Sbr?
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Old 05-03-2011, 06:04 AM   #1
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i have paperwork going through to build a SBR m4, i am collecting info on what i am going buy, i am going with a bushmaster lower and a LMT 10.5" upper with a 1/7 twist, i want to know if that upper can shoot 55 grn 5.56 and .223 for plinking.

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Old 05-03-2011, 12:15 PM   #2
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Originally Posted by deathkricket View Post
i have paperwork going through to build a SBR m4, i am collecting info on what i am going buy, i am going with a bushmaster lower and a LMT 10.5" upper with a 1/7 twist, i want to know if that upper can shoot 55 grn 5.56 and .223 for plinking.
you can but the accuracy wil be bad. that twist rate is really fast for 55grn some bullets may disintegrate in flight due to poor bullet construction you tend to find in super cheap 55grn plinking rounds.

just dont expect really good results from such bullets.
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Old 05-03-2011, 02:48 PM   #3
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you can but the accuracy wil be bad. that twist rate is really fast for 55grn some bullets may disintegrate in flight due to poor bullet construction you tend to find in super cheap 55grn plinking rounds.

just dont expect really good results from such bullets.
i have read around they may break apart in flight but out of a 10.5" they may make it but cool thx for the help, they will be plinking rounds anyway so.
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Old 05-03-2011, 04:09 PM   #4
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The 7 twist in a 10.5" barrel shouldn't be to hard on bullets. The velocity is going to be lower over a 20 or 22" barrel by a whole lot. It is not only twist but speed and time in barrel. Most bullet don't pick up twist for a good 2". That is in part why the Swift was so hard on barrels lots of pressure and lots of heat forcing that bullet down the barrel.

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Old 05-03-2011, 04:47 PM   #5
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cricket,

You may want to consider the 1:9 vs the 1:7. The 1:9 Twist will handle the 55s well and up to the 69 grain range as well. With my RRA 16" 1:9 I can get 1MOA groups off the bags shooting the Federal 55 Grain P-223E ammunition. And American Eagle 55s and Black Hills 55s also shoot well.

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Old 05-03-2011, 07:51 PM   #6
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cricket,

You may want to consider the 1:9 vs the 1:7. The 1:9 Twist will handle the 55s well and up to the 69 grain range as well. With my RRA 16" 1:9 I can get 1MOA groups off the bags shooting the Federal 55 Grain P-223E ammunition. And American Eagle 55s and Black Hills 55s also shoot well.

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I was wanting the a 1/9 twist but a friend of mine is hooking me up with the LMT 1/7 upper with the 10.5" for a GREAT price so im gonna end up going with that, i plan on running 62 grain for real ammo and 55 grain for fun days, i just wanted to make sure that 55 grain will not bust up in the gun, im going to order another AR here soon with a full 20" upper on it so this will only be for close range shots. And if the charts im looking at are right im looking at 950 lbs of energy and somewhere around 2100 fps outa the 10.5" but i dont know if the chart is right so if you have any rough idea of the ballistics feel free to let me know.
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Old 05-05-2011, 06:57 PM   #7
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You should be fine with the 1:7. You want the round to be stabilized out of the shorter barrel, thus the faster twist, especially if you plan on suppressing that flame thrower. 75 grain TAP rounds would be the ticket for close range encounters.

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Old 05-06-2011, 02:58 AM   #8
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You should be fine with the 1/7 and 55gr. An old customer of mine had a Colt Delta HBAR with a Swarovski 6x on it and it would drill neat little holes with any 55gr ammo. Loved the old blue and white box Samson ammo (IMI).

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Old 05-06-2011, 09:03 PM   #9
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Cricket,

For plinking the 1:7 and 55 grain bullets will be fine. They will be fairly accurate. I would say maybe 3-4 inches at 100. Which is not bad for plinking. Just not max accuracy!

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Old 05-06-2011, 10:00 PM   #10
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Sweet, thats good enough for plinking.

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