6.5 Grendel build issues.

[Variable]

Mid length gas on an 18" barrel? I'm guessing your setup is way overgassed, which is completely throwing off your action's timing. Shortening the buffer spring just made it worse.

I'd get either a Sprinco RED spring or a H2/H3 buffer and try again. If neither of these work, you may need an adjustable gas block. Also, try some factory Hornady ammo to rule out your handloads as a contributing factor.

^^^^^^ I'm leaning toward all of this.

Sounds like heavily overgassed to me.


Also
Re: carbon marks behind the gas block--- Fairly common occurence. Not a big deal most of the time. It usually builds a little carbon fouling up in the tiny gap, and then stops leaking. If you are already overgassed, it sure isn't hurting you that some is leaking out.