I have all the parts to build a 16” 6.5g, but I’ve decided I don’t want to mess with hand loading for it so I’m half considering selling them to do a 16” 6.8 instead.

Browse factory ammo and you’ll find much more 6.8 hunting ammo available than 6.5g.

Target/steel shooting or if you handload I think the Grendel is cooler cartridge with more bullet variety, but there’s no question the 6.8 is better for someone who wants to build an upper, buy a case of ammo and go kill pigs...

We certainly all have our way of qualifying our cartridges as best. For me I like bastard cartridges and was selecting between the 338-06 and 35 Whelen. With the same weight bullet the 35 is flatter and faster out of the gate giving it better #s on KE. What is not readily clear to all is that the .338 has better sectional density and will out penetrate the 35 from the start and after 200 the 35 falls down. For me I chose the 338-06. Wonder what ballistic gellitan would show between the 6.8 and 6.5g. I’m thinking the 6.5 would pull ahead far before the 200 yards people are talking about here. This is only conjecture on my part and only opening the subject up for thought before making a purchase based on velocity and KE alone.

Same case same weight powder same weight bullet the bigger bore will always have better #s on paper. Yes I know the 6.5g and 6.8 are different cases but has anyone here compared them side by side? Ok, I’m done rattling, heavy pain meds for bad tooth so I’ll apologize now.

Inside of 300 yards, which is the most effective hunting range for both, no animal will know the difference. You stretch either out past 300 and their killing power will drop off quickly. Neither is a long range hunting round.

If you have a 308 bolt then that is your dedicated stand/deer rifle. The 556 AR is really only good for varmints and coyotes so go get you an upper and switch that 556 in to something good. Your 3 best choices are 7.62X39 or 6.8 or 6.5. just like all the THF'ers are saying. Forget the 300 BO. That is for little girls!! LOL It doesnt do well past 100 yards where the other 3 do just fine past thaT RANGE.

I use a 16" 308 AR with a 3x9 scope. 20 round mags usually. Killed 8 in one sounder, before they got out of sight. Using Chad's 165 gr Sierra Gameking loads.

Interestingly Hornady American Gunner runs a 110 grain bullet at 2570 fps and the American Gunner version of 6.5 Grendel ammo lists 2580 fps with a 123 grain bullet. As for on the shelf ammo the 6.8 is usually represented with FMJ ammo, hunting ammo not so much. Soooo I will look into some other 6.8 ammo to see if I can find some absolute proof of a massive energy advantage.

Hunting ammo is everywhere for 6.8

FMJ is not

Hornady uses a 24" test barrel for their Grendel velocities and a 16" barrel for their 6.8 velocities. That Grendel ammo would be lucky to see 2300 fps in a 16" barrel. THAT is the advantage of a 6.8. MORE energy from a SHORT barrel.

Which 6.8 barrel do we think is the way to go: Wilson combat or ARP ?

I may pick up a 16” in one or the other, or maybe a 14.7” ARP and have a TBAC brake pinned and welded

Those are both great barrels. I would personally choose the ARP. I've had their Grendel and 6.8 barrels and they've all shot as good as I could ask from an AR barrel. I'm sure you'd hear the same thing about Wilson Combat and other manufacturers too.

Ahh, I see now. You are falling for something that has certainly confused many people when comparing cartridges. It is a common mistake to look at ballistics data on an ammo manufacturer's website and fail to account for barrel length, which obviously makes a big difference. When testing for muzzle velocity/kinetic energy of a given ammunition offering, most manufacturers use a 20 - 24" test barrel for 6.5 Grendel and a 16" barrel for the 6.8. That means that the 6.5 G numbers are based on 4 - 8" more barrel than the 6.8.

In the case of the Hornady American Gunner you chose for your comparison, the Grendel load is only 10 FPS faster than the 6.8 despite a full 8" more barrel length. If you compare both rounds using a 16" barrel (The most popular barrel length for AR-15s) you will find the 6.5 to be significantly slower.

Now, I would argue that your comparison is not a fair one, since the 6.8 load you chose has a 110 grain projectile, while the 6.5 load uses a 123 grain projectile. This gives an unfair "advantage" to the 6.8 in this comparison because the 6.8 projectile is roughly 12% lighter than the 6.5 G projectile (lighter bullets are faster than heavier bullets all else equal).

For a more fair comparison, let's look at a 100-grain Nosler at max load out of a 16" barrel in both the 6.5 Grendel and 6.8 SPC. You are looking at roughly 2600 FPS at the muzzle for the 6.5 Grendel (Bill Alexander's own numbers), and roughly 2950 FPS for the 6.8 SPC.

I will say it again. When comparing the 6.8 SPC to the 6.5 Grendel with the SAME BARREL LENGTH, either with apples to apples factory ammo or max loaded handloads, the 6.8 is faster and carries more energy at typical hunting ranges. This is a fact. I hope that clears things up for you!

ARP 16” Scout Profile with 120 sst’s

Out of curiosity how much faster is a 6.8 when they’re both 24”

Edit: yes I get that the whole benefit is the shorter barrel. I want mine as short as possible.

A 6.8 SPC doesn't benefit much from a longer barrel because it uses a fast powder and gets a complete burn in the short barrel, similar to a 300blk. A 6.8 is optimized for a 16" barrel.

The 6.8 gains 20 - 30(ish) FPS per additional inch of barrel. This obviously differs barrel to barrel and powder to powder. There is a law of diminishing returns effect as you get longer and longer barrels. I would guess you would see a gain of roughly 200 FPS in a 24" 6.8 barrel vs a 16". That is a ballpark estimate, though. You would need to know the specific barrel, powder, projectile, etc. to really start to get an accurate number.

Strictly for pigs. My good old 1943 Springfield Armory M1 Garand!

When driving around in a Ranger we just use 00 Buckshot.

Whatever weapon I currently have on me is what I will use including the front bumper of the side x side.

According to guys that have done extensive velocity tests on various 6.8 forums, you'll lose 20ish fps/inch from 12-16" and 10ish fps/inch from 16-24" barrels. I researched a long time and spent a few thousand dollars on various AR calibers before I realized that I want a 16" (or shorter) barrel, and I don't want to handload for a round that I'll use to dump 20+ pieces of brass in a corn field at 2:00 in the morning. That's why I have designated a 16" 6.8 SPC II as my nighttime pig gun.

I am very familiar with the guys over at 68forums, and I certainly believe their results.

I will say, however, that the ARP website directly says that there is a 100 FPS increase with a 20” barrel over a 16” barrel. That comes to 25 FPS gain per inch going from 16” to 20” comparing two ARP barrels, which are known to be as optimized as 6.8 barrels get. If you can’t trust H’s word for 6.8 info, I don’t know who you can trust! My own personal experience has been similar, which is why I suggested 20-30 FPS per inch.

Here’s the link to the ARP 6.8 barrel page which states the 100 FPS increase. You can find it by scrolling down to the 20” barrel and looking at the “barrel length” details below.

https://ar15performance.com/6_8_barrels

ak w/ red dot.