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9/22/2017 12:11:25 AM
Posted: 9/17/2003 8:47:50 PM EDT
This may be a dumb question but I figure I will get the answer. I have a Colt A3 upper mated to a Bushmaster HBAR barrel. Took it to the Range and it's hitting several feet higher than point of aim @ 300-400 yards. I purchased a sight adjustment tool and a Bushmaster front sight that is taller than the GI site, BM said the Colt A3 upper is taller than GI spec and I would need the taller sight?
Either way, how much drop will I get per revolution of the front sight?. Do I need the taller site? I thought you lower the front sight to lower where the bullet strikes? Thanks ;)
Link Posted: 9/18/2003 12:37:11 AM EDT
Originally Posted By titan7: This may be a dumb question but I figure I will get the answer.
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Actually it's a series of dumb questions but we're used to that here. [:)] Did you read the FAQ, the Glossary, the Checklist, and all the rest of the annoucements at the top of this forum?
I have a Colt A3 upper mated to a Bushmaster HBAR barrel.
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What length barrel?
Took it to the Range and it's hitting several feet higher than point of aim @ 300-400 yards.
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You shot it at 300 and 400 yards?
BM said the Colt A3 upper is taller than GI spec and I would need the taller sight?
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Odd, when it comes to flattop uppers (M4s and M16A4) Colt [b]IS[/b] the GI spec.
Either way, how much drop will I get per revolution of the front sight?.
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Depends on the sight radius and what kind of (how many stops) front sight post is on the BM barrel.
Do I need the taller site?
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You shouldn't, it's a stupid fix that will eventaully cause the front sight post to get bent. If you put a non "F" marked barrel on a flattop upper you're going to have elevation problems.
I thought you lower the front sight to lower where the bullet strikes?
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The rear sight moves with the POI, the front sight moves opposite. The taller front sight is a supposed cure because you'll run out of threads on the front sight post before you get it high enough to zero. In reality you need the correct barrel for the flattop upper.
Link Posted: 9/18/2003 12:01:22 PM EDT
I did read the FAQs but did not really get a clear answer. Thanks for the input! the barrel is 20" so I guess 1 click will move POI 3/8". What I do get is this: If it's shooting high, wouldn't you lower the front site? If this is true, how would a taller front sight help? If it's the opposite then I could see how a taller site would help. thanks.
Link Posted: 9/18/2003 4:02:10 PM EDT
Originally Posted By titan7: If it's shooting high, wouldn't you lower the front site?
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A lower front sight post makes you raise the front of the rifle to be on target. aka shots hitting high
Link Posted: 9/19/2003 7:28:34 AM EDT
Originally Posted By titan7: the barrel is 20" so I guess 1 click will move POI 3/8".
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1MOA for 5 pos posts and 1.25MOA for 4 pos posts with a rifle sight radius.
If it's shooting high, wouldn't you lower the front site?
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Second time is a charm titan7, the front sight post moves [b]opposite[/b] the POI. If you want to [b]LOWER[/b] the POI you [b]RAISE[/b] the front sight. If you lower the front sight post you shoot higher. When the standard post is unscrewed (raised) high enough to zero using the shorter, incorrect FSBs, it's barely threaded into its hole. The taller post gets the tip of the post up where it would be using the correct FSB and leaves enough of the threaded shaft in the hole for the front sight post to be stable. It does not correct the problem of having the post stick up past, or near to, the top of the protective wings on the FSB.
Link Posted: 9/20/2003 3:26:01 AM EDT
I had the same problem. Was your barrel installed by Bushmaster? If so send it back to them. They have had issues with barrel alignment due to torque and this happened to me on 2 occasions. They installed a M4 barrel on a Armalite upper for me.
Link Posted: 9/22/2003 11:44:05 AM EDT
Thanks Tweak! I took the rifle out again this weekend and to get zero the top of the front site was almost the same height as the front sight ears. Looks like I will be buying a Bushmaster upper receiver and carry handle and switch out the Colt upper to get around this issue. I will I knew this before starting. Rick, I installed my barrel.
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