unsightable scope

[Guest ADAM]

I'm sure this has been posted before but here goes. A friend of mine just got his first AR, and I gave him a EL cheapo Centerpoint scope 3x16x40 (I believe thats the power) it has been sitting in a safe for quite some time. We shot about 200 rounds thru his gun Friday and could not get any groups at all, My question is are some cheap scopes not able to zero in? This scope was on a 7mm and only boresighted when i had it, and fired once during deer season. The odd thing is is that we were shooting three rounds at a time and the first round was exactly where the crosshairs were but the second round was high left and the third was low right. Is this common, I've never had this problem before.

[Jonnin]

Sometimes its the scope, sometimes its the gun, the ammo, the shooter, or other stuff. Here, if the first round hits and the next couple do not, is it possible the barrel got hot, then cooled, etc?

I would give it a try with 1 shot, then cool down, repeat. Also might do other tests like lock it into a rest to see what sort of groups the gun makes when it is not moved. Its easy to blame a cheap scope (and that is a potential problem) but the best thing to do is eliminate the variables that you can to determine the problem.

[Guest ADAM]

we did have the gun locked down, and the ammo is what all three of us were using and the other two guns were shooting 1/2" groups with ease. he is not an experienced shooter so that did cross my mind so we let if shoot our guns and he could hold a good group. I'm just hoping for his sake that is not the barrel and just the scope. this is a brand new gun and we cleaned the barrel while shooting but not after every round only after every 15-20 rounds.

Thanks for input.

[Jonnin]

well that narrows it down. If the ammo makes 1/2 in other guns, a gun that does not like it may open up some but not *that* much. By locking down the gun, I mean totally, so it cannot be moved, then shoot it one time. Look thru the scope and note how far off the crosshairs the round went. Then shoot 4 more times and check the scope vs placement each time. If the bullets all go in the same hole, but each time the scope is different, you have a scope or scope mounting problem. If the bullets go all over the place, the scope may or may not stink but there is a more important problem to solve!

[Westwindmike]

Put the scope on a known accurate rifle and try it there. That takes out some variables.

[Caster]

What weight bullet, what twist barrel and what distance?

My favorite AR is a 1/7 twist. It will do fair with 55g FMJ at 25-50, but at 100 yards they are all over the map. Put the same ammo in one of my other AR's w/ a 1/9 twist and you can write your name on the target with it. Same for the 1/7 but i have to feed it a longer 75g bullet.

May or may not be your issue, but it's worth checking. 1/7 barrels have had a popularity spurt the last few years.

[peejman]

Does it group well with irons? If not, you have an ammo/twist/barrel/headspace problem.

Bases and rings tightened properly? Do they stay tight?

Are you sure that scope is intended for high-powered rifles? Centerpoint makes good rimfire scopes, but I can imagine a rimfire scope to be all over the map on an AR.

[Guest Broomhead]

My Dad had this same problem with that same scope (same model, power, brand), but it happened with two of them bought back-to-back, also. Both came from Walmart and both ended up being non-zeroable. After he got the scope and rifle shooting within an inch at 25yrds, he would lay the rifle down to reload his mags. The crosshairs moved the second he laid the rifle on it's side. Then, when he picked it back up, the scope would be off 5-6 inches. This happened with both scopes on the same rifle. There were no mount/rail/ring issues, you could actually see the crosshairs shift ever so slightly if you turned the rifle while looking through the scope.

JMHO, but I would blame the scope on this one, just from my(our) experience.

[Guest ADAM]

barrel is 1/9 twist. were shooting 62gr PMC XTAC ammo @ 100yards.

cant check shooting gun open sighted he didnt put rear sight on it when built(well maybe close range cause it does have front sight), scope rings are tight that was checked.

I guess like Mike stated put the scope on another gun and check it there.

Thanks Again

[texfrazer]

If you were cleaning between some rounds, then you could have ended up with some variance. One of my hunting rifles shoots dead on first shot, low left 2nd shot, then high right 3rd shot, then dead on until I clean again. This is repeatable in my rifle.

Thus, you should also try firing 30-40 round through it (it is an AR after all ) with the scope and see if it smooths out over a few rounds.

[bajabuc]

Are the mounts parallel with each other? are they level with each other? were they tightened evenly. There's a section on surplusrifle.com dealing wirh mounting a scope on a mauser that gave very good and insightful explainations about mounts. Even the slightest difference in height of the mounts can make a HUGE difference 100 yards fron the rifle.

[Caster]

Bajabuc is right on that, it's just simple trigonometry. An few thousandths here can be inches over just a short distance.

[bajabuc]

Here's what I would do...it's kinda complicated because math and I don't do well together...Someone you know has a boresight laser. it's a light you put in the chamber and it shoots a laser beam out the center of the bore. If it doesn't then the chamber and barrel aren't inline with each other. (this happens...lots) a little smoke shows the laserbeam. With the rifle clamped in the benchrest check the level of the laser. MAKE IT SO. Mark the dot on the target. Remove the boresight laser. lay iit on each ring mount. (the manufacturer goes through a ton of trouble making sure they're square...it's how you stay in busness) both laser dots from the mounts should be exactly the same and the same distance ABOVE the dot you made with the light in the bore...they're not? play with scope bases until they are. Level? put it all back together...shoot the gun!

Or...check this out http://www.surplusrifle.com/shooting2005/duckeaglepart1/index.asp

Edited April 26, 2011 by bajabuc
additional info

[Dolomite_supafly]

When mouting the scope rings do this. Place them loosely on the receiver, as in wiggle loose but will not fall off. Place the gun on its muzzle then tighten the rings down. This forces the rings to the front of their individual picatinny slot. This keeps the rings from moving under recoil. If you have the rings at the rear of the picatinny slot then each shot they may move forward, affecting the zero.

Next, when mounting the scope snug all the screws down, do not tighten. Then square the reticle to the gun. Then tighten the rings down screw by screw slowly. Do not tighten one screw completely then the next. Again, slightly tighten one screw then move on to the next and continue to do this until the rings are tight, not overly tight but tight.

Next, what type of flash hider or muzzle brake do you have? There are certain ones that are notorious for causing accuracy issues. It has been proven over and over again that they affect the natural harmonics of the barrel in such a way to affect consistency.

The ammo could not play well with the particular rifle. I would suggest trying another brand, perhaps Blackhills or Federal FGMM. Both of those seem to shoot well with a lot of different guns.

Dolomite

[bajabuc]

Dolomite, great advice...I forgot about flash hiders.