Tuning FX Crown - Practicality of changing calibers and getting back to original tune?

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Aimright

Aimright

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Jan 28, 2019
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AZ, United States
How practical is it to change calibers back and forth and and keep the same tune, or does it take a lot of chrono work/ pellet expenditure to get your original tune back? Specifically I am pondering if I could dual duty a Crown with a .177 barrel set up at just under 20 fpe for field target competition and then on occasion (about twice a month) change to a . 25 barrel shooting approximately ~55 lbs fpe for 100 yard work.
 
I would think you could tune to the higher velocity with the .25 barrel, and then see where you are at by changing the TP to .177/.22 or Low and turning down the HS to Min. If you could get close, that would allow you to maintain the same regulator pressure and it should be repeatable by just moving the TP adjuster back to .25/.30 and the HS adjustment back to Max. The choice of barrel length for the .25 barrel would be a consideration also, the longer the barrel, the more velocity you'll achieve. So, if your .177 barrel is 500mm, getting the .25 in 600mm or 700mm would result in more power. Swapping from the 380mm barrel to the 700mm barrel on my .22 Continuum, with no other adjustments, gives me an instant increase of 10 FPE with 18.13 JSB's.
 
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Yes I think that this is practical (to a point), and you would only have to do the chrono work one time.

I say 'to a point' because there is a maximum FPE range you will be able to get out of a Crown just changing the dials, without also having to change the reg pressure. But that range is actually pretty wide.

As an example I recently converted a Mk1 Crown from a .30 cal/600mm barrel to a .25cal/380mm barrel. At maximum settings (.25/.30 on power wheel and HS=MAX) the gun was generating 76 FPE at the muzzle in its original 30/600 configuration w/44.8 gr pellets. With the smaller caliber, shorter barrel and lower settings (power wheel still at .25/.30, HS=3) the gun is now making 37 FPE at the muzzle using 25.4 gr pellets. I made no regulator changes.

Lowering the hammer spring dial further would reduce muzzle velocity even more, but sometimes I find that this comes at the sake of shot-to-shot consistency and accuracy. I did not run any tests (yet) with the power wheel set in the .177/.22 or min positions. That's mostly because I found the gun in it's .25cal/short barrel configuration to be in almost perfect harmonic tune at the HS=4 setting. Gets lots of shots too!😁
 
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It is absolutely practical. I have two Crowns, a Continuum originally in .22 and a MK 2 also originally in .22 cal. The MK2 is now set up as a .30 cal with a 700mm barrel and it is an absolute hammer, yet still extremely accurate. The Continuum gets changed between .22 (using the 380mm, 700mm and a 600mm barrels) and a .25 (using 380mm and 600mm barrels). With the tunes on both guns I can get just about any velocity/power levels I want just through changes to the Power Wheel and the transfer port. I generally don’t mess around with my reg pressures as I have found the guns run efficiently at around 145 Bar.
 
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Thanks guys, looks like you have things pretty well dialed in! I was thinking it would be ideal IF I could set up accurate tunes, one for the .177 and one for the .25 with just adjusting the HS and TP power wheels and leaving the regulator at the same setting for both. The other “IF” is whether the two power wheels detents kept the tunes consistent when they were changed back an forth, and what I am hearing is YES.
 
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The first IF I think is the more relevant one. Every setup is different, and knowing whether you can find an optimal FT setup and still find a setup for the other barrel without touching the reg, is up in the air. It could be possible, but you would need to test. Turning the transfer port down to 177 makes a massive difference in speed. 

The second IF is rock solid. You can easily spin the two dials and get the tune comes right back. I spin the dials for my 22 switching between 18gr, 25gr, and slugs and it goes right back every time and is a amazingly accurate today as it was when I purchased it from Ken. 
 
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The first IF I think is the more relevant one. Every setup is different, and knowing whether you can find an optimal FT setup and still find a setup for the other barrel without touching the reg, is up in the air. It could be possible, but you would need to test. Turning the transfer port down to 177 makes a massive difference in speed.
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Another question comes to mind: whether this would be less likely with the newer MK2 Crown, as it supposedly has different valving and porting for more power over the previous version. 
 
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Easily done with either MK1 or MK2. MK2 just has a higher "top end". A little trial and error( back and forth between calibers) and you'll know when you are close. Then just tweek either the HS pre-tension screw or the reg just a bit to "dial it in" perfect. I'd start with the .177 for 20 ft/lb(more critical) and then see where I was with the .25(usaully less critical as the .25 Kings can be shot from 850 to 900fps and still be accurate at 100 yards). Don't be afraid to experiment because you can always set it back to where you started(especially if you make notes). 

Good luck
 
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Easily done with either MK1 or MK2. MK2 just has a higher "top end". A little trial and error( back and forth between calibers) and you'll know when you are close. Then just tweek either the HS pre-tension screw or the reg just a bit to "dial it in" perfect. I'd start with the .177 for 20 ft/lb(more critical) and then see where I was with the .25(usaully less critical as the .25 Kings can be shot from 850 to 900fps and still be accurate at 100 yards). Don't be afraid to experiment because you can always set it back to where you started(especially if you make notes). 

Good luck
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This ^^^ is sort of what I was thinking. If you set the 177 barrel up on the 177 port and maybe even on min power, you will have 1/2 steps in either side of Min that could be helpful depending on atmospheric conditions. Then you can open it up to 30, and have all the higher settings to have a wide range of available range for the 25 pellets. Without the experience of those big of swings across barrels, I can’t personally speak to that strategy, but it makes logical sense at first thought based on what I’ve seen across my pellets choices across one barrel.

As far as the new MKII goes, it could probably be better, even without trying for more power, because the extra plenum space can allow you to dial the reg down a little more and also give more shots. 
 
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Easily done with either MK1 or MK2. MK2 just has a higher "top end". A little trial and error( back and forth between calibers) and you'll know when you are close. Then just tweek either the HS pre-tension screw or the reg just a bit to "dial it in" perfect. I'd start with the .177 for 20 ft/lb(more critical) and then see where I was with the .25(usaully less critical as the .25 Kings can be shot from 850 to 900fps and still be accurate at 100 yards). Don't be afraid to experiment because you can always set it back to where you started(especially if you make notes). 

Good luck
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Thanks Ghostranger, don’t have one yet but good to know either model should work.



I opted to keep mine within 1 calibre. 

I use a 700 mm barrel for slugs. Pushing 25 grains knockout slugs to 940 fps. 

And then I have a 380 mm barrel for close range low power stuff.

I do everything with the power wheels. The reg stays at 150 bar. 

Super easy and repeatable.
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MoeHofer, My scheme would be to use the gun in both standard and long range extreme field target meets for economic reasons. The long range FT is out to 100 yards and requires a higher FPE (28 to 100) than standard FT which is limited to 20 FPE for the hunter division. The .177 caliber is the superior caliber for hunter field target and for extreme field target the jury is still out on the superior caliber, but my money is on the .25. 
 
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@Aimright

I was looking at another thread and someone mentioned exactly what you want to do, and apparently it worked perfectly with no reg adjustments... go to the last comment.

https://www.airgunnation.com/topic/raw-tm-1000-177/
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Thanks for the link Smok3y, I hadn’t read it before. Also interesting in that thread was the news about FX working on a new .177 liner.
 
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You are right, the .177 FX does not seem to have much of a following and I don’t see many related posts. I did see a post this fall from a member in Denmark that tried a new Superior .177 barrel that did pretty well with certain pellets and speeds. https://www.airgunnation.com/topic/new-fx-superior-liner-177/ If his good groups are representative, that would work for my hunter field target needs.
 
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