issues after ubr and heavy buffer kit...

[broylz]

I have an m&p10 that started life as a hunting model with the camo moe a2 stock and a bull barrel. I ran across the ubr and installed it and then had issues with the factory buffer and spring not coming back far enough to strip a round from the mag. Ordered a heavybuffer.com kit with a 308 carbine buffer and spring designed to go into the 7" carbine buffer tube.

My issue now is the bolt will not always retract far enough for the bolt catch to operate. This is during a functions check as I haven't shot this combo yet.

If I take the buffer and spring out of the buffer tube, the charging handle and bolt will retract as it should.

If I take the bcg out of the upper and push it into the buffer tube with the buffer amd spring in place by hand, it will operate as it should.

When I assemble the rifle as normal and pull the charging handle, it sounds like metal on metal bottoming out but will not go all the way to the rear. It goes far enough for the bolt to catch on the mag follower but not far enough for the bolt catch to operate.

Has anyone with a heavy buffer and ubr combo ever had this issue? Any ideas?

I have built several ar15s and was a unit armorer for the army so I thought I k we my way around a rifle but this is getting passed me a bit. I can't seem to figure it out

 

[Rick_A]

The M&P-10 extension tube is about 5/8" longer than a standard tube.

 

[broylz]

That's why I got the kit from heavybuffers.com. it's designed for use in 308s with a standard carbine tube.

 

[MistWolf]

Either your spring is too long and is binding, or your buffer is too long. It's also possible the RE was cut too shallow

 

[broylz]

RE? Not sure what you mean on that part...

The spring and buffer work independently as well as the charging handle and bcg but has issues when assembled together. That's what's confusing me right now

 

[MistWolf]

RE is short for receiver extension.

The AR system is designed so the buffer physically stops against the back of the RE. If the buffer is too short, the gas key will bang against the upper and cause damage.

If the buffer is too long, the BCG will not fully retract and the bolt will not lock back and possibly will not pick up the next round.

When a spring is completely compressed, the coils will stack on each other. When that happens, the spring cannot be compressed any further. If the spring is too long, the coil stack will be too tall to allow the BCG to fully retract.

If the inside of the RE is too short, again the BCG will be prevented from being fully retracted

 

[broylz]

That's where my confusion lies again. If I take the bcg out of the upper and push it in the buffer tube it goes all the way back and clears the bolt catch. If I keep the bcg in the upper with no buffer or spring, the charging handle will come back far enough to get the bcg to clear the bolt catch as well. When it's all together it won't. ..

 

[MistWolf]

If I take the bcg out of the upper and push it in the buffer tube it goes all the way back and clears the bolt catch

That's because the total length of the moving parts are now shorter. Also, the buffer should always be behind the bolt catch

If I keep the bcg in the upper with no buffer or spring, the charging handle will come back far enough to get the bcg to clear the bolt catch as well

That's because the total length of the moving parts are now shorter. Without the buffer to stop the carrier, it comes back further

 

[Sonny Gunny]

I have an m&p10 that started life as a hunting model with the camo moe a2 stock and a bull barrel. I ran across the ubr and installed it and then had issues with the factory buffer and spring not coming back far enough to strip a round from the mag. Ordered a heavybuffer.com kit with a 308 carbine buffer and spring designed to go into the 7" carbine buffer tube.

My issue now is the bolt will not always retract far enough for the bolt catch to operate. This is during a functions check as I haven't shot this combo yet.

If I take the buffer and spring out of the buffer tube, the charging handle and bolt will retract as it should.

If I take the bcg out of the upper and push it into the buffer tube with the buffer amd spring in place by hand, it will operate as it should.

When I assemble the rifle as normal and pull the charging handle, it sounds like metal on metal bottoming out but will not go all the way to the rear. It goes far enough for the bolt to catch on the mag follower but not far enough for the bolt catch to operate.

Has anyone with a heavy buffer and ubr combo ever had this issue? Any ideas?

I have built several ar15s and was a unit armorer for the army so I thought I k we my way around a rifle but this is getting passed me a bit. I can't seem to figure it out

See thread below:

http://smith-wessonforum.com/smith-...51820-new-year-new-problem.html#post137653952

I did away with heavy buffer and replaced with DPMS buffer and JP spring (JPS-OSC.308) works with no issues, although rifle prefers 168 grain ammo.

11-24-2014036_zps13c23ea6.jpg Photo by AirStink | Photobucket

 

[WR Moore]

OK, the AR10 isn't my thing, but, going from the OP:

The rifle apparently worked fine with the original barrel. There is an A2 type buttstock/receiver extenstion.

When the barrel was changed (what the heck is an ubr?), the rifle short stroked with the original buffer/spring in place with no other changes. This speaks to a lack of gas flow with the new barrel-if the rifle was fired and not dry cycled. Changing the buffer/spring isn't going to do anything for that.

What problems the new buffer/spring are causing are related to the buffer/spring combo, assuming no changes to the receiver extension. The rifle and carbine buffers aren't the same. Neither are the springs.

If I were the OP, I'd put the original barrel back in and see what happens.

 

[broylz]

The ubr is a stock from magpul. Not a barrel...

 

[WR Moore]

Ah-hah! I think you have the source of your problem if it worked with the original stock and receiver extension (buffer tube).

As I noted previously, rifle and carbine length buffer tubes require different buffers & springs. However, the AR10 types aren't my thing. I do know that not all parts are interchangable and that some AR10 versions have certain proprietary parts. If you installed a carbine length buffer tube, you might not have it installed correctly. .308/7.62mm versions of the AR also use different buffers than 5.56mm versions (SFAIK).

If all you changed was the stock, I'm mystified.....unless there's some interference between the new stock and the charging handle.

 

[davkenrem]

OP, Smith & Wesson has stated in many forums that the UBR is not a supported buttstock for the M&P10. That is not to say you can't get it to work. The M&P10 has a proprietary length Collapsible Buttstock Buffer Tube/Reciever Extension and your rifle, a Rifle length RE and a spacer. Their recommendation is do whatever you want as long as you keep the Collapsible Buttstock Buffer Tube/Reciever Extension or the rifle length tube/space and buffer and spring combo. The UBR use a custom/proprietary buffer tube that S&W states will not work with these guns. Do you have your heart set on the UBR? I just put an ACS on my M&P10 and love it. Cheekweld is very comfortable and no riser is needed with my scope. When you start swaping spring, buffers and tubes on these guns most have run into trouble. The Mid-length Gas System and the buffer assembly work together in this design. I'm guessing a carbine length and a rifle length gas system would probably be less picky but most .308 AR's are somehat picky about these parts. I would personally try something else known to work, but you may find a combo that works with the UBR but it will most likely require a longer buffer tube than the UBR has. Good Luck and let us know how it works out.

 

[davkenrem]

Just found this:

http://smith-wessonforum.com/smith-...51820-new-year-new-problem.html#post137653952

 

[MistWolf]

The RE of the M&P-10 measures the same as the AR10 carbine RE.

The UBR uses the Entry Length RE which is a carbine length fixed stock RE used to mount the Entry Length fixed stock. It's not really proprietary

 

[davkenrem]

The RE of the M&P-10 measures the same as the AR10 carbine RE.

The UBR uses the Entry Length RE which is a carbine length fixed stock RE used to mount the Entry Length fixed stock. It's not really proprietary

You are correct sir, propietary was the incorrect word to use. That said, installing a RE shorter than factory regardless of which stock is used is going to be problematic.

 

[henschman]

I am as mystified about your issue as you are. I have previously compared my S&W and DPMS BCGs side by side, and they are identical in length. I see no reason why a buffer tube setup that works on a DPMS wouldn't also at least allow for identical bolt travel on the S&W (regardless of how well it actually functions with its gas setup, etc.). I suppose I would check to ensure that the RE is installed correctly, and isn't screwed too far in or anything like that.

I personally switched my carbine stocked M&P 10 to a rifle length RE and fixed stock setup, using a standard LR-308 pattern rifle buffer and spring, and everything worked fine. Once I fixed an unrelated gas port size issue, the rifle ran flawlessly with either this setup or the original carbine stock setup.

 

[MistWolf]

Measure the depth inside the UBR Entry length RE and compare that depth to a carbine RE. They should be the same. It's possible the RE that came with the UBR is too shallow

 

[broylz]

My ubr measures 6.92" internally.

That said, does anyone know where to get a factory s&w carbine buffer tube, receiver plate and new spring? I still have my original buffer and spacer but did cut the spring thinking that was the issue when it is not.

I have set my mind to ditching the ubr and just using the s&w carbine setup. My rifle is the hunting model originally and came with the magpul moe a2 type stock.

New plan is using the milspec ctr I have with the factory carbine setup and getting a MI m-lok handguard.

 

[MistWolf]

The MP-10 adjustable stock RE is the same as the 6 position VLTOR A5.

How does the length of the buffer Heavy Buffers sold you compare to the length of the carbine buffer?

What is the depth of the RE that originally came with your rifle?

What is the length of the factory spacer used in the RE that originally came with the rifle?

What type of buffer did your rifle come with from the factory? is it a carbine buffer?