I recently purchased a sub 12 ft lbs FX Biathlon mk2 to use in an upcoming 25 light varmint competition. I've been dabbling in Unlimited 50m plus benchrest for some time and am very comfortable with tuning for higher velocities/energy/calibers, but sub 12 presents its own set of interesting challenges. The rifle's regulator came set at a hair above 50 bar from factory, and it actually seems to work very well. The hammer adjuster is on relatively light tension right now, and shows good consistency. I'm a bit nervous about raising the reg pressure and increasing the hammer tension, as to reset it all back requires draining the entire non -removable cylinder each time which takes forever. Intuitively I think the reg pressure seems to be far too low, particularly given the pressure differential from a 230 bar fill? Any thoughts would be highly appreciated.
FX Biathlon mk2 tuning
- Thread starter Brosos
- Start date
Check with FX Sweden before making changes as a competition biathlon rifle is specifially built for off-hand prone and standing 50 meter shooting and is designed around a specific group of low weight wad cutter diabolo pellets.
The twist rate is chosen to stabilize these specific pellets at around 500 to 600 fps with the lowest amount of lock time possible. The trigger pull and hammer strike weight is set as low as possible. These settings help reduce the input to the rifle due to a shooter's high heart rate.
Raising the regulator output pressure may shorten the duration the poppet is open and increasing hammer force with an already lite hammer and spring may not overcome this and your velocities may be reduced.
If you do increase velocities the twist rate may yield a less accurate pellet.
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Had I not read @Troy Bakel's post my suggestion would have been to sight-in the gun and shoot 10 tins of pellets before making changes.
Now, having read Troy's post, my suggestion would remain the same, but using the specialty pellets he mentioned
just my too sense
Edward
Now, having read Troy's post, my suggestion would remain the same, but using the specialty pellets he mentioned
just my too sense
Edward
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The International Biathlon Union sets the standards for summer (air rifle) biathlon. There are 12 ft-lbs rifles shooting 25 meters and 20 ft-lbs rifles shooting 50 meters based on each countries air rifle regulations.
My .177 Impact M3 is tuned to just under 12 ft-lbs.
I did a version of what you suggested.
I purchased 1 tin of the best grade . 177 target competition diabolo pellets for all weights available from 7.0 grains to 10.3 including wad cutters and round nose and spent all of October 2023 testing indoors at 20 yards.
I found 4 weights that produce 5 shot groups 0.20" E to E or less.
Outdoors at 25 meters the pellet weight and thus the tune I choose depends on the wind conditions.
Unfortunately the FX Biathlon for export is hard set to 12 ft-lbs so it is limited in tune ability.
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@Troy Bakel
What is it that makes them difficult to tune for 12 ft-lbs?
What tune is on them when they leave the factory for export?
Thanks
Edward
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The FX Biathlon is tuned to just less than 7 ft-lbs for 7 grain diabolos for sale in Sweden and just less than 12 ft-lbs for 7 grain diabolos for export.
They are "hard" tuned in that the number of regulator washers and their orientation are set manually and usually the regulator has no or very little adjustability.
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Troy
Obviously, the interpretation of "hard tuned" to be hard to tune, or difficult to tune, colored my understanding
Thank you for clearing that up.
Edward
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Finally, after proving to various EU biathlon clubs that I know absolutely nothing about AIRGUN Biathlon I received some emails specifically about the FX MII.
It is primarily a Biathlon 10 meter training rifle that also meets the standards for in door 10 meter sporting class.
The export version can be adjusted between sub 12 FPE and sub 20 FPE.
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