Others Boss modified for STX barrels

[SpindleB]

I decided to see if STX barrels can be used on Smooth Twist rifles. Eventually to try a heavy slug liner. Tom at High Pressure Pneumatics had old unmarked liners for $50. Needed an outer barrel sleeve, that had to come from EuropeAirguns with shipping and Tariffs $100. Carbon fiber sleeve from Utah $30. The barrel connector from Huma-Air $40. Bit more than I envisioned cost wise.

The outer sleeve has to be slightly reduced like 0.5mm x 5/8" to slide into the breech block.

But my Boss now has an 600mm STX liner.
Now I just need to get the big transfer port block and a heavy liner and see how slugs do in the Boss. Or the Bobcat for that matter.

Don't have any real need for slugs it is just scratching my engineering curiosity.

 

[SpindleB]

Now my Boss can be a "shorty".
380mm liner and sleeve.
About 9" shorter than the 600mm

 

[SpindleB]

Got the 600mm STX Heavy liner yesterday and installed it this morning. Wow is it accurate. Hole in hole at 40 yards with H&N 54gr Heavy II slug. Only 815FPS though.

Pulled out the regulator and reset for 170bar. See how it shoots there.

Ordered some NSA 43.8gr slugs too. Lighter slug might be a good idea.

 

[SpindleB]

The Boss with a 600mm barrel is LONG. The STX barrel is not supported the length. Has an STO Sarrissa hanging on the end just to make REALLY LONG.

Had to make a barrel band.
2 big orings around the bottle and a velcro strap to hold it tight. Worked perfectly.

9 round magazines.
Two adjustment shots after tightening the barrel down. 7 shots in almost the same hole at 40 yards. My new most accurate rifle. Raw hm1000x is now #2.

That is some of my best shooting in a while. Not shaking too bad today and cranked down the tripod tight.

 

[Danman]

The Boss with a 600mm barrel is LONG. The STX barrel is not supported the length. Has an STO Sarrissa hanging on the end just to make REALLY LONG.

Had to make a barrel band.
2 big orings around the bottle and a velcro strap to hold it tight. Worked perfectly.

9 round magazines.
Two adjustment shots after tightening the barrel down. 7 shots in almost the same hole at 40 yards. My new most accurate rifle. Raw hm1000x is now #2.

That is some of my best shooting in a while. Not shaking too bad today and cranked down the tripod tight.

View attachment 16512

Phenomenal!...curious if poi will shift around with your custom barrel band setup in different temperature? Some pics of this beast would be nice This gun is a .25?

 

[Pumacarl]

Nice! Not many want to make a boss a project gun, but I get it.

 

[SpindleB]

Phenomenal!...curious if poi will shift around with your custom barrel band setup in different temperature? Some pics of this beast would be nice This gun is a .25?

.30 Boss.
No data on temperature poi shift
Seems pretty stable.

 

[Pumacarl]

.30 Boss.
No data on temperature poi shift
Seems pretty stable.

View attachment 16520
View attachment 16521

Well, I got to say, that is interesting what you did with the orings on the bottle and the velcro strap. I will be very interested in what you think of that long term. I would be concerned with never exactly getting the compression of the strap consistent enough and having it mess with how the barrel wants to vibrate and change the node you're in when the pellet leaves the barrel. With that said, you don't know until you try. I hard bed my mrod and everyone told me it would never be accurate, quite the opposite happened. I can lift that gun by the barrel, it has never been in a case, and has never lost zero. It pays to try new stuff, and keeps the hobby intersting.

 

[SpindleB]

Nice! Not many want to make a boss a project gun, but I get it.

Well, full disclosure, my brother knocked the tripod off his porch with gun attached. Landed barrel pointing down and the barrel was bent. Smooth Twist barrels are non existent. So after a fruitless search I decided to convert to STX. Hard part was the outer sleeve, had to buy that from EuropeAirguns in Spain. Figured since I had the outer sleeve and superior liner why not go with the Heavy liner too. Along the way I got a 380mm liner and outer sleeve too. Carbon fiber inner sleeve too.

Thought about 800mm but EuropeAirguns is not selling to US because UPS was doubling the tariffs and people were refusing delivery, filing a dispute with PayPal and they were losing money. So no outer sleeve.

 

[Pumacarl]

Well, full disclosure, my brother knocked the tripod off his porch with gun attached. Landed barrel pointing down and the barrel was bent. Smooth Twist barrels are non existent. So after a fruitless search I decided to convert to STX. Hard part was the outer sleeve, had to buy that from EuropeAirguns in Spain. Figured since I had the outer sleeve and superior liner why not go with the Heavy liner too. Along the way I got a 380mm liner and outer sleeve too. Carbon fiber inner sleeve too.

Thought about 800mm but EuropeAirguns is not selling to US because UPS was doubling the tariffs and people were refusing delivery, filing a dispute with PayPal and they were losing money. So no outer sleeve.

Well good for you for turning a bad situation into an opportunity! It's fun to treat this sport like a science and not a worshipping religion all the time too.

 

[SpindleB]

Well good for you for turning a bad situation into an opportunity! It's fun to treat this sport like a science and not a worshipping religion all the time too.

Probably in my DNA, 45 years as an Engineer.

I am the resident heretic. No $2,000+ gun is worth that much money unless you are a serious competitor. If it hits what you are aiming at then it is a fine weapon. It is a pellet gun, not some sniper rifle.

Then there are all the 3am "I wonder if I did..." brain farts that require time and money to find out it isnt practical.

And my ability to turn a 7lbs gun into a 13lbs gun...

 

[Dogowski]

The Boss with a 600mm barrel is LONG. The STX barrel is not supported the length. Has an STO Sarrissa hanging on the end just to make REALLY LONG.

Had to make a barrel band.
2 big orings around the bottle and a velcro strap to hold it tight. Worked perfectly.

9 round magazines.
Two adjustment shots after tightening the barrel down. 7 shots in almost the same hole at 40 yards. My new most accurate rifle. Raw hm1000x is now #2.

That is some of my best shooting in a while. Not shaking too bad today and cranked down the tripod tight.

View attachment 16512

Sweet group man. It's great when a plan comes together!

 

[SpindleB]

It appears the NSA 43.8GR slugs are the correct slugs for the Boss with the STX Heavy barrel

FX Boss .30, NSA
Bullet:NSA
Weight: 43.8 gr
Shot count: 9
Low: 858
Hi: 863
Avg: 861
STD Dev: 2
Spread: 5

10/12/25 7:07:27 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:01 AM,861,FPS,72.1,FT Lbs,
10/12/25 7:08:12 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:21 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:29 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:38 AM,858,FPS,71.7,FT Lbs,
10/12/25 7:08:43 AM,861,FPS,72.1,FT Lbs,
10/12/25 7:08:50 AM,858,FPS,71.7,FT Lbs,
10/12/25 7:08:58 AM,861,FPS,72.1,FT Lbs,

 

[SpindleB]

It appears the NSA 43.8GR slugs are the correct slugs for the Boss with the STX Heavy barrel

FX Boss .30, NSA
Bullet:NSA
Weight: 43.8 gr
Shot count: 9
Low: 858
Hi: 863
Avg: 861
STD Dev: 2
Spread: 5

10/12/25 7:07:27 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:01 AM,861,FPS,72.1,FT Lbs,
10/12/25 7:08:12 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:21 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:29 AM,863,FPS,72.4,FT Lbs,
10/12/25 7:08:38 AM,858,FPS,71.7,FT Lbs,
10/12/25 7:08:43 AM,861,FPS,72.1,FT Lbs,
10/12/25 7:08:50 AM,858,FPS,71.7,FT Lbs,
10/12/25 7:08:58 AM,861,FPS,72.1,FT Lbs,

So i decided that internal regulator is a pain in the neck and have modified to use a Huben Power Cricket MAX-ATH regulator. Now I can use 4500psi rather than 3500psi. Haven't filled or tested yet, have to wait for the high pressure compound to set and seal the air chamber.

 

[SpindleB]

Nope on the air chamber seal. Going to have to make a plug with a cap to push down on the hole when there is air pressure.

 

[SILENT SQUIRREL]

Here's a suggestion
If you still have the original threads in the receiver you could use a lane regulator between at the bottle.
Just my 2 scents
Edward

FX Boss AL Bottle Regulator Kit

Enhance your air rifle's performance with our precision regulator, the go-to choice for field target competitors & hunters alike. Don't miss out, Shop now.

laneregulators.com

Pardon Our Interruption...

 

[SpindleB]

Here's a suggestion
If you still have the original threads in the receiver you could use a lane regulator between at the bottle.
Just my 2 scents
Edward

FX Boss AL Bottle Regulator Kit

Enhance your air rifle's performance with our precision regulator, the go-to choice for field target competitors & hunters alike. Don't miss out, Shop now.

laneregulators.com

Pardon Our Interruption...

I have the Huben Power Cricket Max-ATH with the 50cc plenum. I probably have 15 Huben Power regulators. Mostly the Max and Dream Universal.

But some idjit cross threaded his manometer and now has to wait on a BSP tap to hopefully clean up the threads and get the manometer to seal. Probably require so high pressure thread lock to seal again.

 

[SILENT SQUIRREL]

I have the Huben Power Cricket Max-ATH with the 50cc plenum. I probably have 15 Huben Power regulators. Mostly the Max and Dream Universal.

But some idjit cross threaded his manometer and now has to wait on a BSP tap to hopefully clean up the threads and get the manometer to seal. Probably require so high pressure thread lock to seal again.

That same numbskull has visited my workbench too!

 

[SpindleB]

That same numbskull has visited my workbench too!

Threads were so bunged that they couldn't be repaired. Hopefully sealed it completely and will require external regulator from now on. Find out later if I got it all sealed.

No clue how I got that cross threaded. Im thinking they may have been damaged already and I just finished the job.

 

[SpindleB]

Threads were so bunged that they couldn't be repaired. Hopefully sealed it completely and will require external regulator from now on. Find out later if I got it all sealed.

No clue how I got that cross threaded. Im thinking they may have been damaged already and I just finished the job.

Was able to retap the 1/8 BSP to M10x1.0 and put the manometer in with high pressure threadlock. Seals up, no leaks, at that location. Not sure if there are long term issues there but I will deal with that in the future.

But in the process of getting the manometer to seal (before i retapped) I think i got some detritus in the poppet valve. Leaking out the barrel. I have spares so I will let it bleed down and try polishing the poppet and seat and if needed changed the poppet.