Grouping at 100 yd - then suddenly nowhere on paper?

[metroplex]

I had previously brought my Form 1 SBR Kriss Vector to the range at 100 yd using my cut barrel at 7.5" length and it was averaging 5"-6" 5-shot groups at 100 yd. I had then sent it into Kriss for their 6.5" SBR conversion and today was the first time I was able to test it at the range. During initial zero/sight-in, it was shooting low and to the right. I adjusted my Holosun 510C (the same 510C I used the last time) and was getting it on paper. I got some nice 4" groups using the same ammo (CCI Blazer 115gr) and then started to notice my shots were no longer anywhere on paper.

I tried bigger targets, aiming at different corners and even dirt to see POI. I'd adjust to try and compensate, get a few shots on paper, and then the POI would disappear again.

I checked the Holosun 510C mount, checked the barrel for obstructions, etc.... and short of doing a disassembly during cleaning to inspect, I'm kind of out of ideas. I've never had this happen the last time and I put it through its paces with about 250+ rd the last time.

The good news is that it seems to run like a sewing machine, even with a suppressor (Silencer Central Banish 45) that I attached at the end just to try it out for a few dozen rounds. It's filthy and I was getting a lot of carbon/gas blowback but she was running just fine... except for not seeing the impacts. Even with the can on, I did not see any baffle strikes or end cap strikes. So the bullet is leaving the bore straight.

 

[kriller134]

Maybe the holosun took a dump. Do you have a different optic to try?

 

[wade2big]

The chinese optic may have pooped the bed. It’s the most likely by what you described.

 

[metroplex]

I have other optics but I'd have to try them at the next range session. I was really stressed for time this go around. I did have a Primary Arms microprism 3x handy but it wasn't zero'd to the Vector. I do have other American made holo sights (EXPS3-2 and UH-1) that I should probably try.

I have another 510C on the Ruger PC Carbine 9mm that was working fine, got tighter groups this go around at 2.5" (last time was 2.95")

 

[howler]

Take it to 25 yards and work out from there.

 

[AMGtuned]

All that weapon......... and a Holosun??

 

[metroplex]

Take it to 25 yards and work out from there.

It was fine at 100 yd. Then it wasn't fine.

 

[metroplex]

All that weapon......... and a Holosun??

The Vector is just a 9mm PCC. I only used the 510C because it came highly recommended and seemed popular among PCC shooters, it was lighter and smaller than the EXPS3-2 I have. I will try and see what's going on with the Vector and try the EXPS3-2 or UH-1 the next time around. I have an identical Holosun 510C on my Ruger PC Carbine that shoots consistently at 100 yd.

 

[msgriff]

Worth a call to Kriss, could be something in their barrel retention system.

 

[metroplex]

Worth a call to Kriss, could be something in their barrel retention system.

Possibly, but their barrel is basically pinned and riveted to the trunnion. I'll have to examine it closely when I clean it.

 

[msgriff]

Possibly, but their barrel is basically pinned and riveted to the trunnion. I'll have to examine it closely when I clean it.

So, that would leave the optic/mount as the likely culprit.

 

[AMGtuned]

The Vector is just a 9mm PCC. I only used the 510C because it came highly recommended and seemed popular among PCC shooters, it was lighter and smaller than the EXPS3-2 I have. I will try and see what's going on with the Vector and try the EXPS3-2 or UH-1 the next time around. I have an identical Holosun 510C on my Ruger PC Carbine that shoots consistently at 100 yd.

I understand.

I would swap optics and try that, and/or contact Kriss

 

[metroplex]

I am wondering if the 510C can't handle the recoil motion of the Vector? The bolt moves back and down, but slaps vertically up. Those that have shot them can feel it in their cheek bones. You know how rimfire has a different recoiling motion that can damage normal scopes... I am wondering if this is what could have caused the 510C to go bad?

 

[msgriff]

I am wondering if the 510C can't handle the recoil motion of the Vector? The bolt moves back and down, but slaps vertically up. Those that have shot them can feel it in their cheek bones. You know how rimfire has a different recoiling motion that can damage normal scopes... I am wondering if this is what could have caused the 510C to go bad?

Holosuns are rated to 1000G. 9mm is just under 500G. I ran an older 510C for a while on a 358 Win AR, which is over 850G.

 

[metroplex]

Just as an update... I used Strelok, input actual Labradar velocities, measured height over bore for the sights, etc... put my Site Lite SL-150 laser bore sight on the Ruger PC Carbine (which has a black 510C Holosun and was zeroed/functioned fine at the 100 yd range) to check against Strelok data for the bore sight distance.

Then did the same for the Vector with its 510C and it was 52 clicks high. That's a LOT of elevation adjustment that I don't remember doing at the range. What I do recall was that I zeroed this 510C at the range with my Form1 cut 7.62" SBR (CRB barrel cut down, not threaded) and after Kriss converted it to their 6.5" SBR barrel, I don't recall laser bore sighting it or assumed it would be similar. I looked at the CRB data from Strelok and it shouldn't be this much off at 100 yd.

I took the 510C off and shook it in multiple axis, then replaced it to check against the laser bore site. Did this a few times and each time it was the same.

This doesn't explain why I was able to get some decent groups at the beginning and then suddenly have it go off paper.

I did notice that on my Ruger PC Carbine (16" factory threaded barrel) that my Site Lite arbor went into the bore nice and slick, even after ~200rd and many with a suppressor. But on the Vector SBR, I had to use a lot of lube to push down that arbor. The barrel and everything inside of the Vector was really filthy. Could a dirty bore cause that much of a POI change? I had purposely cleaned it with bore tech C4 and copper remover before taking the new SBR barrel to the range. I even borescoped it for any obstructions/defects before I had fired it.

 

[carbonbased]

You know how rimfire has a different recoiling motion that can damage normal scopes.

What?

I think you mean spring-powered air guns aka many (not all) pellet guns. They have a backward/forward motion that beats scopes up.

 

[metroplex]

What?

I think you mean spring-powered air guns aka many (not all) pellet guns. They have a backward/forward motion that beats scopes up.

Yes you got me. Brain fart!

 

[howler]

It was fine at 100 yd. Then it wasn't fine.

Right.. so if you can’t diagnose the issue at 100y, move closer…. Not sure what you’re expecting people on the internet to do if you haven’t tried anything else.

Just as an update... I used Strelok, input actual Labradar velocities, measured height over bore for the sights, etc... put my Site Lite SL-150 laser bore sight on the Ruger PC Carbine (which has a black 510C Holosun and was zeroed/functioned fine at the 100 yd range) to check against Strelok data for the bore sight distance.

Then did the same for the Vector with its 510C and it was 52 clicks high. That's a LOT of elevation adjustment that I don't remember doing at the range. What I do recall was that I zeroed this 510C at the range with my Form1 cut 7.62" SBR (CRB barrel cut down, not threaded) and after Kriss converted it to their 6.5" SBR barrel, I don't recall laser bore sighting it or assumed it would be similar. I looked at the CRB data from Strelok and it shouldn't be this much off at 100 yd.

I took the 510C off and shook it in multiple axis, then replaced it to check against the laser bore site. Did this a few times and each time it was the same.

This doesn't explain why I was able to get some decent groups at the beginning and then suddenly have it go off paper.

I did notice that on my Ruger PC Carbine (16" factory threaded barrel) that my Site Lite arbor went into the bore nice and slick, even after ~200rd and many with a suppressor. But on the Vector SBR, I had to use a lot of lube to push down that arbor. The barrel and everything inside of the Vector was really filthy. Could a dirty bore cause that much of a POI change? I had purposely cleaned it with bore tech C4 and copper remover before taking the new SBR barrel to the range. I even borescoped it for any obstructions/defects before I had fired it.

you can keep messing around and theorizing, or you can take it to 25 yards on paper like I mentioned and see what’s actually going on. There’s no reason to guess a million different times at home and wonder if any of them are the cause while fiddling with laser bore sighters and other junk.

1) Take it to the range.
2) Reshoot it at low yardage, that way even if it does deviate, it’s still on paper and you can get a better idea of the POI change.
3) Try to figure out what’s going on once you see what it’s doing downrange. Swap optics, etc.

 

[metroplex]

And I won't be able to do any testing for over a month, hence asking others for input and not just waste more time at 25 yd of there is a mechanical issue. Again it was fine at 100 yd and then it wasn't. Moving to 25 yd won't necessarily tell me the issue other than yes there is an issue. I will bring more optics the next time but the SL150 showed I was 52 clicks high which is odd. And the SL150 is a pretty damn good laser setup at least to get it on paper (not a cheap Chinese plastic boresighter)

 

[howler]

And I won't be able to do any testing for over a month, hence asking others for input and not just waste more time at 25 yd of there is a mechanical issue. Again it was fine at 100 yd and then it wasn't. Moving to 25 yd won't necessarily tell me the issue other than yes there is an issue. I will bring more optics the next time but the SL150 showed I was 52 clicks high which is odd. And the SL150 is a pretty damn good laser setup at least to get it on paper (not a cheap Chinese plastic boresighter)

Well if you can’t get to the range for a month, that’s not fun. I guess in that case all you have is time. Hope you figure it out.

 

[metroplex]

Well if you can’t get to the range for a month, that’s not fun. I guess in that case all you have is time. Hope you figure it out.

Yea tell me about it. Lots of down time to think things over, I still haven't had time to break down and clean the Vector. However I am leaning towards problems with the 510C. I keep seeing signs of the mount shifting around on the rails of both the Ruger PC and Vector. I tightened the mount as much as possible so that I can still be able to pull the lever/tighten the lever. I suspect it is because the cross bolt is round (and not a rectangular shape like LaRue's recoil stops) and might allow for some shift under recoil?
I'm going to try the UH-1 and EXPS3-2 on the Vector next go around. The 52 clicks of elevation deviation with the 510C probably pointed to some kind of mount/optic issue. Luckily both of my 510Cs are within return windows. This makes 3 out of 3 bad Holosun experiences.