6.8SPC AR15s

[rbernie]

There have been a few threads lately about 6.8SPC, so I thought that I'd post today's range experiences with my two latest builds.

First up is my 'social uses' carbine. It's got a 16" KoTonics barrel on a CMT flattop upper, a GT lower with a CMT lower parts kit, Ace stock, Magpul MAID, YHM front/Mangonel rear BUIS, and a Aimpoint CompM2. Prior to today, it'd only been shot a few times with factory loads to get the Aimpoint on paper.

I shot the carbine offhand at 50 yards and off a rest at 100 yards. Group sizes were right around 3" at 100 yards, with one group being a bit bigger when I really rushed things (five shots in five seconds).

Next up is my hunting rifle. It's got similar componentry as the carbine, only with a 18" KoTonics barrel and a Sightron SII 2.5x-8x on Leupold Rifleman rings/bases. It also has a M1S float tube and a A1 stock with a SierraReseach buttplate. It's also seen less than 20 rounds prior to today, also with factory Remington ammo.

I loaded up some Hornady 115gr HP bullets in SilverState brass (CCI primers) with 27gr H322, and this is what I get shooting five shots in relatively rapid succession:

This is a pretty hot load, and I may back it down a tad. The vertical stringing is probably the load being a little hot. It may also be me just being ham-fisted with the USGI trigger; I may drop a McCormick or a Jard in here before hunting season.

All in all, I'm really impressed with the 6.8SPC and these two rifles. I've been hunting for about five years now with a 7.62x39 AR15 and I've been really happy with the results. I'm expecting the 6.8SPC to give me the same terminal performance inside of 200 yards but to stretch my MPBR another 50-75 yards or so.

That works for me.

 

[strambo]

Just a hair over 1MOA, not bad. Tweaking the load and a better trigger should do it. Good looking rifles, thanks for the report.

 

[RockyMtnTactical]

What is the differences in ballistics with a 6.8 from a 16" and a 18"?

 

[rbernie]

I don't know - I haven't chrono'ed the load yet. I would expect an extra 50-75fps out of the 18" tube; nothing spectacular but a marginally useful boost.

The 16" tube is chrome-lined and the 18" is not, by the way.

I still-hunt and the 18" hunting rifle is set up for walkin' around and offhand use. A 16" tube would have also have been more than fine for that, but I got the 18" tube because I wanted a non-chrome-lined barrel for the hunting rifle (to improve it's potential accuracy). If I get any additional velocity, it's all gravy.

I have a 20" tube on order from DPMS that may show up soon. I wanted a 24", but DPMS had such a good deal on the 20" that I couldn't resist. If it shows a decent velocity gain over the 18" tube, I may swap it into the hunting rifle and set up a DMR-type rig with the 18" tube or sell the 18" tube and buy a 24" long range tube for a third rifle.

 

[GunTech]

How do you rate Kotonics vs White Oak bbls? I am looking at rebarreling my daughter's AR to 6.8 for hunting. WO 18" bbl with matching bolt runs $350.

 

[GunTech]

What is the differences in ballistics with a 6.8 from a 16" and a 18"?

Running some loads through QuickLoad, it looks like 18 inches gets you about 60fps more than 16.

rbernie nailed it.

 

[rbernie]

How do you rate Kotonics vs White Oak bbls?

I got two of the $125 blow-outs from KoTonics. They're fine barrels but they had a reputation for being a bit 'slow'. KoTonics redesigned their barrels (I believe that they have Shaw custom-make them) and their newer barrels have a different land/groove count and a slightly slower twist rate to try and improve velocity a bit. I would expect those barrels to be on par with a WOA, altho I must admit I have no idea who makes barrels for WOA.

Last I checked, a KoTonics barrel was around $225 and the bolt was another $70.