TX 200 p.o.i. Change

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Uglyjohn

Uglyjohn

Member
Oct 5, 2017
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Minnesota, United States
I have a AA TX200 with a Tony Leach 22mm conversion kit aboard. Despite being <12fpe, I chose this gun for Hunter class FT because it is usually my most consistently accurate springer. During the last 2 matches I’ve noticed a significant poi change after about 45 shots in a 60 target match. It started shooting 1/2” high at the close targets to well over 1” high at 55yds. In both cases temp. increased from low 60s to upper70sF during the match and the Sightron S3 (at 16x) is prone to some shift with temp increase but in the OPPOSITE direction (ranges low). Actual distance to 45-55yd targets was verified with bracketing. SO what I’m asking is do you think I have a gun problem or a scope problem? Thanks. Uj
 
Having poi shift as the day warms up is common with some guns and scopes. You are correct there, also correct a out the S3 ranging shorter in heat.

What rings/ mounts are you using with your scope?

Have you tested velocity when this poichange seems to happen? How new is your kit, and what type of breech seal do you have?

Also is this something that is repeatable at home not just in a match?

Cam
 
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MartyMcFly said:
Given the smaller volume of the TL kit my guess it that it’s making more power as the temperature increases. Best way to determine that is to chronograph the rifle before and at the end of the match. This should tell you if the POI is from material warping or higher power.

-Marty
Click to expand...
The TL kits typically slow with temp if it's a delrin bearing kit.

How's the comp tube lockup? When the rifle is cocked? Does the link between the underlever and the comp tube rattle when it's cocked?
 
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Kerndtc said:
The TL kits typically slow with temp if it's a delrin bearing kit.

How's the comp tube lockup? When the rifle is cocked? Does the link between the underlever and the comp tube rattle when it's cocked?
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Do you mean that the delrin expands with higher temp, leading to more friction, or does it become more vicious?

My first thought was that any lubes would become more inviscid and the piston seal would have better sealing when warm, thus better compression… but I guess Occam’s razor points to something simpler like loose parts as you mentioned.

-Marty
 
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MartyMcFly said:
Do you mean that the delrin expands with higher temp, leading to more friction, or does it become more vicious?

My first thought was that any lubes would become more inviscid and the piston seal would have better sealing when warm, thus better compression… but I guess Occam’s razor points to something simpler like loose parts as you mentioned.

-Marty
Click to expand...
The seals and bearings expansion typically offsets the slicker/ warmer lube resulting in a lower velocity. One wouldn't think a slower pellet would not hit higher. Unless it's a recoil thing.

I swapped springs in my setup from a 25 coil 0.118 wire 0.78" od spring to a 26 coil 0.113 wire 0.78" od spring and had to completely change my click chart due to the recoil being less in turn making the poi change. (Same velocity with each spring)

We just need some data. Shoot the gun 3-5 times in the morning. Again mid morning and again in the afternoon and try to mimic match temps. If you're in the sun and your rifle.is in a case at the match duplicate it. Then get some readings.
 
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Experiencing the same POI shift with my Sightron on my Tony Leach 12 FPE TX200. All the other shooters were calling me crazy...those Sightrons are bullet proof (they said). They don't shift (they said). Look at everyone else shooting Sightrons in all the FT competitions (they said)...I've sent at least two Sightrons back to the factory... I was told they were functioning perfectly. My friend has tested my Sightron. He said they are rock solid.

Well I just switched back to my Bushnell 8-32x (the adjustable AO model that Bushnell decided to discontinue) on my TX200. The set up seems rock solid so far. Tested at 10 yards click turret, check POI...then immediately range to 30 yards click turret, check POI...did that multiple times to convince myself that it wasn't me, it wasn't the screws, it wasn't the gun, it wasn't the weather, it wasn't temperature, it wasn't the pellet...it wasn't the moon ...it was the Sightron scope.

Just to re-cap the POI shift on (I think) the Sightron. I think the shift is very subtle. It's not immediate and it's hard to repeat, I don't think it's temperature related. I think with the violent recoil of even a 12 FPE springer...over time, it's enough to jolt or shift those Turret gear and/or erector tube spring. I remember reading Hector Medinas talking about the Tacoma bridge effect within a scope...wondering if this goes on inside a Sightron?

There's a FT shoot this Sunday. That will be the real test of the Bushnell, TX and me. Goal is to be over 70%.

I'll let you guys know what happen after the shoot. If all goes well, I might just put the Sightron back (for grins) ... to see if the POI shifts comes back.

Now that I re-read this, I don't want it to sound like Sightron bashing. I think they are a good scope and a good product. To be fair, while chasing this POI shift, I have corrected many shooter related issues (positional, trigger control etc) and gun related issues (butt hook position, added weight to stock, etc) I'm still in the trouble shooting phase...maybe THEY are right. Then it'll be back to chasing this POI shift issue again.
 
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Spoke too soon. Was shooting the Bushnell and the TX about 45 minutes ago...POI started shifting up. needed 32 clicks to bring the POI back to POA at 14 yards (and stayed at that POA for the next 5 shots). Re-checked all the screws. Everything was tight...hmmm will need to chrono ...the gun next. Got cold and hungry...time to re-fuel. Too discouraged to chrono the gun...eat first.

Oh well back to chasing this POI shift issue after eating

---30 minutes later

Shot some more. Checking POI at 10 and 16 yards. Seems stable (with the new clicks, POA = POI).
Double check all screws...nothing loose. Everything is snug.
Chrono the gun ...shooting at around 11 FPE...exactly where it was tuned to shoot.

I'm totally stumped. Doesn't make sense. The issue is how stable is this new POI...when is this set up going to shift again??? (last time this set up was stable for 5 days of shooting 20-30 pellets/day before shifting today). Not a temperature shift as temp has been very stable here for the last 5 days. And more importantly, what is causing this #$#$#%@ POI shifts???

Maybe bench this set up and see. Was shooting in the WFTF FT position for all the testing so far.

So maybe not an issue unique to Sightron. Or maybe it's a shooter issue..stay tuned.
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Just finished the Sunday FT shoot at Diablo. A very disappointing 46%. Back to the drawing board chasing this POI shifts.
Temperature was pretty stable from 55 to 60 degrees.
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Edit
Update 6/2/23.
No scope issues, No gun issues. POI shifts was all me. ...
Going on a program of really concentrating on shooting positions (holding still, breath control) and trigger control. Sightron is back on the my main Field target gun (TX200). fingers crossed.
 
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