Hi Doc,
I had a FX Crown Gen 1 for 5-6 years and had the same experience.
It was bought with a 500 mm barrel and I later bought both .177 and .22 600 mm barrels.
I even made a 700 mm DIY barrel too with a near solid 25 mm carbon pipe.
The POI shift problem is probably not the Barrel if you have the O-rings on the liner as original.
I tried many solutions to reduce the shift challenge.
I found the shift was extremely bad when using af barrel clamp for the bipod.
It was better with a small picatinni rail fitted to the front of the walnut stock.
But even then its a problem.
I experimented a lot with loose screws, og semi loose screws for the stock.
The best result is where the both screws must be very tight.
I also tryid to make a super tight fit in the stock with epoxi (Aluminium parts were waxed with mold wax.
It did not help much.
The problem is worst when shooting on a bipod. The movement between target generate the slightest twist and you experience a change in POI. If you try putting something that slides easily under the bipod feeds it helps a lot.
Another problem is how much weight or you are push or pulling on the bipod.
Since the POI shift was worst on the bottle support, the problem is the bipod fitted on the stock is far back.
So shooting with the bipod feet pointing 45° forward is a stable base. But again very sensible to how you carry the weight on the stock in the back. Stock just touching the sholder and then supported by a bag, hand or other is difficult to repeat 100% equal when moving to next target.
I used several years a fixed Accutac BR4 G2 and this is stiff and the slightest twist vill generate POI shifts.
Then i bought FC4 g2 that can twist at the front. But this still have too much friction and you still get POI shifts.
Then i Bought a mini Tripod with a ball head that can turn free without was better but unfortunatly difficult to use since the mounting was close to the ballance point.
I tried to cover the stock at the rear with a layer of 1500 gramm lead moving the rifles centre gravity move backwards - that helped a lot.
With barrel I tried many different things. Now i use 5-6 tight fit 3d printed plastic bushes as spacers that keeps the liner absolutely centered.
Its just is very hold sensible. I thought about buing a Sabre Tactical Aluminium stock.
but I found it was better to sell the Crown and bought a FX Impact M4 to replace this.
So now I have a FX Impact M4 Sniper, A Daystate Delta Wolf HP and a Daystate Redwolf.
So to compare .... By far is the least hold sentitive rifles the two daystates. (The deltawolf is only surpreme stable with the optinal barrel clamp)
The Impact M4 is much better than the FX Crown - but still way more sensible that the Daystates.
Both Daystate rifles are also a lot heavier. (My Redwolfs bipod is fitted via a diy 3d printed bottle / picatinni clamp) and even with this the Redwolf is on another level with stability.
The worst hold sensible rifle I own is the Gen. 1 Air Venturi Avenger.
It shoots impressingly good in a one hole group. But when moving to the next target its like lottery where the group will appear. (I did design and 3d printed a new frontend for the Avenger to improve on this- I think my DIY stock made the rifle to be equal to the Crown in POI shifts. - A real improvement but when you like to shoot 10x then its not there)
I did update My Accutac FC4 g2 with a 3d printed clamp that slides easier, together with greasing the inside part of the turning part with very liquid grease with a lot of teflon powder in. Its a major improvement. The best is still to use a mini tripod with a Ball head joint.
I now that a real benchrest front support is probably a lot better - but I havent tried that.
But I spent many hours fighting POI shifts with the Crown. I never won entirely but i achived improvements.
Again - I bet the problem is not in the barrel - its the Body / stock that gives problem.
Weight to the rifle is also a decent help.
Best regards from denmark
