FX M3 .177 heavy slug tuning

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Uwiik

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Mar 10, 2024
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My rifle is an FX Impact M3 700mm sniper spec with plenum, power block, tensioned barrel and dual port dumbed down to .177 caliber. I am pretty much limited to .177 here in my country, so I naturally want to shoot the heaviest slug in .177 for maximum damage when hunting for pests in my farm.

I have had good success in tuning for NSA .178/15gr slugs, easily adjust between 900-1050 fps, reg at 100 bar, macro 13, micro 3.5, valve 3.5-4 lines, very efficient air use, nice one dime grouping at 25 yards. However, for the life of me I can’t get good velocity with the heavier NSA .178/20.5gr slugs. The absolute max velocity I could get was 850 fps and I had to max out everything to get it with reg at 135 bar, macro 16, micro 5 and valve fully maxed out, even a slight reduction on setting would drop it drastically to lame 600-700 fps and it consumes air like a leaking balloon…

What can I do? I am targetting 925 ish fps. I asked the shop and he suggested changing hammer to tungsten and spring too but I am not convinced because as far as I know much heavier tungsten wants 170 bar on reg and there is no way I need 170 bar just to launch a puny .177 / 20.5 grain slug to a proper velocity… Currently I am far far away from maxed out shooting 15gr at proper velocity, there is no way I need to upgrade to tungsten just for 5gr heavier slugs?? Maybe I just missed something??

Please advise and thank you very much in advance!!
 
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15gr slug at 1050fps = 36.7fpe (reg at 100bar)
20.5gr slug at 850fps = 32.9fpe (reg at 135bar)

Observing that it is producing lower fpe with the heavier slug means the pressure is set too high for the amount of hammer strike available. Or in other words there is insufficient lift and dwell to properly drive the heavier slug. Meaning you will indeed need a heavier hammer and/or stronger hammer spring.

Or if you want to tinker a bit first, you could try an in-between regulator setpoint. You may find it will fare better at, say, 115 bar. Considering your target is 925fps with the 20.5gr which is 39fpe, you are only chasing about 6% more energy than the 36.7fpe you achieved with the 15gr slugs. So it may not take much to get there, depending on how much is being lost to bore friction with the longer, heavier slug.
 
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nervoustrig said:
15gr slug at 1050fps = 36.7fpe (reg at 100bar)
20.5gr slug at 850fps = 32.9fpe (reg at 135bar)

Observing that it is producing lower fpe with the heavier slug means the pressure is set too high for the amount of hammer strike available. Or in other words there is insufficient lift and dwell to properly drive the heavier slug. Meaning you will indeed need a heavier hammer and/or stronger hammer spring.

Or if you want to tinker a bit first, you could try an in-between regulator setpoint. You may find it will fare better at, say, 115 bar. Considering your target is 925fps with the 20.5gr which is 39fpe, you are only chasing about 6% more energy than the 36.7fpe you achieved with the 15gr slugs. So it may not take much to get there, depending on how much is being lost to bore friction with the longer, heavier slug.
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Thank you very much for the explanation, this is exactly what I need to hear, the actual explanation of what is happening thus cancelling my assumption. Much appreciated!! I will get the tungsten hammer and spring to try out!

I have tried resetting everything back to factory setting and creep up the reg pressure slowly starting from 80 bar with 5 bar increments until it reached 135 where it reached the maximum velocity with the given slug. The moment I tried 140 bar, velocity dropped like a rock to 600-700 fps and gun doesn’t sound right…
 
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trompis said:
now on your impact you have a 52mm long hammer spring. change it to a 56mm(part number 11500) and you are good to go.
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Thanks so much for the suggestion. I will try the upgrades in steps and spring only seems like the best place to start. FX #11500 is not available locally, Huma Air #1308 is widely available, can I use it? . Alternatively, can I just put spacer to the original spring to create the same effect?
 
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Corvid_hunter said:
There is a YouTube channel called Viking Airgunner that you might find interesting as he shoots the M3 in .177cal.
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Very useful link with simple understandable language, thank you very much. However, my problem is beyond his scope of explanation but I picked a hint where he mentioned that he is using Huma slightly heavier hammer…I guess now I just have to play around with 1st stronger hammer spring, 2nd weaker valve spring and 3rd heavier hammer in order to shoot 20.5gr slug with proper velocity range. I just unable to tune worth a damn before I can get my 20.5gr slug to fly with proper velocity…
 
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I shoot a .177 Maverick, with dual port - heavier hammer - pin probe - heavy liner, and have no problems pushing 20 grain past 1000 FPS.

BUT ! i got the heavy liner to be able to shoot heavy slugs like 20 gr, but i just can not get any 16 or 20 gr slug to fly well,
Viking airgunner have luck with the 16 gr Zans but i am not able to replicate his success, and i have gone thru quite a few boxes of 16 and 20 gr Zan slugs, even in H&N too.

I do hear rumours about FX coming out with a actual slug barrel for .177 and not the " heavy " that if anything is a very slight improvement on the regular barrel in the way of more tight rifling.

I hope this mean a barrel for slugs and not a dedicated barrel for shooting halo slugs that might also work with other stuff, either way, when this materialize i will lean back and look what happen for other PPL CUZ i feel a bit ripped off with the heavy liner in .177
 
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Uwiik said:
Thank you very much for the explanation, this is exactly what I need to hear, the actual explanation of what is happening thus cancelling my assumption. Much appreciated!! I will get the tungsten hammer and spring to try out!

I have tried resetting everything back to factory setting and creep up the reg pressure slowly starting from 80 bar with 5 bar increments until it reached 135 where it reached the maximum velocity with the given slug. The moment I tried 140 bar, velocity dropped like a rock to 600-700 fps and gun doesn’t sound right…
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I wouldn't necessarily go for the tungsten hammer, that's a really heavy hammer for a .177 I would try one of the hammers huma carries.
 
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No it is a brass hammer from a Huma kit, not using the heaviest one, no idea how much it weigh in but heavier for sure than the sub 12 hammer i think is in my FAC rifle from the factory, my Maverick only became a nice gun after many months with the 600 mm barrel and i got a 700 mm barrel for it.

huma-air.com

FX Maverick Slug Power Tune Kit By Huma-Air

FX Maverick Slug Power Tune Kit By Huma-Air to get the maximum performance out of your FX Maverick
huma-air.com huma-air.com

The 600 mm barrel would only shoot Beast pellets well, all other pellets between 800 and 950 FPX did not shoot well at all, but most did if i turned it way down to 600 FPS which is also what the rifle shot factory settings with 13 gr pellets and on MAX power wheel setting ( 575 FPS )
New 700 mm barrel let me shoot what i want at the higher speeds.

As it is now i can reach 960 FPS for the 13 gr Zan slugs just fine with only 70 BAR on the regulator, but i do use 90 - 100 bar normally, the low pressure are somehow not as accurate.
Other shooter like viking airgunner from the same town as me, he i think use a heavier brass hammer and 110 - 120 BAR on the regulator.
BUT NOT tungsten hammer, that is for the big boy calibers only i think, or you at least have to use a heavier valve return spring i think.
 
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At least you can adjust the return spring on the M3, that is not a option on the Maverick.
I have also just replaced the power wheel and small fine adjust screw, with a micrometer

20240214_083129-jpg.435374
 
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Uwiik said:
Had my doubt on the tungsten. I am thinking about doing longer hammer spring and/or weaker valve spring before touching the hammer…
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They are 7.5g and 8.5g.

huma-air.com

FX Impact Hammer Weight Tuning Set

This set consists of 2 different hammer weights for the FX Impact; 1 x 7.5 gram and a 8,5 gram so you can setup your rifle exactly to your own wishes!
huma-air.com huma-air.com

I tried running the eight point five gram with the heavy spring and I could barely fit them in the gun together. If you want to run the heavier spring I would suggest a seven point five gram hammer. Otherwise use the stock spring with the heavier hammer.
 
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FX gotta do something, CUZ as it is now at least with .177, half of the slugs on the market you can not shoot.
Even if i have seen a SA guy shoot 20 gr H&N like a SOB,,,,,,, but i have in no way been able to replicate that either, actually the H&N slugs are even worse in my Maverick, no matter the weight.

I have wasted many many hours and not least slugs trying to get somewhere, but i am left with nothing but a thinner wallet to show for it.
 
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