Pros and Cons of Features- AR styles

[jofreder]

I just purchased a Double Star (5.56) and have been looking around at other AR type rifles and find many different attributes that I would like to learn more about.

Why a fluted Barrel?

Why a Bull Barrel?

Is Chrome lined good? Why?

Why do some barrels offer a 1:8 twist and 1:9 for other types.

Why do the larger calibers use 1:10 or 1:15 twist?

What are the best metals for barrels?

What is better gas or piston?

If I use my lower and put an upper assembly on it with something like a 7.62 would I have to worry about the lower handling the increased pressure?

Does a 9mm round do well in an AR style rifle?


Thanks

[Kaos]

I just purchased a Double Star (5.56) and have been looking around at other AR type rifles and find many different attributes that I would like to learn more about.

Why a fluted Barrel?

Aids in cooling the barrel - on really long barrels it saves some weight as well

Why a Bull Barrel?

Takes longer to heat up, more rigid.

Is Chrome lined good? Why?

Certainly makes the barrel easier to clean, most AR ammo isn't corrosive so that's not an issue. You can gain a slight amount of accuracy by NOT going with chrome (but the shooter is the biggest variable).
Why do some barrels offer a 1:8 twist and 1:9 for other types.

Why do the larger calibers use 1:10 or 1:15 twist?

Different velocities are required for different ammo, the twist and barrel length have a lot to do with this.

What are the best metals for barrels?

Depends what the purpose of the rifle is (target shooting, fighting rifle, CMP rifle)

What is better gas or piston?

Matter of opinion. direct impingement is fine and gets a bad rap. Piston is definitely cleaner though.

If I use my lower and put an upper assembly on it with something like a 7.62 would I have to worry about the lower handling the increased pressure?

It will be fine. There are 50 cal uppers you can snap to an AR lower and the lower is fine during use here. Blast away!

Does a 9mm round do well in an AR style rifle?

Yep if you get the right mag block/bcg/hammer and buffer in place.

Thanks

Any time.

Anyone feel free to correct anything I posted, they were quick and dirty answers.

[jofreder]

What is a bull barrel? The only difference I have seen ( magazines and ads ) is there is no flash suppressor.

[Kaos]

What is a bull barrel? The only difference I have seen ( magazines and ads ) is there is no flash suppressor.

bull barrels are generally much thicker than standard or even heavy barrels. They generally do not taper at all...usually .950 in diameter at the gas port where standard AR's are at .750 normally.

They're much thicker the entire length of the barrel, so they're stiffer and also take longer to heat up which affects your accuracy as well.

Fluting is usually seen on these barrels as a way to lighten them up a bit while still retaining the properties of the bull barrel...as with anything...there are trade offs.

They usually only have target crowns, but you will see some customer ones threaded for muzzle devices to reduce recoil even further. Target/bench guns generally dont take weight into concern very much though so the extra weight takes up even more of the recoil. With 5.56 you can make the recoil almost nonexistant with a very heavy barrel like a 20"+ bull, a JP recoil eliminating muzzle device, A2 stock with lead in it, custom heavy rifle buffer, good glass in a good mount (which adds more weight), a good quality free float tube in rifle length and then a good bipod adapter and a good bipod. You're going to have a heavy ass AR-15 but you'll barely feel it when you pull the trigger.

[synergy]

Bull bbl's are big fat stiff barrels.

Heavy bbls don't swing in temps as much, so they group more consistently...and they weigh a lot more, so the weight helps resist the shooter's movements/ trigger pull.

Stiff bbl's also group better.

[jofreder]

OK great info thanks. Now lets get more technical

Why do the larger bullets need a different twist 1:15, 1:10

What is it again 1:10 is one twist per 10 inches?

And 1:8 vs 1:9 not much difference which is preferred for 5.56 rounds

[synergy]

OK great info thanks. Now lets get more technical

Why do the larger bullets need a different twist 1:15, 1:10

What is it again 1:10 is one twist per 10 inches?

And 1:8 vs 1:9 not much difference which is preferred for 5.56 rounds

The slower twists are better for shooting varmint bullets.

The faster twists are better for shooting heavier bullets.

The faster the better for anti-personnel ammo, I dunno how well 1:8 works with 77gr stuff.

[kevindsingleton]

Different twist rates are designed to stabilize different bullets at different velocities. My 22-250 has a 1:14 twist rate, which is intended to stabilize similar bullets used by the AR, but at much higher velocity. Every bullet has an ideal spin rate/velocity combination that will produce the greatest stability, thus the best accuracy, in any given set of conditions.

Typically, the .223 Remington ammunition coming out of the factories is designed to function well at the standard 1:9 twist rate of most .223 barrels. Some factory ammo, and most handloaded ammo, will use a different combination of components that can benefit from the faster 1:8 or even 1:7 twist rates sometimes seen on AR-15s.

[mojo]

What is it again 1:10 is one twist per 10 inches?

Yes. twists /per inches
1/7 = 1 twist per 7 inches
1/9 = 1 twist per 9 inches

[Kaos]

It's interesting to note that I've been able to shoot 55-77gr out of 1:7 and 1:9 and attain similar accuracy from both.