AR9 - When to remove Pinned Weight from BCG?

[OdinXcore]

Greetings,

I recently built an AR9 and had a massively successful range session. About 400 rounds with a few minor malfunctions.

I shot 115 Gr ball, 124 gr ball and 147gr flat nose ammo.

I noticed with the 147gr; sometimes it would shortstroke, and sometimes it wouldn't feed (Flat nose with no real feedramp)

As a new AR9 builder, I'm curious. With my 7.5oz Kaw Valley Precision buffer and PCC Spring, is the weight in my Toolcraft Gen2 9mm Glock bolt even necessary? Was this extra weight responsible for the 147gr failing to cycle completely? Does it put too much stress on the bolt catch when it slams into it?

As it is pinned, I'd have to buy a new punch to remove it. Which, isn't really a problem, but I'd rather know for sure before spending money right now.

I appreciate any insight y'all might offer up.

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[Alexx1401]

Greetings,

I recently built an AR9 and had a massively successful range session. About 400 rounds with a few minor malfunctions.

I shot 115 Gr ball, 124 gr ball and 147gr flat nose ammo.

I noticed with the 147gr; sometimes it would shortstroke, and sometimes it wouldn't feed (Flat nose with no real feedramp)

As a new AR9 builder, I'm curious. With my 7.5oz Kaw Valley Precision buffer and PCC Spring, is the weight in my Toolcraft Gen2 9mm Glock bolt even necessary? Was this extra weight responsible for the 147gr failing to cycle completely? Does it put too much stress on the bolt catch when it slams into it?

As it is pinned, I'd have to buy a new punch to remove it. Which, isn't really a problem, but I'd rather know for sure before spending money right now.

I appreciate any insight y'all might offer up.

They make different weight buffer's but the cheapest way I can see to "tweak" this would be the counter weight. I would not try totally removing it but, I would try using less. Either buy another one if they will sell one. Should be very cheap since it's just a piece of round stock with a hole in it. If they do not want to sell one I would see about buying a chunk of round stock and make a new one. Make one say%25 lighter, drop it in and try. If you can get another I would maybe try drilling some holes in it to get it lighter. Little trial and error to see what weight works best. Watch you fired brass at each reduction for signs the bolt is too light.

 

[spookshack]

Ar9 bolt weight removal

My bolt weight came loose at a match today. Turned my gun to a single shot for the last 2 stadges (steel challenge). What are the pros and cons for running without the weight in the bolt?

forums.brianenos.com

 

[powermad]

You are already running on the low end of buffers for an AR9.
AR9 tuning is kinda tricky, generally a 21-23oz total mass (carrier + buffer) is what you want depending on the recoil system.

I use a carbine buffer tube, Springco green spring (rifle) and a Vltor A5H4 (6.8oz) buffer.
I have a Law Tactical folder and the adapter goes into the rear of the carrier.
I knocked out the buffer weight to install the adapter as they were both about 2oz.
It ran and ate everything I put through it but felt like it was a bit harsh and was flinging brass into orbit.
I cut the carrier slug down to fit the Law adapter adding another 1.2oz bringing my total mass to 23oz.
That seems to be the sweet spot for mine.
Still eats everything, Blazer 147gn, 9mm NATO, HST 124 and 147gn, etc.
The recoil is better and seems smoother with less dot bounce and it's piling up brass a few feet from me now.
I'm using a KVP PCC bolt carrier and Linear comp with Endo mags.

 

[s1xty7]

This isn't a helpful post, but with as much trouble as people seem to have with AR9s and yet how often people seem to love them, it reminds me of turboed RX-7s. The idea is great, and when they run it can be amazing, but they are very fiddly to keep running and not nearly as practical as you would think they should be. If I ever build one, I'll paint it bright red, put a wing on it, and etch a picture of a Wankel rotor on the side!

 

[powermad]

Now that I have a better grip on how they work and what's available I'll be doing another upper with a different system.

CMMG Radial Delayed Blowback system.
Which is their barrel, carrier and mags that are similar to Endo mags.
A carrier tuning kit is available with 3 different weights to fine tune it.
It's designed to use with a carbine weight buffer and spring.
Shaving 5oz's off the reciprocating mass would be nice and would make it a bit softer.
I'm still going to use a Green spring and a Vltor A5H0 (3.8oz) to start with and get a carrier tuning kit.

 

[turbo_vanner]

Now that I have a better grip on how they work and what's available I'll be doing another upper with a different system.

CMMG Radial Delayed Blowback system.
Which is their barrel, carrier and mags that are similar to Endo mags.
A carrier tuning kit is available with 3 different weights to fine tune it.
It's designed to use with a carbine weight buffer and spring.
Shaving 5oz's off the reciprocating mass would be nice and would make it a bit softer.
I'm still going to use a Green spring and a Vltor A5H0 (3.8oz) to start with and get a carrier tuning kit.

THIS IS THE WAY. Just finished my 5" build with CMMG's pmag conversions. everything from 115fmj to 147 defensive rounds fed and ejected, and everything locked the bolt back after the last round. Easily a pound lighter, less recoil, and quieter when suppressed.

Only thing is a suspect ejector spring, but only time will tell whats up with that.


As for OP's problem, I used to run a Spinta 9mm bcg with the weight, and a 10oz buffer, but reduced power action spring. I also had the feed ramp on my barrel cut a little deeper and wider by a gunsmith to get the 147s to feed right. It still cycled fine with all that mass, but I mainly shot it suppressed, which cycles a lot harder. I would say try knocking the weight out, a punch is certainly cheaper than trying a lighter buffer.

 

[PriklyPete]

THIS IS THE WAY. Just finished my 5" build with CMMG's pmag conversions. everything from 115fmj to 147 defensive rounds fed and ejected, and everything locked the bolt back after the last round. Easily a pound lighter, less recoil, and quieter when suppressed.

Only thing is a suspect ejector spring, but only time will tell whats up with that.


As for OP's problem, I used to run a Spinta 9mm bcg with the weight, and a 10oz buffer, but reduced power action spring. I also had the feed ramp on my barrel cut a little deeper and wider by a gunsmith to get the 147s to feed right. It still cycled fine with all that mass, but I mainly shot it suppressed, which cycles a lot harder. I would say try knocking the weight out, a punch is certainly cheaper than trying a lighter buffer.

I use to have barrel feeding problems and now use barrels from Macon Armory located in Macon, Georgia. They also make a dead bolt buffer that is 4" long that can be used with a standard 223 spring without a spacer. I agree that between the bolt and the buffer the total weight should be between 21 & 23 oz. The barrels purchased from the Macon Armory are guaranteed to feed, these boys know what they are doing.

 

[PriklyPete]

I have been building 9mm pcc's for several years and now use barrels and buffers purchased from Macon Armory located in Macon Georgia. Their barrels are guaranteed to feed and the buffers are dead blow and can be used with a standard 223 spring. I agree that the combined weight between the buffer and bolt should equal between 21 & 23 oz. Happy Shooting!