FX DRS consistency issues

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MTC

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I purchased a FX DRS classic last year, 500mm barrel, synthetic stock, 0.22 cal, FAC version. I have run a few hundred pellets through it now down at my local 25 m range - JSB Hades .22, 15.89 gn and JSB Monster, 24.39 gn. It is accurate but chrono results lead a lot to be desired -over several 3 mag strings (42 pellets) the standard deviation on my FX radar Chrono is probably 3-fold what I get on my other PCP's - AA 410, HW100, BSA R-12, FX Maverick. I wondered if the AMP regulator was subject to some bedding in? But over several months the results are no better. Typical standard deviations are 10-12 Fps with a high/low spread of some 30-40 Fps. I am beginning to wonder if the AMP regulator should be replaced while still under warranty?
This is the performance straight out of the box - no monkeying with the reg and hammer tension and it currently makes about 23 ft lbs in factory settings.
Forum members ideas would be welcome!
 
I have the same with mine and even bought another amp reg and that's the same so have now bought a huma for it after watching a video comparing the 2 of them. My gun is sub 12 but the creep and slow refill after a shot plus poor consistency is horrendous and I know the gun has no leaks so it not that
 
I have passed mine back via the local dealership who tested it on their chrono and agreed it wasn't up to spec. It has been sent off to the UK distributor (Sportsman's Gun Centre) under warranty. When it returns I will test it on the dealer's chrono with a full mag before accepting it back! I looked at the Huma air regulator but decided that since the gun was under warranty then best not monkey around with it at this stage. Thanks for your comments. Is there a known issue with recent AMP regulators?
 
DRS arrived back after several months at SGS and just tested again. Power increased to 30 ft lbs approx but regulator issues seem still present. Maybe I am expecting too much from a gun at this price? - but first 2-3 shots from a cold start are typically 40 ft/sec lower and then settles. I suspect the power was increased but reg remains unchanged. Three mags worth, 42 shots with JSB Hades Monster .22 at 25.39 gn pellets gives the following using FX Chrono with initial low velocity 4 shots neglected:

1. ft/s ft lb 2. ft/s ft lb 3. ft/s ft lb

std dev
[td width="48pt"]
759.8​
[/td][td width="48pt"]
32.6​
[/td]​
[td width="10.3516%"]
747.1​
[/td][td width="9.5703%"]
31.5​
[/td]​
[td width="10.3517%"]
736.6​
[/td][td width="9.5702%"]
30.6​
[/td]​
[td]
7.5​
[/td][td]
0.6​
[/td]​
[td width="10.3516%"]
10.0​
[/td][td width="9.5703%"]
0.8​
[/td]​
[td width="10.3517%"]
8.2​
[/td][td width="9.5702%"]
0.7​
[/td]​

I use the gun for hunting and a bit reluctant to blast off 3-4 shots at a session start since it disturbs the environment. For longer range shots the the velocity drop is an issue at the start of any session.

So jonnybravo266 - did the Huma regulator improve things? It's not that clear from your post?
Are there known issues with AMP regulators - or am I being too fussy?
Forum ideas very welcome.
 
You say it's accurate but the chrono results vary. On what grounds do you conclude the reg is faulty?

If you have pressure readings confirming the reg isn't controlling pressure within +/-5bar you are on the right track. Otherwise it could be the action, the chrono or way the gun is set up.

I'm guessing the 7.5, 10 and 8.2 are fps std deviation, which is rubbish irrespective of not including the first few low shots. If you posted the actual MV results over a full string (or shorter strings over the fill range) including a good number of shots off reg, we might be able to make an informed judgement.
 
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@MTC
Just out of complete chance this vid popped up on my youtube today. I have no idea about FX guns (maybe one day I'll be able to afford one :love:) to know if this is applicable to your FX DRS but he has the exact same problem. Hopefully this helps.

 
^^^
As above , set up correct they are very good

My 25 fac has a very low spread
 
Many thanks for all your knowledgeable advice. I suspect that this is probably a case of enhanced regulator creep with a small leak reducing plenum pressure after standing OR hysteresis in the Belleville washer stack not settling back identically OR basic seal problems. I have been advised that a well set up reg should give MV standard deviations of <=5 fps? I attach an EXCEL file of 3 mags worth of shots for comment. Thanks again for your comments and assistance.
 

Attachments

Reading this thread by chance and have 2 questions for 2 statements here.

Initial post said rifle is accurate BUT chrono readings..........
If accurate should we even worry,no mention of wayward shots etc.

Secondly ,there was mention of belleville washers not resetting back.
Always see the washers being black and not really smooth,does polishing help?
 
MTC said:
MV standard deviations of <=5 fps
Click to expand...
I'm a bit dense on SD, but isn't it based on deviation from the norm (peak of bell) so can't really be quantified as a rule of a number of fps?
Screenshot 2025-05-12 052357.webp

When/if I get time I will chart your string, I can't read columns of numbers, I like pretty pictures. As for the rag stack I can't comment coz I ain't seen it. Are all discs the same thickness and in a ()()() type configuration?

Buglecall said:
Secondly ,there was mention of belleville washers not resetting back.
Always see the washers being black and not really smooth,does polishing help?
Click to expand...
I don't polish mine, any "settling" issue has always been me failing to seal between piston and set screw correctly. It's taken a long time and many slaps round the head from @Hmangphilly to get me to realise that, but I'm there now.
 
Good sub-12 standard deviation would be <2fps.

@sagalout can plot the data but it won't tell us much about the set-up. My earlier post still applies.
BallisticBill said:
I'm guessing the 7.5, 10 and 8.2 are fps std deviation, which is rubbish irrespective of not including the first few low shots. If you posted the actual MV results over a full string (or shorter strings over the fill range) including a good number of shots off reg, we might be able to make an informed judgement
Click to expand...

The off-reg data is important because it tells us something about the consistency of the action. If the variations (about the trend) continue off reg there must be irregularity in the action.
This thread might help understanding:

BallisticBill

Thread 'Reg or Action Fault? Reading the shot string.'

Variations in a regulated PCP's power and velocity? How to determine, is it the reg or the action causing the problem.
I've seen some sketches posted by @sagalout but no examples of real data. So here are some real results and my thoughts.

Reign string & pressure 2-1.png

  • The gun is coming off reg at around shot #130 at approximately 95bar.
  • The off-reg profile looks good, with small shot-to shot variation from off-reg trend. So the operation of the hammer and exhaust valve looks good. Off-reg trend is not plotted but you can see clearly where the big variations end.
  • The large drops in MV...
  • Like
 
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Screenshot 2025-07-16 025644.webp

Output is not good 😂. If you got a plenum leak that should be obvious from bottle pressure loss over time and needs to be fixed before looking for any other cause. Once you fixed the leak do what Bill says.
 
DRS went back under warranty with very helpful response from SGC. They said it was way out of spec. A number of problems were identified:
1. Marks on the valve pin and with runout on the pin indicating a slight bend. Valve, valve seat and internal O ring replaced.
2. Regulator piston and screw intact - but replaced anyway.
3. Problems with the Belleville washer stack - one incorrectly dished and another out of spec. on thickness.

Tests at SGC on a 18 shot string with 18 gn pellets indicated mean velocity of 882.8 fps with standard deviation on shot velocity of 3.3 fps giving about 31 ft lb muzzle energy. I'm very happy with that!

I hope these data may help others who may have problems with their DRS but clearly highlights the issues FX are having with quality control and the recent bad press. Pity, the DRS is a nice lightweight, pointable gun.

The gun has not been returned yet but on return I will take to the range for my own testing and report back.
 
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