5.56 vs 6.5 Grendel, velocity, and energy debate!


I would like to hear everyone’s opinion on running 5.56 against 6.5 Grendel.

I have a few dilemmas

The grendal has a bullet nearly twice the weight, uses about 3 grains more powder and has about the same muzzle velocity. The 5.56 is a good out to 500 or so yards where the Grendal is out to 1000 yards. The Grendal is simply too much for inside 200-300 yards. They each have their place, but very little over lap.


Accurate as always TR. my questions are drawn from the fact that the military adopted the 10.3” barrel for the MK18 and they noticed that the rifle performed much better with the 77gr OTM round.
So I started to ponder what could fit that size (in a standard AR-15 lower) and be a better round (heavier) and still have a midrange accurate cartridge, And be affordable.
Well you can find 6.5 Grendel for about .26 cents a round.
In a 12” barrel let’s say the velocity is at ~2,200 FPS. With a 100gr projectile.
To me that would fit a lot of different criteria in my opinion.


Have you considered the 300 blackout? It’s a good heavy round, and tends to work well in shorter barrels, also has sonic and sub sonic options.


300bo is a no for me. It doesn’t beat 6.5 Grendel in price or velocity especially.
There is an agreement to be made for 300bo is a short barrel and suppressed.


OK, I went down and took a picture of a .223, a .300 blackout, and a 6.5 Grendal side by side. IMO, and this is only MY opinion. The Grendal makes for a poor choice on close to intermediate range. Around here Grendal is about $25 for a box of 20.

I personally feel the Grendal doesn’t shine until it’s in a 20" or greater barrel. I’m not sure how the bullet would react to a shorter barrel. It could start to tumble, I just don’t know. I’ll look around a bit, but most barrels tend to be longer if I remember right.


Thank you for taking your time on researching this question.
P.S. nice loader under the ammo!


I did a little quick looking, most are 18" to 22" lengths. I did however find a 12.5" barrel. Now you have me intrigued. Being a shorter barrel you would likely lose about 200-300fps


Yep, the @Podavach_Loaders work really well.


6.5 Grendel 2200-2300 FPS with a 12” barrel pending weight of bullet.


Grendel is a better round overall, logistics ftw though.



Sounds about right, 2700-2800 is about what they do. I’ve seen load data on 90gr bullets in the area of 3900fps. I need a set of dies to start reloading. Also need a set of 300 blackouts.


This one is almost half the price.



How does the 6.8 SPC/2 stack up to the Grendel?


From what I have seen 6.5 Grendel in a 10” is roughly 2,100 FPS. Now just add 100FPS for each added inch of barrel.


Good question. Depends on what you want to do, but I do know that Grendel can go supersonic out to ~1,200 yards. 6.8spc as far as I know can’t do that. I think it goes subsonic at 900-1,000 yards- pending barrel length and bullet weight


Both are the same grain, however the SPC is a bit slower so therefore has less energy on target. The Grendal is a longer narrow bullet while the SPC is a bit wider but shorter.


I haven’t found this formula to be very accurate. I find 50-75 fps per inch of barrel. However, other factors need to be considered. Shooting a round made for a 20" barrel from a 12" barrel will result in a greater loss of velocity because the powder burns too slow and you get a fireball. Now shoot a round from a 20" barrel that was loaded for a 12" barrel and again, you lose velocity because all the powder is burned up in the first 12" of barrel.


Makes sense, what about .224 Valkyrie?