Potentially over-gassed AR

[agabriel]

Hello,

Since moving to NH, I added magpul furniture and a collapsible stock to my play AR. The AR was running well before the rebuild and now the bolt won't lock back after the last round. The brass deflector has a line from the ejection port across to where the deflector ends. Since the AR was running great before, I suspect the new recoil setup is running fast - faster than the magazine follower can keep up.

Okay, so based on a few google searches it seems like more weight may be needed in the recoil buffer. I have never taken a recoil buffer apart. How much more weight should be added when it comes apart?

Thanks,
Anthony

 

[RImike]

Rifle or Carbine length? Did you change the buffer tube from one size to another? What length is the gas tube? Have you cleaned it and lubed it properly? Something here isn't adding up, we need more info.

 

[Fixxah]

If the buffer tube and barrel are the same it should function the same. Did you use different ammo this time around?

 

[F2386]

Did you change the recoil buffer and recoil spring when you switched to the collapsible stock? M4 style stocks have a different buffer and recoil spring than rifle length stock assemblies. I believe there are differences in the stiffness of the recoil spring.

 

[mac1911]

What parts did you actually change.

 

[agabriel]

I replaced a bushy fixed M4 (MA legal) collapsible stock for this:
http://www.amazon.com/gp/product/B00Z8ATIHI?psc=1&redirect=true&ref_=oh_aui_detailpage_o04_s00

The bushy buffer is a rifle recoil buffer and the new one is a carbine buffer. It looks like the one in the photo, but isn't black.

The rifle has a 16" barrel. Mid length furniture - this is actually what I put on up front:
http://www.amazon.com/gp/product/B015L71QWC?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00

I do keep the rifle clean and lubed. I was not running the same ammo at the range. I had a hundred rounds of old military green tip ball.

Best,
Anthony

 

[mikelawtown]

might sound dumb but is your Buffer retainer there?
View attachment 153923

 

[agabriel]

might sound dumb but is your Buffer retainer there?
View attachment 153923

Yes, it still there. The bolt carrier is also indexing correctly with it.

 

[mikelawtown]

where in NH are you? I have a new spring and Buffer you can try out to count that out. some P Mags have issues with the Bolt catch also. using same Mag?

 

[agabriel]

I am in Hollis and belong to Pelham. I'm game to try a new or known good one.

Based on Google, it sounds like the recoil buffer could just be a little to light. Has anyone actually rebuilt a light one? Info on a successful rebuilds are a bit thin...

 

[mikelawtown]

I am in Hollis and belong to Pelham. I'm game to try a new or known good one.

Based on Google, it sounds like the recoil buffer could just be a little to light. Has anyone actually rebuilt a light one? Info on a successful rebuilds are a bit thin...

you buy a New one not rebuild. they are like 23.00 at Bravo Company and 15.00 at Del-Ton.
I can meet you next weekend at Pelham if interested just let me know late in the week

 

[Tallen]

Verify your buffer spring is in fact carbine length by comparing it to your old one. It should be shorter but not by much. A rifle length buffer spring in a carbine tube would prevent the bolt from locking back on an empty mag.

 

[agabriel]

The image below shows the backed of the rifle, the underside of the bolt carrier, the new recoil buffer and spring, the old recoil buffer and spring, as well the old faux collapsible stock.



If I order a new recoil buffer, should I go for a carbine H, H1, H2, or H3?

Thanks,
Anthony

 

[bigblue]

Do you have a rifle length gas system on the barrel? What is the distance from the chamber to the gas block?

I have a hard time imagining a rifle length buffer system being paired to a mid length barrel but stranger things...

 

[mikelawtown]

Do you have a rifle length gas system on the barrel? What is the distance from the chamber to the gas block?

I have a hard time imagining a rifle length buffer system being paired to a mid length barrel but stranger things...

what he said, never saw that rifle buffer in a fixed M4 stock. You don't need to go higher than a H buffer

 

[warwickben]

I have a hard time imagining a rifle length buffer system being paired to a mid length barrel but stranger things...

Why ? I have a rifle length buffer on a carbine gas length upper .
Used the same lower on mid and rifle length gas uppers.
Mixing gas port position and buffer setups are not a problem.
The problem you get are when you have a heavy buffer to slow down a over gassed system and put a correctly gassed upper on it .

 

[W.E.C]

Put the old one back on and bring the new set up to the range.
if the rifle functions fine,
change over with same ammo and mag.
eliminate one thing at a time.

 

[jasons]

The buffers that come in cheap collapsable stock kits are often lighter than they should be, and sometimes don't have the reciprocating weights that they should have. Do you have a postal scale or something that can weigh the buffer? When you shake it back and forth can you feel weights inside sliding around?

 

[agabriel]

The rifle has a 16" barrel and mid length gas tube.

The old buffer shaked around. The new one does not. The old buffer actually doesn't work with the new setup - I tried. I can't pull the bolt all the way back with the old recoil buffer and spring...

 

[bigblue]

He means put the old buffer tube on as well to test.
If your new buffer is super light then going to an H1 buffer could help.

Why ? I have a rifle length buffer on a carbine gas length upper .
Used the same lower on mid and rifle length gas uppers.
Mixing gas port position and buffer setups are not a problem.
The problem you get are when you have a heavy buffer to slow down a over gassed system and put a correctly gassed upper on it .

Because (generally) they are paired together: gas length & buffer weight work together. Tuning a rifle length buffer system to a mid-length gas tube can obviously be done but you are seeing the result of such a system: The modular advantages are compromised. Its great if you leave the buffer tube alone but clearly owners don't always want to do that.

 

[mikelawtown]

A regular carbine buffer should be 3.0 ounces . That itch my phone is usually 3.7 3.8

 

[warwickben]

He means put the old buffer tube on as well to test.
If your new buffer is super light then going to an H1 buffer could help.



Because (generally) they are paired together: gas length & buffer weight work together. Tuning a rifle length buffer system to a mid-length gas tube can obviously be done but you are seeing the result of such a system: The modular advantages are compromised. Its great if you leave the buffer tube alone but clearly owners don't always want to do that.

Your over thinking it. The bolt doesn't know the position of the hole in the barrel .
If the hole is the correct size the bolt should always see the same amount of pressure to unlock it and force it backwards .


The recoil system difference are only due to length requirements for the stock .
New sig upper , same recoil springs and bolt weight for all barrel lengths .

Look at basically every other locking bolt gun. They use a standard recoil system for all barrel lengths .

 

[mac1911]

I am in Hollis and belong to Pelham. I'm game to try a new or known good one.

Based on Google, it sounds like the recoil buffer could just be a little to light. Has anyone actually rebuilt a light one? Info on a successful rebuilds are a bit thin...

I found a listing one time a while back for tungsten weights for buffers, one weight was like 11.50?

 

[bigblue]

Your over thinking it. The bolt doesn't know the position of the hole in the barrel .
If the hole is the correct size the bolt should always see the same amount of pressure to unlock it and force it backwards .


The recoil system difference are only due to length requirements for the stock .
New sig upper , same recoil springs and bolt weight for all barrel lengths .

Look at basically every other locking bolt gun. They use a standard recoil system for all barrel lengths .

The timing of when the hole gets the gas is different regardless of how large the hole is.

 

[mac1911]

I replaced a bushy fixed M4 (MA legal) collapsible stock for this:
http://www.amazon.com/gp/product/B00Z8ATIHI?psc=1&redirect=true&ref_=oh_aui_detailpage_o04_s00

The bushy buffer is a rifle recoil buffer and the new one is a carbine buffer. It looks like the one in the photo, but isn't black.

The rifle has a 16" barrel. Mid length furniture - this is actually what I put on up front:
http://www.amazon.com/gp/product/B015L71QWC?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00

I do keep the rifle clean and lubed. I was not running the same ammo at the range. I had a hundred rounds of old military green tip ball.

Best,
Anthony

The Bushmaster M4 had a rifle length buffer ? Would that even fit in a My tube ? Any chance you mixed up spring or buffer from one to anothere

 

[warwickben]

The timing of when the hole gets the gas is different regardless of how large the hole is.

Look at any other gas operated locking bolt gun. There recoil system is the same for all barrel lengths .

Only time mass really matters is stright blow back and enough weight strip and chamber a round .

 

[agabriel]

A few more points:
1) The rifle never malfunctioned with the old parts with cheap ammo through decent ammo. I never dug the faux collapsible stock, so it was replaced after moving to a free state. It was throwing brass at a ~4-4:30 angle before.
2) I did purchase an inexpensive tube and the buffer could be underweight.
3) Other than the last round, the rifle works and ammo is cycling correctly. It is actually (still) throwing brass into a nice small pile. I didn't make a mental note of the angle from me. The rifle is coming to the range in a few days and I will analyze this angle. Graphic found online - will ref on request.

4) Since the rifle ran correctly before, I'm fine calling the rifle okay and one of the new parts suspect - probably the recoil buffer or recoil spring. The question is which and the easiest and more inexpensive technique to derive an answer.
4a) I'm assuming if the rifle ejects between 2:30-3:00 (relative to the graphic) than the weight isn't off by much. This leads me to what others have said, an H weight recoil buffer will pull the brass back a little more and slow the rifle down.
5) I'm wondering if my rifle can run a standard weight buffer recoil, since the bolt carrier is not as heavy as an M16 bolt carrier (ref my first picture for bolt carrier pic).

So is my logic correct?

Anthony

 

[bigblue]

Look at any other gas operated locking bolt gun. There recoil system is the same for all barrel lengths .

Only time mass really matters is stright blow back and enough weight strip and chamber a round .

Someone posted the timing differences between gas tube lengths earlier this month, wish I could remember the thread. It might have been dcmdon who posted it, I forget. The timing effect isn't much but its there. You've seen the pics of my 12" upper that scrapes a tiny bit off the case head, that's the kind of thing you will see due to the rotating bolt and timing variances.


OP: Is there any chance you bought new PMAG's at the same time you changed the buffer setup?

 

[agabriel]

Good question. I purchased a stash (30ish) of USGI 20rnds mags during the ban. I haven't thought about purchasing new ones in a long time...

I may have a 10 rnd bushy mag floating around somewhere. I purchased it before the USGI ones turned up. Perhaps it will get a round or two pushed through it during the week.

 

[bigblue]

I just ask bc sometimes pmag's can have difficulty locked the bolt back depending on the setup.