AR9G Build - Need help

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  • SigDog

    Active Member
    Feb 11, 2013
    173
    West Virginia
    Building an AR 9mm pistol.
    Last thing I need to know are which buffer and spring to use.
    Did the searches, plenty on 9mm carbines, but couldn't find anything on pistols.
    My search kung fu is weak.
    So which buffer and spring do I need?
    THANKS in advance!

    M0DzFMk.jpg
     

    SigDog

    Active Member
    Feb 11, 2013
    173
    West Virginia
    Aero Precision lower, upper and handguard.
    Stern Defense 9mm mag block, bolt and barrel.
    Assorted lower parts, what was laying around.

    The Stern mag block fits in the magwell, locks in with the mag release on the receiver. Has another release built into it to drop the mags.

    Hopefully it works well.
    We shall see.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    308 flat wire spring, and one of the usual heavy 9mm buffers like the Spikes ST-9X (7.7oz, IIRC).
     

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    The Stern mag block fits in the magwell, locks in with the mag release on the receiver. Has another release built into it to drop the mags.

    Hopefully it works well.
    We shall see.

    So if you hit the mag release on the lower it'll drop the mag block?
     

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    Yes, the mag release is at the bottom rear of the mag block, you push it forward to drop the mag.

    Sorry, I meant if you hit the AR's mag release, will it drop the entire mag block out of the AR magwell, or is there something in place to stop that?

    I ask because the various types of Hahn blocks had things in place to prevent that. I like the looks of this one, including the bottom paddle release for the Glock mags. I just wouldn't love it if the whole thing would fall out of the lower if you hit the AR mag release.
     

    gmharle

    Active Member
    MDS Supporter
    Dec 29, 2015
    824
    Millers, MD
    Sorry, I meant if you hit the AR's mag release, will it drop the entire mag block out of the AR magwell, or is there something in place to stop that?

    I ask because the various types of Hahn blocks had things in place to prevent that. I like the looks of this one, including the bottom paddle release for the Glock mags. I just wouldn't love it if the whole thing would fall out of the lower if you hit the AR mag release.

    It has some set screws that that lock it in place. Looking at getting one of these myself. Her is an install video from their website.
    https://getstern.com/pages/install
     

    j_h_smith

    Ultimate Member
    Jul 28, 2007
    28,516
    308 flat wire spring, and one of the usual heavy 9mm buffers like the Spikes ST-9X (7.7oz, IIRC).

    I'm not sure you can use a 308 style (Tubbs) spring with the pistol buffer tube. I use the Tubbs spring on my carbines, but never tried it on the pistols. I think that spring will bottom out with the shorter pistol buffer tube.

    As far as the buffer itself, I've always used the 20-24 oz formula. That's is, weigh your buffer and bolt. They should total 20-24 oz total weight combined. I've had good success with this. My pistols I just use a regular AR15 spring and utilize the 20-24 oz rule too.

    For me, I use a 5.6 oz buffer on all of my 9mm AR9s but the 7.7oz buffer still gets you with the 20-24oz range.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    I'm not sure you can use a 308 style (Tubbs) spring with the pistol buffer tube. I use the Tubbs spring on my carbines, but never tried it on the pistols. I think that spring will bottom out with the shorter pistol buffer tube.
    Oops, I forgot that it was just a pistol-sized buffer with that stock (I mean, "brace"). Yes, you will want an extra-strength 5.56x45 flat wire spring.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Tubb .308 flat spring will work on a pistol/carbine length buffer. Solid height is shorter than a standard carbine spring solid height.

    If you have a stubby buffer like some of the collapsible braces do then an AR15 Length Tubb is needed.

    O.P. please post the picture of the original buffer the stock came with. A 9mm buffer is often longer than a D.I. Buffer to limit bolt travel on blowback guns. You can't get this wrong as too much bolt travel can damage the dummy carrier key, the lower, and the bolt catch.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,819
    Tubb .308 flat spring will work on a pistol/carbine length buffer. Solid height is shorter than a standard carbine spring solid height.

    If you have a stubby buffer like some of the collapsible braces do then an AR15 Length Tubb is needed.

    O.P. please post the picture of the original buffer the stock came with. A 9mm buffer is often longer than a D.I. Buffer to limit bolt travel on blowback guns. You can't get this wrong as too much bolt travel can damage the dummy carrier key, the lower, and the bolt catch.

    I have Tubb's 308 springs in both my 9mm AR builds. They both have SB PDW braces on them. Both have Spike's ST9-X heavy buffers as well. The buffers bottom the spring out before the bumper on the buffer touches the back of the tube. Thinking I may need a spacer in there if one exists for that. I've got a couple K rounds through one gun with no obvious problems.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    I have Tubb's 308 springs in both my 9mm AR builds. They both have SB PDW braces on them. Both have Spike's ST9-X heavy buffers as well. The buffers bottom the spring out before the bumper on the buffer touches the back of the tube. Thinking I may need a spacer in there if one exists for that. I've got a couple K rounds through one gun with no obvious problems.

    Thanks for that input my friend. I couldn't remember the internal length of the PDW Tubes
    You're teaching me stuff now :)
     

    mike j

    Member
    Feb 14, 2018
    37
    Annapolis MD
    Building an AR 9mm pistol.
    Last thing I need to know are which buffer and spring to use.
    Did the searches, plenty on 9mm carbines, but couldn't find anything on pistols.
    My search kung fu is weak.
    So which buffer and spring do I need?
    THANKS in advance!

    I used a kaw valley precision 7.5oz buffer and just switched out to a kaw valley xtra power spring last week. I have a sb tac sob brace and tube
     

    bilbravo

    Active Member
    Apr 30, 2013
    417
    Baltimore (District 46)
    Aero Precision lower, upper and handguard.
    Stern Defense 9mm mag block, bolt and barrel.
    Assorted lower parts, what was laying around.

    The Stern mag block fits in the magwell, locks in with the mag release on the receiver. Has another release built into it to drop the mags.

    Hopefully it works well.
    We shall see.

    Thanks for the details. I was looking at that mag well block before, but at $180 it's a tough sell over some of the others that are well under $100.
     

    SigDog

    Active Member
    Feb 11, 2013
    173
    West Virginia
    O.P. please post the picture of the original buffer the stock came with. A 9mm buffer is often longer than a D.I. Buffer to limit bolt travel on blowback guns. You can't get this wrong as too much bolt travel can damage the dummy carrier key, the lower, and the bolt catch.

    Here's the pic. Really small buffer, definitely not H3/H4 size/weight.
    Spring looks like a regular carbine spring maybe?

    Also, THANKS for all the help here guys!

    OjR4QFz.jpg
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,819
    Here's the pic. Really small buffer, definitely not H3/H4 size/weight.
    Spring looks like a regular carbine spring maybe?

    Also, THANKS for all the help here guys!

    OjR4QFz.jpg

    The spring and buffer for the Maxim PDW brace are proprietary. You can not use any other parts(except a proprietary JP SCSS made for this brace). They do offer a variety of buffers to suit the different calibers be they DI or blow-back.

    From their site:


    Maxim CQB Buffer in Standard, H1, H2, and Pistol (9mm,40S&W,45ACP) & Spring System (Proprietary buffer & spring)
    OR
    JP Silence Capture Spring System – XS (Proprietary & Exclusive to Maxim CQB Stock) ;
    Standard, Heavy, and Pistol (9mm ONLY).
    DO NOT MODIFY A BCG TO MAKE IT COMPATIBLE. DO NOT REMOVE THE WEIGHT FROM 9MM BCG’S. NOT RECOMMENDED FOR SELECT FIRE.

    Hope this helps!
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    The spring and buffer for the Maxim PDW brace are proprietary. You can not use any other parts(except a proprietary JP SCSS made for this brace). They do offer a variety of buffers to suit the different calibers be they DI or blow-back.

    From their site:




    Hope this helps!

    Excellent!
     

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