View Full Version : Tuning S&W MP15
As we all know these guns are notoriously over gassed. My dad has one he bought back in 2008. He dont shoot it much, but he decided he was tired of picking up brass in front of the firing line or losing his brass at the indoor ranges since it ejects out to the 2 oclock position.
I brought out my "tool bag" so to speak to help tune it. It had a C buffer in it from the factory with what I assume to be a GI spring. I believe the gun has around 1000 rounds through it, no more than 1500. It has a semi auto carrier. I didnt break the bolt down to see what type of extractor spring it had or if it had an o ring or anything else. All testing was done with federal XM193.
So gun ejects to 2 oclock ish with c buffer. Strong ejection about 3-4 feet I guess.
Put H buffer in it: gun ejects to 2 oclock, but not quite as far, maybe 2 feet.
Put H2 buffer in it: gun ejects to 2 oclock, but hits the table about a foot away.
Decided to swap out BCG's with one from my SBR(FA carrier, AAC bolt) to see if the ejector or extractor was weak. My 300BLK SBR ejects subsonics at 4-5 oclock and about 5 feet so it has very strong ejection. I know its a good BCG.
Go back to C buffer: 2 oclock with 3-4 foot distance
H buffer: 2 oclock 2 foot ejection
H2: 2 oclock 1 foot ejection
WTF OVER.
So it seems that all I am doing is slowing the ****er down, but thats not changing the ejection angle like its supposed to do, its just making ejection weaker. This is with 2 different BCG's(and I know the AAC BCG out of my SBR is good to go, no extractor issues, no ejection issues).
So im at a loss as to what the next step might be to get this gun to run "correctly" with ejection at 4-5 oclock. If I thought the extractor or ejector was bad I would get new springs, but I really dont think they are bad on the S&W BCG after having the gun function exactly the same using a known good BCG(unless my AAC BCG is bad as well, but I doubt that).
Where would you all go with this?
Right now I just put the C buffer back in it so at least its reliable even if its running to fast and throwing brass forward. I didnt trust leaving it with weak ejection.
On mine, I run an A5 buffer system with an A5H4 buffer and a Sprinco Green spring with an o-ring on the ejector spring. It ejects a round 2:00-3:00, but has been 100% reliable. I've been wanting to try an adjustable gas block, hoping it will help smooth things out like you're talking about. Brass does always seem to find it's way to the other side of the firing line, which at my local range, you're SOL at that point. Both of my other rifles eject around 4:00, but one is intermediate gas, and the other is a 300BLK carbine gas.
I would like to find a way to bring my M&P15 around to the 4:00 position just for the convenience of not losing brass.
On mine, I run an A5 buffer system with an A5H4 buffer and a Sprinco Green spring with an o-ring on the ejector spring. It ejects a round 2:00-3:00, but has been 100% reliable. I've been wanting to try an adjustable gas block, hoping it will help smooth things out like you're talking about. Brass does always seem to find it's way to the other side of the firing line, which at my local range, you're SOL at that point. Both of my other rifles eject around 4:00, but one is intermediate gas, and the other is a 300BLK carbine gas.
I would like to find a way to bring my M&P15 around to the 4:00 position just for the convenience of not losing brass.
Yea im not going to spend any money on a Vltor A5 setup and some other springs to just end up with the exact same ejection. The gun is 100% reliable as is. I would venture to say with an H buffer it would also be 100% reliable. With the H2, it was to slow for my comfort and just not ejecting far enough. I know some will say "if it clears the gun, its ejecting plenty", but I like to see good healthy ejection.
My dad doesnt really want to spend much money on this gun and going to adjustable gas and a free float tube and all that doesnt interest him.
I may still try a new extractor kit from BCM just to rule that out even though im almost 100% sure that isnt the issue.
If the H2 buffer is weak on ejection, it IS NOT overgassed. H2 should be where it runs.
If the H2 buffer is weak on ejection, it IS NOT overgassed. H2 should be where it runs.
Im wondering what the issue could be then. With the c buffer its throwing brass HARD to 2 oclock and beats the shit out of your shoulder so to me thats 2 signs that its running to fast. So my gut said "slow it down" which only lead to weak ejection NOT a change in ejection angle.
I dont want to just throw parts at the gun in the hope I find a magic combo.
As we all know these guns are notoriously over gassed. My dad has one he bought back in 2008. He dont shoot it much, but he decided he was tired of picking up brass in front of the firing line or losing his brass at the indoor ranges since it ejects out to the 2 oclock position.
I brought out my "tool bag" so to speak to help tune it. It had a C buffer in it from the factory with what I assume to be a GI spring. I believe the gun has around 1000 rounds through it, no more than 1500. It has a semi auto carrier. I didnt break the bolt down to see what type of extractor spring it had or if it had an o ring or anything else. All testing was done with federal XM193.
So gun ejects to 2 oclock ish with c buffer. Strong ejection about 3-4 feet I guess.
Put H buffer in it: gun ejects to 2 oclock, but not quite as far, maybe 2 feet.
Put H2 buffer in it: gun ejects to 2 oclock, but hits the table about a foot away.
Decided to swap out BCG's with one from my SBR(FA carrier, AAC bolt) to see if the ejector or extractor was weak. My 300BLK SBR ejects subsonics at 4-5 oclock and about 5 feet so it has very strong ejection. I know its a good BCG.
Go back to C buffer: 2 oclock with 3-4 foot distance
H buffer: 2 oclock 2 foot ejection
H2: 2 oclock 1 foot ejection
WTF OVER.
So it seems that all I am doing is slowing the ****er down, but thats not changing the ejection angle like its supposed to do, its just making ejection weaker. This is with 2 different BCG's(and I know the AAC BCG out of my SBR is good to go, no extractor issues, no ejection issues).
So im at a loss as to what the next step might be to get this gun to run "correctly" with ejection at 4-5 oclock. If I thought the extractor or ejector was bad I would get new springs, but I really dont think they are bad on the S&W BCG after having the gun function exactly the same using a known good BCG(unless my AAC BCG is bad as well, but I doubt that).
Where would you all go with this?
Right now I just put the C buffer back in it so at least its reliable even if its running to fast and throwing brass forward. I didnt trust leaving it with weak ejection.
Cheap USGI buffer springs are pretty close to worn out when you get the gun. At the least, change it out every 2-3k or 2-3 years.
C4
Cheap USGI buffer springs are pretty close to worn out when you get the gun. At the least, change it out every 2-3k or 2-3 years.
C4
ill throw a new one in.
Im wondering what the issue could be then. With the c buffer its throwing brass HARD to 2 oclock and beats the shit out of your shoulder so to me thats 2 signs that its running to fast. So my gut said "slow it down" which only lead to weak ejection NOT a change in ejection angle.
I dont want to just throw parts at the gun in the hope I find a magic combo.
That makes sense. Almost NO set up is optimal with a CAR buffer. IMO, there's nothing to fix here. Yeah... a nice 4 oclock ejection is nice, but I'm not going out of my way to get it.
Do the flick test. Pull the BCG out of the rifle, load an empty case into the bolt face and press it against the ejector. Now let the brass fly and see how far it goes. If the brass is just trickling out of the ejection port, it's a sign of weak ejection. Carrier speed that's too fast can mask weak ejection
I have a same era very overgassed m&p15. Running a sprinco red and a h2: takes the snap out of it somewhat and it still shoots low end WPA and bear with no issues.
Springco blue spring and H2 buffer fixed mine. I then switched the upper to a BCM 14.5 and it runs immaculate.
Sorry was away at Knob Creek all weekend.
Do the flick test. Pull the BCG out of the rifle, load an empty case into the bolt face and press it against the ejector. Now let the brass fly and see how far it goes. If the brass is just trickling out of the ejection port, it's a sign of weak ejection. Carrier speed that's too fast can mask weak ejection
I put a completely different BCG in it(factory AAC) that runs in the other gun like a top and still had the same issue. That leads me to believe that the BCG that is in the gun is good as far as the ejector and extractor go. I can also try with a couple of the LMT BCG's I have that also run like tops.
I have a same era very overgassed m&p15. Running a sprinco red and a h2: takes the snap out of it somewhat and it still shoots low end WPA and bear with no issues.
Im worried that the Sprinco Red(basically a +2) would slow it down even more, especially when with the H2 it was already running very sluggish IMO. Maybe the red spring rate curve is different from a normal GI spring though.
Springco blue spring and H2 buffer fixed mine. I then switched the upper to a BCM 14.5 and it runs immaculate.
Well of course putting a new upper on it would fix the issue completely.
I might try a Sprinco White(GI), Blue and Red to see what they do. I need to add a couple to my tuning kit anyway(I have all 4 buffers in it already and a BCM GI spring to help tune new builds that my buddies all seem to buy the cheapest shit possible and wonder why it dont run).
Im confident I can find the right combo, but it just seems weird to me that every thing done to slow it down doesnt actually produce the results that it "should" i.e. change the ejection angle.
I might try a Sprinco White(GI), Blue and Red to see what they do. I need to add a couple to my tuning kit anyway(I have all 4 buffers in it already and a BCM GI spring to help tune new builds that my buddies all seem to buy the cheapest shit possible and wonder why it dont run).
Im confident I can find the right combo, but it just seems weird to me that every thing done to slow it down doesnt actually produce the results that it "should" i.e. change the ejection angle.
To be honest I wouldn't overthink the ejection angle too much if its running well, just find a combo you are happy with - self trial and error is always they best way.
Another thing that affects ejection angle is the function of the ejector - my M&P15 has had 10000 rounds+ through it, and has once broke the ejector spring (I've not had this happen on any other AR and I put it down to its very overgassed nature as being the culprit, basically giving the spring a pounding). Even when the spring was broken, it still ejected the cases, but they started 'dribbling' out of the ejection port at 1 o'clock, which alerted me to the problem. I found I could depress the ejector easily with my little finger, and when I removed it noticed the spring had broken in two places making it weak. New spring in fixed the problem and put the ejection back to a normal pattern (but even then and with the red spring/H2 combo, mine still isn't 5-6 oclock either, more like 3-4. But as mentioned, the rifle is really solid and reliable so no cause for concern.
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