If you just want to build these guns and use the RTB carriers because that's all you could find... Get an adjustable gas block. Don't be lazy, dimple the danged barrel and install it correctly. Then I'd start with a carbine or maybe Springco white-hot spring and an H buffer. If I had one handy I'd try an H2 buffer as well but it's probably not necessary. Since the carrier is so light you'd want to go heavier to compensate for the missing mass. Then turn down your gas until your ejection is at 3 o'clock and your bolt locks back on an empty magazine every time.
I agree with all that you've said & concluded from your trials, & that's exactly what my advice if he really wants to use those carriers............& he did say that he has (Seekins) AGB's already.
As far as light carriers, there's those that have the weight reduced by a couple of oz, then there are Ti & Al carriers that another 3-4 oz lighter.
The ones are are only a couple of oz lighter are easy to run, but as the weight goes down further, a lot more dicking around, different buffers/springs & AGB's need to be tuned to get them optimized.
MM
