AR9 buffer/spring/spacer question

[shootsacanon]

Needs pics of gun; Will update with that later.

I put together an AR9 pistol, which is cycling fine for 2 range trips of about 100 rounds each. Looking at some of the spent cases today, I’m wondering if I need a heavier spring, buffer, or a stack of quarters in the tube. Seems like maybe they need to stay in the chamber a little longer?

I put the buffer on a food scale & I think it weighs about 3.3 oz if I recall.

 

[jpm2953]

Are they reloads?

 

[shootsacanon]

Are they reloads?

Factory. I forget if these were Remington Range Bucket or WWB. I can’t quite tell from my pic, but I can nail it down.

So I did some more googling & I guess carbon fouling on the outside of brass cases is typical of blowback guns? Also possibly too low pressure to seal the case inside the chamber. Some of the RRB rounds felt considerably softer, like the bolt moving slower & more of a “push” recoil. The WWB rounds all felt hotter & more consistent in their recoil.

 

[Spikey]

Need a heavier buffer. H3 with spring and 5 quartets works for me. H3 with spring , Spikes block and two quarters works for me. 7.5 ounce buffer with spring works for me Using 115 gr reloads. 9mm all work different. Bolts vary in weight and this factors in. A little trial and error is needed . If you were closer I’d lend you parts for trial and error .

 

[Spikey]

A lot of very knowledgeable guys on here so you will get more ideas

 

[Allsmiles]

I use an 8pz buffer and 308 carbine buffer spring in my AR9 carbine with 16" barrel. Runs fine both suppressed and unsuppressed with little gas in the face. These are blowback guns so you have a lot of lead way.

 

[DanKATL]

KVP 7.5 oz solid SS Blowback buffer with their extra power spring (which is a 308 spring) seems to run well on a 16" barrel without messing with quarters.

 

[Spikey]

KVP 7.5 oz solid SS Blowback buffer with their extra power spring (which is a 308 spring) seems to run well on a 16" barrel without messing with quarters.

That’s what I run. Forgot I had the 308 spring tho. Very reliable set up

 

[Spikey]

As an aside. If doing a pistol build I’ve always used the JP captured silent spring This not a cheap part but very very reliable. I have this in three 9mm SBR builds and in a few other builds Most with the Maxim stock .
It’s my set up of choice . JP has an excellent ( but expensive) bolt. Spinta has a less expensive bolt that works very well As I said earlier a bit of trial and error involved. As to gassing I can’t address that as all my AR builds are done on side charging uppers They close out with a trap door so gas goes out the ejection port .

 

[shootsacanon]

Thanks for the tips guys. Just ordered an 8 oz buffer and 308 spring.