POI shift from session to session FX Impact stx vs RAW

I experienced a similar problem with my FX Crown 177 during a 25 yd bench rest match a couple of weeks ago. I watched the pellets walk their way first left then back, then down. No way to predict where they would fall. This is an extreme accuracy venue, with no external issues: gun stays on the rest and no wind inside. The difference is only a few mm at 25yds, but makes a difference in the score. I nearly matched my pcp score with my springer. 

Anyway, I am thinking that it was the barrel spacer orings as well. I am experimenting with slightly larger ones as well as 90 duro ones.

BTW, I also have a similar problem with my RAW TM1000. The tensioned barrel shifts after each shot and when moving the gun. I am trying a thread locker and rear vent and spacer to help eliminate this problem. So this isn't unique to FX

Dan

If someone could machine a piece (or two, one for each side) similar to the one in this picture that mounted on the side picatinny rail it could possibly eliminate the POI changes. Maybe 3D print?

I don't think locking the outer barrel sleeve or the shroud in place will help too much, if the inner barrel moves. Hence the thought to use 90 duro or larger orings to help keep the inner barrel in place more securely. 

For my Dreamline the FX service folks used larger diameter orings, when I had it back in for service, and it helped considerably with accuracy. It just had other issues after that, so I couldn't use it for benchrest. For my Crown, I removed the shroud and only used a 0-db moderator to help eliminate the variables. I just added 4 orings, with one larger one right at the end. There seemed to be a bit of play between the liner and the barrel end fitting. I also used Ernst's hint to use tape to keep the orings in place, so they don't walk their way away from the proper location. We'll see if my fix works on the next benchrest. 

I only have guns that won't shift poi. Hate chasing after a moving poi from a barrel getting bumped. Heavy barrels, tensioned barrels all important to me.

Not sure how you guys are having poi shift with a Leshiy. The barrel is literally encased in the whole frame. Meaning the barrel can't move. Unless your screws aren't tight holding the barrel I think it's more an issue with hold, or your scope, mounts something. I've put 2 tins through mine with a red dot and killed over 100 birds and never once adjusted the red dot after the first sight in. 

I don't think locking the outer barrel sleeve or the shroud in place will help too much, if the inner barrel moves. Hence the thought to use 90 duro or larger orings to help keep the inner barrel in place more securely. 

For my Dreamline the FX service folks used larger diameter orings, when I had it back in for service, and it helped considerably with accuracy. It just had other issues after that, so I couldn't use it for benchrest. For my Crown, I removed the shroud and only used a 0-db moderator to help eliminate the variables. I just added 4 orings, with one larger one right at the end. There seemed to be a bit of play between the liner and the barrel end fitting. I also used Ernst's hint to use tape to keep the orings in place, so they don't walk their way away from the proper location. We'll see if my fix works on the next benchrest.

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Now I understand the situation better. I thought it was an issue with the barrel sleeve not being secured (stiff) enough and then having the sleeve and shroud susceptible to movement because of that.

My .22 crown was one of the most accurate airguns I ever put my hands on... sadly, as has been mentioned about, it had a zero shift almost every time it came out of the gun case or safe. I was forced to sell it because I lost all confidence in the rifle and I primarily hunt with my Airguns. I’m still bummed and I’ve contemplated giving the crown a shot again and trying to figure out a way to get a LW or CZ barrel secured to the receiver better. 

The telescoping shroud was definitely part of the problem. Back when I had my Crown there wasn’t an option to get a fixed shroud unfortunately. I experimented with removing the shroud completely and threading a mod onto the barrel liner cover, this seemed to help but I still had POI shift. I’m guessing a fixed shroud would tension the barrel a bit more and improve things. 

The shroud on FX guns only provides sound suppression. It does not attach to anything on the gun, so it cannot provide any barrel support. Those "O" rings do nothing except possibly damping vibrations, which in fact on any air gun are either minimal or non-existent. Please remember the issue is shifting zero, not accuracy.

POI shifts are unacceptable on a hunting rig. Having said that I've seen a lot of videos of guys moving from place to place with their FX Impacts and they don't seem to have an issue nor at least don't mention it. 

I had this experience as well with a Crown. I could count on it to shoot good groups, but day-to-day changes in POI were common. FX is innovative, and their ultra adjustability appeals to many folks. I have read that some owners hunt with them without issue, and that they absorb the usual minor bumps in the woods without affecting POI. I don't know whose experience is more the norm, but I would not have been comfortable using my Crown as a hunting rifle. My Royale 400, in contrast, has been rock solid with its one-piece ST barrel. I guess it's an old and boring platform to many shooters, but I sure hope it's one that FX maintains. 

The shroud on FX guns only provides sound suppression. It does not attach to anything on the gun, so it cannot provide any barrel support. Those "O" rings do nothing except possibly damping vibrations, which in fact on any air gun are either minimal or non-existent. Please remember the issue is shifting zero, not accuracy.

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Ya, like I said I got out of my crown quickly and well before the fixed shroud was ever an option so I’m unfamiliar with how it attaches. My Crown literally drove tacks. I loved everything about it, except the POI variances. I take great care of my equipment and never subject anything to abuse. My experiences were based on very average range use and hunting trips and out of the dozens of airguns I’ve owned over the years, I’ve never seen a similarly consistent poi shift. 


For example, I would pack my Crown in a Pelican hard case, drive an hour out to shoot / hunt, take the rifle out and I knew I would have to re confirm zero. It destroyed my confidence in the rifle. Maybe I had a bad one, maybe not. I have about a 12 year background in aerospace engineering / machining and I attributed the poi shift directly to the barrel... both the way it interfaces with the receiver and the way the ST liners are secured within the sleeve.


Again, my crown and most all the crowns I’ve seen shoot very well.....

Off topic but as far as airgun shot cycle harmonics are concerned, here is a very cool video. 


https://m.youtube.com/watch?v=OksIysh0eTU

Good video. Having the option of buying/using a barrel band of sorts would be nice for FX to offer.

I experienced a similar problem with my FX Crown 177 during a 25 yd bench rest match a couple of weeks ago. I watched the pellets walk their way first left then back, then down. No way to predict where they would fall. This is an extreme accuracy venue, with no external issues: gun stays on the rest and no wind inside. The difference is only a few mm at 25yds, but makes a difference in the score. I nearly matched my pcp score with my springer. 

Anyway, I am thinking that it was the barrel spacer orings as well. I am experimenting with slightly larger ones as well as 90 duro ones.

BTW, I also have a similar problem with my RAW TM1000. The tensioned barrel shifts after each shot and when moving the gun. I am trying a thread locker and rear vent and spacer to help eliminate this problem. So this isn't unique to FX

Dan

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In my experience, if the POI change while shooting (where the gun sits still on a bench, on stable temperature) is a sign of the barrel needing cleaning. Or if it has just has been cleaned, and need to break in. My crown in .22 had that issue. I could hardly shoot 100 shots after a clean barrel, before the POI started to drift. 3 shots may hit hole in hole, and then it starts to drift, and then maybe five shots later, 3 new shots may hit hole on hole again another place, and then it repeated itself. When I inspected the liner with a flashlight, I could clearly see lead fouling, especially at the end of the barrel where it is choked. The solution for that issue can be to polish barrel, or lube the pellets. It is still a annoyance, because it lead to myself scratching my head several times, wondering what was happening, and lead to allot of frustration.

I am not saying some guns might have different POI shooting from session to session, but I think it is important to distinguish between a dirty barrel, and a barrel or liner moving. 

That’s a possibility, but what I normally see from many airguns straight across the board, including the ST and STX barrels is you will see your average group size slowly increase as the fouling builds up. The smooth twist rifles I’ve owned were really good about shooting well, be it dirty or clean. My Daystate Wolverine R on the other hand, is a finicky broad and will let you know when she’s dirty. As soon as 50 yard groups can no longer be covered by a dime, she wants a scrubbin’.


I think this thread reveals many of the possible variables that could contribute to what some people are experiencing with regards to a zero shift in the ST / STX rifles. Interesting topic and the kind of stuff I personally love to tinker with and think about. In my next life I wanna be an airgunsmith. Haha. 

I stayed with my streamlines for this very reason. The design didn’t seem as robust to me in the new fx offerings. Glad now I didn’t sell them. My streamlines hold poi everyday no changes. If the new guns had thicker barrels I would probably get one.

I stayed with my streamlines for this very reason. The design didn’t seem as robust to me in the new fx offerings. Glad now I didn’t sell them. My streamlines hold poi everyday no changes. If the new guns had thicker barrels I would probably get one.

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Absolutely agree. If I wanted a woods, walking rifle, I would try to find a Streamline, not sure how available they are now. I believe it is essentially a cylinder version of the Royale 400, which I really like. If so, the Streamline should be a handier version of the same rifle, and well suited to hunting. 

That’s a possibility, but what I normally see from many airguns straight across the board, including the ST and STX barrels is you will see your average group size slowly increase as the fouling builds up. The smooth twist rifles I’ve owned were really good about shooting well, be it dirty or clean. My Daystate Wolverine R on the other hand, is a finicky broad and will let you know when she’s dirty. As soon as 50 yard groups can no longer be covered by a dime, she wants a scrubbin’.


I think this thread reveals many of the possible variables that could contribute to what some people are experiencing with regards to a zero shift in the ST / STX rifles. Interesting topic and the kind of stuff I personally love to tinker with and think about. In my next life I wanna be an airgunsmith. Haha.

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HI SocalTrail, 

Does the barrel diameter relate to the frequency of required barrel clean, would a smaller caliber like 0.177 need to be cleaned more frequently? I am interesting in a 0.177 cal PCP to increase shot count per fill to avoid/minimize refilling at the local rifle range. If the 0.177 requires clean every 100 shot, as an example, that would mean cleaning the air gun at the range. 

Thanks!

Makes me wonder if the aluminum STX barrels are expanding and contracting with heat and cool. It doesn’t take much, and i’d be curious moving forward the folks that have these problems with guns that use removable liners, if they possibly shared how the gun is being stored and at what temps they go to from storage to the bench, and vice versa.

if any of you that have pulled out an STX liner and have seen the o tings that hold the barrel floating, depending on how their placement was to begin with when installed, a liner that expands and contracts from temp changes could easily be “nudged” to favor one side inside the barrel. A twisted up o ring or one not perfectly in place could have an effect on how that barrel is tracked inside, wether concentric or off to one side.

Not an expert on scope innards or how they are engineered, but I know they have a lot of aluminum parts all prone to expansion and contraction. Maybe that’s affected, also?

if I can try to make myself remember, when fall and winter comes i’d like to track and compare how many point of impact change treads there are when compared to now. Seems in this warmer weather I’ve seen a good handful of point of impact change treads along with low velocities coming from the first two shots on regulated guns.