Scopes and Sights Discuss firearm scopes, sights and related accessories here.

Zero'ing issue

Old 01-24-2021, 06:44 PM
  #1  
Fork Horn
Thread Starter
 
Join Date: Oct 2004
Location: Arlington, TN
Posts: 280
Default Zero'ing issue

To give my S&W M&P15 a little more versatility, I acquired a Palmetto State Armory .300 blackout upper. I've put a UTG Bugbuster 3-9 scope on it with a .75 inch riser to get the sight line up high enough. I am planning on using this setup for deer hunting next season as the woods I hunt limit my shots to 100 yards or less. I found some Winchester Deer Season XP 150gr ammo after getting the barrel, but I literally can't get any shots on paper at 50 yards. I've maxed out the scope adjustments trying to get things line up.

So I bought a cheap laser bore sight on ebay and when I put the thing in the barrel, the dot is just a little low and to the left of the crosshair center at about twenty or thirty feet. It seems that should mean that I should at least get something on paper on a standard sight-in target that is probably 18-24 inches square. What do you think? Is it just that the barrel really doesn't like the 150gr ammo? So far it's been the only stuff I've found.

I've got one box of ammo left and I'll go back again at some point and set up on the 25 yard line.
xd9x19 is offline  
Old 01-24-2021, 07:05 PM
  #2  
Nontypical Buck
 
Join Date: Nov 2014
Posts: 2,702
Default

sounds to me like something is mounted wrong here
if I was you, I would take gun to a decent gun shop that has a smith on hand and look things over for you, shouldn;t cost much if anything and solve your issue's for you
that you you got a really BAD scope
that isn;t the highest quality of optic there so??
just saying!

but if your laser bore sight is showing your 20+ ft off, that is seriously OFF, no scope is going to have that much adjustment in it!!

you can also try getting a MUCH larger target say a 4ft x 4ft cardboard one and just see if things are grouping or not too
but I say you have something mounted wrong here!
mrbb is online now  
Old 01-24-2021, 07:30 PM
  #3  
Fork Horn
Thread Starter
 
Join Date: Oct 2004
Location: Arlington, TN
Posts: 280
Default

Thanks. This is my first time to do something like this, so you're probably right about a mounting issue.
xd9x19 is offline  
Old 01-25-2021, 06:24 AM
  #4  
Nontypical Buck
 
Nomercy448's Avatar
 
Join Date: Oct 2009
Location: Kansas
Posts: 3,760
Default

If you are putting a laser boresighter dot just a little low and left of the crosshair when viewed at a distance of 20ft, then your bullets are hitting high at 100yrds. Way high.

This is a really, really common mistake folks make when using laser bore sighters, especially in AR-15’s.

An AR-15 will typically have a 2.4-2.6” scope height over bore. When you bring the crosshairs to a laser boresighter dot at 20ft, you’re drawing a TIGHT X between the line of sight of the optic and the bore axis - you’re dropping that 2.6” within 20ft. Extending that X to 100yrds (280ft past the intersection), your bore axis is now pointing 36” above target. A 150grn SST at 1950fps will fight about 4” of absolute gravitational drop by 100yrds, so I’d bet you’re striking somewhere around 32” high at 100yrds, quite a bit over the top of your 18-24” paper.

When I laser boresight AR’s at short distance (typically 30ft across my shop), I use a printed page with two target centers 2.6” apart, hanging vertically. I place the laser dot on the bottom target, then zero the crosshair to the top target. I’ll dial up the number of clicks necessary to accommodate a 100yrd drop - typically ~1.5-2MOA for 5.56/223 (6-8 clicks on a 1/4MOA or 1/4IPHY scope), then shoot at a 25yrd target, which should print about 1.5-2” high, or shoot at 50yrds, which should print about 1/2” high, then move to 100yrds.

But trying to center the crosshair on the laser dot at short distance just doesn’t work.
Nomercy448 is offline  
Old 01-25-2021, 07:06 AM
  #5  
Fork Horn
Thread Starter
 
Join Date: Oct 2004
Location: Arlington, TN
Posts: 280
Default

Nomercy448, at the range I felt like your avatar. Wile E Coyote, "genius". Thanks for the feedback. I'll probably chat with an old neighbor who is an ex-marine and see if we can get together and get it dialed in.
xd9x19 is offline  
Old 01-25-2021, 07:07 AM
  #6  
Super Moderator
 
Bocajnala's Avatar
 
Join Date: Dec 2006
Location: Trumbull County, Ohio
Posts: 8,698
Default

EXCELLENT post Nomercy.

-Jake
Bocajnala is offline  
Old 01-31-2021, 09:02 AM
  #7  
Nontypical Buck
 
Nomercy448's Avatar
 
Join Date: Oct 2009
Location: Kansas
Posts: 3,760
Default

I’ve just seen way too many new rifle owners, especially new AR owners, fall into this trap. One unfortunate consequence I have seen too often: One local indoor 100yrd range I often use has cable tracks as target runners, in a decade shooting there, I recall at least one instance each year where at least one of the lanes is shut down because some unwitting new rifle owner used a laser boresighter at home in their livingroom, then managed to shoot the runner cables because their rifles were zeroed a few FEET above target.

I offered one option above - sighting the optic to be 2.6” above the dot at 20ft, then shooting at 25-50yrds. Another option: actually boresight the rifle. Open the upper, pull the carrier, and sight through the barrel at the target at 50 or 100yrds. Zero the optic and the barrel on the target at the same time, dial up 4” at 100 to account for your cartridge’s drop, and fire at 50yrds. Either method works, same principles are applied in each case. It typically only takes me 5 rounds to confirm zero with any rifle, AR’s included.
Nomercy448 is offline  
Old 01-31-2021, 12:05 PM
  #8  
Nontypical Buck
 
Big Uncle's Avatar
 
Join Date: Dec 2009
Posts: 1,780
Default

"I offered one option above - sighting the optic to be 2.6” above the dot at 20ft, then shooting at 25-50yrds. Another option: actually boresight the rifle. Open the upper, pull the carrier, and sight through the barrel at the target at 50 or 100yrds. "

You were given good advice. The key is to use some practical distance (50 or 1100 yards) like the above comment recommends. The short distance with the laser (20 -30 feet) and the big difference between the center of the bore and the scope caused the problem.
Big Uncle is offline  
Old 02-02-2021, 03:00 AM
  #9  
Nontypical Buck
 
Join Date: Feb 2003
Location: Eastern wv
Posts: 3,077
Default

just remember at the end of the muzzle, MOA is around .007".
RR
Ridge Runner is offline  
Old 02-08-2021, 07:24 AM
  #10  
Fork Horn
Thread Starter
 
Join Date: Oct 2004
Location: Arlington, TN
Posts: 280
Default

Quick update. Well, ammo cost and availability being what it is, I bought a $22 set of flip-up sights on ebay to try out. Dropped them on my AR without any adjustments and the 150 gr ammo hit straight on but 4-8" inches high at 50 yards. I didn't spend the time to make adjustments to the front sight. I'll do than when I have more ammo available. I'm just happy to convince myself the new barrel shoots straight and isn't throwing flyers all over the place. Definitely a scope mounting issue.


Last edited by xd9x19; 02-08-2021 at 07:28 AM.
xd9x19 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.