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Posted: 10/23/2004 7:25:54 PM EST
I just broke in my new AR with EOTech sight today.

Unfortunately, I was at a 25 yard indoor range, but that was fine for me considering I just wanted to try it out and see if I could zero the sights (EOTech and BUIS).

Anyway, I had a reasonably tight grouping (about 2 inches diameter), but they were all hitting about 3-4 inches above center.

Is it true that bullets begin travelling in an upward trajectory until about 150 yards and then travel downward? I was using Remington UPC 55gr.

I'm just trying to figure out if I need to adjust my sights or if this is normal.

Thanks.
Link Posted: 10/23/2004 7:55:53 PM EST
The sites are dsigned so that when you look through the rear sight at the front site post the rifle is angled up just a little (Taller front sight). This allows the bullet to begin it's flight slightly upward to a certain point in the distance where it will start to fall. This gives you a longer and flatter (+/- a few inches, which is why the military teaches aim COM) overal trajectory. It is alo the reason you can BZO the rifle at short distances like 25, 30 and 50 yards. The bullets are still going up and the targets at that distance are in the same line of flight say at 25M and 300M (or close). So yes the bullet does go up at first, but only cause the barrell is pointing up a little. I hope this helps.
Link Posted: 10/23/2004 8:40:48 PM EST
[Last Edit: 10/23/2004 8:59:41 PM EST by JimGA]
Someone correct me if I'm wrong, but at 25 yards, the impact of your bullet should be low...1.2" lower than the target.

groups.msn.com/TheMarylandAR15ShootersSite/zerotrajectories.msnw

Check that out. Basically, if you want a flat shooting zero out to 220 yards, use the IBZ, which means zeroing at 50 yards. At distances shorter than 50yrds, you should be a little low. At all ranges between point blank and 220 yards, you should be within 2" or so of point of aim.

Someone correct me if I'm wrong, cause if I am, I'd have to go back to the range and rezero my rifle..
-Jim


-BTW - What BUIS are you using? If Arms #40, I think you need one of those taller front site posts, unless your upper is Colt (which comes w/it). I had one installed on my Bushie, and it matches up just right with my #40.

This could explain your problem..if you are shooting high at 25 yards, you need to raise your front site post. If you're unable to raise it high enough to zero correctly, then you should get the taller front site post. It's a pretty inexpensive item.

Link Posted: 10/23/2004 9:09:02 PM EST
[Last Edit: 10/23/2004 9:12:36 PM EST by niceguymr]

Originally Posted By JimGA:
-BTW - What BUIS are you using? If Arms #40, I think you need one of those taller front site posts, unless your upper is Colt (which comes w/it). I had one installed on my Bushie, and it matches up just right with my #40.

This could explain your problem..if you are shooting high at 25 yards, you need to raise your front site post. If you're unable to raise it high enough to zero correctly, then you should get the taller front site post. It's a pretty inexpensive item.



Oh no Please!!!!! Not more $$$ on this rifle Please!!!! [>(]

What I have is a GG&G MAD BUIS. It is the BUIS that EOTech recommends for use with their Holosights. I personally spoke with their representative and he himself uses it on his AR and says it's ideal. Not that we've concluded yet that this is the problem, but if so, couldn't I just get a taller front site (not base, just the site - do they make those?).

Also, check out the ballistics for the rounds I was using. I was using the Remington UMC 55gr. I don't really understand these charts but maybe someone here can help explain to me.

www.remington.com/ammo/ballistics/centerfire/results.asp?cal=6
Link Posted: 10/23/2004 9:17:23 PM EST
[Last Edit: 10/23/2004 9:19:23 PM EST by JimGA]
I've never used the GG&G buis so I can't comment on how that is supposed to work.

First, I'd go back to the range and raise the front site post on your rifle to see if you can get your hits to land 1.2" inches lower than point of impact at 25 yards. If you can't get your front post high enough to do this, then go with this $5 solution.


Here is your $4.99 solution:

Bushie Tall Front Sight Post


If anyone has a better solution, feel free to chime in.


-Jim
Link Posted: 10/23/2004 9:37:44 PM EST
What is the length of your barrel? Notice that in those charts, they used a 24" barrel for test purposes. If you have a 16" or 14.5" barrel, the trajectory will behave differently.

Link Posted: 10/23/2004 9:42:35 PM EST

Originally Posted By JimGA:
What is the length of your barrel? Notice that in those charts, they used a 24" barrel for test purposes. If you have a 16" or 14.5" barrel, the trajectory will behave differently.




Good point, I have a 16" barrel
Link Posted: 10/23/2004 10:12:01 PM EST
If you're shooting 4 inches high at 25 you're going to shoot really high at 100. That's probably a 600 yard zero or something.
Link Posted: 10/23/2004 10:14:04 PM EST

Originally Posted By Stove_Pipe:
The sites are dsigned so that when you look through the rear sight at the front site post the rifle is angled up just a little (Taller front sight). This allows the bullet to begin it's flight slightly upward to a certain point in the distance where it will start to fall. This gives you a longer and flatter (+/- a few inches, which is why the military teaches aim COM) overal trajectory. It is alo the reason you can BZO the rifle at short distances like 25, 30 and 50 yards. The bullets are still going up and the targets at that distance are in the same line of flight say at 25M and 300M (or close). So yes the bullet does go up at first, but only cause the barrell is pointing up a little. I hope this helps.



You say this like it's some kind of unique feature. How the hell else are you going to sight in a rifle?
Link Posted: 10/23/2004 10:31:03 PM EST
Like I said, raise your front site post...alot...doing this will make your hits will land lower. Keep raising your front site post until your hits land about 1.2" below where you are aiming (at 25 yards). At 50 yrds, you should be dead on.


Link Posted: 10/24/2004 6:25:50 AM EST
JimGA,

I had a similar problem with my Bushy 20" upper with stock FSB and sight post combined with a KAC 600m rear BUIS. I ended up twisting the front sight post so far out that you could almost see the threads on it... My question is - does the Bushy front sight post you listed above fix this problem of mine? If so, I'll get a couple...

Thanks,
Spooky
Link Posted: 10/24/2004 10:42:09 AM EST
The only BUIS that I've used is an Arms #40. I sighted mine in yesterday just fine, and did not have to raise it an obscene amount in order to get it right. I've no experience with the KAC or GG&G buis, so I really can't comment about them. But I have a hunch that they may indeed require the higher front post, if you have to raise it so high that the you could almost see the threads.

-Jim
Link Posted: 10/24/2004 11:20:59 AM EST
Jim,

Any chance you can measure how much longer the extended Bushy post is compared to a regular sight post?

Spooky
Link Posted: 10/24/2004 11:26:19 AM EST
A "tight" 2 inch groups at 25 yards? If this is an accurate desciption, that rifle has more haints in it than you think.
Link Posted: 10/24/2004 11:29:03 AM EST

Originally Posted By Spooky130:
Jim,

Any chance you can measure how much longer the extended Bushy post is compared to a regular sight post?

Spooky



That would be .040".

I posted about it here: www.ar15.com/forums/topic.html?b=3&f=118&t=205618
Link Posted: 10/24/2004 11:50:26 AM EST
SNorman...

Thanks! I just read your other thread and it spells it out perfectly... For your other post - the sight picture in the forward ears maybe a little different, but seeing daylight underneath the flat part of the front sight is even harder to get used to!

Spooky
Link Posted: 10/24/2004 2:07:28 PM EST
[Last Edit: 10/24/2004 6:18:53 PM EST by niceguymr]
Edited.
Link Posted: 10/24/2004 5:38:01 PM EST

Originally Posted By niceguymr:

Originally Posted By Maddogkiller:
A "tight" 2 inch groups at 25 yards? If this is an accurate desciption, that rifle has more haints in it than you think.



I'm not so sure what this comment means, but I don't think a 2 inch group with 40 rounds is too shabby considering it's my first time using an AR. In your 'expert' opinion, what do you think might be wrong with my rifle? Perhaps someone with your level of expertise who may have 1" groups could teach me something. I guess a few more posts and I'll be caught up to you and shooting 1" groups. Thanks for your help!



it seems from the tone of your response that you have mistaken my post as a slight against you or your rifle. It was not. I was giving you the benefit of the doubt in regard to your shooting skills. Since you have stated that you are new to shooting ARs, I would say that you are doing fine. I am sure that your groups will tighten up substantially as you send more rounds down range.
Link Posted: 10/24/2004 5:43:41 PM EST
So the gun/optic combo had never been zeroed before? In this case it is perfectly normal that the gun isn't hitting exactly at your point of aim. That's why you zero it.

If it had been zeroed before, what range did you zero it at?
Link Posted: 10/24/2004 5:50:16 PM EST

Originally Posted By niceguymr:
...I had a reasonably tight grouping (about 2 inches diameter)...



My 30 year old Red Ryder can do that!
Link Posted: 10/24/2004 6:21:52 PM EST
[Last Edit: 10/24/2004 6:44:53 PM EST by niceguymr]

Originally Posted By Garand06:

Originally Posted By niceguymr:
...I had a reasonably tight grouping (about 2 inches diameter)...



My 30 year old Red Ryder can do that!



Who the F*#K cares?

I appologize in advance for the attitude I'm about to express, but I created this post for help, not for you to brag about yourself or your toys. I never claimed to be a marksman or that my rifle is the best. I just came to seek the expert advice of experienced AR owners so that I can correct the problem I'm having. I'll never understand why people come in here and brag to compensate for whatever other inadequacies they may have. Gee wizz! Please only post a reply if you have any thoughts or suggestions to help me with my problem. People that come to this thread don't care about your 'Red Ryder'. IF you want to brag to me about something, send me an IM. If you want to brag to the entire ARFCOM population, start your own damn thread.

Now back to the original issue at hand:
Can anyone tell me where to find one of those 'taller' front iron sight posts for a Colt AR? Any recommenations? I noticed a post above referencing a link to a thread about a taller Bushmaster front iron sight post. I didn't think that would fit with mine, but someone tell me if I'm wrong.
Link Posted: 10/24/2004 7:24:07 PM EST

Originally Posted By niceguymr:

Originally Posted By Garand06:

Originally Posted By niceguymr:
...I had a reasonably tight grouping (about 2 inches diameter)...



My 30 year old Red Ryder can do that!



Who the F*#K cares?

I appologize in advance for the attitude I'm about to express, but I created this post for help, not for you to brag about yourself or your toys. I never claimed to be a marksman or that my rifle is the best. I just came to seek the expert advice of experienced AR owners so that I can correct the problem I'm having. I'll never understand why people come in here and brag to compensate for whatever other inadequacies they may have. Gee wizz! Please only post a reply if you have any thoughts or suggestions to help me with my problem. People that come to this thread don't care about your 'Red Ryder'. IF you want to brag to me about something, send me an IM. If you want to brag to the entire ARFCOM population, start your own damn thread.

Now back to the original issue at hand:
Can anyone tell me where to find one of those 'taller' front iron sight posts for a Colt AR? Any recommenations? I noticed a post above referencing a link to a thread about a taller Bushmaster front iron sight post. I didn't think that would fit with mine, but someone tell me if I'm wrong.



You're wrong. The sight post is a standard unless colt came up with a new way to dick with the sizes of parts.
Link Posted: 10/24/2004 9:04:33 PM EST
[Last Edit: 10/24/2004 9:11:36 PM EST by JimGA]
That Bushie front post should fit.
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