I'm confused...

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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I'm confused...

Postby powerhead357mag » Sat Nov 19, 2016 2:45 pm

I went to confirm zero on my rifle before heading up north to hunt. I have a 50yd zero and it put 5rds into one ragged hole at 50. I step back to 200 which should be about a 6in drop and fire 5rds and it was barely and inch low from my 50yd zero? That's with factory hornady 250ftx at 2250fps and handloaded Barnes 275xpb at 2170fps. Through a Tromix 18in barrel any ideas as to why it's shooting so "flat"?
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Re: I'm confused...

Postby Al in Mi » Sat Nov 19, 2016 5:53 pm

my guess is scope height....................but I wouldn't complain!!
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Re: I'm confused...

Postby powerhead357mag » Sat Nov 19, 2016 7:16 pm

2.7in over bore height. I've shot at 300yds and been 28in low. So I think something screwy is going on.
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Re: I'm confused...

Postby Hoot » Sat Nov 19, 2016 7:41 pm

The 450b flies like a shuttle cock. Quick off the racket, darts out to a given distance, then dies. Its not unusual for a 50yd zero to travel a long range before crossing zero again. Countless online resources cover how the ballistic arc runs. As Al implied, a lot depends upon how high the scope mount factors in. I myself, mount all my scopes so that the forward bell barely clears the barrel by about 1/8-1/4 inch. I have some that I can't get the front scope cap on if its made from too thick a material.

Also as Al said, count your blessings! ;)

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Re: I'm confused...

Postby powerhead357mag » Sun Nov 20, 2016 5:26 am

Hey hoot,
I've run it through 3 ballistic apps Strelok+, shooter, and sniper calculator. All of them say around 7.3in low at 200 for a 50yd zero. That entering in the scope height, bullet bc, and true muzzle velocity. I'm still kinda stumped
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Re: I'm confused...

Postby Jim in Houston » Sun Nov 20, 2016 1:01 pm

powerhead357mag wrote:Hey hoot,
I've run it through 3 ballistic apps Strelok+, shooter, and sniper calculator. All of them say around 7.3in low at 200 for a 50yd zero. That entering in the scope height, bullet bc, and true muzzle velocity. I'm still kinda stumped


If it's repeatable at the range, use it on the hunt.

I have to admit, I can't explain the trajectory. The Hornady Ballistic Calculator shows a significant drop (almost 10" at 200 with a 50 yd zero) using some nominal inputs for velocity and scope height. That matches my expeirence in the field.
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Re: I'm confused...

Postby powerhead357mag » Sun Nov 20, 2016 1:44 pm

It is repeatable. The only variable is that when shooting at 200yds, at 100yds the bullet enters a 60ft long by 40in diameter pipe. Then exits to impact the target. I wouldn't think the bullet flying through a tube would make any difference.
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Re: I'm confused...

Postby Hoot » Sun Nov 20, 2016 8:07 pm

Just a thought. Are you shooting prone or from a bench? Uphill, downhill, or fairly level? Wind probably not an issue since it happens on different range trips. Possibly some odd barrel harmonic going on. Varmint Al's Web page discusses barrel harmonics, but if you were catching it on the upswing, you would have to dial it out to hit at 50. You can be off a lot in terms of zero at long range and still get a good group at 50 due to the proximity. A test would be to zero at 100 and see how it does when shot at 200, 300, etc.

Grasping at straws for an explanation.

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Re: I'm confused...

Postby Al in Mi » Mon Nov 21, 2016 6:02 am

i'll toss this out, what if the upper is bore crooked so the barrel, in this case, would be pointing up?

or barrel being bent up, dunno, just thinking from a windy blind this morning.
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Re: I'm confused...

Postby powerhead357mag » Mon Nov 21, 2016 7:52 am

Shooting level. On the same gun rest I always use. The gun has been shot numerous at 50 and 300. Which the drop is perfect at. This was the first time shooting it at 200. I'm going to try it again today and not fire through a pipe halfway down range. I think the bullet flying though that pipe has something to do with it. This gun has always been a tack driver
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