9MM AR-15 style Carbine Build Documented

dontpanic · Feb 21, 2016

Jasonshooter said:
Has anyone else had trouble with their bolt catch bending ? This seems to be a real problem with the 9mm builds , I've done all I could to limit bolt travel and switched springs and buffers ... Any of you guys had this issue ?

Do you have a 9mm bolt catch? They are more robust than milspec. You can also use a spacer in the buffer tube. Generally you only use this spacer if you have issues. You can also use 7 quarters or a length of PVC.

http://stores.9mmar.com/spikes-tactical-9mm-buffer-spacer/

I would just try the quarters and see if it helps. Then if it does use the RRA stop or PVC.

Jasonshooter · Feb 21, 2016

dontpanic said:
Do you have a 9mm bolt catch? They are more robust than milspec. You can also use a spacer in the buffer tube. Generally you only use this spacer if you have issues. You can also use 7 quarters or a length of PVC.

http://stores.9mmar.com/spikes-tactical-9mm-buffer-spacer/

I would just try the quarters and see if it helps. Then if it does use the RRA stop or PVC.

I only have a mlspec bolt catch installed , I can't seem to find a dedicated 9mm bolt catch , I bent them on both pistol and carbine , I assume they would have to be made from a stronger metal, since there's only limited space in the receiver , any idea where I can find a few of them ? Thanks for the reply.

MKR03 · Feb 22, 2016

Jasonshooter said:
Has anyone else had trouble with their bolt catch bending ? This seems to be a real problem with the 9mm builds , I've done all I could to limit bolt travel and switched springs and buffers ... Any of you guys had this issue ?

What kind of buffer are you running? I use a Spike's ST9X and have zero issues. It's a dedicated 9mm buffer and it's longer than a carbine buffer which helps with bolt over travel. Heavy carbine length buffer + spacer OR extended length 9mm buffer (no spacer) may solve your problem.

dontpanic · Feb 22, 2016

Jasonshooter said:
I only have a mlspec bolt catch installed , I can't seem to find a dedicated 9mm bolt catch , I bent them on both pistol and carbine , I assume they would have to be made from a stronger metal, since there's only limited space in the receiver , any idea where I can find a few of them ? Thanks for the reply.

After I posted yesterday I looked for one. They seem to be sold out everywhere. Usually RRA, Brownells or 9mmar.com carry them.

ashershapiro · Feb 22, 2016

Nice build. I threw a Wolf extra power buffer spring into my build. If yours runs fine with your preferred ammo then it might not be necessary.

Kramer · Feb 24, 2016

Prophetic

Took the new carbine down to the NRA (indoor) range in Virginia.
If you have not been to this range, it is well worth the trip.
You can shoot most anything and it is 150 feet in depth.
I shot another 100 rounds through the carbine and tested it
at 150 feet. It was very accurate. The last thing I did was
fire 15 rounds rapid fire. Was able to control it very well.

When I got home, I decided to clean it and the bolt catch fell
off as I disconnected the upper from the lower! The bolt catch
had split right at the hole where the pin goes through:

Here is a photo of it before it was installed:

Either you posters put a curse on me or were prophetic.
I read a lot of forum posts about the issue with 9mm AR builds
and it seems there are potentially two things going on.

1) The buffer is too light/too small/needs spacer
(as pointed out in this thread in prior posts)

2) The slot the bolt catch rests in is too wide and the
bolt catch torques when the bolt hits it and the torque
breaks it.

I was using a "9mm buffer". I took it out and measured it.
It is 3.25" long and weighs 5.4 oz. Pretty sure this is
the spec size for a colt smg that this is modeled on.
I looked around for heavier buffers and the only ones
I could find where the Q-buffer and the spikes tactical
ST-9X. The Q-buffer is $75. The spikes is $50. Went with
the spikes. It is supposed to be 8.5 oz and slightly longer
than mine.

I ordered two bolt catches from Brownell. They are not trivially
cheap ($13-$15), so hope I can solve this. I plan to examine the
fit of the catch in the receiver and possible use some shims to
try to get a tighter fit if possible.

So for now I have a bolt-catchless carbine. Ah well, it was a little
too good to be true. Now reality reasserts itself. Hopefully
I can solve this and continue to enjoy my new carbine.

p.s. I updated my previous posts with the final build-out and
range test.

rsj1231 · Feb 24, 2016

Nice build! Here's the tool you need for the front sight adjustment...

http://www.amazon.com/gp/product/B0...rue&ref_=ox_sc_act_title_1&smid=ATVPDKIKX0DER

blankford · Feb 24, 2016

rouchna said:
Nice work. I built my own as well. It is now a suppressed SBR.

I'm in love. Rouchna, what's something like that run you when it's all said and done?

jasonk1229 · Feb 25, 2016

threads like this are the reason mds hooked me thumbs up on the build

clandestine · Feb 25, 2016

The gun is undersprung, underbuffered, and has too much bolt travel. The spikes buffer is a move in the right direction but you need a better action spring.

A Tubb Flat Wire Buffer Spring will help.

Use quarters in the back of the buffer tube to limit travel. You want the bolt to just clear the bolt catch.

Im quite good with 9mm ARs.

Gambler · Feb 25, 2016

clandestine said:
The gun is undersprung, underbuffered, and has too much bolt travel. The spikes buffer is a move in the right direction but you need a better action spring.

A Tubb Flat Wire Buffer Spring will help.

Use quarters in the back of the buffer tube to limit travel. You want the bolt to just clear the bolt catch.

Im quite good with 9mm ARs.

I really have to get in on one of your classes, I have a feeling the knowledge would be invaluable. Of course I'll probably find out I built them all wrong

clandestine · Feb 25, 2016

Gambler said:
I really have to get in on one of your classes, I have a feeling the knowledge would be invaluable. Of course I'll probably find out I built them all wrong

I do get that sentiment from some students. I tell them if it passed the class they should be fine and to follow the standards they learned from all builds or rebuilds going forward.

Kramer · Feb 25, 2016

rsj1231 said:
Nice build! Here's the tool you need for the front sight adjustment...

http://www.amazon.com/gp/product/B0...rue&ref_=ox_sc_act_title_1&smid=ATVPDKIKX0DER

Thanks rsj1231. I hope I ordered the right one.
-Kramer

Kramer · Feb 25, 2016

Buffer Spring

clandestine said:
The gun is undersprung, underbuffered, and has too much bolt travel. The spikes buffer is a move in the right direction but you need a better action spring.

A Tubb Flat Wire Buffer Spring will help.

Use quarters in the back of the buffer tube to limit travel. You want the bolt to just clear the bolt catch.

Nice looking SBR clandestine!

So I presume this is the spring you are talking about?

Tubb Precision AR-15 CS Buffer Spring

I am curious why you think it helps. I see on the web page a bunch of things it does:
"Extended life"
Same power as "extra power" springs
"bolt will remain locked a little longer"
"unaffected by temperature"
"perfect consistency"

My understanding of the 9mm buffer is that the quarters as spacers will stop the buffer just as the bolt clears the bolt catch when you use the right number of quarters. At that point it seems a "lower power" spring would be better since the bolt would then travel forward without as much speed. Just trying to understand all that is going on as best I can. I know you are the expert, so want to learn. If it really will help, $22 is pretty reasonable price (less than two bolt catches worth

)
-Thanks, Kramer

clandestine · Feb 25, 2016

Kramer said:
Nice looking SBR clandestine!

So I presume this is the spring you are talking about?

Tubb Precision AR-15 CS Buffer Spring

I am curious why you think it helps. I see on the web page a bunch of things it does:
"Extended life"
Same power as "extra power" springs
"bolt will remain locked a little longer"
"unaffected by temperature"
"perfect consistency"

My understanding of the 9mm buffer is that the quarters as spacers will stop the buffer just as the bolt clears the bolt catch when you use the right number of quarters. At that point it seems a "lower power" spring would be better since the bolt would then travel forward without as much speed. Just trying to understand all that is going on as best I can. I know you are the expert, so want to learn. If it really will help, $22 is pretty reasonable price (less than two bolt catches worth )
-Thanks, Kramer

Thats the one. If you get it DONT cut it.

You are correct on regular AR "Extra Power" Action Springs. They would deliver more power when pushing the bolt into battery which can lead to Bolt Catch damage on a 9mm AR. The Flat Wire Springs have a more even load and actually close at the same speed at a Standard AR Action Spring. They have more resting load and dont stack to solid height which helps slow things down. They also last 100x longer than standard springs.

I cant count how many 9mm AR's that I have helped others with, that were still were not running right, even with heavier 9mm Buffers. In every case they wouldnt run "right" until they used this spring in conjunction with limiting bolt travel and a good heavy 9mm long buffer.

Kramer · Feb 25, 2016

clandestine said:
Thats the one. If you get it DONT cut it.

You are correct on regular AR "Extra Power" Action Springs. They would deliver more power when pushing the bolt into battery which can lead to Bolt Catch damage on a 9mm AR. The Flat Wire Springs have a more even load and actually close at the same speed at a Standard AR Action Spring. They have more resting load and dont stack to solid height which helps slow things down. They also last 100x longer than standard springs.

I cant count how many 9mm AR's that I have helped others with, that were still were not running right, even with heavier 9mm Buffers. In every case they wouldnt run "right" until they used this spring in conjunction with limiting bolt travel and a good heavy 9mm long buffer.

Thanks for the clear explanation! One David Tubb spring ordered.
-Kramer

Kramer · Feb 25, 2016

Keymod Handgrip Panels

I bought some panels to put on the keymod handguard to make it more pleasant to grip:

BCM GUNFIGHTER KEYMOD Panel Cover

They came today and I installed them on my carbine. They were hard to install. Finally did it by placing them on the handguard and then sliding a 3/8" rod of steel over them almost like a rolling pin using both hands. Took tons of pressure, but it worked. Last one did not want to go in at one end; ended up taking it off and reversing it and then it installed fine. I think they look really nice and feel much better than the raw metal:

MKR03 · Feb 25, 2016

Kramer said:
They came today and I installed them on my carbine. They were hard to install. Finally did it by placing them on the handguard and then sliding a 3/8" rod of steel over them almost like a rolling pin using both hands. Took tons of pressure, but it worked. Last one did not want to go in at one end; ended up taking it off and reversing it and then it installed fine. I think they look really nice and feel much better than the raw metal

You think those were tough to install? Try Noveske's keymod rail panels. I have a Noveske NSR (which I like a lot) on one of my rifles, but after hours of trying to get Noveske's panels to fit, I gave up and bought some from BCM and I'm glad I did.

Kramer · Feb 25, 2016

MKR03 said:
You think those were tough to install? Try Noveske's keymod rail panels. I have a Noveske NSR (which I like a lot) on one of my rifles, but after hours of trying to get Noveske's panels to fit, I gave up and bought some from BCM and I'm glad I did.

Guess I didn't know how lucky I was

rouchna · Feb 26, 2016

blankford said:
I'm in love. Rouchna, what's something like that run you when it's all said and done?

Thank you. Without the stamps and suppressor, around $800.

9MM AR-15 style Carbine Build Documented

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