Standard 5.56 vs Light-weight Contour Barrels

[HorizontalMike]

How many of you have shot and compared the standard Sport-II with the M&P15T barrels? I just picked up a 15T and while visually comparing the barrels, I found quite difference.

I decided on adding the MP-15T for long distance shooting, so I added a Vortex Viper PST Gen II 30mm Tube 1-6x 24mm. I kept my Sport-II with Iron Sights but added a Holosun 510C Reflex Sight for SD/HD.

I understand that:

• M&P15T has an 8:1 twist
• SportII has a twist of 9:1

Other than that, what are some others' experiences with the M&P15T Carbine?
Does the MP15T barrel dissipate heat better/worse?
Recoil?
Fun factor?
And ..?????

 

[Velle]

Sport II has a 9:1 twist.

 

[vonn]

Intended use is what I look at when comparing AR versions. You can pretty much configure one to meet any requirements you might have. Enjoy!

 

[S-W4EVER]

I definitely prefer lightweight barrels on my AR's (and two of my favorite AR's are my Colt AR6520 & AR6720 carbines). I really don't see the need for a heavier barrel on a semi-auto carbine.

This being said, my S&W M&P15A is my truck gun.

 

[HorizontalMike]

Sport II has a 9:1 twist.

Got it! Thanks! Must have had a brain fart...

 

[murphydog]

I think he meant to write 1:9 twist - 9 turns in 1 inch would be a pretty fast spin.

 

[WR Moore]

Mike, when you ask about heat dissipation, does your 15T have the HBAR/Designated Marksman profile barrel? That is, is the section under the hand guard close to an inch in diameter?

The primary advantages to the heavy profile barrel are that the heavier barrel takes longer to heat up and the heavier cross section reduces vibration effects. The greater surface area should/might dissipate heat better than a pencil barrel. The extra weight up front also helps stabilize your hold on target.

The 1-9 twist will stabilize up to the Hornady 75 gr HPBT (not the A-max). The furthest I've taken that bullet is 600 yards, it has a wind drift very like a .308 match bullet I've used for decades.

 

[Velle]

I think he meant to write 1:9 twist - 9 turns in 1 inch would be a pretty fast spin.

Yeah I did.

 

[HorizontalMike]

Mike, when you ask about heat dissipation, does your 15T have the HBAR/Designated Marksman profile barrel? That is, is the section under the hand guard close to an inch in diameter?

The primary advantages to the heavy profile barrel are that the heavier barrel takes longer to heat up and the heavier cross section reduces vibration effects. The greater surface area should/might dissipate heat better than a pencil barrel. The extra weight up front also helps stabilize your hold on target.

The 1-9 twist will stabilize up to the Hornady 75 gr HPBT (not the A-max). The furthest I've taken that bullet is 600 yards, it has a wind drift very like a .308 match bullet I've used for decades.

Hey! You are spot on! This is the type of stuff I am seeking. ONLY had this M&P15T ~2days, AND AT LEAST WE SKIPPED THE TORNADOES/STORMS, of the past couple of days...

Really interested in the shooting dynamics with a 1-6X scope, "without" doing a bare metal "Iron Sights" sighting. Well honestly, I look forward to it but would appreciate some info of what to look for...

 

[germansheperd]

A 1:9 is probably the best all around seeing as how most people shoot 55 and 62 gr bullets.
1:8 and 1:7 twist are better for your 69-77gr .223 and 5.56.

 

[rockquarry]

A 1:9 is probably the best all around seeing as how most people shoot 55 and 62 gr bullets.
1:8 and 1:7 twist are better for your 69-77gr .223 and 5.56.

No firm rules on any of this, but what's been mentioned are good rough guidelines. The only ARs I have are Colts with 1 in 7" barrels. Most of my shooting has been with the 65 Sierra GK and 69 Sierra MK as well as the Hornady 68 and 75 Match bullets. All shoot very well, though the Sierras are consistently a bit more accurate than the Hornadys. Nevertheless, all good bullets.

Surprisingly, to me anyway, these barrels will shoot 55 grain bullets very well, as accurately as a 1 in 12" twist barrel. My CZ bolt-action has a 1 in 9" barrel; can't really see any significant difference between it and the Colt 1 in 7" barrels. Try all the bullets and weights you can. Some might not follow the rules and surprise you with how well (or poorly) they shoot.

 

[WR Moore]

We had a bunch of Colt HBARs with 1-7 twist. After 20-30 rounds of soft point 55 gr, the bullets would start coming apart enroute to the targets. We sent a couple sample rifles and ammo to Federal and they suggested a bullet with a heavier/thicker jacket. They also said they'd never seen that before. (?????) No issues with FMJ.

American Rifleman did a test some years back and 1-9 delivered superior accuracy (than 1-7) up to about 75 gr, depending upon bullet length. My 1-9 bolt gun is sub half minute with the 69 gr SMK & 75 gr Hornady HPBT.