FX FX liner lock nut (jam nut) sanity check -- how tight?

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stovepipe

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May 13, 2024
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Idaho
I know the answer to the question "how tight should my jam nut be" is going to depend on liner length, caliber, fpe at the muzzle, whether the rifle is using o-rings as spacers between the liner and the barrel housing or a carbon fiber spacer instead. There are probably a lot of other things to take into consideration that I'm not even thinking of. And I know that a lot of the answers are going to be given in terms of how many turns after hand tight rather than torque specs -- either one is fine with me. I just need a sanity check.

I've got an fx maverick 30 cal sniper with a 1:18 twist liner and a carbon fiber spacer between the liner and the barrel housing. I'm shooting nsa 54.5 grain slugs at about 950 fps, but might go to 980 fps. Either way that's in the 109 fpe to 116 fpe range. The liner is trying to spin the slug to the right, but if the jam nut is too loose, then the liner will slip (spin) to the left. I want the jam nut to be tight enough to prevent the liner from slipping, but I don't want to bend my liner. I can't really tell if the liner is slipping or not and there doesn't seem to be any way to know for sure.

Currently I'm tightening my jam nut 1/16th of a turn after fully hand tightening, but I'm wondering if that's really enough -- is 1/8th of a turn OK without bending the liner?

The FX motto "not too tight -- not too loose" causes irreversible insanity.

stovepipe
 
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stovepipe said:
FX sarcasm gladly accepted 24/7. I try to hide it, but with every word I write or speak about FX airguns, three years of naughty words are trying to find their way into the verbiage. How is it that I (an average guy) now knows more about FX regulators than FX does? I don't want to be smart -- I just want to shoot stuff!

stovepipe
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I'm not going to claim to know more about my Mavericks than FX but....I'm on the verge of being a close 50th. I started fixing the bad #1 reg on my BRAND NEW gun, finding other mistakes they'd made assembling it, getting a used Maverick that some idiot had destroyed and fixing it...and watching a hell of a lot of videos and talking to folks here. I admit, I like messing with stuff.
 
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stovepipe said:
The thing about the mav and regs and liners, etc. is that you really need to think about what you want it to do (if it's not already doing it) and research what it would take to make that happen. I'm talking about slugs vs pellets, light vs heavy, max range for accuracy, hunting (and what) vs target shooting, etc. Trying to pick bits and pieces of reliable info from youtube vids and forum posts can be a major pain in the ass -- there's always something they're not telling you. Sounds like your mav is shooting accurately and at 905 fps I expect your shot count per tank fill is pretty good. If you want more power from the mav, it can shoot at 109 fpe comfortably and it's easy to go with a single regulator setup. The only hard part of the single reg setup is that you might need to take out the reg and figure out a better belleville washer stack that is happy in the pressure range you plan to work in.

stovepipe
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Belleville washer stack, ask for and you shall receive.....You'll be buying a LOT of them to get the thicker ones, something in the 100 range. All measurements are on the edge of the washer. Measurement's are in inches. Standard 11 stack

1720366033819.png
 
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hotspark said:
.42 .48 .53
Is 0 missing after the decimal point? Or am I missing something 🤔
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You know, that a great question, I bounce back and forth between Metric and English....hang on let me go see what I did.

Numbers are metric

I did stacks then adjusted the regulator for the minimum then maximum pressure. The max on the last one was in the area of 155-165 bar, don't know why I didn't note it on my chart.

I did match the thicknesses as closely as possible in each stack, to keep the all working the same when they comprised and released.
 
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huntr said:
www.capefearairguns.com

FX Airguns Liner Lock Removal Tool

FX Airguns Liner Lock Removal Tool Easily remove and install your FX STX Barrel liner lock with this tool. Insert this tool into any tool that accepts 1/4" drive to quickly remove the liner lock from your STX barrel. Only for .177cal through .30cal. The .35cal liner lock uses a different style...
www.capefearairguns.com www.capefearairguns.com

I think if you go an ⅛-¼ past hand tight you're going to cause trouble.
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I think that's generally a good approach. What most people forget is that you are putting the liner in compression when you torque the nut down. I wonder if that pressure changes from thermal expansion when the temperature changes. It shouldn't, since all the materials are the same, but it would be an interesting test.
 
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bigHUN said:
The pressure will change ... because ... the tube material expands/contracts with Temp shift. According to specs both are same stainless S but different wall thickness-OD-length.....
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I often times think about what thermal expansion/contraction is doing to different parts of my rifle. It's especially tricky to think about when one part of the rifle is in direct sunlight and an adjacent or internal part is shaded from sunlight. I guess only people with a lot of experience with the same rifle in lots of different weather conditions would even have a chance of predicting the effect. I guess that's what separates the experts from the beginners. I'm in the beginner category, but I think a lot about the physics involved when it comes to shooting.

stovepipe
 
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stovepipe said:
I know the answer to the question "how tight should my jam nut be" is going to depend on liner length, caliber, fpe at the muzzle, whether the rifle is using o-rings as spacers between the liner and the barrel housing or a carbon fiber spacer instead. There are probably a lot of other things to take into consideration that I'm not even thinking of. And I know that a lot of the answers are going to be given in terms of how many turns after hand tight rather than torque specs -- either one is fine with me. I just need a sanity check.

I've got an fx maverick 30 cal sniper with a 1:18 twist liner and a carbon fiber spacer between the liner and the barrel housing. I'm shooting nsa 54.5 grain slugs at about 950 fps, but might go to 980 fps. Either way that's in the 109 fpe to 116 fpe range. The liner is trying to spin the slug to the right, but if the jam nut is too loose, then the liner will slip (spin) to the left. I want the jam nut to be tight enough to prevent the liner from slipping, but I don't want to bend my liner. I can't really tell if the liner is slipping or not and there doesn't seem to be any way to know for sure.

Currently I'm tightening my jam nut 1/16th of a turn after fully hand tightening, but I'm wondering if that's really enough -- is 1/8th of a turn OK without bending the liner?

The FX motto "not too tight -- not too loose" causes irreversible insanity.

stovepipe
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Nice post. Just had a discussion about this with my brother a couple of days ago.After reading I’m thinking about getting something like this in 10mm. Just for the sole reason of being consistent.


 
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Isn’t one end of the liner notched or has a concave ring machined into it ?? I assume if installed correctly this would prevent the liner from indexing while shooting. I just can’t imagine this being a thing. I’ve owned a bunch of fx guns and never experienced this. I know I would have as when flipping the barrels around from slug port to pellet port this is definitely a thing. Spinning from a shot definitely not.
 
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