Barrel Length Questions

[FREEDOMMMM!!_and_Trucks]

Hey guys, I'm sure this has been hashed out multiple times, so I'm sorry to bring it up again but this is my first grendel so I'm a little in the dark. I'm getting an Atheris match build and I'm not sure what barrel length to get. I want it for the tactical DMR role, as neither my duty rifle or my CQB are set up to go the range. I'm not interested it making 1000 yard shots, but I want something that can drop things peeking behind cover in the 300-500 yard range. From what i've seen, there's not a huge velocity bump going up to a 20" from a 16." My question is, are there significant gains in accuracy and/or velocity to be made from the extra 4" that would offset having to lug it around? In my mind, since I'm not trying to push the range as far as I can, it doesn't seem like I need that extra velocity but maybe I'm missing something. Thanks for the thoughts!

[A5BLASTER]

Velocity difference will be 80 to 100 fps. Barrel length has lil to do with accuracy. In fact shorter barrels with the same profile of a longer barrel tend to be more accurate because of less barrel whip.

For the ranges you stated 16 inch will be more then enough to accomplish your goals.

[Bigs28]

https://www.65grendel.com/forum/showthread.php?14389-LaRue-6-5-Grendel-Rifles

Just for reference. Not sure if your wanting to hunt coyote or elk at 300-500 but.......

[FREEDOMMMM!!_and_Trucks]

Velocity difference will be 80 to 100 fps. Barrel length has lil to do with accuracy. In fact shorter barrels with the same profile of a longer barrel tend to be more accurate because of less barrel whip.

For the ranges you stated 16 inch will be more then enough to accomplish your goals.

thats what I figured but I thought I'd ask to make sure. Thanks!

[VASCAR2]

Take a look at this thread I posted velocities from several barrel lenghts.

https://www.65grendel.com/forum/showthread.php?23754-I-m-brand-new-to-AR-s

[lazyengineer]

So there are a lot of ways to assess this - in the end it comes to buy what makes ya smile! But if you do want to get analytical on it; here's my criteria for assessment.

1) range to 1000 ft-lb energy (for standard hunting ranges; some say 800 ft-lb is OK). This is your distance of optimal/ethical terminal effectiveness (depending on who you talk to at least)
2) range to transonic flight (~around 1250 fps or so can be when various subsonic destabilizing eddies can start to form) Also look at range to subsonic, which is around 1100 fps.
3) what is the purpose of this gun, and the appropriate balance of weight to performance? Usually I want my gear to be cross-purpose capable.

Two tools to help you with that
1) Any ballistics app (I prefer Strelok - Pro); run it to give you velocity and energy in 10 yard increments out to 1200 yards.
2) Gordons reloading tool, which will give you muzzle velocity of any particular load as a function of barrel length. i.e. it gives a travel curve down the barrel showing you the velocity of the bullet at any point. Just look up almost any reloading recipie for your particular bullet, and put it in there; then adjust the powder charge until the exit velocity matches up with whatever is published for whatever their published BBL length is, and you have it. Use the velocity at 12, 14.5, 16, 18, 20, 22 for your math in Step 1 above.


If you do comparisons based on those first 2 criteria, you see and learn quite a lot. For example, criteria 1 ( @800 ft-lbs for varmints... and such), shows that BBL length in 5.56 makes a tremendous difference in relative "terminal" range. And shows that 16" actually has almost double the terminal range of a 14.5" (depending), and 20" can be double that. In 5.56, BBL length can matter. If you read BlackHawkDown, they complain about how ineffective the 14.5" was at any distance beyond shooting across the street. The original 20" spec of a skinny light 20" M16, is a much better spec than it gets appreciation for today - I think at least.

For Grendel, the math on those two gets interesting. Even little 12" can impress; with 1000 ft-lb energy at the more typical <200 yard hunting ranges. And if you are at high altitude, even a 12" can be supersonic (i.e. still relatively accurate) out to 1,000 yards (depeneding). Kind of incredible. While Grendel was original developed with long barrels in mind (it seems), it really shines in the shorter barrel configuration as well. FWIW, I'm working on a build for a 14.5" skinny barrel with a pin and weld brake, to be that ultimate optimization of size and weight to distance and performance (without SBR/pistol reliance), for this reason. Obviously that won't be a 1000 yard gong-banger, but it can be if I point it that way, as it'll still be supersonic at that distance.

I will say, you don't HAVE to go short, to be handy. One option also that folks seem to not appreciate is that a skinny profile longer barrel can have similar weight and balance(ish) to the common thick-countour shorter BBL; but giving you the advantage of that longer ballistics. (i.e. M16A1)

Also, BBL length advantages are most profound the shorter your start from. Going from 12" to 14.5", will in general have more benefit that going from 16" to 20". That's why I tend not to mess with 22" or longer barrels much, as the length does start to get unwealdy, for only so much advantage. Depends on the roll - if you want a bench-bipod-blaster, that goes from car to bench, get a nice 26" heavy barrel. But then, why did you even bother going Grendel and not just go Creedmoor, if you want to do that? To my eye, the entire point of Grendel is optimized performance in as small a package as you can get. If I want to hit really hard really far, and am willing to put on a few extra pounds to do it, Grendel isn't the route I'm going.



Just my opinion - run what brings ya joy; and it's OK to like stuff I don't like

[grayfox]

I think you should also factor in some "margin" to the "max" you want to go.
Ex: for bullets that open "down to" 1800, I mark my limit as ~2050-2100.
If I want a barrel to handle 500 yd, I look for one that can do 550 or 600, because of course that "thing" out there doesn't calibrate its distance to you at the exact distance you want it to be.

You should always give yourself a little room to bargain with.

Just a thought.

I have a 16-er but most times I reach for my 20". That's just me however.

[7mmtcu]

go 20 and be happy! in most situations you will never know the dif. between 16 and 20 but an extra 100 fps is nice to have as a reserve.

[JASmith]

This resource gets you velocities for changes in barrel length, charge weight, and bullet weight:

http://shootersnotes.com/velocities-and-pressures/velocity-estimator/

[Dt219]

Between my guns and friends guns, and yayhoos on the YouTube the avg I have come up with is roughly 25fps per inch. It almost always calculates out that way.