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Grendel group - DaneNorthman - 02-17-2019
Hello all, I hope some of you experts can help me out here with a question. I am new to the grendel, built one as an excuse to bud another AR. The question I have is: at 100 yards I am hitting 1.5" high. At 250 yards my group has moved 6.5" right and 5.5" low. The day at the range in question there was no wind. Has anyone else encountered a "wandering" group? I'm leaving in two days to chase some aoudad and would love to take the grendel. I'm shooting a ballistic advantage 20" barrel on an aeroprecision lower, using 123 gr. Hornady black ELD. I hope to hear from someone soon. Thank you
Grendel group - VASCAR2 - 02-18-2019
That doesn’t sound normal. I would ensure the hand guard or attachments are not hitting the gas block. I’d also check the barrel nut to see if it is tight. I’d also check to make sure the flash hider, compensator or thread protector are not loose. Also look at the flash hider or muzzle brake to ensure the bullets are not hitting the muzzle device. If the bore is not centered in the barrel or the threading is not square you can encounter bullets hitting muzzle devices. I’d also check to ensure the scope is tight, rings and mount to the rail.
I’ve seen scopes go bad and if everything is tight I’d try a different optic.
Remember on an AR-15 your scope is 2.5” to 2.75” over the center of the bore which comes into play with down range ballistics. With more traditional bolt action rifles where the center of the scope is 1.5” over the center of the bore you would sight in 1.25-1.5” high at 100 yards so your shots would hit on medium size game out to 250-300 yards.
To get an AR-15 to shoot 1.4” high at 100 yards I used a 45 yard zero. The biggest concern I have is that your rifle was 6.5” right. The 5.5” inch low doesn’t sound to far off the ballistics I got using the Hornady ballistic calculator.
![[Image: 40164224463_4e278918f9_z.jpg]](https://farm8.staticflickr.com/7821/40164224463_4e278918f9_z.jpg)
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Grendel group - Bigs28 - 02-18-2019
Do you have a level on your rifle to make sure your gun is level when shooting at the range?
Grendel group - DaneNorthman - 02-18-2019
Thank you for your responses. Everything on the gun has been checked and rechecked, (due to the problems I had with 2 bear creek arsenal barrels) once I put the ballistic advantage barrel on i went from 4.5" groups at 80 yards, to clover leafs at 100 yards. The 6.5" right and 5.5" low would be right based on the tables I have studied, IF there was a 90 degree 10mph wind. Unfortunately it was dead calm. I don't have a level on the gun but I did use levels to mount the scope. For assistance on the range I have a bipod and a few decades of 500+ yard paper killing experience. I'm starting to wonder if it isn't the "break" of the trigger yanking me down and over.
Grendel group - Javman - 02-18-2019
That's why I like to zero at 200 yds and then check at 100 yds to see if it is me, the ammo, gun etc! Hope you get it checked out before your hunt, good luck!
Grendel group - StoneHendge - 02-18-2019
Almost sounds like your scope and bore aren't aligned. Remember that a scope zero is just where the 2 lines from the bore and scope meet at a particular point. Aside from remounting, an easy way to check would be to see if you group to the left at say 25 yards. What scope/mounts are you using?
Grendel group - Arkhangel5 - 02-18-2019
I will second what Javman said.
I would try zeroing the rifle at 250-300yds, then dial in your 100yd dope and see where the bullets are impacting, then move on from there.
There should not be a large horizontal shift dialing down, and will give an idea where to start looking for issues.
Assuming you have enough time that is.
SY
Grendel group - LR1955 - 02-18-2019
DaneNorthman Wrote:Thank you for your responses. Everything on the gun has been checked and rechecked, (due to the problems I had with 2 bear creek arsenal barrels) once I put the ballistic advantage barrel on i went from 4.5" groups at 80 yards, to clover leafs at 100 yards. The 6.5" right and 5.5" low would be right based on the tables I have studied, IF there was a 90 degree 10mph wind. Unfortunately it was dead calm. I don't have a level on the gun but I did use levels to mount the scope. For assistance on the range I have a bipod and a few decades of 500+ yard paper killing experience. I'm starting to wonder if it isn't the "break" of the trigger yanking me down and over.
DNM:
If you have a bunch of marksmanship experience like it sounds like you do, you would be able to see that you had a bad trigger pull. Particularly one that pushed the barrel about 3 minutes. Unless your eyes were closed when you fired the shot, you didn't jerk the trigger. I agree totally with Stonehenge. Either your optic is screwed up, your barrel is way off center from your optic, or the optic is not mounted properly on your rails.
Here is what you can do if you want.
First -- check to see the cross hairs are level and the mount is properly secured to the rail. Have seen mounts that were partially secured to rails which causes all sorts of problems with a zero. My bet is both are fine.
Second, put the rifle down on the ground with the bipod and stand directly over the rifle and look straight down and see if the optic and barrel are aligned (pointed in the same direction). Really. I have done this and much to my surprise -- I have seen rifles where the barrel and optic were pretty far out of alignment with each other. Some were due to poor workmanship and barrels that were installed poorly and others where the rail was not aligned with the upper. I would look closely at this one.
Although somewhat more rare, sometimes the barrel maker cuts the bore crookedly. This is like a barrel being installed crookedly. That one is harder to see with the eye. Not really sure how to check that one but it is a possibility.
If you want you can check the tracking but I bet that is fine too.
LR55
Grendel group - Klem - 02-19-2019
DN,
You are talking about a 2.5MOA horizontal drift between 100 and 250. There is nothing peculiar about the calibre you can blame. As you say it's not the wind. That is too much specific drift for it to be ammo. If your groups are statistically valid (i.e. not one or two shots on the edge of their respective MPI) then the gun or shooter caused it.
Grendel group - Sinclair - 02-19-2019
[QUOTE=LR1955;22
Although somewhat more rare, sometimes the barrel maker cuts the bore crookedly. This is like a barrel being installed crookedly. That one is harder to see with the eye. Not really sure how to check that one but it is a possibility.
If you want you can check the tracking but I bet that is fine too.
LR55[/QUOTE]
It can be done, I have done it myself. Its late, I am tired and this is my third attempt to reply. I will try again in the morning. Sorry us old men need our rest.
Grendel group - DaneNorthman - 02-19-2019
Thank you for all the input. My inclination of the trigger pull being the culprit is due the fact that in full zoom my crosshairs completely cover my point of aim at 250 yards. I'm just a beat up veteran trying to make it as a carpenter so nice high zoom quality glass scopes aren't a staple in my gun cabinet. I am going to disassemble/dismount everything and "rebuild" the gun a final time. The scope and rings I'm using are UTG. I hope to find the problem, I am anxious to see what this baby will do against some aoudad and big Texas hill country boars.
Grendel group - VASCAR2 - 02-19-2019
I hope you figure it out DaneNorthman. Just be leery of over torquing your scope. I use a torque wrench set to scope manufacturers specifications, usually 16-18 inch pounds. Some mounts show 30 inch pounds for the mount to the picatinney rail.
Grendel group - LR1955 - 02-19-2019
DaneNorthman Wrote:Thank you for all the input. My inclination of the trigger pull being the culprit is due the fact that in full zoom my crosshairs completely cover my point of aim at 250 yards. I'm just a beat up veteran trying to make it as a carpenter so nice high zoom quality glass scopes aren't a staple in my gun cabinet. I am going to disassemble/dismount everything and "rebuild" the gun a final time. The scope and rings I'm using are UTG. I hope to find the problem, I am anxious to see what this baby will do against some aoudad and big Texas hill country boars.
DN:
When you fired the shot, were the cross hairs in the middle of your target or did they move? If they moved, did they move to the point where your shots went? If your eyes saw this and registered it with your brain, you 'called your shot'. Calling your shot is an elemental marksmanship task. You said you had shot a lot at 500 yards so my assumption is that you can call your shots. You may not be doing it, though.
It is amazing how this simple task can be used to troubleshoot either human or mechanical performance. If the shots went to your call, nothing is wrong with your zero. If they didn't go to your call yet you still shot a group of some sort, your zero needs adjusting. If you were calling your shots but the results were totally random and well over two minutes of angle from your calls (for very good shooters this will be under one minute) something is really wrong with your equipment and you then have to isolate it as your sighting system, rifle, or ammo. Sometimes it is a combination but mostly it will be primarily one of these three mechanical things. It is a very simple way of troubleshooting a problem and your eyes are just fine for doing so. Trust your eyes.
Use a bigger aiming black so you can get your cross hairs centered. Or, spray paint a nice, sharp, white circle on a piece of cardboard and use that as an aiming point. Which ever one you choose, the black must be big enough so your cross hairs can be centered and centered easily -- without eye strain or you questioning what you are seeing. Doesn't really matter what color but white on black or black on white gives the most contrast and thus is easier for your eyes to see a center. Sounds like you are using a thick hunting sort of cross hair. Probably half a minute wide. Easy to see if you have adjusted the ocular lens so it is clear. Use a four minute black or white aiming point. That ought to be pretty comfortable for you to see and ought to let you put the cross hair in the middle very quickly and easily.
LR55
Grendel group - bj139 - 02-19-2019
Op:
Are you adjusting the scope at all between these distances? I have used scopes that moved 3MOA when adjusted to 2MOA movement.
I took a Bushnell out of service that had this problem and replaced it with a cheaper scope that did not.
I didn't remember if the scope rings were Gorilla tight or not.
Also, VASCAR mentioned that overtorquing the scope rings bound up the erector assembly in the scope.
I read somewhere that someone had this problem with a Vortex scope.
I have no other ideas what could cause it.
Grendel group - DaneNorthman - 02-19-2019
Upon reassembly the problem seems to have vanished. I would hate to think the shop that installed the barrel did something wrong but when assembled here at home everything has tightened up. She's shooting straight and I'm loving the 2.5" groups at 250 yards. I was beginning to think the problem might have been me, glad to know I still got it. Thank you all for the assistance and knowledge. I think it was just like my truck, had a gremlin that needed eviction.
Grendel group - pacificpt - 07-04-2019
Glad you got it worked out, hope to see a picture of the rifle leaned up against an Aoudad!