Mk262 - 18” vs 20”

[JediGuy]

It seemed like the Mk262 was designed to be used with the SPR.

Is there benefit gained from a 20” barrel with this ammunition, or was the round designed to reach peak velocity potential with the 18” barrel?

[markm]

It seemed like the Mk262 was designed to be used with the SPR.

Is there benefit gained from a 20” barrel with this ammunition, or was the round designed to reach peak velocity potential with the 18” barrel?

There will be a velocity increase when going from 18 to 20" with every .223/5.56 round I can think of. If we had an 18" barrel, I'd chrono the difference this weekend.

[miyagi]

The difference in MV between a 18" and 20" barrel is pretty subtle. Typically in the 10-50 fps range if I remeber right. The Mk12 SPR is a 18" variant, and is used regularly for engagements in the 400-600 yard range, if that helps ya any. The only reason I'd own a 20" is because I'm kind of fond of the M16A2/A4. If I were building my own AR for any other reason though, I'd go with the 18".

[redpillregret]

I chrono’ed the difference between 16”, 18”, and 20” barrels with MK262. 16”-18” gained 20 FPS. 18” to 20” gained 15 FPS.


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[JediGuy]

With those very slight velocity increases, is that due to the powder mostly burning sooner?

The reason I ask is sourcing for a SPR-ish rifle. I use Mk262 in my 12.5”, and I plan to use the same for this rifle. I have my “fun guns” zeroed with cheaper stuff. So, an extra two inches wouldn’t bother me (that’s...), but if it isn’t going to have a benefit, I’d go 18”.

[Fatorangecat]

I have an 18" setup and the 20fps doesnt do much.

[ABNAK]

I have an 18" setup and the 20fps doesnt do much.

Hell, for that matter (according to the info redpillregret posted) the ~ 35fps total from a 16" to a 20" is rather negligible too. A well-balanced 16" barrel should be just about as good, "well-balanced" NOT meaning an A2 profile!

[redpillregret]

Hell, for that matter (according to the info redpillregret posted) the ~ 35fps total from a 16" to a 20" is rather negligible too. A well-balanced 16" barrel should be just about as good, "well-balanced" NOT meaning an A2 profile!

It made me give up my 18”. All barrels have variance but that was my results with two BCM SS barrels and a Colt 20”. I’ve heard of as much as a 50fps jump from 18”-20”...still not worth it for me. I’ll stick with 16”.


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[longshot2000]

There is a big difference between 18" and 20" barrels that is not widely known. Yes, you will get a little improvement in velocity from 18" to 20," but more importantly, the pressure and dwell time on a 5.56 NATO round is tuned for various pressures, gas port sizes and locations, and distances (most importantly) from gas port to muzzle.

20" with a rifle length gas port is optimal. Works well for many, many years. The 18" presents a pressure imbalance that results in premature gas port erosion (read: increase the gas port size and gas flow over time). We are talking about after a few thousand rounds, so it may or may not affect everyone, but this is well documented.

For the Navy's SPR, which become the Mk12 sniper rifle in 5.56mm had/has a 18" Douglas SS barrel. For some reason, the Douglas barrel has performed much better than other blanks in 18." Better than some other more well thought of top-notch barrel blank makers. It must be in the steel that Douglas uses.

Thus, for weapons designers that we work with, and customers, I recommend a 20" barrel over 18," all other things being equal. For those who want an 18" barrel, I recommend using a Douglas blank, unless your overall shooting will be of relatively smaller numbers, as the erosion will not take place right away. It is a high-volume shooting issue. And, keep in-mind, that a barrel is a normal wear item, like brake pads and rotors on a car, so you can always just replace the barrel when wear starts to show.

[redpillregret]

There is a big difference between 18" and 20" barrels that is not widely known. Yes, you will get a little improvement in velocity from 18" to 20," but more importantly, the pressure and dwell time on a 5.56 NATO round is tuned for various pressures, gas port sizes and locations, and distances (most importantly) from gas port to muzzle.

20" with a rifle length gas port is optimal. Works well for many, many years. The 18" presents a pressure imbalance that results in premature gas port erosion (read: increase the gas port size and gas flow over time). We are talking about after a few thousand rounds, so it may or may not affect everyone, but this is well documented.

For the Navy's SPR, which become the Mk12 sniper rifle in 5.56mm had/has a 18" Douglas SS barrel. For some reason, the Douglas barrel has performed much better than other blanks in 18." Better than some other more well thought of top-notch barrel blank makers. It must be in the steel that Douglas uses.

Thus, for weapons designers that we work with, and customers, I recommend a 20" barrel over 18," all other things being equal. For those who want an 18" barrel, I recommend using a Douglas blank, unless your overall shooting will be of relatively smaller numbers, as the erosion will not take place right away. It is a high-volume shooting issue. And, keep in-mind, that a barrel is a normal wear item, like brake pads and rotors on a car, so you can always just replace the barrel when wear starts to show.

I don’t believe Douglas uses any formula for steel different than other manufacturers. Wasn’t the MK262 round designed for the MK12 specifically?


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