Heavies,
Sounds like your grendel is gassed right.

I’m crossing my fingers on mine.

I picked up a 20 or 22 barrel that I believe is rifle gas - I’m hoping the longer dwell time(?) reduces the chamber pressure enough to help longevity. 

Oh well, will see if I over thought or wrongly thought it thru.....and overspent with little or no gains :-)

Aaron,
Good info to know!  For my x39, I only used my regular 5.56 lower.  I thought I read that for x39 and 6.5, a carbine tube, spring and buffer were ok.   I better go back and read more about x39 and Grendel.

I already bought my bolts but I’ll tell my friends to look into the Cason and LMT bolts

Np bro. Yeah im sure carbine gas will work just fine. As long as the gas port diameter are correctly sized. I think thatll pretty much go for everything. Iirc my gas port diameter on a x39 middy was .099". So if it has carbine gas it just has to be smaller than that. But you are correct, rifle length is the softest shooting due to dwell time. The less time a bullet has to travel in a barrel while redirecting gas rearward equals Less wear and tear on your rifle. For cason engineering, he didnt have a website up, i found him on a forum,  m4carbine.net or arf.com. the only problem bout lmt bolts, is their lobster extractors. Where as cason uses regular extractors in terms of design (like any 5.56 from failzero, or wmd.) Yeah im a bcg snob. Sorry lol. Oh now failzero makes x39 bcgs. Im sure their top notch as well. I know their customer service is. No questions asked they sent me a new carrier, even though it was sitting in my room for months. It was my backup bcg. The gas key wasnt torqued down. Nor was staked. Lol. I could move the key. Then i sent mine in after I received a new one cause the shipping label came with the new one.

Edit: totally read your post wrong. Yeah carbine buffers should be fine, but rifle buffers/tube will always be more smooth. God i have to find a vid on it. This guy explained it well and better than i ever can. Kinda why the vltor a5/ bcm a5 was invented. Rifle spring but you can use carbine type stocks. Best of both worlds.

Btw i run tubbs flat wire springs in all my ar15s🤣

6 ARC - ar15 platform
308, 6.5cm - ar10 platform

end of story

Yea my friend told me bout the arc a couple nights ago. Seems interesting. Also the somewhat failed 25-45 sharps. I forgot that even existed until i was reminiscing my src bcg but thats for my 556. Lol

Wow.
6mm ARC.
That’s one to keep an eye on.

https://www.thefirearmblog.com/blog/2020/06/03/hornady-announces-6mm-arc/

And in the spirit of thread, it’s at an even number. 6. (Millimeters though. I guess it would be a .236. )

Why not a .25 caliber ?

Probably because it is pretty close to 6.5 (Grendel)
And 65 sounds sexier than 25

The real question is why there is no 6.9
:-)

(Maybe there is.....idk)

Aaron
I checked on the buffer tube, spring and buffer for x39 and Grendel.  it seems like a 223 set up lower will often work for the various calibers but depends on the gas port size. 

Apparently, most makers try to design their uppers to “drop in” to a 223 based lower.  I assume they design on the most commonly used bullet grains.  If outside that band or using a can....will need to tweak with an agb and/or changing the buffer system

My bca x39 upper ran fine on my 223 lower.  (Sold it...Hbar barrel and I wanted something lighter and had a better reputation for qc)

I picked up a used psa x39 upper from IrishD and hope it runs ok with my 223 lower