Leaving for the range now...
Going shootin' with my 16" BCM middy w/ FSC556 (and regular handguards). I'll be running Tula .223 (from CTD), Walmart 55gr Federal value pack, REAL M855 (accidentally misplaced into my buddy's gear bag on the way back ;) ), and BVAC 5.56 NATO pressure ammo with the Hornady 75 grain TAP bullet.
I'll advise on which buffer is best for the 16" middy; H2 or H3.
I'll also be using standard carbine buffer spring, Springco Blue 'standard' power CS buffer spring (which I suspect is still stronger than standard), and Tubbs CS flatwire buffer spring.
Details will be up this evening.
Thank you to everybody else, including Markm and IG for the great info and pix. That's what makes this forum great, gentlemen. Kudos. :)
Just got back from the range...
I fired about 200 rounds of M855, BVAC 75gr 5.56mm, Tula .223, and Federal .223 value pack.
I used my carbine:
BCM 16" middy upper w/ standard handguards
FSC556 on muzzle
Spike's Tactical Nickel boron (Fail zero) FA BCG
Spike's Nickel boron (fail zero) combat trigger
Spike's carbine lower
BCM extractor upgrade (no o-ring)
McFarland Gas ring
Blackjack Buffers replacement rounded polymer buffer tip
Slip 2000 EWL
Springco Blue CS Buffer spring + H2:
I started my test with the following setup using the Springco Blue standard power buffer spring and an H2 buffer. This setup worked perfectly using all ammo. It cycled and locked back on empty using the Tula .223.
Springco Blue CS Buffer spring + H3:
Next, I used switched-in the H3 buffer. The rifle shot smoother still. Function was perfect using all ammo as well.
Tubbs Flatwire CS Buffer spring + H2:
Then, I tried the Tubbs CS flatwire buffer spring using the H2 buffer. It shot smoother than the Springco Blue + H2, but not quite as smooth as the Springco + H3. No malfunctions using any ammo.
Tubbs Flatwire CS Buffer spring + H3:
Expecting failure, I gave this combo a try. I'm glad I did. It also functioned perfectly using all ammo. It even locked to the rear using Tula .223. The tula .223 really did feel like a rimfire conversion. Holy shit. The gun shot really smooth, even using the full power NATO pressure BVAC and M855 ammo. I tried this combo last, thinking that if the gun worked using this combo after getting all dirty, then I'd be okay and ready for more extended trials. I tested lock-back on empty repeatedly using Tula ammo...using a variety of PMAGs, brownells mags, and C-products magazines. All worked perfectly. I stopped after 200 rounds due to my stall time being up.
Caveats:
I'm using a coated BCG and hammer (actually all of the trigger group); this serves to reduce friction in the action. I cannot attest to the performance of a normal phosphated BCG using the Tubbs and H3 since I cannot calculate the frictional losses associated with the phosphate coating vs the nickel boron coating of my BCG. I can tell you that hand-cycling my AR feels like it is on ball bearings, and there was noticeably more friction when I was running a phosphated CMT FA BCG.
So there you go....if you're running a 16" middy, you can run the stronger spring and an H3 if you use a FZ/Spike's BCG and at least a coated hammer.
However, my test sample is small. Pix to follow if my wife can find the friggin camera I bought her. :rolleyes:
In the interest of tinkering, I am considering testing a Springco Red Extra power buffer spring or an even heavier buffer (I have a buddy who uses a super-heavy rifle buffer from Slash at Heavybuffers dot com and loves it) made from a Stainless steel body and all tungsten weights; it's supposed to be .9 oz heavier than an H3.
As for the WHY...here's my hypothesis: I think my 16" middy can run the H3 + Tubbs CS flatwire spring due to the extra dwell time afforded by the additional barrel length in front of the gas port and the reduction in friction provided by the fail zero coated components.