AR in 6.5 Grendel?

[melensdad]

I don't get the 6.8 Rem SPC either. It seems like a slightly better round than the current 223/5.56 but it really runs out of steam pretty quick and the overall cartridge length prevents using high ballistic coefficient bullets so basically its a short range round.

Originally Posted by indyjoe

Then build up a 6.5. I'm a newbie AR building, but comfortable with typical entry level gunsmithing. . . I'm willing to pay for good parts, if they actually add to reliability and accuracy, to a point.

Realize that its more than just good parts. Real accuracy comes from making sure those parts are trued up properly in addition to simply using good parts.

[melensdad]

I've been getting some questions about my 6.5 Grendel and figured I'd go back into my files and dig out a ballistic chart, this is one of several that I have, it is a pretty good guideline to compare several different Grendel rounds, but also to compare the Grendel to some other rounds. Some of what I wrote in PMs was based on my recollections and may not have been 100% accurate, this chart is better than my memory!!!

I couldn't figure out how to post up a PDF file so I converted it to JPG so it may not be as easy to read in this format but I hope this helps some of you with your rifle choices. Honestly I think that many of the current rounds are pretty darn good so choosing between them is really pretty much splitting hairs.

[zsm]

does anyone have a pic for comparison?

[indyjoe]

Originally Posted by zsm

does anyone have a pic for comparison?

Of the two rounds 6.8 and 6.5?

[melensdad]

Originally Posted by zsm

does anyone have a pic for comparison?

Here is an excellent photo (wish I had taken it) it shows why the 6.5 Grendel has such superior ballistics. The 6.5 rounds are long and sleek and the 6.8 rounds are fatter and stubbier.


Refer to the ballistic chart a couple posts above, you'll see that a 6.5 Grendel can push a 123 grain bullet faster than the 6.8 can push a 115 grain bullet. The Grendel's case is shorter and fatter and that allows for more efficient use of powder, it is also very inherently accurate as the case is very similar in proportions to bench rest competition cases.

Ballistically the Grendel rounds are very slick bullets, hovering one side or the other of .5 BC, some very comfortably reach .54. The 6.8 rounds run under .4 BC so they tend to run out of steam very quickly because their drag coefficient is simply not good enough to allow them to slice through the wind.

On ballistics alone, the 6.5 Grendel carries 500 Ft Lbs of Energy out 50% farther than the 6.8 Rem SPC despite the fact that at the muzzle the Rem has more velocity and more energy.

[indyjoe]

Originally Posted by melensdad

On ballistics alone, the 6.5 Grendel carries 500 Ft Lbs of Energy out 50% farther than the 6.8 Rem SPC despite the fact that at the muzzle the Rem has more velocity and more energy.

The other advantage is that they ARE slower in the barrel. Not only do your get more energy down range, but less barrel wear because that energy comes from ballistic coefficient, rather than brute force.

[melensdad]

Originally Posted by indyjoe

The other advantage is that they ARE slower in the barrel. Not only do your get more energy down range, but less barrel wear because that energy comes from ballistic coefficient, rather than brute force.

Well I will agree that there is no evidence that the 6.5 Grendel is hard on barrels, in fact it seems to be gentle on barrels. But that said, I'm not sure that the 6.8 is a barrel burner either, I suspect it is not.

The reality is that the 6.8 is better than the Grendel out to maybe 50 or 100 FEET, but get beyond that and the brick like shape of the thick shouldered 6.8 bullets slow them down and they have less energy and less velocity than the Grendel before you reach 100 yards. Honestly if I was in a close quarters battle with a bad guy (like INSIDE a house) then I'd probably want the fattest bullet I could find, and that would mean the 6.8 Rem would be a better choice. But by the time the bullet begins to fly out your front door and gets to the roadway in front of your house, the 6.5 Grendel is already showing itself as the better round.

Sadly neither is legal for deer in Indiana, but both would do a great job. For coyotes I'd much prefer the Grendel with its ability to reach out long ranges and if used with the correct bullets would do a great job of killing the dogs without destroying the pelts.