S&W M&P 10 - opinions?

[Reloadron]

OK and I agree it should not be that big of a deal. I did notice something. I have my old original AR 10 barrel sitting here. Earlier I posted a few numbers I was unsure of but I can tell you guys this as fact. My original AR 10 is an Armalite about 20 years old. Originally it came with a stainless steel barrel. The gas port hole is .080".

Before I would enlarge any gas port I would see what the rifle shoots or what it doesn't shoot well. While I don't own a M&P 10 my overall read is there is no shortage of members here who swear by those rifles. So while there are a few comments on the web they seem a small number when compared as to how many of the things are out there.

I would place the barrel in a few V blocks just for support and exactly as mentioned bore slow and sure as a broken bit in a barrel would suck. I would also be real curious as to exactly what the existing hole diameter is? Like I mentioned, those numbers I tossed out are just stuff I saw on the web and we know that road.

Ron

 

[wally]

The gas port hole is .080".

There will be some interaction with the barrel wall thickness along with the length down the barrel where the port is drilled.

I'd trust the manufacturer and let them fix it if there is a problem.

I've opened up a few gas ports on non-standard caliber AR SBRs. I used a pin vice and the next number drill that didn't fit the port and essentially used the drill bit to ream it out by hand. One size up and test is probably a safe way to go. If it strips the next round from a full magazine and locks open on the last shot you're done. The trade off is you could be over gassed with full power ammo. A heavier buffer might help, but there is always an adjustable gas block to save the day.

 

[henschman]

FYI my short-stroking is occurring with Lake City M80 ball. It's not cheap, weak surplus... it is pretty much the best quality 7.62x51 you can get. I can maybe see designing the HBAR, non-threaded, Camo stocked M&P to only run on commercial hunting ammo, but a collapsible stocked, pencil barreled carbine with a flash hider? What exactly were they going for, and what kind of ammo did they expect most shooters to be running through these rifles?

 

[MistWolf]

Lake City M80 Ball is loaded to 7.62x51 pressures which is less than 308 Winchester pressures.

Makers get raked over the coals for tuning their 5.56 ARs on low pressure ammo because the rifle is then over-gassed when full pressure ammo is used. It's said that those makers over-gassed their ARs to avoid complaints from shooters about their new rifles choking on low pressure ammo. Looks like there's some truth to that claim

 

[agtman]

I guess you could argue that it also doesn't work, because unlike with a Kaboom, if your M&P 10 short strokes, it doesn't self destruct and potentially maim you or someone next to you. But With either argument you would be missing the point of my analogy, I'm not talking about total quantities of a gun out there having issues, I'm talking about the percentage of a certain gun out there having issues, and more importantly the perception of the percentage of a certain gun having a given issue.

Dude, it was your analogy and you're still missing the point.

Okay, let's try it this way. Your M&P 10 runs & shoots fine if limited to commercial .308 ammo, and my LMT LM8 runs & shoots fine without restrictions as to ammo type, i.e., .308 Win or 7.62 mil surp.

The point you & MistWolf are missing is that guys who are interested in acquiring some make of AR-10 are, generally, coming from one of three experiences with gas-guns: (1) an M1A, M1G (in .308) or FAL-type, in which they've shot both types of ammo without issues; (2) from the 5.56/.223 AR-15 experience, in which shooting either mil-spec 5.56mm or commerical .223 ammo isn't an issue, at least for 99.9% of those rifles, carbines, or properly set-up SBRs; or, (3) both (1) and (2).

In other words, except in the case of a precision shooter, who understands and accepts the limited ammo-parameters of something like a high-end GAP-10 rifle, guys looking at the various makes of AR-10s on the market, none of which I'd call cheap, aren't interested in laying out cash for an ammo-finicky rifle.

If their M1A or AR-15 ran perfectly on a mixed diet of commercial or mil-spec/mil-surplus ammo, why would they settle for an AR-10 that doesn't?

 

[MistWolf]

5.56 AR carbines with barrel lengths of 16 inches and less, do NOT run well on all types of ammo. If the gas port is sized to run reliably on low pressure ammo, it's over-gassed for full pressure ammo. Recoil will be harsher, carrier speeds too high and there will be a problem with carrier bounce. Over gas the AR enough and problems with extraction and ejection start popping up. If the gas port is sized to run well with full pressure ammo, problems short stroking will be had when the lower pressured ammo is used.

M14s are tuned to run 7.62x51 pressure ammo. When the M14 dominated Service Rifle matches, competitors avoided commercial pressure loads because of accelerated wear. FALs have an adjustable gas block and when tuned for softer recoil with NATO ammo, tend to recoil harshly with commercial loads. Most shooters of the M14 and FAL don't see these problems because they generally only use military ball in their rifles.

Right or wrong, S&W intended the M&P-10 to be used as a sporting rifle and tuned it to use commercial pressure ammo. Ammo loaded to 7.62x51 pressures is normally loaded with FMJ bullets that are unsuitable for hunting. The shooter has the option of opening up the gas port so the rifle will reliably function with military ball ammo.

What is getting lost in the noise about the Big Smith being finicky about ammo are all the things S&W got right

 

[agtman]

5.56 AR carbines with barrel lengths of 16 inches and less, do NOT run well on all types of ammo.

That was noted; hence, my use of the phrase, a "properly set-up SBR." You're quibbling. I've got a 10" 5.56mm SBR with the port enlarged, an H3 buffer, and a KX3. Recoil is nice and smooth, no "carrier bounce," and no issues with any ammo. It's easily do-able. The info is out there.

Right or wrong, S&W intended the M&P-10 to be used as a sporting rifle and tuned it to use commercial pressure ammo. Ammo loaded to 7.62x51 pressures is normally loaded with FMJ bullets that are unsuitable for hunting. The shooter has the option of opening up the gas port so the rifle will reliably function with military ball ammo. * * *

Smith makes two M&P10 models, right? Who said owners of the standard Smith M&P 10 w/ the FH would use it only for "hunting?" Did S&W ever publically express or advertise that as a design limitation on the "intended use" of the standard model? What about shooting the standard model in local matches, or just for an afternoon of general plinking with decent (not crap) quality mil surp ammo, or, possibly, having it in one's collection as a go-to rifle for SHTF scenarios? Smith came out with a camo, heavy-barreled version of the M&P10 (sans FH) specifically intended for hunting.

Smith makes two different versions of the same model, one dedicated for hunting; the other ...?
Well, whatever the intended use is, it's ammo-diet is limited to spendy commercial .308, apparently.

What is getting lost in the noise about the Big Smith being finicky about ammo are all the things S&W got right.

No doubt Smith got a lot right in the design of the M&P10. Its price-point is attractive and, as I said, I really like the camo version which I would use solely for hunting and gladly accept the limitation of feeding it only commercial .308 hunting loads.

But for my first AR-10-type rifle, I wanted one that came w/o a restriction or, at least, a limitation that excludes using 7.62 ammo unless I first threw more money at a 'smith to open the port and then experimented tuning it w/ different buffers and/or springs. It's the same reason, along w/ price, that I didn't choose the GAP-10, not wanting to be confined to shooting only pricey Match ammo.

Britian chose the LMT 7.62 MWS over the competition for many reasons, but you can be assured that two of those higher up on the checklist were reasonable accuracy and reliable function under combat conditions shooting a wide variety of .308 and 7.62 ammo (mostly the latter).

 

[Welding Rod]

556 rifles can be finicky too. My BCMs do NOT like 223 ammo, being prone to short stroking. They are built as 556 guns. In spite of this BCM has generally been held as one of the "top tier" manufacturers in the AR community. I was pretty disappointed when I found my "top tier" guns choked on 223 ammo my Rock Rivers ate with no problem. However I have never had a malf with 556.

Same deal here it seems. The guns were optimized for the pressure level of what is stamped on the barrel. Since I hand load almost all my 308 ammo it isn't a big deal to me, but I did have some surplus 762 (South African and either the German one DAG and/or Anerican Eagle - I forget now) that I wanted to burn up in the gun and it definitely didn't like it.

 

[dvdcrr]

now I am thinking about opening my gas port, and if your going to tear it down that far might as well do the float hansguard. Any suggestions on gas block and handguard ?

 

[B!ngo]

Apologies in advance if I fail to be following all of the facts here:

When reading through the statements in this thread, it seems like the issue at hand here is how a given .308 semi designer chooses the average gas pressure level of the round being used as the design center of the gun. Then, based on ranges of parts choice and manufacturing sophistication, the range above and below that average gas pressure can be stretched up to the point of under-gassing or carrier banging.
There's an implication that the LR8 has a wider range than say the AR10 implicitly because it is a better-designed or manufactured gun. This may in fact be true.
But it may also be true that the manufacturer chose a safer (lower pressure) average and is willing to allow the owner to just deal with a modest amount of carrier hits and or to build the mechanism so that those hits don't yield such a serious blow to the hardware.
What I don't understand is whether the practical gas pressure range of the .308-7.76 round(s) is simply greater than the basic mechanical capabilities of semi-auto design can cope, and whether a manually adjustable gas block is the best solution to solving this problem. I know when evaluating a Kel-Tec RFB some time back, some felt that the need to adjust the gas system was a negative, even though it could help deal with the issues being discussed here.
B

 

[agtman]

But it may also be true that the manufacturer chose a safer (lower pressure) average and is willing to allow the owner to just deal with a modest amount of carrier hits and or to build the mechanism so that those hits don't yield such a serious blow to the hardware.

That's a good point. But remember, the issue of a sharp recoil impulse and "carrier bounce" is frequently addressed through the use of heavier buffers and/or spring-weight combinations by the end-user. Clint at HeavyBuffers advises on this issue all the time. He's very knowledgable about 5.56mm/.223 and 308/7.62 ARs - as well as the unsuppressed and suppressed variable. The use of a can on these gas-guns changes the equation too. Plus, he's a great guy to deal with. Very quick to respond to emails. Just FYI ...

http://heavybuffers.com/products.html

 

[Hoser]

The previous issue of NRA Warrior Magazine had a review of a M&P-10.

http://viewer.zmags.com/publication/9da8872b#/9da8872b/40

 

[MistWolf]

That was noted; hence, my use of the phrase, a "properly set-up SBR." You're quibbling. I've got a 10" 5.56mm SBR with the port enlarged, an H3 buffer, and a KX3. Recoil is nice and smooth, no "carrier bounce," and no issues with any ammo. It's easily do-able. The info is out there.

Not "quibbling" at all. A properly set up SBR still has a limited pressure range where it runs reliably. (In fact, because the gas port taps the gas where pressure is higher, it becomes more difficult to get the gas port diameter just right.) Go below that and it short strokes. Go above and recoil gets sharp. The sharper recoil comes from the buffer hitting it's stop hard. Get too far above that and problems with carrier bounce and extraction/ejection arise

Smith makes two M&P10 models, right? Who said owners of the standard Smith M&P 10 w/ the FH would use it only for "hunting?"

You are the only one saying any version of the M&P-10 is to be used strictly for hunting. Stating "S&W intended the M&P-10 to be used as a sporting rifle" is not the same as saying owners of the M&P-10 would use it only for hunting.

There is more to tuning an AR than simply opening up the gas port to run on heavier buffers. There is more to controlling carrier bounce than simply adding weight to the buffer. Also, he H3 buffer really isn't a "heavy" buffer. It's nearly the same weight as the rifle buffer which is the standard. Another thing to keep in mind is that the BCG of the Big Smith starts off heavy.

One advantage to the Big Smith being ported to run on commercial ammo with a carbine weight buffer is that the owner has the option of opening it up. If it had an overly large port, the only option would be to install an adjustable gas block

 

[itsa pain]

An hour after the MP 10 was announced guys were praising it upside down and inside out without it being proven for years in the field. S&W did not even seem to prove the gas port hole. DPMS is the cheapest 308 AR very accurate and reliable and been around for years and has seen much usage

 

[agtman]

You are the only one saying any version of the M&P-10 is to be used strictly for hunting. Stating "S&W intended the M&P-10 to be used as a sporting rifle" is not the same as saying owners of the M&P-10 would use it only for hunting.

Now you're quibbling again, Chief. Re-read what you posted:

S&W intended the M&P-10 to be used as a sporting rifle and tuned it to use commercial pressure ammo. Ammo loaded to 7.62x51 pressures is normally loaded with FMJ bullets that are unsuitable for hunting.

You asserted that S&W intended the M&P10 to be "a sporting rifle" and then connected its limitation to .308 ammo to "hunting." And by Smith's own advertising, the camo version is the dedicated "hunting" model.

So what's the other model for? Being a range poser?

One advantage to the Big Smith being ported to run on commercial ammo with a carbine weight buffer is that the owner has the option of opening it up. If it had an overly large port, the only option would be to install an adjustable gas block.

That's an option for the owner if he has the know-how and the tools. If not, then he has to shell out more cash to pay a competent 'smith to enlarge the gas port.

Seems like it would have made more sense up front to buy an AR-10 that runs reliably without issues regarding ammo. Buy right the first time, cry not at all.

 

[Gtscotty]

Agtman,
Do you even have any experience with the M&P 10 or are you just parroting info you heard on the internet. All you've done is brag about the rifle you bought for twice the price, and trash the rifle that is the subject of this thread. My favorite part is that you keep repeating that M&P 10s can't digest 7.62x51 like it is a fact. Mine has run WWB, Tula, and every thing else I've fed it from day one. Did your M&P 10 refuse to run 7.62x51? It seems like the vast majority of people with real experience on the rifle are happy with them, why is your second hand opinion more valid than their experience. We get it, you love your brand of AR 10, go troll elsewhere.

 

[Reloadron]

now I am thinking about opening my gas port, and if your going to tear it down that far might as well do the float hansguard. Any suggestions on gas block and handguard ?

If opening the port up makes you feel good, then by all means open it up. Your barrel so have at it. While I disagree with MistWolf that it can be as simple as chucking up a bit in a hand drill here nor there. Not everyone has a large selection of tools at their disposal and a hand drill will make the hole bigger as well as any other setup. Just keep something in mind, once that little hole becomes bigger there is no going back. You can't make the hole smaller once you make it bigger.

As I said earlier I do not own an S&W M&P10 rifle. I built my AR 10 about 20 years ago and unlike today with an AR 10 or for that matter AR 15 at the time the selection was limited. Very limited as to the AR 10 in fact.

As to the S&W gun being particular as to certain ammunition? Betas the hell out of me as mine has always shot whatever 308 or NATO I put in it, however, I shoot mostly my own home brew stuff. We have no shortage of M&P 10 owners in these forums and for the most part I have seen mostly very good personal reviews of the rifle. It seems well priced and does what it is supposed to do. I have seen no complaints as to the rifle being choosey as to 7.62 NATO verse 308 that I recall.

My only suggestion is to be damn sure opening the gas port is a solution to the problem before you do it.

Just My Take,,,,
Ron

 

[MistWolf]

For me, chucking up a bit in a hand drill to open up an existing hole isn't a big deal. Doing so has been a routine part of my job for the past 30 years. Once I realized just how small the bits are, I would follow Wally's example and use a pin vise instead to prevent the bit breaking in the hole

 

[76shuvlinoff]

And a welder can fill a hole to start over if needed.

 

[dvdcrr]

I can respect that point of view, thanks Ron.

 

[Ltorote]

Gas port size

I am having cycling issues with everything I tried including 165 gr SST and SGK handloads loaded a tad hot. Fail to load, and sometimes jammed cartridges. I swapped to a H2 buffer which eliminated the jams and made the Fail to feeds less frequent (1 of 5 or 6 instead of EVERY.)

The best factory ammo, though not perfect, was Winchester 150 Super X ( can't find anything heavier in stores).

I pulled the gas block off and just checked the gas port size via the few drill bits I have.

A 1/16 drill bit would not even slide in, so I went ahead and drilled it out with that bit, even reaming it a tiny amount since 1/16 is only .0625. My next size bit is 5/64 so I did not want to go that big yet.

If I still have cycling issues, I will get the bits mentioned above and try increasing gradually.

 

[Reloadron]

I am having cycling issues with everything I tried including 165 gr SST and SGK handloads loaded a tad hot. Fail to load, and sometimes jammed cartridges. I swapped to a H2 buffer which eliminated the jams and made the Fail to feeds less frequent (1 of 5 or 6 instead of EVERY.)

The best factory ammo, though not perfect, was Winchester 150 Super X ( can't find anything heavier in stores).

I pulled the gas block off and just checked the gas port size via the few drill bits I have.

A 1/16 drill bit would not even slide in, so I went ahead and drilled it out with that bit, even reaming it a tiny amount since 1/16 is only .0625. My next size bit is 5/64 so I did not want to go that big yet.

If I still have cycling issues, I will get the bits mentioned above and try increasing gradually.

Just make real sure there is a gas problem before enlarging the gas port diameter. Which brings us to does anyone know what the port diameter should be? Not having a good functioning M&P 10 I don't know.

Also welcome to the THR forums.

Ron

 

[Ltorote]

Cycling issues fixed

OK just got back to the range yesterday. It would seem that drilling/reaming the gas port with a 1/16" bit did the trick!

A chrono'd some bullets and proceded to sight in the rifle. Everything cycled, left the bolt open on the last round.

No fail to feed, eject, etc. Ran like a champ!

Even the PRVI 145gr stuff went off without a hitch. I loaded 3-5 rounds in the mag at a time, just to force some more last round situations. The bolt held open every time.

 

[Reloadron]

Good deal on that note. Would have been real nice if the thing left the factory working correctly but at least you now have a good functioning rifle that works the way it should.

Ron

 

[henschman]

I e-mailed S&W on the off chance that they would fix my undergassed rifle under warranty even though I wasn't the original purchaser. They said they are sending a postage-paid shipping box, so here's hoping it comes back working right. It would be easy for me to drill out the port myself, assuming that is indeed the problem, but if S&W will do it for me, even better. I have plenty of other gun projects to spend that time on!