AR15 upper assembly question

[Kruel J]

The receiver face can be off square from the receiver bore/rail plane. It happens. I would contact PSA before attempting any disassembly.

I would argue that the chances of his UTG scope failing are MUCH higher than the receiver being off square. It probably happens, but its damn rare.

 

[Koda]

I would argue that the chances of his UTG scope failing are MUCH higher than the receiver being off square. It probably happens, but its damn rare.

this is the question here.... I know its a cheap scope but its barely used and barely a year old. I bought it to just play around with and it worked fine on my other upper and that is why I dont suspect the scope has gone bad.

 

[Kruel J]

If you're not in a hurry I am RSOing this Sunday. Bring your rifle, and I'll bring my .300BLK AR. We can swap the optic off mine and do some testing.

 

[Koda]

heres a pic of the target. The 3 shots closest the bullseye are with mbus open sights and they are zeroed at 100yards nicely. The two shots that are 4 inches low are with the UTG scope maxxed out, will not adjust any higher. This is at a 25yd initial zero. (the windage adjusted easy...)

 

[Kruel J]

So the MBUS sights zeroed fine but the UTG doesn't??


You should have led with that. I'm now really convinced its the optic.

 

[Koda]

If you're not in a hurry I am RSOing this Sunday. Bring your rifle, and I'll bring my .300BLK AR. We can swap the optic off mine and do some testing.

would love to take you up on that but I will be traveling the next two weekends so this project is on hold but I wanted to see what others more knowledgeable say in the mean time. Im thinking of another range day sometime in sept though...

 

[Koda]

So the MBUS sights zeroed fine but the UTG doesn't??


You should have led with that. I'm now really convinced its the optic.

I wasnt certain if the two sight systems compares. I dont know how much travel open sight systems have for elevation adjustment. If the upper assembly is not square by a fraction I could see open sights being able to easily compensate for that since the front sight is on the handguard not the upper receiver....

 

[solv3nt]

What's your experience level with scopes? Not to belittle your experience, but a scope elevation adjustment is opposite that of iron sights; you move the cross hairs to the hole.

Took me a few shots to figure that one out

 

[Koda]

What's your experience level with scopes? Not to belittle your experience, but a scope elevation adjustment is opposite that of iron sights; you move the cross hairs to the hole.

Took me a few shots to figure that one out

I pride myself in easy sight ins... not new to zeroing a scope at all and typically have it done in a few rounds as long as the ammo groups well enough. Same for iron sights.

 

[Mygrainman]

I'm pretty sure it's an optic issue, but I'd be curious to see a pick of the barrel extension. Does it appear to be flush all the way around like this one?
Then again if it wasn't you'd have lockup issues with your bolt.

 

[Koda]

I'm pretty sure it's an optic issue, but I'd be curious to see a pick of the barrel extension. Does it appear to be flush all the way around like this one?View attachment 1009321
Then again if it wasn't you'd have lockup issues with your bolt.

I cant even see in there like that pic to compare but have no lock up issues, so far the thing has has zero malfunctions but I havent shot much thru it maybe less than 60rds.

 

[Prefontaine]

What's your mount for the optic? Is it possible that the bases/mount is off?

 

[Mygrainman]

I cant even see in there like that pic to compare but have no lock up issues, so far the thing has has zero malfunctions but I havent shot much thru it maybe less than 60rds.

Ya it's a little like trying to get a look at your own… nevermind

 

[Member 34319]

I dont have a proper way to accurately measure the 1.215 but thats good to know. What I can measure seems good (pic). Im estimating my scope is about 2.9" above the bore.... Id have to look up the total MOA adjustments of the scope and somehow compare with the calibers trajectory and scope height.
View attachment 1009252

Based on your measurements, if the scope is zeroed back to original, or in other words centered. The bullet would be hitting paper 2.9" below your point aim. A slightly out of spec receiver and or scope mount might give you an additional 1-2" of play in any direction depending on how poorly they are made. If they are manufactured well. They shouldn't drift the basic 2.9" of scope to bore that drastically. So, like I said, you either did something off when trying to zero, like dialing up instead of down. Or the scope is busted. Or the upper/mount is wildly off spec.

 

[Koda]

Based on your measurements, if the scope is zeroed back to original, or in other words centered. The bullet would be hitting paper 2.9" below your point aim. A slightly out of spec receiver and or scope mount might give you an additional 1-2" of play in any direction depending on how poorly they are made. If they are manufactured well. They shouldn't drift the basic 2.9" of scope to bore that drastically. So, like I said, you either did something off when trying to zero, like dialing up instead of down. Or the scope is busted. Or the upper/mount is wildly off spec.

Im ruling out operator error and scope mount... Ive zeroed enough scopes easily and replaced the scope mount with a new one just for troubleshooting this problem. Its either the scope or the upper build... Im really hoping its the scope. I will have to try centering the scope and remove the bolt and see if I can detect by eye a 2.9" difference thru a bore sight at 25yds in the backyard (with the upper removed from the rifle...).
I should also try this on the old upper, in fact take that one to the range and rezero. It worked once before, if it doesnt work on that upper again then its the scope...

 

[TTSX]

I had this exact issue with a PSA upper. Optic was a cheap Bushnell, mount was aero one piece. My friend now owns the upper and zeroing and 100 was easy. I'd suspect your optic before anything else

 

[Koda]

I had this exact issue with a PSA upper. Optic was a cheap Bushnell, mount was aero one piece. My friend now owns the upper and zeroing and 100 was easy. I'd suspect your optic before anything else

Im leaning towards the cheap optic but its that the optic worked fine on my old upper build and thats what bothers me. Maybe it got knocked around enough ... I hope. Id rather it be the optic.

 

[Member 34319]

Im ruling out operator error and scope mount... Ive zeroed enough scopes easily and replaced the scope mount with a new one just for troubleshooting this problem. Its either the scope or the upper build... Im really hoping its the scope. I will have to try centering the scope and remove the bolt and see if I can detect by eye a 2.9" difference thru a bore sight at 25yds in the backyard (with the upper removed from the rifle...).
I should also try this on the old upper, in fact take that one to the range and rezero. It worked once before, if it doesnt work on that upper again then its the scope...

Another inquiry.

Snap a picture of your iron sights on the rifle you were able to group well with. If they are heavily adjusted as well, you should be able to determine if it is the scope or upper/rail. Most irons don't require a ton of adjustment if mounted to a properly made rifle with decent components.

 

[Greenbug]

A theory for you....
Sounds like you could have a mount with MOA built into it mounted backwards?

 

[308]

There is a reason POS scopes are cheap.