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Fitting STX Barrel to an FX Boss

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Cybergrizzly

Member
Apr 3, 2019
20
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Panama
I am interested in fitting a Smooth Twist X barrel to an FX Boss. The diameter of the barrel sleeve apparently needs to be reduced about 0.125mm x 5/8" long to fit the action block. The threaded wall thickness is not thick enough but might hold.

I read that member "Glem.Chally" did some fitting but could find more details as to what exactly was done. The ST barrel is about 14.0mm diameter and 13.75mm where it fits into the action. The STX barrel coupling and barrel inlet are fine with 13.75mm but the STX barrel sleeve is 14.0mm diameter and needs to enter the Boss action block about 5/8".

Can anyone provide some information ?
 
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Yeah you need to turn the sleeve down to fit the action. Diameter is too big.

And yeah there isnt much meat there, has to be done slowly and carefully. It came to me already sanded down by Chuck for use in a streamline but it needed a bit more love to fit the Boss. Its holding well with no issues.

Then for the brass inlet you can use a crown one i think, or the impact with some filing to make it more like the Boss one. (Otherwise transfer port wont line up) i used an impact one modified.
 
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So just something to consider: You can purchase reamers for remarkably reasonable prices in very precise sizes. You might do better to just gently run a reamer into the front of the Boss action where I presume it is just a smooth tube. This would make your Boss STX quick-change compatible, and would preserve critical thickness on the rear of those threaded outer barrels which are already unbelievably thin. Also, if you screw it up, FX has been refusing to sell STX outer barrels as a stand-alone thing, forcing you to buy a whole barrel assembly. This means a replacement Boss action might actually be a less expensive mistake than the outer barrel. 

Food for thought. Please keep in mind that A) I'm just some nut on the internet and B) I don't own nor have converted an FX Boss to do anything so idiot-check my suggestion first before deciding to go with it. :) 
 
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STO: The idea of the reamer is good but bear in mind that 13.75mm is the diameter of the barrel end that actually enters the action block and fits snugly to be fixed with 3 set screw grubs. If I would to use a reamer to deepen 5/8" long the action block hole to 14mm, one set screw would probably set on the barrel sleeve and not onto something really solid.

Snowbird: Ok. Maybe that was what was available to Glem at the moment and besides maybe the Boss barrel inlet transfer port is too large for .25 caliber.

I have a .30 and a .25 caliber STX barrel kit, so I was planning on using the Boss barrel inlet for both instances. For .25 I would still need to order the lever linkage and pellet probe and a .25 Royale magazine.
 
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I used the impact one because thats what i had and wasnt hard to modify it. I imagine the Boss one would work but thats 30 cal. Im shooting .25 and .22 from the Boss. Theres no .22 or .25 Boss inlet.

STOs idea is good, I had an adapter made up to be able to use any of my Royale barrels in the Boss. .22 ST, .22 LW, .25 ST, .25 STX

Royale parts for cocking and chambering (if you want .22 or .25) are the pellet probe itself and the caliber specific delrin probe guide. (You only need the breech side probe guide, the rear one is the same in any cal)

Cant use the Boss inlet for .25 its the wrong caliber.

You only really need the cocking arm assembly if you dont want to push the pins out, the whole linkage is identical between Royale and Boss. (Cocking arm, little rod, pins)
 
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Id say they can both shoot sub MOA in .25 pretty regularly. Ive gotten .643" 5 shot group at 109 with the original ST and many many under an inch. My last time out with the A liner was shooting amazingly. I have a place to go shoot now (other than the range) and have been busy with work so havent done too much target shooting with the STX yet.

Then with the .22 ST i got it cheap so i bought the cocking parts to shoot both calibers from my R500. I wanted to shoot slugs so i bought the .22 unchoked LW and had great results with baracuda match and able to hit paper at 218y with that. Excellent results with NSA and VK slugs. Amd definitely hunting accurate with the MP molds slugs.

Then bought the boss action and some parts i needed to merge my royale into a complete boss action. More power for fun and slugs. Went from 45fpe to 62fpe going from royale 500 to boss.

I got several threads about it on here that show fps and targets.

St or stx in .25 king heavies mk1 or 2 ive had great results with both. And same great results with the 25.4 kings or the aa version are good too.

In .22 of course the 18.1s even over 1000fps were shooting well from the lw, 880-950 from the st. I dont shoot much .22 lately.

Hell yeah it was worth it, so much that i bought all the parts to make a second one :)

Boss in a box is that thread if youre interested.

Edit....oh that kind of worth it. If you want to shoot slugs id say yeah. If you want to shoot pellets only save some money and just put a st from an impact in after some minor mods.
 
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hey guys , i dont want to offend anyone , but have yall reached a conclusion as to how good this smooth twist technology is for airgun accuracy . i remember it was well promoted . i had an fx typhoon in .22 for a moment and i was not as impressed as i am with choked l.walther and even choked .25 green mountain (.25 mrod groups at 55 yards were better than the .22 fx typhoon) . this came to me before i heard about cz barrels , but i just decided to stick with walther , bsa , hw barrels . there was some talk about using 4 groove barrels for target - like less grooves was better . maybe that was tim at mac1 explaining that - i was probably asking about smooth twisters . what do yall think ?
 
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