Massive POI Shift Overnight

[Airgun_N00B]

A good while ago, I bought a Kral Arms Puncher Jumbo, and it groups fantastic, but I had a sentinel scope on there, and the POI kept changing. The turrets on that scope were already a bit too sketchy for me, sometimes taking 3-4 shots to get "settled in" after an adjustment, so I just bought an Aztec Emerald 5.5-25 sfp. Fantastic scope, absolutely love it. It was easy to zero, and the tracking is phenomenal. Well, after zeroing it at 50 yards last night, I brought the gun inside, refilled it, and let it sit overnight. This morning, when I took it out at 50 yards again, same shooting position, target distance, no wind in either scenario... There was an 8.75 MOA verticle change. The power is the same, the distance, position, all that is the same... It just dropped by 8.8 MOA. I zeroed it again and it is grouping perfectly. Little bigger than dime-sized groups at 50 yards, I'll attach a photo. My first thought was the scope rings must be loose (fx no limit scope rings), but all the screws on it for attaching to scope, gun, and verticle adjustment are snug. I also thought maybe the silencer or shroud was loose maybe, but they seem very snug as well. Is there anything I may be missing here? This isn't the first time this has happened. It never happens while using the gun. It always happens overnight, though not all the time. The gun is stored on the ground, standing on the bipod. It is out of the way, and doesn't get bumped or anything while not in use.

 

[DanielL]

Not familiar with that particular gun but I did have similar issues with an Umarex Gauntlet. Just leaving it on it's side for an hour would cause the POI to drift. It changed every time I brought it out. I finally fixed the issue with a few things.

1. Made sure barrel mount was nice and tight...all set screws were torqued down and loctited.

2. Similarly tightened shroud firmly and has to also tighten the part the shroud was tightened down to.

3. Removed the shroud brace ring which was putting a side load onto the shroud.

Good luck.

 

[elh0102]

I'm not familiar with that rifle, but, for POI to change that much, something almost has to be moving. You mention a shrouded barrel. If there is an air stripper than supports the shroud, I would check that for good attachment, as well as the shroud, barrel and silencer. 

 

[DanielL]

I forgot to mention I also greased the o-ring, between the barrel and shroud so that they would slide freely and not hang up.

 

[Black2086]

I was also having a POI shift with a Zbroia Kozak that was a shroud issue.. It was the shroud and air stripper/stock moderator. If you cleaned gun, if you bumped shroud, or if you held your mouth wrong the POI would change. I ended up throwing the shroud and stock moderator away and put a DonnyFL on it... High price to pay but it solved all issues... Good Luck

 

[easyridemm]

Just another thought. I had a similar problem on one of my Edguns. I had a very slow leak in my regulator. It never happened while I was shooting the gun because the regulator cycled fast enough not to show a problem. Let the gun sit over night and there was a change in my POI. Once I started to shoot everything was fine again. Hope this helps.

 

[Airgun_N00B]

I only tightened the shroud, and not the barrel itself. I was a bit scared to take it apart. I'll give it a try when I get home after work

 

[brawler1588]

Is it possible the grub screws that hold the actual barrel in place backed out?

 

[ackuric]

Does this rifle use a baffle system with a spring behind the baffles in the shroud? If so any change in tension on the spring which is then applied to the barrel tweaks the barrel in the rotation the change was made... for my marauder I remedied this by cutting shroud at the end of barrel leaving enough space to re-thread in front of the muzzle, then making an adapter and an external 'LDC' that has clearance between it and barrel so there is no longer shroud tension on the muzzle end of the barrel, which 100% remedied any and all POI shifts my rifle had from shroud tension.

 

[BarryW]

Try to torque your scope mounting screws. I had same issue as you. Do not over tighten. Barry

 

[Yo]

A good while ago, I bought a Kral Arms Puncher Jumbo, and it groups fantastic, but I had a sentinel scope on there, and the POI kept changing. The turrets on that scope were already a bit too sketchy for me, sometimes taking 3-4 shots to get "settled in" after an adjustment, so I just bought an Aztec Emerald 5.5-25 sfp. Fantastic scope, absolutely love it. It was easy to zero, and the tracking is phenomenal. Well, after zeroing it at 50 yards last night, I brought the gun inside, refilled it, and let it sit overnight. This morning, when I took it out at 50 yards again, same shooting position, target distance, no wind in either scenario... There was an 8.75 MOA verticle change. The power is the same, the distance, position, all that is the same... It just dropped by 8.8 MOA. I zeroed it again and it is grouping perfectly. Little bigger than dime-sized groups at 50 yards, I'll attach a photo. My first thought was the scope rings must be loose (fx no limit scope rings), but all the screws on it for attaching to scope, gun, and verticle adjustment are snug. I also thought maybe the silencer or shroud was loose maybe, but they seem very snug as well. Is there anything I may be missing here? This isn't the first time this has happened. It never happens while using the gun. It always happens overnight, though not all the time. The gun is stored on the ground, standing on the bipod. It is out of the way, and doesn't get bumped or anything while not in use.

You're using Picatinny and NOT 11mm scope rings right? Yo!

 

[Raden1942]

All good advise. I will add try taking your shroud off completely and see if it still happens. If it does check the scope rings and possibly locktight them. Do not get any locktight on plastic or you will have a gun that literally cracks apart in your hands. Ask me how I know. I like to narrow down causes to poi shift by eliminating all possible causes first. You probably have some screws backed off somewhere definitely check the barrel set screws. Goodluck.