I own a S&W m&p 15 sport and love it 250 rds through it and no jams. But I hear that with a carbine length gas system the gun will be unreliable again so far no problems. It does have m4 feed ramps and a semi auto bolt NOT an m16 bolt. The main purpose for this rifle is a SHTF rifle/home defense. So is this type of gas system good to go or not?

Depends on the gas port diameter, buffer weight, spring weight, lube, ammo...

Get the picture?

Where in the world did you hear that a carbine gas system is unreliable? Don't listen to anything else that person says.

That said, I don't think I would rely on a sport rifle for HD/SHTF, unless it is just a temporary solution.

I have no clue on the spring weight or gas port diameter sorry but the buffer weight is 3.0 oz ammo is standard xm193 ball and I keep it well lubed

5.56 ammo is hotter than .223
If you are going to shoot it exclusively, I'd go with a heavier buffer.

I'm willing to guess that the gas port on that barrel is oversized to accommodate weaker steel cased ammo.

That combination served shooters for DECADES before it became cool to have heavy buffers, midlength gas systems, etc.

That is the standard way all carbines were sold for YEARS.  It's fine.

You might find a heavy buffer is nice to slow unlocking of the bolt, especially in heavily over-gassed systems.  But if it aint broke, there is nothing to fix.

Why - if he isn't having any issues?



Where in this thread was steel cased ammo brought up?

The rifle works great and that is a great point that I never thought of

Well considering he's got a lighter bolt carrier, a carbine weight buffer, a probable oversized gas port....
Maybe he might want to slow things down a bit.

And 250 trouble free rounds is a poor indicator of reliability for a defensive weapon.

As for me mentioning steel cased ammo...
Underpowered ammo is why manufacturers oversize gas ports.

Guns are mechanical. Meaning that they work in a system. If one part fails, then other parts can fail as well. Generally speaking, you don't mess with a working system unless something fails and when something fails, you replace it one at a time.

Now, as far as your questions, no you should not change out your system unless there are issues or you know what you want. Simply changing something to something else doesn't necessarily make it reliable. As far as a m16 full auto bolt, the reason people say change it is simply due to the fact that commercial bolts tend to be "inferior" to certain degree due to metal makeup and so on due to the fact material is taken out of it to prevent someone from installing a auto sear on it by accident (which again on modern ar15s it's impossible to install a auto sear without damaging the receiver at some point in the 80s you could simply drill the hole at home). With that said, modern bolts tend to be good to go no matter if it is semi auto or not.

That's nonsense.
Technical boards are not the place for gun store misinformation.

This is something that would make me not listen to another word you say...  The M&P 15 Sport will work for HD/SHTF just as well as any other rifle in their line.  Folks have relied on sporting guns for home protection for decades... ever hear of a Remington 870?  SHTF, you use whatever you have on hand.  I have a Sport and a BCM.  Either rifle will serve me fine for HD or SHTF.

That's some great info thanks for it I do have a mossy 500 that I love but the sport ar by S&W by my experience of 250 rds seems to be great and accurate (Ik only 250 rds but still). All internet accounts say its a great rifle too even for SHTF look at what nutnfancy said!!!

Just a FYI the H2 buffer is the standard buffer in the new M4A1 the Army is issuing.

Before just swapping action springs and buffers, you need to first understand why it is done, and what it will do. The XM177E2 had a cyclic rate of 600 rpm (rounds per minute) to 975 rpm; where the current spec for the M4 is 700 rpm to 900 rpm. This is due to the mechanical constraint of the weapon system. When the cyclic rate drops below the lower limit you risk the weapon short-recoiling. Past the upper limit you risk the bolt over-running the magazine follower or bolt-catch.

When using heavier weight action springs, or heavier weight buffers; one effect is the weapons cyclic rate changes. With the gas system remaining constant (i.e. no adjustable gas block or changing of the barrel gas port size), lighter buffers and springs will increase cyclic rate where heavier weight springs and buffers will decrease the cyclic rate. As long as the weapon stays within its range of cyclic rate, it'll function.

Now, other reasons people choose heavier weight springs and buffers is to increase bolt lock time to allow more heat to transfer from the case to chamber wall, as well as, to allow more time for the case to contract from the chamber wall before extraction. This way the extractor doesn't have to force out the case.

Other reasons are for weapons that are over-gassed, as already mentioned, which can over compress the buffer's urethane bumper leading to a possible carrier key strike with the lower, or ripped case rims due to early extraction.

So, before just swapping springs and buffers, it's best to read up on the how's and why's before just swapping out parts.

The US Army seems to think carbine length systems are pretty reliable, in general.

Thanks for the comment ik its only a sport but I do live in an urban environment. That's why I think its an ok SHTF rifle there is not much dust where I live.
You are right the military has used a carbine length gas system for a long time now.

Everything you said above is incorrect, and misinformation.

When there is no such thing as "full auto bolt" or semi-auto bolts.  When people speak to this topic, they often mis-speak (as the OP did) and meant to say full auto bolt *carrier* versus semi-auto carrier.  This isn't a discussion of metals, this simply means the carrier got an extra step of machine work to cut a little metal from the bottom of the carrier so it could not possibly trip an auto-sear.  This was the standard for decades, until it was clarified by the ATF as unnecessary and most manufacturers went back to placing unmachined, or "M16" carriers in civilian rifles.  It has nothing to do with placing an "auto-sear by accident".

The discussion on bolt material is a different discussion, and is not really relevant this this thread.  However, it is true with the rush for manufacturers to fill the demand of bolts in the past couple years, we started seeing bolts made of 4140, 8620 and 9310.  Bolts should not be made of 8620 or 4140 in general, as these don't have the properties necessary to last very long.  9310 is still being debated somewhat, as many manufacturers feel it meets or exceeds (with proper heat treating) the standard milspec material of Carpenter 158.  During this rush to fill demand, we saw at least one manufacturer sell a ton of Bolt carriers with bolts that were improperly heat treated, and/or made of improper metals, and a high count of reported lug breakage was being reported.

Maybe he doesn't have the money for a better rifle, and in that case it would be understandable. But I know that I wouldn't trust my life to a rifle designed with the intention of being purpose-built towards saving money and cheaping out in some places. Not trying to derail this thread, but I would much rather rely on a higher quality rifle, especially if I had the funds to do so.

Which does not have a 16" barrel.

I didn't have the budget to go with a BCM or Colt tbh, but I still feel like the M&P sport would be a great SHTF rifle. I guess only a high round count and a run and gun could tell.

How much did you pay for the rifle?
http://palmettostatearmory.com/index.php/catalog/product/view/id/18920/s/psa-ar-15-complete-b5-sopmod-bravo-lower-no-magazine-black-1/category/4284/
http://www.bravocompanyusa.com/BCM-16-Mid-Length-Upper-Receiver-Group-p/bcm-urg-mid-16.htm
$640 and all you need to add is inexpensive charging handle, MOE handguards and BUIS.

670$ including ffl

Where S&W cut costs aren't going to make a difference.  No forward assist... some modern training practices don't use one anyway.  No ejection port cover, no big deal.  No heat shields in the hand guard... another who cares, especially if you plan to put on a rail system or change out to Magpul gear.  The BCG is the same as they use on the whole S&W line.

Like I said, I have the Sport and I have a BCM...  if in a time of urban unrest, I'll grab one and my son will grab the either.  Makes no difference to me which one I pick up.

There is nothing wrong with a M&P 15 Sport.  Use the money saved for ammo and trigger time.  Experience with the platform will serve you better than the forward assist and dust cover.

I agree and its good to hear that thanks i do have all magoul gear on it too

On all my carbines, pistols, and SBR's, I installed H2 buffers or heavier. No issues whatsoever

Yeah, I have no technical knowledge to say this way or that way or this is better or that is better.  But I have put 9mm buffers in carbines with no apparent problems.  I need to get it out and shoot it in the extreme cold to see, but I like the idea of slowing down that recoil impulse a little because it has been said that the carbine gas system is a tad bit harder on the bolt and such.  More violent than a 20" gun.   And a 16" with carbine gas seems a bit more so because of the extra dwell time.  

The 9mm buffer I have is an an M4ger 14.7" w/ A2 perm right now.  But it works with .223 ammo thus far.  The 9mm buffer is not much heavier than a standard rifle buttstock buffer and people put carbines on lower with rifle stocks quite a bit.  And I've never heard of anyone having a problem.  Correction, I think a member on here recently said he was getting some short stroking with like an H buffer and a carbine, but it was the first time I've every heard somebody with that.  And I'm skeptical that just an H buffer would cause that.  But it's possible.