TX200 MK3 Inconsistent Velocity readings

[milegajo 595]

Hi all,

 

I'm not having much luck with my rifles at the minute...

 

Had a quick test of my 'go-to' gal today. First reading 11.58ft/lbs with JSB Exacts as always... next reading 9.85ft/lbs WHAT THE HELL!?

 

took 10 shots with JSB exacts and had a 55 fps variation!

 

Scratched my head, stripped her down, loads of factory gunk (she's pretty new) removed that, same. Tried spacers thinking power was low. Sear wouldn't catch.

Whilst stripping down I noticed the previous owner (sammy_78) had crushed a pellet in the breach, so cleaned that out. Same result.

 

Cracked open a tin of RWS Superfields, they fitted very snug indeed but yielded a 12fps spread.

 

JSB Exact 4.52mm Averages ft/lbs = 10.91 / fps = 764.7 - 55 fps spread

RWS Superfield Averages ft/lbs = 10.67 / fps = 756.1 - 12fps spread

 

My 97k isn't bothered by either

 

JSB Exact averages 10.8ft/lbs / 763 fps - 13 fps spread

RWS Superfield averages 10.38 ft/lbs / 745.8 fps 11 fps spread

 

It niggles the crap out of me despite Superfields being ok. She was doing fine and now not.

 

Is it worth bothering to tinker? If so, what should I do? Would a tuning kit (thinking a vortek one) be the end of my woes? Should I contact Air Arms? Should I just piss in the wind like I seem normally to do...?

[Tony Naylor 0]

just a idea check the breach washers (there should be 2 in there )

[milegajo 595]

Yeah, haven't looked yet, am hoping a newish rifle shouldn't need those replacing, but I may have to face facts based on those readings...

[pianoman 3,587]

Hi milegajo.

Give my dear friend Andy a PM (AndyFR1968 here). He is very knowledgeable on spring rifle technical workings and tuning issues with them. And describe what you are experiencing.

 

He may be able to offer a practical remedy.

 

The only thing I can think of is the spring of your TX200 is not perhaps, as young as it should be and it's about to crack. This, after all is where the rifle's power and consistency stems from; everything else serves to regulate and control that natural output. But they can only work with what the spring gives them.

 

My TX200HC .177 did this before its spring went west. Power went from 16 down to 7ft/lbs!

 

But that was after 10 years of hard hunting had passed through it.

 

Hope the cure is not too far or expensive away for you fella!

 

Best wishes.

 

Simon

Edited March 28, 2012 by pianoman

[milegajo 595]

Tah muchly Simon!

[andyfr1968 772]

As mentioned above, breach seal. If a pellet's been trapped in there then that's the most likely culprit but it's odd that there should be such a marked difference between two quality brands of pellet Let us know how you get on, mate

 

Simon..... I'll give you a call over the weekend

[milegajo 595]

Something solved it. Not sure exactly as i did a few things. Turned spring the other way. A touch of gun grease around the breech and breech seal. A smidge of grease behind piston seal. I also lost my second circlip... see thread HELP! Yes, I'm an Idiot...

Readings now show an average of 798.5fps with just 6 fps variation with JSB Exact 4.52 and 775.1fps with 13fps variation with RWS Superfields.

[milegajo 595]

thanks to all for the suggestions.

[andyfr1968 772]

I think you've a slightly damaged breach seal that the grease has fixed in the short term. I'll bet the problem soon comes back, mate, but I hope it doesn't

Edited March 28, 2012 by andyfr1968

[milegajo 595]

I'll keep tabs on it and buy replacement seals in readiness. Can't grip the cylinder in order to unscrew the nut on the end which i guess is how you access them...