Help, AR15, can't get any better that 3-4" groups at 50 yrd w/scope, sights f/bench. what could be the problem

Question

300 rounds, good trigger, 16" chrome lined barrel, no wear on the bolt face, no binding, misfires, or ejection problems. I'm stumped. Please help

300 rounds, 11 diff. brands and bullet weights, good trigger, 16" chrome lined barrel, no wear on the bolt face, no binding, misfires, or ejection problems. I'm stumped. Please help

300 rounds, 11 diff. brands and bullet weights, good trigger, 16" chrome lined barrel, no wear on the bolt face, no binding, misfires, or ejection problems. Scope works perfect on other guns. I have built other guns that shoot sub moa, but this ar has me stumped. Please help

Answer 1

I would be leaning towards rings/base also. Have you tried shooting it with the iron sights? If you can get a decent group using the stock peep sights, you've elminated ammo and the gun as a potential problem. If not then you've eliminated any scope or components as a problem and know that it's the gun or ammo. You said the scope works fine on other guns, so if you are getting good groups with the irons sights you know it's not the gun or ammo, that leaves only the rings and base as a potential problem.

Answer 2

Is your gun a flat top or are you using a carry-handle mount?
I've seen carry-handle mounts that wouldn't hold a repeatable zero.
The solution for this is toss the 29.95 carry handle mount and get the 79.95 carry handle mount, and then loc-tite it in place.

What is the twist of your barrel?
1/7, 1/9, 1/11? , This factor, in combination with bullet weight can have an effect on accuracy. There is a "best load" for specific twists.

Is your rifle chambered for .223(commercial), or 5.56(surplus military)? Same thing? Well, sort-of, but not exactly.
There is a slight difference in chamber dimensions between the two, that while not preventing ammo interchangability,
may have an effect on accuracy.

If you can answer these questions, I'll edit in an educated guess. Without "being there", it's hard to say.

Answer 3

What kind of ammo did you use? commercial or military? reloads? what bullet weight? What manufacturer is the weapon? What barrel twist? need more info to give a solid answer. But, many ar's have a few inherent problems that affect accuracy. Fit of lower to upper, excessive play here allows too much movement between the time you pull the trigger and the firing of the firearm, this also lets the point of impact change slightly. Is your group consistent in where the bullet hits or is it scattered around the target?
Pre ban or post ban barrel?
A post ban barrel can have a damaged crown on the barrel, this will impact the accuracy.
Check every pin for looseness or slop.
Have you had it checked for head space? check go, no go and field, and excessive chamber will cause accuracy problems and can be dangerous..
Look thru the barrel with a light and check for depth of grooves and deformities.
check the barrel nut for tightness.
If you have a 1-9 twist, you should be firing the heavier bullets.
Are you firing from a solid rest?
If sights and scope are both showing a group that large, then you can eliminate them as the cause. and move on.
These are just a few ideas, like I said, we need more details. Also, NEVER reload for semi auto military type firearms using commercial primers. THEY ARE TOO LIGHT and can cause slam fire which will destroy your rifle. You MUST use Military primers. You will see that CCA and winchester offer Primers with a different # for bolt action and semi auto rifles. Military primers are heavier (less sensitive) and are forced into the primer pocket and then crimped to keep them from backing out under rapid fire recoil. To see what I mean, load a round into your magazine and place it in the rifle, then release the bolt with the firearm in a safe direction. then remove the round from the chamber and look at the primer, you will see that the firing pin has slammed forward and left a dent in the primer. With light primers, this would have fired the round. Military semi auto's don't have a spring to keep the pin back. The pin is free floating. JUST FYI

Answer 4

This depends on many things. What type of bullet are you using?

AR mostly come with either a 1:8" or 1:9" twist. You can shoot up to 75gr 22 cal bullets with these twist.

Bullet type: If you are shooting FMJ (Full Metal Jacket) that is about the best your going to get. FMJ bullets are not meant for great accuracy they are meant to be cheap because the military shoots a lot of them.

For best accuracy in any firearm you need to reload. I know many people do not want to invest the time money and effort it takes to start reloading. Look for some good factory match ammo from Black Hills, Hornady, Federal ect. Hornady TAP 69gr round I bet would tighten up your groups. Most of your match ammo will have one of two types of bullets either a HPBT (Hollow Point Boat Tail) or Hornady make what they call the A-Max these are very accurate bullets with a polymer tip. their Ogive is very long for a small bearing surface and work well in the fast twist barrels like those found on AR platform rifles.

You do not mention what the manufacture of your scope is. You are not going to get the same results from say a BSA as you are from Burris or Leupold.

Answer 5

My first reaction was 'Why is he sighting in a AR at 50 yards using a scope?'

My money is on a scope or mount issue.

You could simply check the gun's accuracy by using iron sights....if you had them. Also, move that target out to a distance where a full powered round can stabilize in flight.

Answer 6

Try different ammo.

EDIT, Ok apparently it's not the ammo, check your scope rings to make sure everything is tight. If that's not it, try a different scope unless you know for a fact the scope that's on it now holds zero. I had a Bushnell Banner scope that had wandering reticle disease, you never knew from one shot to the next where the bullet was going to hit because the reticle wandered around. It took me a while to figure it out and once I did, I quickly replaced the scope.

Answer 7

What type of scope. I had a trijicon reflex, borrowed from a buddy and it shot about the same at that distance. With iron sights I'm shooting .5" at 50 yds and with the reflex I'm shooting 4" at 50 yds. So definitely a scope problem there.

Did you build the rifle?

Answer 8

notthena may have hit on something ,they changed the twist in one of the models cant remember the twist but it was put in to stabilize the heavier bullet 60 or 70 grains as a possed to the 50 -55 grain cant remember the paticulars had forgot about it until i saw the other posting.but i remember that with the odd twist you could hit crap with a 55 grain bullet .other than that normal stuff,check mounts for tightness ,the crown for damage ,may just not be a shooter not all rifle are .good luck

Answer 9

It may be that you are using an inexpensive ammo not suited to your firearm and its twist rate. different guns like different ammo, you'll have to try a few different grains/manufacturers until you find something your ar really likes.

it may be that your sight is not properly sighted in, and than there is always the big thing, human error

thats all i can think of...have you had your sight checked? and has it been shot by different people to make sure you are not doing something incorrectly?

Answer 10

I'm guessin Human error on this one. Go back the the basics of breathing and trigger squeeze. Rifles are only as good as the person holding them.