mp sport 2 scoped shooting very low

[rodney winston]

based on all good accuracy reviews i purchased a new ar15 sport put a 4x12x40 vortex diamond back scope on 2 inch tall millet rings.took it to my bench rest sighted in at 40 yards which should be 1.5 high at 100 yards and zerod at 200 yards roughly. instead with 40 yard zero it was 10 inch low at 100 yards and roughly 36 inches low at 200 yards [hit a few yards in front of target that was 24 inches above ground] tried second set of mounts then second scope same results .results dont seem phisacly possible first ar but i own many bolt rifles sending to s&w .any thoughts on what might be wrong im thinking barrel seat or warp.many ar15s are only shot at indoor ranges where this problem would go un noticed wonder if there are others out there like this

 

[cyphertext]

You're right, that doesn't seem possible. If the round is on target at 40 yds, it shouldn't change trajectory so dramatically. Are the rounds keyholing at 40 yards? What about 50 - 100? That is the only thing I can think of.

What type of round are you shooting? What is the weight?

 

[sgoss66]

Agree that is totally messed up. Were you shooting at paper? If so, did you notice keyholing at 100 yards, by chance?

EDIT -- sorry, cyphertext beat me to it with basically the same answer!

 

[sgtsandman]

Possible problem with the scope?

 

[cyphertext]

Possible problem with the scope?

That was my first thought, but then I re-read his post and he he said he changed mounts and tried a second scope with same results.

 

[sgtsandman]

Hmmm... Missed that. That's what I get for not having enough sleep.

 

[Goblin]

What exact ammunition are you using? Brand, bullet weight and bullet type?

 

[McE]

2 inch tall millet rings.

Got a pic?

 

[rodney winston]

ive used trula 55 and 62 grain cheap ammo and pmc 55 grain bronz . at 50 yards i had decant groups of .5 to .75 inch . at 100 yards the groups opened up to 2 to 3 inch the creepy trigger didnt help but ive shot my siaga ak 47 with better groups and its trigger is the worst one ive ever used feels like a semi auto pistol using double action

 

[ChattanoogaPhil]

Two inch tall?

Rings are typically measured by the height of the scope ring base to the bottom of the ring. One inch is the proper hieght for an AR platform. 2in tall would put sight over bore at a whopping 3.5 inches. If you zeroed at 40yds you'd be about 5 inches high at 100.

In any event, did you actually zero at 40yds by shooting the gun or was this a bore sight? Otherwise, what you are describing can't happen absent a flopping loose barrel or other significant defect, and even at that the results would not be consistent as described. Unless you are doing something goofy like hand feeding the wrong caliber ammo, just send it back.

 

[Goblin]

Check to see that everything is tight, including the barrel. Like Phil, I'm puzzled as to how that can happen without something being loose.

 

[Inusuit]

I'd pull the scope and shoot it with irons to see if you still have a problem. I agree with other posters that something is seriously amiss here.

 

[rodney winston]

going shooting tomorrow supposed to be 60 degrees ill take new ar to try iron sights.on the ring height i measured from center barrel to center scope 2 inches probably 1 inch rings but all was tight and scope came off 243 hunting rifle always kept good zero same as cheaper simmons i took off 22 mag. s&w sending box for return for repair

 

[lrrifleman]

For your rings, you want to select the ring height based on the diameter of the scope's objective lens bell. You want a clearance between the objective bell and the rifle of about a quarter inch.

From the sounds of your problem, it sounds like you may have one of two problems. The first, which is the least likely, is that the rings have an internal offset insert in one ring to provide about a 20 minute offset for long range shooting. This type of ring was often used with Leupold and Millet one piece, windage adjustable bases. Along this line, you may find that the height of the lowerhalf of the ring from the base contact point to the bottom of the ring saddle is not uniform. You can ascertain uniformity by miking the lower half of your rings.

The second problem, which might be the culprit, is that the picatinny rail on the upper receiver is not true, and is not parallel with the centerline of the bore. This can be easily determined by miking the front and rear of the receiver off of the top of the rail.

I hope that this might help.

 

[ChattanoogaPhil]

Ring hieght on an AR platform isn't determined by the size of the objective bell. Heck, most low magnification AR optics like 1-4x don't even have a "bell". 1in tall rings are typically used for proper cheek weld.
The aperture on AR iron rear sight is about 1.4in above the reciever. That height is what you're mimicking with 1in tall rings plus half the tube diameter of the scope.

Offest rings would not deliver what the OP is describing either. In order to get the bullet to cross line of sight at 40 yards "zero" there is a trajectory of the bullet rising in relation to line of sight. On an AR with 1in tall rings as the OP now says, the scope will be about 2.5in above bore. That 3000fps bullet doesn't magically reverse trajectory at 40yds to end up 10 inches below line line of sight at 100yds as the OP describes. Doesn't matter if line of sight is being adjusted with offset rings, a canted base like 20 or 30moa or internal scope adjustment. No matter... with a 40yd zero that bullet is still rising in relation to line of sight at 100yds. No magic bullet, rings or scope.

For your rings, you want to select the ring height based on the diameter of the scope's objective lens bell. You want a clearance between the objective bell and the rifle of about a quarter inch.

From the sounds of your problem, it sounds like you may have one of two problems. The first, which is the least likely, is that the rings have an internal offset insert in one ring to provide about a 20 minute offset for long range shooting. This type of ring was often used with Leupold and Millet one piece, windage adjustable bases. Along this line, you may find that the height of the lowerhalf of the ring from the base contact point to the bottom of the ring saddle is not uniform. You can ascertain uniformity by miking the lower half of your rings.

The second problem, which might be the culprit, is that the picatinny rail on the upper receiver is not true, and is not parallel with the centerline of the bore. This can be easily determined by miking the front and rear of the receiver off of the top of the rail.

I hope that this might help.

 

[jimbo728]

2" tall rings? The rings I use on my Sport are only 20mm from base to centerline. Looseness, bad scope not withstanding, I bet the problem is that your mount puts the scope too high off axis.
Jim

 

[ChattanoogaPhil]

The higher the scope is mounted above the bore the higher the bullet will strike above line of sight at 100yds with a 40yd zero. The OP is describing the bullet striking 10 inches below line of sight at 100yds with a 40yd zero.

So no, mounting the scope higher above the bore would not create a magic bullet as the OP is describing.

2" tall rings? The rings I use on my Sport are only 20mm from base to centerline. Looseness, bad scope not withstanding, I bet the problem is that your mount puts the scope too high off axis.

Jim

 

[Magload]

The only way this could possible happen is if the OP has figured out how to get the bullet to cross the line of sight the second time at 40 yards which would mean that the bullet was then dropping after 40 yards. I don't think this could happen where would the first crossing point be, the chamber? Don

 

[cyphertext]

Something is wrong with the barrel... again, I bet the round is tumbling and keyholing.

 

[ChattanoogaPhil]

The only way this could possible happen is if the OP has figured out how to get the bullet to cross the line of sight the second time at 40 yards which would mean that the bullet was then dropping after 40 yards. I don't think this could happen where would the first crossing point be, the chamber? Don

The chamber.... funny.

Actually you can get 10 inches below line of sight at 100yds with a 40yd zero if shooting with a muzzle velocity of around 900fps instead of typical 5.56 velocity of around 3000fps. The first time the bullet would cross line of sight would be less than 30yds then cross again at 40yds. That's why I left open the possibility of the OP hand feeding goofy ammo. In any event, I think the OP made the right decision to send the rifle back. If nothing else it will give him time to think about it.