Is 34 fps spread good on a 2k gun?

Houston, you have a problem. Wild guess, you're pumping way too much air out of that thing, Drain it screw in the reg, carefully and slowly start working your way up, start at 115 and see what happens, my guess is you'll wind up in the 120-125bar range, then some fine tuning on the Micro and Macro adjusters. Your SD should be about 5 or less. Others with that gun can offer more exact advice.

Like HogKiller said above. Try for a tune that is about 5% below the knee (KNEE meaning max FPS at that tune) for an optimal tune. That means at your desired tune, you will reach a max speed by adjusting the HS for a certain reg pressure and FPS will NOT increase anymore and may drop, so 5% under maxed out FPS. You should also look up tunes for your M series here at the PCP posts, that will get you a tune that is very close for your gun but might need minimal adjustments from there because every gun is usually a little different. I believe you can tighten up your ES.

Airmanator said:

Ok thanks guys. I need to work on tuning my gun then. I just get reg to 140 bar, valve to kine 4, don't mess with reg or valve anymore and just use power wheel as my tune. Guess that's not good.

Click to expand...

No you need to drop the reg pressure then SLOWLY start raising it in little tiny increments as you approach max speed. If you pass the point you'll know where that it, and rinse and repeat the degassing but this time just turn your reg in half a turn or so. Doing anything else first will be a waste of air, time and pellets. Remember you must degas the gun, remove the tank, start backing the reg out until it starts to leak, then fire the gun a few times, it should start to leak down faster. Failure to do this can damage the regulator. It is possible but not advised unless you like rebuilding regs, fire the gun and immediately turn in the reg screw a fraction of a turn. Not for the faint of heart. Don't even think of doing it without firing first.

JSB mkll weight distribution alone can cause 15-20 fps spread fwiw. Must weigh and sort to get it down to <10 fps, at least with JSB MKll.

And its " 5% from the plateau ", which is referred to as the knee.

-Matt

Sounds like time for a reg rebuild kit.

Your starting velocity is in alignment with your ending velocity. Listen to Stubbers, weigh your pellets. That’s your problem with those .25 big boys. I’m not saying to not listen to everyone else because they are right about one thing, you probably don’t need to shoot them that fast. My 600mm FX liner liked them around 915-920fps. Those pellets when I used to shoot them drove me crazy, until I sorted them. You don’t need to throw any of them away, just shoot pellets in the same weight group. When you run out, start using the next weight group. You might not even have to make a scope adjustment. But it will ease your obsession with numbers.

A $100 guitar that is in tune, will sound better than a $2000 guitar that is out of tune.

Potentially 23 FPS ES alone from 1.7gr tuned at the plateau...which is the low end of my 32.9-33.6 tin, and the high of my 33.7-34.4 tin.

-Matt

sorting pellets will probably be good to get the last few bit of variations out. But it seems to me that your gun is not in tune with a too high reg pressure vs probably too low HS. I'd suggest to max out your hammer spring (both macro and micro) and take a few shots, just to note the speed you'll get. Probably way too high.
From that point I'd suggest to do a proper tuning as you can read in the posts above. There is good info on YT as well on this matter.
My (personal) rule for a properly tuned gun is an extreme spread of 10 with a standard deviation of 1. You can probably go even lower, but I don't see the point of that (except for bragging rights ;-) ).

If using JSB pellets, sort them and then try again. Tune to the weight closer to the "intended" weight if still having issues.
Also, what are the intervals between shots? The quicker you shoot, the less time the reg has to recover. Firewalker has raised a good point regarding a possible regulator rebuild being in order.

First step is to get the gun shooting a reasonable speed for pellets. 950-960fps is not it. Even if it was a good tune they would not be accurate. I would get them below 920fps and 850 is not too slow in my opinion. My little P35-25 can only push them about 780 and they are accurate (and the ES is lower than this even when I fall off the reg). I think that means dropping the regulator setting as has been suggested. Starting low and going up only to get to your desired speed is definitely the way to do this. You should drain the gun before turning the regulator down (at least on my guns) but you do not have to drain it to go up. So go down, try a really low setting and turn it up if you need to. You need to have a reasonable match of the hammer spring to the regulator setting as you go down and then up. If you are close, I would fine tune the hammer spring more to find out what the maximum velocity is at that regulator setting and then see if 5% less is where you want to be. I generally am shooting groups as I do this since I want not just my target velocity but also an accurate tune. If you get to a tune in the 850-920 fps range I would try a few groups to see how accurate it is. You may find your gun prefers to shoot them at the low or high end of the range or right in the middle.

That spread is not in alignment with what the impact is capable of and it ain’t due to not sorting pellets. What others are saying about tuning. I believe 140 bar is way too high for 33.95. Start there. Yes to get that consistent 3-4 fps spread you would probably have to sort pellets. I have never sorted a pellet in my life and my m3 was pretty easy to get to a 10-12 fps spread with heavies. I forgot to ask what length barrel do you have? Also, completely up to you but I shot mine a lot slower, right around 900 fps with stellar accuracy. That would deliver you a lot more shots.

I'd suggest to have your pressure at 100 bar to start. Max out hammer spring. Next you shoot and increase pressure until you reach about 950 fps. And after that you tune down hammer spring and valve adjuster until your reach about 900 fps. Once you're there you can play with the hammer or valve adjuster to search for the most accurate setting (accurate in terms of small groups).

Airmanator said:

I see ppl saying my reg is too high. What should my reg be for the jsb heavy mk2 .25? As for barrel length, my barrel is the .25cal 600mm slug liner A 9from 2019. Twist rate I believe is 1/20. Seem like 850-920 fps is prefer for this pellet. I will tune it down.

Click to expand...

850-920 fps is a not the ideal speed... pellets don't magically start spiraling at 950 fps, too many factors...likewise tunes don't magically start going wonky at 950 fps, and we're discussing tune.

Too much false info here.

• 140 bar is not too high, its actually quite ideal, at the most I'd lower it 5 bar.
• Its clear you're tuned too close to the plateau, and if that's the case, 140 bar is great for a 910-920 fps tune as you'd be 3-4% from plateau
• Your regulator very likely does not need a rebuild
• 850-920 is NOT the magical range for pellets, they can do fine depending on their design between 700-950 fps...some will do fine at 700, others won't, some will do fine at 950 fps, others won't. Too much generalization suggesting 850-920 strictly.
• Being tuned AT the plateau will make your spread higher more-so when your pellets are unsorted, being tuned 5% from plateau will help.
• Being tuned AT the knee which is 5% from plateau with sorted pellets will give you the best results, even at 140 bar
• A regulator SHOULD refresh faster than you can reload a pellet, however not all regulators are built well, and if its an AMP reg then give it a moment between shots

-Matt

Airmanator said:

Ok. I see ppl saying their gun shoot 3-4 fps spread. Like Really? My gun is the fx impact mk2 .25 cal. Reg set to 140 bar. Valve on line 4. Power wheel is m3 set to number 10. Shooting jsb heavy mk2 33.9 gr brand new tin, un-sort. This my shot string from 250 bar. I shoot till it falls off reg, I only count the ones before it falls off reg. Is this good tune or can it be better? How are ppl getting less than 5 fps spread. Is that even possible? What is an acceptable spread for a 2k gun?

Click to expand...

Yes, it is certainly possible. Here are my last two 23+ shot strings on the gold .30 Skout Epoch with AEA 50.5 grain pellets unsorted.

~140 bars on Reg is fine, you look for a shorter Dwell by reducing the Hammer Spring and monitor the speed.
(with Valve open to 5th line-assuming you shall know what length/stiffness Valve Spring you have there...is it a stock Valve?). Different spring wire OD behave a slightly different when adjusting Valve.
When you get a Max speed (with Max Hammer), deduct about 20-30 fps that is your goal with HS. From there start tightening the VS down the next 20-30 fps and that will tighten the ES/SD.
I have the MK2 with .25x700 but also .25x600 and .22x600 with any kind off liners. But my Valve and Hammer springs are "custom" I don't remember anymore what were the stock dimensions on those, along the years I have collected a small box full with springs...
The JSB 34gn MK1 or MK2's my gun shoots them best BR results about 880-900, but still not good enough for me. This game never ends.

Ok, first let me say upfront that I was mistaken I'm set to 137.2bar. Maverick 600mm barrel, slug port and slug probe, not pin. I can tighten them up but...meh...I don't care that much, I splat ground squirrels just fine at 50 - 125 yards.

The AEA's are better in both of my Mavericks (.22 and .25) and my Raptor (.25), slightly better. If I was shooting competition I'd be using them.

JSB 33.9 unsorted, AEA 33.9 Unsorted


jsb 33.95gr .25 33.95. #7. 0,R. 11/11/23


Shot count: 12

Low: 939 FPS
Hi: 958 FPS
Avg: 945 FPS
Spread: 19 FPS
STD Dev: 4.6 FPS



AEA .25 33.9. #7. 0,R. 11/11/23

Shot count: 15

Low: 935 FPS
Hi: 951 FPS
Avg: 942 FPS
Spread: 16 FPS
STD Dev: 4.1 FPS