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Posted: 8/20/2016 8:46:36 AM EDT
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I'm new to the 9MM AR and working through some issues.
My question(s) is why does the buffer have to be so heavy? I'm running the KAK heavy buffer and standard carbine spring. Is this a good combination? What are the deciding factors for changing weight? |
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Quoted:
I'm new to the 9MM AR and working through some issues. My question(s) is why does the buffer have to be so heavy? I'm running the KAK heavy buffer and standard carbine spring. Is this a good combination? What are the deciding factors for changing weight? Retarding the bolt travel and speed. |
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9mm ARs function by simple blowback operation. Unlike a 5.56 AR which uses delayed gas blowback on a locked bolt, the only thing holding a 9mm bolt closed is the pressure of the action spring, and the only thing slowing the rearward movement of the bolt upon firing is the combined resistance of the buffer mass ad the action spring. So without that extra heavy mass in a 9mm system, the bolt would cycle too rapidly, accelerating wear to many parts in the system and promoting early breakage: broken bolt catches, buffer bumper breakage, "egged out" FCG pins, etc. on top of being very "violent" to control. |
| Without the extra mass in a blowback it becomes a safety issue..........as reciprocating mass (combined weight of bolt and buffer) decreases, the probability of a case rupturing due to early extraction increases exponentially. I usually run a combined weight on 9mm around 20 to 21 ounces. |
| 9mm buffer is longer the 223/556 one reason for this is so you dont break the boltcatch ive had a spikes tatacle in one and a palmetto state armory in there lower both work great. and HAHN PRECISION - AR-15/M16 9MM DROP-IN CONVERSION BLOCKS from brownells work great to |
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One important thing to remember that a stronger spring can also slow down the bolt. This will reduce felt recoil, as it the cyclic rate slows down.
I am using a Tubb 308 flat wire spring + NFA Bolt + H3 5.4oz buffer + ~13 quarters to add further tension to the spring. I've also tested a SpringCo red spring and it worked perfectly. I still get lockback every time. This is with an 8" barrel. Here are some spring weights taken by David Tubb: A2 (old) - 7.6lb closed, 14.5lb open A2 (new) - 9.1lb closed, 16.7lb open Tubb Flatwire - 10.5lb closed, 16.3lb open Tubb .308 Flatwire - 13lb closed, 16.7lb open SpringCo (White/standard) - 8.3lb closed, 16.3lb open SpringCo (Red/Enhanced) - 10.5lb closed, 18.4lb open SpringCo (Orange/Extra) - 13.9lb closed, 24.8lb open You can see that the Tubb spring puts more force on the bolt when it is closed than a traditional round wire spring, which is good for the 9mm AR since it's blowback. |
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Usps delivered my kaw valley precision buffer & spring from joebob yesterday.
The buffer is 7.5 oz and the spring is visibly thicker, less coils per inch. After replacing a PSA carbine buffer & spring, the ejection location stayed the same but instead of 20-25 feet away the shells made a neat pile @ 10 feet. Recoil was noticably less, not 22lr less but not much worse. KVP's buffer is longer than a car. but i dont have lrbho so i wasnt worried about breaking a bolt catch. |
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Quoted:
Without the extra mass in a blowback it becomes a safety issue..........as reciprocating mass (combined weight of bolt and buffer) decreases, the probability of a case rupturing due to early extraction increases exponentially. I usually run a combined weight on 9mm around 20 to 21 ounces. Awesome. That is a great bit of info Thanks |
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