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Discussion Starter · #1 ·
When the S&W M&P Sport was 1st introduced it had a 1 to 7 twist and a 5 grove rifled barrel. I am looking for one like that but would like it in 20". I may not be looking in the right places but I can't find such a barrel. Any suggestions?....:) Thanks
 

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you could reach out to S&W or you could check with the various barrel manus out there for a 20" barrel with a 1:7 twist. Not sure how many grooves they have though. the next thing is to get the right profile to match your AR. you'll probably also have to change out the gas tube to accommodate the longer barrel.
 
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I've never understood the whole barrel twist thing. Could someone explain it?

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Barrels have lands and grooves to impart spin to the projectile. depending on the ratio, it denotes how fast the projectile will be spun by the rifling. a 1:7 means that it takes 7" to complete 1 rotation of the spiral. a 1:9 means it takes 9" to complete it's rotation. the higher the second number, the SLOWER the bullet spins. Heavier bullets tend to perform better with slower spins. Lighter bullets like faster spins.
 

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When the S&W M&P Sport was 1st introduced it had a 1 to 7 twist and a 5 grove rifled barrel. I am looking for one like that but would like it in 20". I may not be looking in the right places but I can't find such a barrel. Any suggestions?....:) Thanks
I have one of the first M&P Sports and while the barrel does have the 5R rifling, melonite, and it is a 1:8 twist. The 2nd version came with a 1:9, 6? groove barrel, and a non-melonite branded same type finish.
 

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I've never understood the whole barrel twist thing. Could someone explain it?

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The tighter the twist, the heavier the bullet you can use. the 1 in 7" was determined to be able to stabilize a 72 grain tracer bullet in sub zero temps. Colt recommended the 1 in 9 for barrel life and using the SS108/M855 bullet which is 62 grains.

National match shooters like 1 in 8" for the heavy match bullets between 68 and 72 grain.

The original twist that returned devastating wounds in the early days of Vietnam was 1 in 14". This twist just stabilized the bullet to give enough accuracy out to 300 yards. On impact it often tipped or tumbled. However, in arctic environment, the denser cold air cause instability and accuracy problems with the standard 55 grain and was changed to 1 in 12". This ruined the terminal ballistics in a tropical setting.

Today, the 1 in 7" over stabilizes the bullet causing shorter barrel life due to increased friction, and drills nice neat holes in the enemy that can be patched with a band-aid if nothing vital is hit.

The Marine Corp is looking at all copper hollow points. :devil:

Maloy
 

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Barrels have lands and grooves to impart spin to the projectile. depending on the ratio, it denotes how fast the projectile will be spun by the rifling. a 1:7 means that it takes 7" to complete 1 rotation of the spiral. a 1:9 means it takes 9" to complete it's rotation. the higher the second number, the SLOWER the bullet spins. Heavier bullets tend to perform better with slower spins. Lighter bullets like faster spins.
While "experts" vary quite a bit on the actual twist rate per bullet weight, that's the gist of it. Something to keep in mind is that the twist rate is really based on the bullet length and not the weight...but since nobody sells bullets by length, it makes for a handy rule of thumb. ;)How Barrel Twist Rate Affects Ammunition Choice

How to Pair Barrel Twist Rates with Bullets - Guns & Ammo

Twist Rate Stability Calculator | Berger Bullets
 

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When the S&W M&P Sport was 1st introduced it had a 1 to 7 twist and a 5 grove rifled barrel. I am looking for one like that but would like it in 20". I may not be looking in the right places but I can't find such a barrel. Any suggestions?....:) Thanks
I got my 18" 1:8 .223 Wylde barrel here:

http://www.primaryarms.com/BarrelLength+20"/MCategories+AR-15-Barrels

You will need a new rifle length gas tube as well, but everythinng else should be OK unless you have the D-Ring and drop-in handguard setup with A2 sight/Gas block setup. If that be the case, then it's time to freefloat your handguard too :)
 

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Discussion Starter · #12 ·
I have one of the first M&P Sports and while the barrel does have the 5R rifling, melonite, and it is a 1:8 twist. The 2nd version came with a 1:9, 6? groove barrel, and a non-melonite branded same type finish.
Thanks for the correction. I was trying to go by memory and that can be dangerous at my age...:)
 

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Yissnakk: "I got my 18" 1:8 .223 Wylde barrel here:

http://www.primaryarms.com/BarrelLen...+AR-15-Barrels

You will need a new rifle length gas tube as well, but everythinng else should be OK unless you have the D-Ring and drop-in handguard setup with A2 sight/Gas block setup. If that be the case, then it's time to freefloat your handguard too

This is the exact barrel specifications I would look to buy if I was building an AR.
 

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Discussion Starter · #16 ·
Ok. So maybe I start thinking about just building a AR the way I want it..:)? It's kind of like taking a stock motorcycle and customizing it. One thing leads to another..:). Thanks for all of the ideas and suggestions.
 

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Ok. So maybe I start thinking about just building a AR the way I want it..:)? It's kind of like taking a stock motorcycle and customizing it. One thing leads to another..:). Thanks for all of the ideas and suggestions.
If you start modifying one, you'll end up with a bunch of extra parts and start thinking that they'd work for a back-up AR...then you'll want to paint it odd colors....
 

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Ok. So maybe I start thinking about just building a AR the way I want it..:)? It's kind of like taking a stock motorcycle and customizing it. One thing leads to another..:). Thanks for all of the ideas and suggestions.
Funny a glocks can be the same way. I just recently drank the glock koolaid this year. The 23 is my first, then the 42 for my wife. I've got a G19 frame I'm going to modify, and a slide all ready to go on it.
 

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