77gr SMK velocity difference between 16" and 18" barrel - Larue Stealth upper

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Have the 16" Stealth but wonder if I should upgrade to the 18" for a little more velocity. I read every thread on this subject in the last 10 years and still am not totally sure. I understand the velocity loss between 20" and 18" is minimal but a little sharper between 18" and 16", not to mention 14.7". 100fps?

FWIW, The 16" Stealth upper mates really well with ACOG TA11J-308G and MK262, the 300 meter mark is right on the money, it matches the 168-grain trajectory. How much would MOA rise with a 18" barrel?

[markm]

Negligible and not worth it.

1. You can check your POI and know it if it's critical for target shooting or competition.... and,

2. If you're talking about slaying bodies when our civilization collapses.... no one is lasering every enemy, every shot. You're going to make an experienced estimation on the fly and hold accordingly.

[Onyx Z]

Has the internet even been around 10 years?

https://www.m4carbine.net/showthread.php?80882-Battle-for-light-precision-supremacy-The-Recce-Rifle-Vs-The-SPR

There's really no need for 18" over 16". You're talking <100fps difference. You already have a 16", so I'd just roll with it. But it sounds like you really want an 18"er if you are still unsure after all this time.

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Thanks for sharing that thread. Some links are dead but the info is valuable.


This is a good question, particularly in light of newer loadings, more portable rifles and improved optics.

Take a look at the ballistics table below using MK262 round in 16" vs 18" BBL. The MVs were obtained using chrono data from the Hide and entered into JB Ballistics. Rock's barrels may differ from this, but probably not appreciably so.

At 500 yards the delta in energy is only 34 ft lbs, decreasing to 6 ft lbs at 1000y. The bullet goes subsonic right at 800y in the 16" and 830y in the 18" (not shown in the table). There's obvioulsy more drop from the 16", but nothing a good optic and shooter couldn't overcome. In effect, they're very damn close.

Given the above, I'd easily go with the lighter 16" Reece, but FWIW, I wouldn't feel comfortable trying to take down a BG with < 500 ft lbs of energy at 500+ yds. Then again, I'm not a sniper ;)

EDIT ABOVE- forgot to mention that the ballistics data were derived at sea level, 59 degrees, 29.92 pressure, yada yada. Speed of sound, trajectory, etc will vary with changes in pressure, temp and altitude.

[justin_247]

Have the 16" Stealth but wonder if I should upgrade to the 18" for a little more velocity. I read every thread on this subject in the last 10 years and still am not totally sure. I understand the velocity loss between 20" and 18" is minimal but a little sharper between 18" and 16", not to mention 14.7". 100fps?

FWIW, The 16" Stealth upper mates really well with ACOG TA11J-308G and MK262, the 300 meter mark is right on the money, it matches the 168-grain trajectory. How much would MOA rise with a 18" barrel?

Since you already have the 16" Stealth upper, I would say that the "upgrade" really is not worth it. If you did not already own a precision rifle upper, I'd say go with the 18", but since you already do, the costs do not justify the very, very minor improvements in velocity that you'll get.

What length is your rail? If you're looking for an "upgrade", you can cut a lot of weight off your upper by installing a 13" BCM KMR - between 4 and 9 oz., actually. It would make your upper a lot more enjoyable to work with.

[strambo]

I wouldn't go with an 18" over a 16" from the start just because the velocity increase is so small. No way I'd pay extra to swap a barrel. Shoot it out, then get an 18" if you want since you'll need a new barrel anyway!