Sighting in AR

lkenefic · Sep 9, 2016

Hey everyone, I was recently at the AGC range in Marriottsville trying to sight in a new build with Bushnell TRS25 red dot optic. I don't have a bore sighting tool, so I put the optic on and hoped for the best with 55 gr Federal. The rifle: YHM lower with CMMG parts kit, YHM flattop upper built by a local company in WV... the name escapes me... gun show purchase. The barrel is 1/7 twist, medium contour... anyway, my first rounds down range at 50 yards were on the paper, albeit a tad to the right and low. I adjusted the optic... all looks good. I shoT about 30 rounds like this. All bullseyes and 10 ring. Next, I switched to 62 gr. Green tip American Eagle. Now, I'm not even on the paper... I put the target at 25 yards... STILL not on the paper. I thought I might have been much to the left after looking at where the bullets were hitting downrange, and made a sight adjustment, but nada. OK, here's where it really gets interesting... I went back to 55 grainers... same Federal load... and I'm not on paper. Soooo... I'm thinking that something happened to the optic or the mount, but I'm hard pressed as to what I did... ie, nothing obvious... dropped, gouged, spinning the adjustment knob, etc. It started raining heavily the last time I was out, so I've not been back to the range since. I was hoping to get out this weekend to troubleshoot... any suggestions would be most appreciated. Thanks.

jimbobborg · Sep 9, 2016

Did you use blue loctite during the sight installation? They do come loose.

outrider58 · Sep 9, 2016

Try bore sighting it? You can do that at home. Also, double check all your mounts

Glaron · Sep 9, 2016

outrider58 said:
Try bore sighting it? You can do that at home. Also, double check all your mounts

I had problems with my first ar-15 optic.

A bore sight laser fixed it, it can be done at home.

I defer to those with more expertise.

moojersey · Sep 9, 2016

Yeah sounds like the sight came loose and moved / lost its zero. I would buy a .223 laser boresight. Worth their weight in gold.

lkenefic · Sep 9, 2016

Thanks all... I did locktite it in place the night before... perhaps it didn't cure? I'll try again this weekend. Any local sources for a .223 laser boresight? Or, is this something that can be done on a per customer basis at a local shop? I like to give the local guys some $$ when the opportunity presents...

Indiana Jones · Sep 9, 2016

loctite means dick if you didnt follow the manufactures torque specs. did you go hand tight or use something like a Wheeler FAT Wrench?

Erno86 · Sep 9, 2016

If you have a gun rest and a rear bag...it's possible just to place the separated upper in the rest, and bore sight it at a small object on the 100 yard backstop berm.

davsco · Sep 9, 2016

i love tech toys but a lazer boresighter really isn't necessary, certainly for something where you can pull the bolt and look down the barrel (ie, ar-15 or any bolt gun).

jimbobborg · Sep 9, 2016

Or if you have a front and rear iron sight you can use that, too.

Uncle Duke · Sep 9, 2016

Erno86 said:
If you have a gun rest and a rear bag...it's possible just to place the separated upper in the rest, and bore sight it at a small object on the 100 yard backstop berm.

Or better yet, a sheet of cardboard (white if you have it) a couple of feet wide with a centered bright orange target dot that you can easily see when looking through your bore. Set it up at 25 yards and you'll very quickly see on the white where you're grouping initially. Move your distance out from there as desired.

outrider58 · Sep 9, 2016

I have never owned or used a laser bore sight or any other bore sighter for that matter. The trick is (not really a trick), you have to bore sight on something at least 30 yds away. It gets me on paper every time.

The reason I asked Ikenefic was, when he got home, he could peak through the bore and check to see that everything still lines up.

d33rhunt3r · Sep 12, 2016

From what I've read, using a heavier grain bullet would be more beneficial. I also have a 1:7 rate and researching has shown people tend to prefer upwards of 70 grain. But as usual, everyone has their preference, different experiences, etc.

On my first optic, I used 70 grain and was having 1.5" groups at a 100 yards, which I won't complain about for my first AR, and first real experience with it. I've changed optics now and will have to test things out again

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