an AR kit or purchasing upper/lower to save some cash, but the M&P15 Sport is tempting for the price

I've built an AR from a Del-Ton kit. I would consider Del-Ton the best of the major AR kit manufacturers, but I think the S&W Sport would be a better rifle in most ways and something I would personally have more confidence in, for hardly any more money than a DTI kit + stripped lower (remember shipping and FFL transfer fees on the lower).

 

[ugaarguy]

I have a M&P9 with the melonite, the slide and rails wear pretty easily on metal to metal surfaces, and I have heard the slide wears easily from holsters, but Dont know about the bore.

The slide or the black finish? The black finish isn't the melonite, but rather a finish applied over the top the nitrocarburized (melonited) steel. The nitrocarburizing process draws all the carbon to the surface of the steel (think case hardening on steroids) making it extremely hard. Nitrocarburized steel, left untreated, looks a dull, flat gray color.

The inside of the M&P Sport's bbl. has no black finish over the steel after meloniting because it would serve no purpose. S&W M&P-15 bbls. are made by T/C, as confirmed to me by very reliable sources. The combination of near chrome lined wear resistance, without the accuracy robbing affects of said chrome lining, make nitrocarburized bbls. very attractive to me for a semi-auto rifle.

Nitrocarburizing a T/C manufactured 5R bbl. should make for one heck of an AR bbl. The fact that you can get that bbl. on a S&W M&P-15 for under $700 is a mistake some bean counter at S&W had to have made . If you must have the dust cover and forward assist you can get a complete M4 upper from BCM for $100.

 

[Fabius]

How could this normal barrel in the M&P15 Sport handle casual Semi-Auto firing?

I found a 1967 Army study comparing barrel life of chrome lining, nitrocarburizing and untreated 4150 chrome moly barrels. The test was to fire 200 rounds per minute of 5.56, 80% ball and 20% tracers, stopping every 600 rounds to check the barrels.

Chrome lined barrels lasted an average of 38,000+ rounds. Nitrocarburized barrels lasted an average of 28,000+ rounds. Untreated barrels lasted an average of 6,000+.

They tested 2 chromelined and 2 nitrocarburized barrels to failure (bullet yaw of 15 degrees in 20% of shots). 5 untreated barrels were tested to failure (presumably because they failed at lower round counts).

The answer to your question is that a melonite treated barrel is not a normal barrel, its treated to increase surface hardness and wear resistance. In that test it greatly extended barrel life over untreated steel. The results are consistent with other information I've seen regarding the surface hardness that is achieved using melonite treatment. Not quite as wear resistant as chrome lining, but 4 to 5 times harder and more wear resistant than untreated steel. 28,000 rounds firing at 200 rounds per minute is way more abuse than my M&P Sport will ever see.

Plus, meloniting does not change the dimensions like chrome lining does. With 5R rifling (the rifling used in the Army's sniper rifle, Obermyer, Kreiger and TC target rifles), the Sport barrel should give better accuracy. 5R rifling also provides a better gas seal and higher velocity.


Link to Army study: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD822736&Location=U2&doc=GetTRDoc.pdf

 

[Fabius]

I wish it cost like $650 with Chrome Lined, Id be all over it.

See my post immediately above. For civilian, semi-auto use, the melonite treatment should, for all practical purposes, give more barrel life than most civilian shooters will ever need with greater accuracy and muzzle velocity than a chrome lined barrel. After doing some research, I bought the Sport because I think that the melonite treated, 5R rifled barrel with 1:8 twist rate could be a better overall barrel configuration than the chromelined, 6R, 1:9 twist rate barrel that costs considerably more.

 

[Breakmyfootoff]

I bought an M&P Sport just a few days ago. I was prepared to spend up to 750.00 for an AR and was considering several different makes including Bushmaster, Doublestar, Del-Ton, and the M&P Sport. After THOROUGHLY researching and comparing all of them it seemed clear the the Sport was the best bang for the buck.
All the people in this thread are posting accurate info on the Sport barrel. The 1 in 8 twist is a great option that will allow the usage of the widest range of 223 bullets available. The melanite treatment gives the barrel almost the same durability of a chrome lined barrel, but without the accuracy loss associated with chrome lining. They saved a little money by using 4140 CM steel instead of 4150, but compensated by using a heavy profile barrel that will handle heat better. On top of all that, they gave it 5R rifling which increases accuracy, velocity, and further increases durability. All that should make it one of the most desirable barrels available for an AR of any price range.
The other 2 features that really sold me on the Sport are the LMT bolt carrier group which is MPI'd and has a properly staked carrier key, and a lifetime warranty from one of the largest and most reputable gun manufacturers in the world.

 

[arizona98tj]

S&W M&P-15 bbls. are made by T/C, as confirmed to me by very reliable sources.

I wouldn't find that too surprising since S&W owns Thompson Center.

 

[saddlerocker]

Thanks Fabius, thats basically the info I was looking for.

As long as it can handle some semi-auto firing it sounds good. I like the 1:8" twist and the 5R rifling.

I was looking into a del-ton kit as well, Its nice that you can customize it and get the options you want, but would be significantly more expensive, and I dont know the reliability of the parts.

 

[Fabius]

All that should make it one of the most desirable barrels available for an AR of any price range.

That was my thinking, based on the research that I did. I think that Smith and Wesson has a winner here. I think that its the best deal on the AR market right now.

 

[ugaarguy]

I put my money where my mouth is, and picked up a Sport today. The only thing it's really missing is heat shields in the handguards. It got a little warm on the handguards running 100 rounds through it. Shielded handguards are cheap though - $23 for dual heat shielded M4 type from BCM.

 

[Breakmyfootoff]

Congrats on a new gun purchase! Always a fun experience. Keep us updated on how it works for you. I wonder if you can just buy heat shields to add to the current hand guards?

 

[Fabius]

Congrats on the purchase. You're not the first person to comment on the hand guard. I haven't noticed mine heating up excessively, but as you said, a carbine double heat shield hand guard can be found for under $30.

I've had my Sport for about 6 weeks now and I'm glad that I bought an inexpensive AR, because its hard to resist the temptation to start adding things to it. I bought a carry handle for it, because I like the look. However, after several range trips I realized that my old eyes needed better optics. I've added a Vortex Strikefire Red Dot. Also found a Spikes Tactical ST-T2 buffer to replace the standard buffer. Both of those have worked out great.

This is my first AR, so I'm experimenting with the platform and figuring out what I like. The base price of the Sport makes it easier to justify spending money to try out accessories.

 

[rustedangel]

Any thoughts on the lack of a 2 stage trigger? That seemed to have been standard among other rifles I was looking at, but you can get a kit for like $120 and the price point on this rifle is attractive. I am shopping for my first black rifle.

Do'h! I accidentally posted in the wrong M&P 15 thread

 

[christcorp]

Chrome and melonite barrels have triggers??? Cool.