You are getting .38/40 carbine ballistics outa that AR of yours, that's pretty good!
I've thought about getting the Smith FPC in 10mm, as my 9mm FPC is a fun time, but I haven't done anything about that yet. Still mulling it over. They sling brass like a sonuvagun, and the 10mm deserves good handloads, so slinging brass isn't a fine thing.
I don't know that the Banshee is any better, which is why I keep mulling on it. I DO like the Banshee's lockup better, as the FPC is straight blowback, with no lockup at all.

 

...I DO like the Banshee's lockup better...

The radial locking concept is interesting, but I believe one of our members has had nothing but trouble with his.
Too powerful, or too weak? | 1911Forum

 

The picture below ws "pre-SBR Form 1 Giveaway" days. So this is a New Frontier Armory with a Mil-Spec upper. What you don't see is the:
10oz Tungsten Buffer -https://kawvalleyprecision.com/product/kvp-10oz-tungsten-blowback-buffer/
4.6oz Bolt Carrier weight - 9mm CARRIER WEIGHT EXTRA HEAVY

or if you want to simpify things Joe Bob's has the whole package (except for the 4.6oz Bolt weight)- PCC Buffers & Springs for Sale at Joe Bob Outfitters!


This gun ejects Hornady 180gr @ 1150fps about 4'oclock and 3-4ft away. I use a brass Catcher on 10mm and 38Super Ars because of it's availability. It also provides a way to assess the brass. No Bulges. Accuracy is superb and works well on Hogs and Coyotes.

I was fortunate I didn't require a lot of "mix and match" on weights/springs/buffers. OBTW, it's the same combo in my 45acp AR. The 38 Super only needed the 7.5oz buffer, and a 4.6oz Bolt Barrier weight. The Buffer Spring is a Mil-Spec spring.

 

That setup is probably appropriate for the short barrel on your gun. I’m using a 16” barrel, which gives me higher velocity.
It seems to work fine with some powders, and bullet weights, but I think that it will have problems if I change to slower powders, or heavier bullets. But, I haven’t tested those yet.
I thought I had reached the limit to adding weight to my setup. But, I just figured out how to add more weight. Which I may do once I get my lathe repaired.😊

 

I'm running a 16" barrel, using a full case of #9 slightly compressed and a 155 XTP. Getting around 1800 FPS IIRC.

 

I found a supplier that has 8-1/2" carbine extensions. That allowed a longer/ heavier buffer and buffer extension. Drilled and slugged the SS buffer extension with 2 tungsten weights, turned a collar to add some more weight. I think I'm at the max weight attainable for a buffer with carbine extension just under 20oz. Run a sprinco orange spring. Set a brother up from another forum with the same setup and his is running great. A real shooter after messing around a bit.

 

That 12.5oz buffer looks like similar to the one I got from Foxtrot Mike that weighs 11.5oz. I put together a buffer spacer weight ( for lack of a better term) using a 3/3” copper water line end cap, with 3 tungsten weights JB welded together. It weighs about 5.6oz.
I’m considering taking a KAK 11oz buffer (actual weight is 10.8oz), and boring out them stem. Then adding some tungsten AR buffers.
That should give me a combined weight of around 36oz(16.1+14+5.6). Whether that will be enough, I don’t know.

 

Should be good. I make my own but the KVP buffer or the Oden (or the Quarter Circle 10) all make a good place to start. Really want as many felt or rubber spacers and tungsten weights as possible to reduce BCG bounce. Solid stuff not so good. There is a seller on the internet that has bulk tungsten buffers half the price as buying the 3 packs.

The 10mm Lightning

 

8-1/2" carbine extension:

Long Buffer Tube - Just Right Carbines

Long buffer tube, internal depth 8.5".

justrightcarbines.com

Bulk Tungsten weights:

https://www.ascendmetals.com/store-policies

Just a cool picture: