18" or 20" for SPR?

[Headshot]

My little brother is building me a 6.5 Grendel upper for SPR usage. He and I are waffling back and forth on which barrel length to finalize on, so I figured that the tribe here might be able to give a few reasons for both, so my ears are open...ok, my eyes since this is a forum...lol.

[Paul Groth]

The 18" barrel will be more compact and handle better. It depends on how far you are trying to shoot with an 18" barrel you on average losing about 120fps vs a 20" barrel. Your velocities with a 123gr bullet will still average about 2460 fps. If you step up to a heavier bullet the velocity loss will be much less. Here is a very good article about velocities out of different barrel lengths.

https://www.jprifles.com/document_pd...ELS%20_129.pdf

[Yondering]

The truth is it doesn't matter that much; you choose the compromise you want. Do you prefer a more compact rifle? Get a shorter barrel. More reach? Get a longer barrel. There is no "right" length unless you're just wanting to copy someone else's rifle.

Estimations of how fast your barrel will run or how much faster a 20" is than an 18" are purely guesses, especially if you're comparing different manufacturers. The article Paul linked is a good example of that, with one 20" barrel being about 80 fps faster than the other with the same ammo, the 22" barrel being slower than one of the 20", and the 18" running almost the same speed as the 14.5". Obviously making a comparison from those single samples would be misleading at best, but it does illustrate that a lot more goes into velocity than just barrel length. In that article the 18" barrel was evidently a very slow barrel, but in general, apples to apples, there isn't that much difference in 18" and 20" speeds with the Grendel. I'm guessing Paul's estimate is a typo, you should be in the neighborhood of 2600-2650 or a little more with either barrel length, and not more than 50 fps between the two if you're comparing the same manufacturer.

Another thing to point out about the 6.5 Grendel is that it doesn't gain all that much with longer barrels compared to some other cartridges; I see about 2300-2350 with my 12.5" barrel and only 2600-2650 with 20", so you don't lose as much by going with the shorter barrel in this cartridge.
It wasn't all that long ago that conventional "wisdom" was that you needed a long barrel to make the Grendel effective, but this has been proven false. If you really want more range though, go with the 6mm version - the 6mm ARC. It's also effective in short barrels, but really stretches the range capabilities of the AR with longer barrels.

[Paul Groth]

It wasnt a typo i was giving an average from reloading books i have using same powder, same powder, same brass with the same barrel manufacturer. I even specified it was an average not exact numbers.

[Yondering]

It wasnt a typo i was giving an average from reloading books i have using same powder, same powder, same brass with the same barrel manufacturer. I even specified it was an average not exact numbers.

OK, but you're about 200 fps low, as that article you linked shows using their numbers for factory Hornady 123 A-max (if you recognize that their 18" was a very slow barrel). Average numbers from load data don't mean much if they're not from the best powders, because they give up a lot of velocity.

[sloughfoot]

There is a lot more to being a rifleman than being part of a stack kicking in doors. I have many uppers. Some short, some as long as 24 inches....I am 70. I can't imagine being part of a stack anymore. I have done it..The 20 inch was not a detriment. FWIW

[Dorkface]

Kinda sounds like the right answer is buy the highest quality match barrel you can in either length.

[Yondering]

Kinda sounds like the right answer is buy the highest quality match barrel you can in either length.

This!
Especially now with iffy quality control on cheaper stuff, and lower availabilty of good stuff.

[Redbug]

I might add...using the cheaper 100 grain Wolf steel case...the ballistics and drop are almost the same as the 123 grain Hornady stuff out to 200 yds. (Zero at 200, and at 300 yds only about 1 inch lower than the 123 grain brass). Enjoy that Wolf stuff for training/plinking and saving a dollar.

[LawDog]

If you haven't been through it already, Yondering posted some good info recently on a different question that I had. Some of it may help answer this question, too. Here:
http://www.warriortalk.com/showthrea...e-Longest-14-5