My 9mm AR was filthy

j_h_smith · Aug 27, 2017

jimbobborg said:
Bolt catches get broken quite often on these carbines, especially if you're using a milspec catch. IIRC most complete 9mm lowers have a beefier version.

And at this point, I'm going to have to get some professional help on my 9mm. Mags that work fine one day jam up the next. I'm wondering if it's the bolt itself that's causing this? Even one of my ASC mags that was working fine acted up.

Take a few pictures of the bolt and lets see what ya have.

rayrevolver · Aug 27, 2017

Some folks add quarters to limit the travel of the BCG. They put about 0.75" worth in the RE so the bolt can't hammer the catch on the return, when empty.

For some reason, $2.25 worth is what I remember.

For me, I made my custom buffer 0.75" longer and so far, so good. If you buy a 9mm specific buffer they are usually longer for this reason.

bfoosh006 · Aug 28, 2017

jimbobborg said:
Bolt catches get broken quite often on these carbines, especially if you're using a milspec catch. IIRC most complete 9mm lowers have a beefier version.

And at this point, I'm going to have to get some professional help on my 9mm. Mags that work fine one day jam up the next. I'm wondering if it's the bolt itself that's causing this? Even one of my ASC mags that was working fine acted up.

What is your 9MM setup ? What buffer , spring, Colt pattern or Glock ?, ammo ....

Check you mags for ANY burrs that might be causing your mag to "pause"... easy to check and fix with a 5gal or 1gal wooden paint stir stick.

Oops ... and controlling bolt over travel is pretty important... no one wants broken parts. Adding quarters at the bottom of the buffer tube is a simple fix. As little travel as practical ( about 3/16" ) makes the cyclic group ( spring and buffer and heavy BCG ) less likely to build up enough momentum to bang the crap out of bolt catch.
There is also an extended 9MM buffer "type"... does the same thing, but can only be used in a 9MM.

Photo from the internet...

You can see what the quarters would do... just like the various aftermarket spacers.

If anyone decides to get an extended 9MM buffer I strongly suggest this one... being configurable means you can "tinker with your buffers weight easily.

9MM Configurable Extended Buffer... ( no spacer or quarters needed )
https://www.kakindustry.com/ar-15-parts/lower-parts/buffer-tubes-and-parts/ar15-config-9mm-buffer-system

Up to 10.0 oz configured buffer or less.

Conventional Carbine Configurable Buffer ....
https://www.kakindustry.com/ar-15-parts/lower-parts/buffer-tubes-and-parts/ar15-buffer-system

CONFIGURE AND TUNE YOUR BUFFER FOR YOU SPECIFIC NEEDS

USING DIFFERENT COMBINATIONS OF THE SUPPLIED PARTS

A = ALUM

S= STEEL

T = TUNGSTEN

A A A 1.7 OZ
S A A 2.2 OZ
A S S 2.6 OZ
S S S 3.0 OZ
T A A 3.0 OZ
T S S 3.8 OZ
A T T 4.3 OZ
S T T 4.7 OZ
T T T 5.6 OZ

The above list could be used with the Extended buffer as well with a little extra math...

And I strongly suggest the buffers with moving internals... solid ones can "bounce".. just like a steel hammer off of a steel anvil... a sliding weight buffer acts like a deadblow hammer on a steel anvil and hit with a solid thud.

jimbobborg · Aug 28, 2017

I'm using the same setup since I started this thread. The only real problem I'm having is empties not ejecting fully and getting jammed on top of the next round being fed. I've used a variety of commercial 115gr 9mm rounds and my 147gr loads. I'm using a Colt pattern setup. I have a dedicated 9mm lower and upper, 9mm CMMG buffer, $1.50 in quarters, and a Wilson 9mm barrel. Not sure who made the bolt. I'll get pics up later.

j_h_smith · Aug 28, 2017

jimbobborg said:
I'm using the same setup since I started this thread. The only real problem I'm having is empties not ejecting fully and getting jammed on top of the next round being fed. I've used a variety of commercial 115gr 9mm rounds and my 147gr loads. I'm using a Colt pattern setup. I have a dedicated 9mm lower and upper, 9mm CMMG buffer, $1.50 in quarters, and a Wilson 9mm barrel. Not sure who made the bolt. I'll get pics up later.

How long is the barrel? Use my chart above to make sure your buffer weight is what is recommended. Is this set up with a pistol or carbine?

You didn't describe your buffer spring either.

My apologizes if you did list this, I'm just now really getting into this thread.

jimbobborg · Aug 28, 2017

j_h_smith said:
How long is the barrel? Use my chart above to make sure your buffer weight is what is recommended. Is this set up with a pistol or carbine?

You didn't describe your buffer spring either.

My apologizes if you did list this, I'm just now really getting into this thread.

It has a 16" barrel, with a CMMG 9mm buffer, which weighs 5 ounces. I'm using a standard carbine buffer spring right now. I was using an AR-10 carbine spring, but it's slamming the bolt too fast.

It's working fine with new magazines, it's the older magazines that came with the lower I bought that are giving the gun fits. There's definite drag when cycling full Colt mags, enough to cause the bolt to not fully recoil and eject the empty. Davsco may have seen the result of this this past Saturday.

j_h_smith · Aug 28, 2017

Can you post a few pictures of the bolt?

outrider58 · Aug 28, 2017

Will polishing the bolt bottom help reduce drag? That's what we do on our ARs.

Sent from my XT1585 using Tapatalk

j_h_smith · Aug 28, 2017

outrider58 said:
Will polishing the bolt bottom help reduce drag? That's what we do on our ARs.

Sent from my XT1585 using Tapatalk

This is just my opinion, but unless your bolt is milled using a chisel, it should be smooth enough to work fine.

However, I always like to see a picture of the bolt. First to see how it's milled and secondly to see if there are any obvious drag marks. We all know the mag is the weak point in this design. We also know that a heavy buffer is needed. Now many are recommending a heavier buffer spring.

I've done all this and one of my carbines still isn't reliable unless I use 147gr fmj ammo. It runs fine with this combo, but throw in some 147hp or 124 and it runs about a 90-95%. Forget about the 115gr. It's not reliable at all.

My son has done some work with FNC and Surefire, maybe I'll get him to ask around and see if they have any ideas on this.

bfoosh006 · Aug 28, 2017

jimbobborg said:
I'm using the same setup since I started this thread. The only real problem I'm having is empties not ejecting fully and getting jammed on top of the next round being fed. I've used a variety of commercial 115gr 9mm rounds and my 147gr loads. I'm using a Colt pattern setup. I have a dedicated 9mm lower and upper, 9mm CMMG buffer, $1.50 in quarters, and a Wilson 9mm barrel. Not sure who made the bolt. I'll get pics up later.

Sounds like you need to bend the ejector...

https://www.google.com/search?q=Bending+the+ejector+on+a+9mm+AR&source=lnms&sa=X&ved=0ahUKEwi4xp-uivrVAhUE62MKHZADAXEQ_AUICSgA&biw=868&bih=482&dpr=1.25

DevinRPD · Aug 28, 2017

just build a 9mm ar pistol recently and have shot about 500 rounds through it, 400 of which were 115gr and havent had a malf yet. i would put the reasoning on the kak 9mm extended buffer which weighs 8oz. i just switched from an ar10 flat spring to a KAW extra power and the recoil is noticeably less also. id say the majority of problems people are having with their 9mm AR's is either in the buffer system or the mags

outrider58 · Aug 28, 2017

DevinRPD said:
just build a 9mm ar pistol recently and have shot about 500 rounds through it, 400 of which were 115gr and havent had a malf yet. i would put the reasoning on the kak 9mm extended buffer which weighs 8oz. i just switched from an ar10 flat spring to a KAW extra power and the recoil is noticeably less also. id say the majority of problems people are having with their 9mm AR's is either in the buffer system or the mags

I wonder if there isn't a little bolt bounce happening as well. Just spitballing.

DevinRPD · Aug 28, 2017

outrider58 said:
I wonder if there isn't a little bolt bounce happening as well. Just spitballing.

Bolt bounce meaning as the bolt closes it bounces off the barrel extension? i keep hearing this term but wasnt sure what the cause was or how you would know if its bouncing or not

outrider58 · Aug 28, 2017

DevinRPD said:
Bolt bounce meaning as the bolt closes it bounces off the barrel extension? i keep hearing this term but wasnt sure what the cause was or how you would know if its bouncing or not

In this case, the bolt recoils in the forward cycle into battery, only to rebound rearward slightly. Not a big deal as long as it goes back into battery. I think it is usually caused by too light a buffer.

Sent from my XT1585 using Tapatalk

bfoosh006 · Aug 28, 2017

Bolt bounce can happen under a variety of conditions... and can be a big issue in full auto firearms.

Watch the video... you can see how you might have firing issues with an out of battery round or a Failure to fire.... especially in a non locking Blowback 9MM.

This is why I recommend the configurable buffer... sometimes ya gotta tune your setup.

BEAR IN MIND all rifles can behave differently with different ammo... so just because one of the buffers in the video shows the least BB... that doesn't mean your 20,000 rds fired / never changed a spring firearm will react the same way.... it is a complicated thing.

And note the difference just from the ammo.

https://www.youtube.com/watch?v=575Q0O41u5s

And....

https://www.youtube.com/watch?v=pRn68HwZf34

And a buffer with no weights... No Deadblow effect

https://www.youtube.com/watch?v=y2GeugjmeF0

outrider58 · Aug 28, 2017

bfoosh006 said:
Bolt bounce can happen under a variety of conditions... and can be a big issue in full auto firearms.

Watch the video... you can see how you might have firing issues with an out of battery round or a Failure to fire.... especially in a non locking Blowback 9MM.

This is why I recommend the configurable buffer... sometimes ya gotta tune your setup.

BEAR IN MIND all rifles can behave differently with different ammo... so just because one of the buffers in the video shows the least BB... that doesn't mean your 20,000 rds fired / never changed a spring firearm will react the same way.... it is a complicated thing.

And note the difference just from the ammo.

And....

And a buffer with no weights... No Deadblow effect

My point in mentioning was to say this could add to already occurring problems.

And to add to your point about ammunition, as ARs go, 9mm ARs tend to be the pickiest eaters of them all. Find what your gun likes(if you reload, this is real easy) and try to stick with those choices.

Heavy buffers are a no brainer as well as stiffer springs. I prefer the Tubb springs because of their longevity. YMMV

jimbobborg · Aug 28, 2017

bfoosh006 said:
Sounds like you need to bend the ejector...

https://www.google.com/search?q=Bending+the+ejector+on+a+9mm+AR&source=lnms&sa=X&ved=0ahUKEwi4xp-uivrVAhUE62MKHZADAXEQ_AUICSgA&biw=868&bih=482&dpr=1.25

This only happens with specific magazines. If a magazine isn't present, it ejects no problems. With the Colt and C-Product mags, hard jams with spent brass stuck under the charging handle. With the new ASC mags, runs like buttah.

I'd post a picture, but I don't have an image site that lets me do that.

j_h_smith · Aug 28, 2017

jimbobborg said:
This only happens with specific magazines. If a magazine isn't present, it ejects no problems. With the Colt and C-Product mags, hard jams with spent brass stuck under the charging handle. With the new ASC mags, runs like buttah.

I'd post a picture, but I don't have an image site that lets me do that.

Take your picture. Save it on your computer. Reply to this message and down below you will see a box that says MANAGE ATTACHMENTS. Click on that and you can upload your picture directly to this thread without needing a host web page.

You may have to go to ADVANCED when you respond to this or any other message. It's under the Additional Options area below your response.

bfoosh006 · Aug 29, 2017

outrider58 said:
My point in mentioning was to say this could add to already occurring problems.

And to add to your point about ammunition, as ARs go, 9mm ARs tend to be the pickiest eaters of them all. Find what your gun likes(if you reload, this is real easy) and try to stick with those choices.

Heavy buffers are a no brainer as well as stiffer springs. I prefer the Tubb springs because of their longevity. YMMV

Oh, I hear you and I was sharing videos so anyone that is not familiar with bolt bounce could see what I mean.

As for 9MM carbines being picky eaters... my PSA after a little polishing and tinkering ( buffers and springs ) feeds dang near all 9MM ... out of the 129 different OEM rounds I chrono'd only abou7-8 had dismal feeding, and of those most all were bullet setbacks.....with a surprising amount of those being FMJ ( Syntech Fed. Colt Brand loaded be Double Tap oddballs., so I wrote those off as poorly manufactured ammo or HPs that were just to dang big ( SIG V-Crown )

So I guess what I am saying.... if I can make my Economy PSA run, with its PSA $30 Colt Pattern mag block... then there is hope for most all 9MM Carbines.

jimbobborg · Aug 29, 2017

Do I keep dicking around with my current upper or do I just drop $400 and get this? http://palmettostatearmory.com/psa-...ht-keymod-railed-moe-rifle-kit-516446675.html

My 9mm AR was filthy

The #1 community for Gun Owners of the Northeast

Member Benefits:

Ultimate Member

Active Member

Active Member

Oddball caliber fan

Ultimate Member

Oddball caliber fan

Ultimate Member

Eats Bacon Raw

Ultimate Member

Active Member

Active Member

Eats Bacon Raw

Active Member

Eats Bacon Raw

Active Member

Eats Bacon Raw

Oddball caliber fan

Ultimate Member

Active Member

Oddball caliber fan

Users who are viewing this thread

Log in

Forum statistics