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[ARCHIVED THREAD] - Buffer Spring / Weight questions: Building AR-9

Posted: 2/11/2017 9:48:45 PM EDT

KVP recommends "Extra" power buffer springs for 9mm Carbines:

KVP

My understanding is that 308 springs are the same whether they be in a Carbine buffer tube or a Rifle buffer tube. That lead me to believe that AR15 RIFLE length springs would do the job of a Carbine length 308/9mm spring.

Now in assembly, I have found that while using a rifle length spring, the BCG just BARELY comes past the Bolt Catch.

SO... Can I assume it's safe to forego the extra power spring, and just add more weight to my buffer?

Posted: 2/11/2017 10:21:05 PM EDT

[#1]

Quoted:
KVP recommends "Extra" power buffer springs for 9mm Carbines:

KVP

My understanding is that 308 springs are the same whether they be in a Carbine buffer tube or a Rifle buffer tube. That lead me to believe that AR15 RIFLE length springs would do the job of a Carbine length 308/9mm spring.

Now in assembly, I have found that while using a rifle length spring, the BCG just BARELY comes past the Bolt Catch.

SO... Can I assume it's safe to forego the extra power spring, and just add more weight to my buffer?

View Quote

And remember this simple tid bit of info.... When COLT built the 635... all they did was set a 9mm upper on a M16 lower with CAR stock, and made a 5.5oz CAR buffer to run in the CAR tube with CAR spring..

What about all the gizmos we supposedly need to run 9mm ???

Posted: 2/12/2017 12:21:43 AM EDT

[#2]

The rifle length recoil spring has too many coils for the space available in the carbine buffer tube. The rearward travel should stop when the buffer contacts the end of the buffer tube. Not when the recoil spring reaches its solid height. Measure the length of your buffer under the head. Count the coils in the recoil spring and multiply the number of coils by the wire diameter. This is the solid height of the spring. The solid height of the spring must be less than the length of the buffer not counting the head.

Go with the heaviest carbine recoil spring and a pistol caliber buffer. Pistol caliber buffers are heavier than an H3 carbine buffer.

Posted: 2/12/2017 1:19:21 AM EDT

[#3]

I have two 9mm ARs
I'm using spikes 9mm buffers in both, I have used standard carbine buffer spring's in both without issue.
One of them I have switched to a Tubbs flat wire spring.

Posted: 2/12/2017 1:31:19 AM EDT

[#4]

Quoted:
KVP recommends "Extra" power buffer springs for 9mm Carbines:

KVP

My understanding is that 308 springs are the same whether they be in a Carbine buffer tube or a Rifle buffer tube. That lead me to believe that AR15 RIFLE length springs would do the job of a Carbine length 308/9mm spring.

Now in assembly, I have found that while using a rifle length spring, the BCG just BARELY comes past the Bolt Catch.

SO... Can I assume it's safe to forego the extra power spring, and just add more weight to my buffer?

View Quote

Get a carbine spring.
Get a 5oz or 5.5oz buffer. I also recommend a buffer bumper like NFA or Spikes to help control stroke length
Shoot gun.

THEN when it's operating 100% on the basic stuff, you make subtle changes to improve it however you want to.

.

Posted: 2/12/2017 9:44:11 AM EDT

[#5]

to add to what Mr Jeep commented about the weight... if you plan on shooting USPSA PCC and you reload....be sure to develop the load first... a 3.6 charge of WSF and 135 coated Bayous give me a 148 power factor out of my 16" barrel... runs with a 5.2 oz rifle buffer and rifle spring... 21.5 oz total for buffer and bolt

Posted: 2/12/2017 10:31:54 AM EDT

[#6]

Quote History

Quoted:
t runs with a 5.2 oz rifle buffer and rifle spring... 21.5 oz total for buffer and bolt

View Quote

Since 2003 w/ 7oz A2 rifle buffer & A2 rifle spring

Attached File

Posted: 2/12/2017 12:07:43 PM EDT

[#7]

Like others have said... the buffer spring must have adequate "freetravel" .

I run in my 16" Colt pattern... Tubbs Flatwire 308, and a ( currently ) Spikes 8oz solid.... bark and blast is noticeably lessened over the OEM Carbine spring and 5.5oz 9mm buffer.

I am swapping out the Solid core 8oz Spikes with a KAK "Configurable 9MM Extended Carbine buffer" with a 6.9ish oz ... mostly because of the I think there are real benefits to a "deadblow" type buffer over a solid one.

I will add.... I have tried numerous spring / buffer combos.... and beyond a doubt, the 308 traditional spring was ( IMHO) quite abusive to the carbine.... it would "slap" the BCG so hard against the breach, much like a hammer on an anvil.

FYI .... info from David Tubbs spring measurements.

This video....
https://www.youtube.com/watch?v=8fMVZbrnvu8

A2 (old / used) - 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 / .308) - 13.9lb closed, 24.8lb open"

Swapping to the Tubbs 308 Flatwire was a dramatic difference.... the Flatwire is more of a variable power spring>

Posted: 2/12/2017 12:20:27 PM EDT

[#8]

The distance that the buffer and bolt assembly travels on a 9mm is critical to preventing premature failure of the bolt wcatch. Since it's a blow back design, adding weight to the buffer and spring pressure can help accomplish those things. There are also several options to make a spacer to prevent over travel.

The Vltor A5 buffer happens to be available in heavier weights and happens to be longer than a carbine buffer by the exact same amount that is recommended to prevent over travel if you are going to use a spacer. Dropped into a carbine buffer tube with a carbine spring and 9mm upper, it works quite well.

Posted: 2/12/2017 12:42:59 PM EDT

[#9]

Quote History

Quoted:
The distance that the buffer and bolt assembly travels on a 9mm is critical to preventing premature failure of the bolt wcatch. Since it's a blow back design, adding weight to the buffer and spring pressure can help accomplish those things. There are also several options to make a spacer to prevent over travel.

The Vltor A5 buffer happens to be available in heavier weights and happens to be longer than a carbine buffer by the exact same amount that is recommended to prevent over travel if you are going to use a spacer. Dropped into a carbine buffer tube with a carbine spring and 9mm upper, it works quite well.

View Quote

I was wondering how the A5 worked with a 9mm. I recently picked one up for my AR57 upper to solve bolt bounce problems but I haven't gotten out to shoot with it yet.

Posted: 2/12/2017 4:32:24 PM EDT

[#10]

I'm building a 10.5" AR-9, and I went ahead and ordered the pistol caliber carbine blowback kit, which has the 7.5oz buffer, and extra power carbine spring and carbine tube. I recon it should be ok?

Posted: 2/12/2017 6:12:30 PM EDT

[#11]

Quote History

Quoted:
I was wondering how the A5 worked with a 9mm. I recently picked one up for my AR57 upper to solve bolt bounce problems but I haven't gotten out to shoot with it yet.

View Quote View All Quotes

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Quote History

Quoted:

Quoted:
The distance that the buffer and bolt assembly travels on a 9mm is critical to preventing premature failure of the bolt wcatch. Since it's a blow back design, adding weight to the buffer and spring pressure can help accomplish those things. There are also several options to make a spacer to prevent over travel.

The Vltor A5 buffer happens to be available in heavier weights and happens to be longer than a carbine buffer by the exact same amount that is recommended to prevent over travel if you are going to use a spacer. Dropped into a carbine buffer tube with a carbine spring and 9mm upper, it works quite well.

I was wondering how the A5 worked with a 9mm. I recently picked one up for my AR57 upper to solve bolt bounce problems but I haven't gotten out to shoot with it yet.

A bit more info can be found here:
http://www.ar15.com/forums/t_3_122/654146_NOW_WITH_PICS_9mm_bolt___VLTOR_A5_buffer___Standard_Milspec_Carbine_Buffer_Tube___The_perfect_combo_.html

Posted: 2/13/2017 12:12:18 AM EDT

[#12]

I run nothing but a standard carbine spring and the extended buffer I make on 9mm, both semi and full auto. By adding or removing lead shot the buffer is adjustable from 5.5 to 7.5 ounces. Extra power springs do nothing but increase the forward velocity of your bolt increasing the likely hood of damage to your firearm.
It is a blowback action...it ain't rocket science. Bottom line...there is no substitute for mass with a blowback action.

Posted: 2/13/2017 9:21:14 AM EDT

[#13]

https://www.blitzkriegcomponents.com/ProductDetails.asp?ProductCode=AR15%2DKYNJP%2D9C

this is the route i took expensive , yes but its soooo nice

Posted: 2/14/2017 1:14:55 PM EDT

[#14]

I'm using the YHM 9mm buffer. It's extra long to control the stroke length so you don't have to pad the bottom end of the carbine tube with quarters, though that solution IS cheaper.

Posted: 2/14/2017 1:44:52 PM EDT

[#15]

The YHM 9mm buffer is 5.9 ounces.

What is the optimum weight for a 9mm buffer and bolt?

Do loose weights within the buffer do anything?

Posted: 2/14/2017 2:12:36 PM EDT

[#16]

I actually bought the components for my AR9 build today. KAK 9mm buffer (5.5oz), standard carbine spring, and spacer. That will be put into my Shockwave dimpled extension and blade.

Posted: 2/14/2017 5:36:25 PM EDT

[#17]

Quoted:
I actually bought the components for my AR9 build today. KAK 9mm buffer (5.5oz), standard carbine spring, and spacer. That will be put into my Shockwave dimpled extension and blade.

View Quote

This is my setup along with a kaw valley bolt. Over 1.5 lbs of mass does a nice job delaying the bolt. I went back and forth between wolff xtra power spring and regular and decided to stick with the regular. The Xtra power spring was slamming the bolt forward too violently.

I run a 5.5" BA barrel, no suppressor.

Edit: I actually have the KAK heavy 9mm buffer.

Posted: 2/14/2017 6:08:56 PM EDT

[#18]

You neither need nor want a high power spring in a 9mm. It takes very little force to strip a 9mm from the magazine and chamber it, and there is no bolt locking to accomplish. All a high power spring will do is batter your parts around severely as noted by previous posters.

No, high power springs are not a substitute for mass (weight) in the reciprocating parts in a blowback system. Just no.

Nor should a spring be what stops the Bolt/Buffer travel.

Posted: 2/14/2017 6:20:17 PM EDT

[#19]

Quote History

Quoted:
You neither need nor want a high power spring in a 9mm. It takes very little force to strip a 9mm from the magazine and chamber it, and there is no bolt locking to accomplish. All a high power spring will do is batter your parts around severely as noted by previous posters.

No, high power springs are not a substitute for mass (weight) in the reciprocating parts in a blowback system. Just no.

Nor should a spring be what stops the Bolt/Buffer travel.

View Quote

FWIWW - high power spring should make it easier to shoulder bump, but otherwise I agree that it's a poor choice.

Posted: 2/14/2017 6:44:29 PM EDT

[#20]

Quote History

Quoted:
You neither need nor want a high power spring in a 9mm. It takes very little force to strip a 9mm from the magazine and chamber it, and there is no bolt locking to accomplish. All a high power spring will do is batter your parts around severely as noted by previous posters.

No, high power springs are not a substitute for mass (weight) in the reciprocating parts in a blowback system. Just no.

Nor should a spring be what stops the Bolt/Buffer travel.

View Quote

Yeah, not sure why people think it helps with delaying the opening. You're talking about a few extra pounds of preload trying to counteract thousands of pounds of force. Mass, as you say, is the only answer in blowback.

Only thing it does is keep the buffer from slamming into the back of the receiver extension as hard which can change felt recoil to something a little less sharp. But yeah, if it's going to either slam goimg forward or backwards, I'd rather it be backwards into the delrin tailpiece designed to take the beating.

Posted: 2/14/2017 11:26:33 PM EDT

[#21]

What are your guys' thoughts on using a NFA modular BCG (16.7oz) along with a KVP pistol buffer kit (KVP 7.5 oz SS Blowback Buffer and KVP XP SS Spring)?

Posted: 2/19/2017 10:54:56 PM EDT

[#22]

I like the look of the full stock. Do you use any kind of spacer in the tube to prevent the bolt from going back too far?

Posted: 2/20/2017 10:05:02 AM EDT

[#23]

I'm not SBR 7_11 that posted the pic, but I use the NFA bumper that came with their lower for my rifle stock/tube... I tried a couple of quarters to fine tune, but later removed them... stock rifle buffer and rifle spring

Posted: 2/20/2017 9:54:59 PM EDT

[#24]

Thanks. That's exactly what I needed to see.

Posted: 2/21/2017 10:55:21 PM EDT

[#25]

Quote History

Quoted:
I like the look of the full stock. Do you use any kind of spacer in the tube to prevent the bolt from going back too far?

View Quote

I run A2 stock with rifle spring and rifle buffer as designed.. I do not use any spacers, Eugene and COLT not do it..

As to spacer thing, I dont use bolt hold open ast shot, as I run mine on Uzi mags since I got block back in 2003 to use plain old Uzi mags (I am Uzi owner since March 1986) to which Uzi dont have bolt hold either

Only thing I have done is dump the guts from A2 buffer and machined a brass dowel to slip fit inside buffer body, bringing weight to 7oz... this buffer runs my short 9mm and (2) shorty 556 barrels fine and dandy

Posted: 2/21/2017 11:27:16 PM EDT

[#26]

Quote History

Quoted:

I run A2 stock with rifle spring and rifle buffer as designed.. I do not use any spacers, Eugene and COLT not do it..

As to spacer thing, I dont use bolt hold open ast shot, as I run mine on Uzi mags since I got block back in 2003 to use plain old Uzi mags (I am Uzi owner since March 1986) to which Uzi dont have bolt hold either

Only thing I have done is dump the guts from A2 buffer and machined a brass dowel to slip fit inside buffer body, bringing weight to 7oz... this buffer runs my short 9mm and (2) shorty 556 barrels fine and dandy

View Quote

You should add a spacer. It prevents a fired case from dropping into your fcg pocket causing a very annoying jam.