I can't find a good explanation on the barrel, things like the twists why the twist r the way they are. What its made out of. Cqn someone help me better understand my barrel?

I suggest you go to:Smith & Wesson and look up the details.

Briefly, your barrel is 4140 chome-moly alloy steel with a hard chrome plating on bore & chamber to better resist gas erosion. The twist rate is 1-8, which should stabilize bullets to 75-77 grains. You should be aware that the rifling twist is fast enough that some very light (40-50 gr) varmint bullets may come apart while in flight.

The barrel uses the traditional S&W 5 lands & grooves rifling pattern and the 5R form. The "R" indicates that the side of the land that takes the rotational load from the bullet is at less than a 90 degree angle to the groove. The reduces friction and wear on the rifling and, at least theoretically should allow a slightly faster bullet velocity and longer barrel life.

I thought the barrel wasn't Chrome but stainless with a melonite coating on it.

Double checked, I made the mistake of assuming that if they plate the bores on the rifles we buy, they do that for all. Melonite coated it is, and it by spec it isn't stainless-4140 isn't stainless.

Spec sheets & websites sometimes have mistakes, you can always call S&W to double verify what the website notes. I'd suggest doing the magnet test, but some stainless is magnetic. Since they don't seem to supply the target version of the weapon with a stainless tube, I expect all barrels are 4140.

So what is the progressible twist they mention? So much to learn about just the barrel.
So it is a stainless barrel with a protective coating?

NO! 4140 is a carbon steel alloy with the primary alloy materials being chromium and molybdenum (chrome-moly, as indicated by the 41 series numbers at the front of the steel type spec.) , it is NOT stainless. According to the website, the finish is melonite.

I'm not sure where you might have got any idea about a progressive twist. I don't believe there are any commercial rifle barrels currently being made with progressive twist. The 1-8 twist spec means the rifling makes one complete turn in 8 inches.

So what grain ammo is best for 1/8 barrel

The bbl. on the Sport is, indeed, progressive twist R5 rifling according to S&W.

"Extended Life, Melonite® Barrel Coating with 5R Rifling"

Any decent .223 or 5.56 ammo should be fine, including the heavier rounds.

I'm not too old to learn, kindly post a reference for the rifling being gain /progressive twist. Nowdays, that form is generally restricted to artillery pieces.

There is no mention of that in any information that I found on the factory website. Convention is that a rifling twist spec of 1-8 indicates conventional rifling twist. In addition, the TC arms site (wholly owned subsidiary of S&W- www.tcarms.com/technology/5r_rifling.php) explains the 5R rifling form and makes no mention of gain twist rifling.

Will, perhaps I misunderstood the term "progressive" in regard to the 5R profile used in the sport. I found the following instructional.

" Obermeyer 5R land profile, which tapers the land on one side. Claimed 5R benefits are reduced fouling, better gas sealing, and higher velocities. We do think that cut-rifled barrels, in general, tend to exhibit long useful life. Metal stress is minimized with cut-rifling, and this method, when done right, produces bores which are very uniform and concentric. "

And from Obermeyer's site...........................

What does it mean when a barrel is said to be a "5R"?

5R is the form of rifling I developed for use in most target barrels and in many sporting barrels.
These barrels have 5 grooves, and the lands have angular sides. I have observed that bullet jackets
will deform such that they remain closer to the R-form lands than they will to the sharp-edged
lands present in conventional-style rifling. This reduces powder fouling at the corners of the
grooves. The angled form of the lands also helps to reduce jacket failures in quick-twist barrels.

faq

Sorry if I misled or misspoke. My main point was to state my impression that the Sport's bbl. is superior in many ways to the std. S&W 1/9 twist chrome lined used on earlier rifles than the Sport.

Not SS. It is 4140 Chromoly barrel.
Yes, the barrel is a tapered rifling. It starts at about a 1-12, and tightens to a 1-8. This is a VERY GOOD thing; the bullet starts with a low twist rate and then speeds up the twist right at the end. It means a much longer barrel life. The slower twist allows the bullet to accelerate with less friction, and less barrel erosion at the throat. The barrel will throw 55gr and heavier ammo equally well. Your real concern would be the hyper speed of really light bullets that are made for varmints; they might tear apart from the twist force. They won't do this in the barrel, but after leaving the rifle, they might run buck-wild or disintegrate. Also, with the 5R rifling, the edges of the lands are at 65 degree instead of a 90. This means a little less harsh grab on the bullet, and slightly smoother flow for the gases down the pipe. It means a higher round count before the barrel is shot out.

Thanks so much for the great explanation!

Kindly cite a reference source-preferrably from the factory- for the gain/progressive twist claim. Undocumented internet claims need not apply.

The various claims for superiority of gain twist generally proved to be insignificant when applied to small arms. There simply wasn't enough difference to either matter or to justify the expense of the system. That's not true for artillery pieces, but that's not what we're talking about.

Now, if you want to claim that the 5R rifling form-the profile of the lands & grooves- is "progressive", improved, a technical advancement etc, OK. It is supposed to reduce barrel wear, bullet distortion and friction and improve long range accuracy potential. However, a chrome plated conventional rifling form barrel will have a much improved resistance to gas erosion caused by high volume fire. So the comparative advantage of either type barrel is highly dependent upon your usage of the weapon.

" However, a chrome plated conventional rifling form barrel will have a much improved resistance to gas erosion caused by high volume fire. So the comparative advantage of either type barrel is highly dependent upon your usage of the weapon."

LOL, kindly post an authorative link to confirm the superiority of chrome lining over melonite (specifically, not just over stainless or chromoly steel) coating as far as gas erosion is concerned, using the same standards as you requested for the twist.


Just teasing you. The real point is the melonite treated bbl. for the most part, seems to be better suited to the casual shooter who wouldn't wear out a bbl. for many years. I have seen many claims for increased velocity from melonite treated bbls. and certainly think the R5 has a fan club amoung experienced shooters so use other than for fully auto or select fire weapons seems an improvement to me. YMMV and that is your priviledge but lets not get too far into the one upsmanship here.
This is one of the few sights that has successfully avoided that and I, personally, like it that way.

Absolutely correct. My comment on extended life of chrome plated bores is based upon comparative barrel replacement intervals during our CQB training modules using dedicated training weapons. After which unplated conventionally rifled barrels generally wouldn't (We bought one batch of rifles without plated bores. Nevermore!) group on a B27 @ 25 meters. I rather doubt the rifling form would make a significant difference.

The reference to the tapered rifling can be found if you search S&W M&P15 sport reviews. Look for ' The Truth About Guns | Exploring the ethics, morality, business, politics, culture, technology, practice, strategy, dangers and fun of guns article. It features the director of marketing for S&W talking about the rifle. It covers the basics of why they chose to omit the FA and dust cover, and covers the basics of the rough specs of the rifle. There was another tech report regarding the tapered barrel twist.
FWIW, the reasoning for my statement on the rifling did indeed come from a couple of reports centered on ultra long range shooting rifles, and yes most of the info was also based on references to artillery guns. The theory holds the same, only to smaller degrees, as the projectile is smaller.

Finding something for you NOT on the internet, and then posting it for you ....ON the internet is a misnomer, and not really feasible. (It would then be posted on the internet......) As to longevity and an actual round count before the barrel loses it's baseline accuracy??? I dunno. I am at 3k now, with 3-1/2 months owning the rifle. Let's see how many I am at in say 1 year. I can guarantee it will be near 10- 12,000 rounds by then. I'm curious to see how it holds up long term. I don't shoot hot loads, only factory ammo or factory reloads. It should do pretty well.

Thanks for the information, I didn't see the subject raised, will have to look again when I have more time. I haven't got a real bias against the internet, just the prevalent lack of documentation of information.

Let me 'splain something: I used to be a machinist. There are 3 typical ways to produce rifling- single point cutter (the old classic manner), broach and button. Broach and button have been the predominant production method since WWII. Neither can cut gain twist since the angle of the rifling twist has to be included in either the broach or the button. Or at least that was supposed to be true for conventional rifling forms.

It's possible that the rifling form shown in the TC link does allow gain twist to be executed by button rifling. I've also noted that some companies are claiming to use EDM machining to cut rifling. Perhaps this is the system being used.

At any rate, this gives me something to research when I have the time. Frankly, I don't consider the AR platform to be an ideal way to realize the theoretical advantages of gain twist rifling. The bench rest/long range target market would seem to be the most receptive market.

However, there is an experiment you can do yourself. Insert a cleaning rod from the breech with a brush on the end that's a tight fit in the bore. Mark the rod where the end of the receiver is and make an index mark. Push the rod in until it makes one complete revolution. Do the same near the muzzle and check the distance needed to complete on rotation. Let us know how it compares. Thanks.

If you look it up under "gain twist" you come up with a lot of sources that identify it or talk about it. I am sure you can find the publications in printed literature, but it talks about the fact that it is used to keep lighter bullets from fragmenting in the barrel, and allowing very good accuracy throughout the range of weights available for the .223/5.56x45 rounds. I just did an open search using bing and came up with quite a few sources, including upper management at Smith and Wesson. I haven't found the process by which they do it, but I do believe that they do. Also after studying the history of the parent platform, they originally started with a 1 in 14 and then a 1 in 12. It wasnt until they started talking about going with a Sierra bullet that they determined that they needed to go to a 1 in 9.5 to enable a bullet with a very low ballistic coefficient to maintain its impact force and the gain twist allows the throat of the barrels to wear less than just spinning it right up.

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Grover Oathkeeper

I was doing some research on the difference between chrome lined barrels and Melonite. If you want to read something interesting check out the friction coefficient between the two. In the following attachment they show that the friction difference is tremendous with Melonite winning by a mile. It is very much a technical read but after reading posts by the people in this forum I feel that everyone will understand it.

http://www.burlingtoneng.com/wear_resistance.html

and two explaining Melonite and the Melonite Process, it is a treatment not a plating.

http://www.burlingtoneng.com/melonite.html

http://firearmshistory.blogspot.com/...-ferritic.html

and Sir you keep referencing the corrosion resistance of chrome especially over Melonite, one more thing to read,

http://www.burlingtoneng.com/corrosion_resistance.html

after studying this I believe that you will understand why I would look for a Melonite treated barrel over a chrome lined barrel any day. I hope you enjoy these articles and Have a wonderful Day

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Grover Oathkeeper

Oh lots here to read.

Many folks no the ez way to count twist.
Take a rotating cleaning rod and place a dot on it to count,
Also make a Mark at the muzzle to measure length.
Pull a tight wet patch through which will spin against the riffling, count the dot you placed on the rod. Now on a standard barrel you only have to do this for foot of barrel, on the sport you must count the first 8in. then the last 8 in.
This should give you 2 twist rates based on what you counted.

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Light, Accurate,Versatile M&P

So on my barrel, this method counts a little odd, the first 11 in. is about 1 & 11
and the last is about 1 & 5. So some where in the middle of the two I can't count the transition accurately. This may be a little diff. for everyone but in my big bores this method is usually dead on.


the overall in our 16 in. barrel is 1.5 turns being the first 11 in. is 1 full turn.
Any one come up with a different number?

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Light, Accurate,Versatile M&P

That makes sense. My 300 whisper has a 1:7.5 twist, but when viewed from the breach end, it looks like a LOT more twist.

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Rod
M&P 22A, 40c, 15A, 15-22

So if we average them 11+5/2=8...There ya go!

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Grover Oathkeeper

The barrels have progressive rifling; it starts with lower twist and tightens up at the front of the barrel. It's one of the reasons the Sport barrel should give you an extremely long barrel life. Less spin as the bullet starts its' forward rush, then the spin tightens as it gets close to the end of the path. Makes for very stable flying downrange.
It's rarely done on a rifle, and usually done on big guns, like artillery. I think S&W did it as a test bed to see how long barrel life can be extended for, and to also see if it will be worth doing on later production runs of other rifles.

Just a note to advise that the previous posts were applicable to the 2012 and older M&P 15 Sport. Starting in 2013, the barrel for the Sport is a 5.56 Nato, 1:9 twist, with Melonite treatment. The 1:8 twist, 5R barrel is no longer used on the Sport.

The M&P 15T will still have the 1:8 twist, 5R barrel though, per S&W.