My New Barrel Just Arrived!

Waited 3 mos for my custom barrel from X-Caliber. 20" 0.308 Win, 1:8 twist w/5 lands.

This will be my first AR-10 build. Time to jig up the lower and get this sucker drilled and milled!


Why 1/8 twist? 1/10 is pretty standard.


That’s exactly why I had to go custom. I couldn’t find a standard barrel under 1:10.

I prefer to run 220 gr and heavier. All the calcs say 1:10 is too unstable.

I run 1:7 on my 300BLK barrels for the AR-15 platform. And since I reload, the same pills work in both cartrides. Plus, I run an AAC SR-7 for my 300BLK builds, which screws onto their flash hider. I can swap it right over to this big boy, no problem, as it was originally designed for the 0.308 Win.

Getting the biggest bang for my buck (pun intended).


Ok you realize you can’t load those heavies hot in an AR platform. Subs are going to be ok and mild to medium will be good but hot ( bolt gun) loads will not work well I your AR.


toolbox GIF


took me a minute to get the relevance to the thread :facepalm:


I’ve almost pulled the trigger on a couple of their barrels. They state right up front it’ll be 16 weeks so you beat the over/under. Their prices seem reasonable, just hadn’t heard from anyone using them.
Keep us up to date.


Yeah, my brain is odd and that’s all gify had when I looked quick, nice barrel tho, sorry to almost derail


Noticing a lot of dwell on that barrel also, be some fine tuning of loads and possibly gas/mass, specially with a can.

What are you using for buffer weight, spring, gas block, gas port diameter? Asking for a friend.


@shooterrex - I have never built or worked on a AR10, my experience is w/AR15s (223 Wylde, TAC6, 6.8 SPC ll) and only a dozen or so. I agree the 1:8 twist in a 308 win is really really fast. But in a AR Gas Rifle there is even more to think about regarding twist.

The 6.8 gurus figured out that 1:11 was more accurate than 1:10. This was based on the 6mm BR guys who figured that the too fast twist causes the bullet to wobble longer before going to sleep. Consequently the bullet drops faster and drifts more (spin drift?).

A lot of folks think twist is a weight thing, but it is also a length thing and a friction thing. Longer lighter mono need faster twists in certain rifling need more twist etc. So…

A 1:8 might be good for heavy and long powder coated hard cast. A 20" inch with the right powder could get them up to speed and stabilized. For accuracy you want to be as heavy and long as possible. So…

How heavy & long could one go in a AR308 1:8 20"? Assuming a PC hard cast, a adjustable gas system and whatever you would you use for a buffer etc?

Asking for me, because I just may get around to a short action gas rifle. For PC hard cast. :grin:


All I know is in these gas guns they can’t take the chamber pressure that bolt guns can. I have some 190gr Hurtenburger match ammo that shows signs of pressure in my 308ars but is fine in my bolt gun. Most people shooting the heavies are trying to get long range and have about max powder behind them. My M118 175’s are about the heaviest I want to shoot in the AR’s . If loaded subsonic no problem.


If you are not going for velocity AR’s can handle big and heavy. Small frame platform’s do up to 600 gr, I’ve loaded up to 405gr in my 458. Can’t imagine the parameters you describe would be a problem in a large frame.
EDIT: Looked in Loaddata, heaviest bullet for 308 shown is Berger 300gr at around 2000 fps. That in my opinion (not based on any data) could be too hot for AR. You would need to work up a load with a powder that could be reduced safely. If you are going for subsonic, could try trail boss might be enough pressure left to operate the BCG, especially with that long dwell. I’ll bet a 220 gr cast with trail boss has been tried before in a AR, google around. Not apples to apples, but we launch 45-70 subsonic with trail boss


Will do.

Yeah, when I ordered the site said 20 - 22 weeks! So, I was very pleasantly surprised.


What do you mean by “won’t work well”? The worst case is you rupture a casing or blow up the gun with too much pressure.

Maybe you beat up the buffer tube, but I run JP Rifles captured spring, and they offer a kit so you can tension up.

In any regard, it’s moot, as I don’t reload to “run hot”. I’m more focused on sub-sonic loads to “run quiet”. But that’s me.


Hah, I love that gif. I’d love it more if he rotated to a hidden set of weapons. Right tool for the right job!


As far as I can tell, an H2 weight should be sufficient. I usually run JP Rifles “silent captured spring” systems.

When I designed my first 300BLK, I was worried about supers and subs, and looked at adjustable blocks, but it occurred to me that a beefier tension spring should clear things up, so I went up in tension untill a low velocity (950 fps) factory load would just lock back on empty mag reliably.

When I shoot subs, it ejects as if under-gassed. When I add the silencer, it ejects at the low end of the sweet range.

When I run supers, it ejects as if slightly over-gassed, but I never have issues. I frequently alternate subs and supers, because it brings everyone to my lane to see “what in the hell is this guy shooting”, and because it’s fun.

So quiet, so smooth to shoot silenced subs, and felt recoil is absolutely minimal. No cheese grater sound - just the action of the bolt.


I don’t know if I buy into the “over-stable bullet” theory. I’ve seen stability issues with subsonics and silencers that have asymmetrical baffle stacks that settle down over distance, but I believe higher spin instability and “spin drift” is a myth. I just haven’t seen any hard data on either that couldn’t be accounted for by untested variables. It also tends to defy Newtonian motion physics, and since doing those calcs is how I earn my living, I’d have to get a solid explanation of why this seems to be. My mind is open, but I’d need to see the data.

If stability is related to length, then only from the BC angle of the bullet design, which is why rifle rounds have higher BC than pistol rounds.

I mostly run 220 gr Lapuas, but I have some 240 gr, and I’ve seen load charts up to 260 gr, but I can’t find those commercially and have heard you must hand cast at that weight.

I have no intention to use an adjustable block. I don’t expect it to be a problem, as I’ll tune the gun with the buffer spring. 308 Win is a new adventure for me, but so was 300BLK and the front-end research I put into that paid off. So, we’ll see.


Fair. I’m not a distance guy. I’m a “will this punch through stuff” guy.

My 300BLK guns should pass through IIIA like you aren’t wearing it. If I’ve done my homework, this one should punch through up-armored vehicles like they were Priuses.


Exactly so. My stuff is about running quiet while still hitting hard. Yes, I’m 3x slower than a 223, but I’m 5x heavier. More energy at lower speeds at close quarters.

Also, do you have that 300 gr load data?


I love them on large frame builds, for several reasons. Large frame “Sweet Spot” is lot tighter then their small frame cousins, not even in the same ballpark. I know it’s possible to build a large frame with out that will shoot sub and super, can or no, but a good AGB sure makes the process easier.

Must be time to re-up my meds, don’t see any 300 now. Must have been looking at 230 gr.
Edit: both Barns and Lee have 250 gr data, can’t find anything published heavier then that.