1st AR-15 purchase

Eugene Stoner's ubiquitous Black Rifle, the AR-15 has become
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morbius
Posts: 356
Joined: Thu Nov 20, 2008 8:32 pm

1st AR-15 purchase

Post by morbius » Tue Apr 28, 2015 9:25 pm

I just bought a new Armalite M-15 DSR15. The double-lapped chrome lined/chrome moly barrel has a 1:7 twist rate. The gun is chambered for 5.56x45mm/.223 Remington cartridges. The salesperson advised me that this barrel would shoot truer with heavier bullets than with lighter ones. What does the group recommend? I am using Troy BUIS front and rear. Thanks.
"A nation of sheep will beget a government of wolves". - Edward R. Murrow

TSiWRX
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Re: 1st AR-15 purchase

Post by TSiWRX » Tue Apr 28, 2015 10:19 pm

Some quickie reads:

http://www.ar15.com/content/page.html?id=186
http://www.m4carbine.net/showthread.php ... 1-7-vs-1-9

But there's really no need to get even to that stage - the bigger question you've gotta ask yourself is what kind of targets you'll be shooting at, at what distances. :wink:

If all you're doing is plinking at the 25 yard line or taking "tactical carbine" classes where you're pushing out to the 100 yard line, max, then it really won't matter at all what you're shooting.
-Allen

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MyWifeSaidYes
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Re: 1st AR-15 purchase

Post by MyWifeSaidYes » Wed Apr 29, 2015 1:10 am

morbius wrote:... 1:7 twist rate...
It takes more effort for me to spin my 17-year-old son on a tire swing than to spin my 13-year-old daughter.

Overcoming the rotational inertia of a bullet works the same way. A heavier bullet needs to be spun 'harder' than a lighter bullet to get to a particular rotational speed.

As a general rule, from a barrel with a 1-in-9 twist, as your bullet weight moves up from the 50-grain range to the 60-grain and 70-grain ranges, your bullets will leave the barrel spinning slower.

As you move to a 1-in-8 or a 1-in-7 twist, the heavier bullets will spin more quickly. Of course, so will the lighter bullets.

When you are shooting lighter bullets out of barrels with a faster twist, the higher spin rate may affect your accuracy just as much as a slow-spinning heavy bullet. This can often be overcome by using match-grade bullets.

Test fire various types of ammo from a bench rest (10-round groups) and find out what seems to work best for YOUR rifle.
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Old Timer
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Re: 1st AR-15 purchase

Post by Old Timer » Wed Apr 29, 2015 10:30 am

MyWifeSaidYes wrote:

Test fire various types of ammo from a bench rest (10-round groups) and find out what seems to work best for YOUR rifle.
Best answer ever! All barrels seem to have a life of their own when it comes
to what they like to digest.
That seems to hold true on all parts of the components, powder, primer, and bullets
as well.
So Mote It Be.
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