Kral Arms A question for you "Unregulated PCP tuners"

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Motorhead

Motorhead

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Nov 1, 2018
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In reference to my Kral Super Duty project.
See: Kral Project

Lightened the hammer, changed hammer spring and some minor trigger work sense last time.

Here is what the shot profile is looking like with a 1500 psi spread going from 3000 down to 1500 psi.
* Actually done on a fill stopping at these pressures and chrony testing.

1500 psi is 849 fps
2000 psi is 903 fps
2500 psi is 880 fps
3000 psi is 845 fps

So we have an ES of @ 55 fps in this unregulated 1420 cc capacity air beast as currently tuned.
I'm thinking for the quantity of shots there is going to be that it is very doable for an open field 100's of shots per day squirrel whacker !!!

So for you unregulated guys .... how is this tune ? ( I'm a regulator tuner and this was very time consuming )

Thanks,
Scott
 
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I wouldn't call myself an unregulated PCP tuner, but I do shoot a lot of unregulated guns, even in field target, and it looks fine to me. And this isn't likely anything you don't already know....

Generally an unregulated tune plots out as a bell curve, low fps as the pressure is too high, climbing to eventually peak out/plateaus at the correct pressure window, then fps gradually decreased again as pressure comes down.

Once the parameters like desired pellet weight, hammer weight, hammer spring tension, port restriction, etc are decided, the way to a tighter ES with an unregulated gun is to shoot within a narrower window of pressure. If an es of 55 is fine (which it likely would be for most squirrel whacking/pesting, than shooting over a wider range of pressures like you're talking will indeed increase the shot count (again, at the cost of a wider ES).
 
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An ES of 55fps for 100s of shots sounds like an excellent tune.

Personally, I prefer my unregulated rifles over my regulated rifles. Mostly because nothing about the function of the unregulated rifles ever changes.

How a person sets-up the tune can depend on how each individual person intends to use the rifle. I always tune for a 'bell curve' where the first and last shots match velocity. I have never had an unregulated rifle where my tune allowed more than an ES of 30fps. That number gave me velocities for my first few, and last few shots where POI change was irrelevant for the game I hunted, and the ranges I took my shots. Recently I got a small (0.3L) bottle to carry in my pack while out on foot hunting ground squirrels. Now, I changed my tune on my unregulated squirrel rifles to where they have single digit ES. Fewer shots per fill, but I have the small bottle to refill.

This works for ME, but may not be practical for other folks and how they use their rifles.
 
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I just graphed out a 72-73fpe tune I JUUUSSSTTTT barely started working with, this data is from the first chrono session. This is a Condor SS .25 using cast MP molds .25/47.6grain slugs. This is without even sorting the slugs, they were still warm from the casting actually. So there are improvements to be had, in various ways.

Vertical axis is fps, horizontal axis is shot count. As-is, I'm looking at a fill pressure to 2200 psi, and refilling after 1900 but before I get to 1800 psi. From this prelim data I could expect 12-13 shots within that pressure window, starting at 798 fps, climbing up to 845-850, and then ending back around 800fps. So about a 50fps spread. The lone peak fps coincided with a slug that didn't fit like the rest, so some sizing and sorting by weight will tighten this up. I also need to use a different transfer port jet and probably dial in some hammer tension. Going down in port size seems to have a bit of a regulating-like effect for non-regulated PCPs.

Just an example. In a lot of ways I prefer working with unregulated. I know dang sure the regulator isn't ever acting up in my USFT and 1720T and Disco before I sold it, and Condor, etc.


1747779181070.png
 
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BBGunn said:
An ES of 55fps for 100s of shots sounds like an excellent tune.

Personally, I prefer my unregulated rifles over my regulated rifles. Mostly because nothing about the function of the unregulated rifles ever changes.

How a person sets-up the tune can depend on how each individual person intends to use the rifle. I always tune for a 'bell curve' where the first and last shots match velocity. I have never had an unregulated rifle where my tune allowed more than an ES of 30fps. That number gave me velocities for my first few, and last few shots where POI change was irrelevant for the game I hunted, and the ranges I took my shots. Recently I got a small (0.3L) to carry in my pack while out on foot hunting ground squirrels. Now, I changed my tune on my unregulated squirrel rifles to where they have single digit ES. Fewer shots per fill, but I have the small bottle to refill.

This works for ME, but may not be practical for other folks and how they use their rifles.
Click to expand...
You should see the looks I get when I tell people at field target matches that I have an ES of 25ish fps with my USFT. They look even more shocked when I win. They're all hunting single digit ES, and fretting about it when their gun is throwing 12-14fps spreads. I get a kick out of it on a regular basis.
 
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Franklink said:
You should see the looks I get when I tell people at field target matches that I have an ES of 25ish fps with my USFT. They look even more shocked when I win. They're all hunting single digit ES, and fretting about it when their gun is throwing 12-14fps spreads. I get a kick out of it on a regular basis.
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Much easier to tune ES at home than travel and practice shooting. Tuning ES works well with my ADHD and OCD. Congrats on your skills and hard work.
 
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Struckat said:
Looks good to me! And like Hobbyman I would narrow the band depending on the need for accuracy.
Click to expand...
The share was deliberate in seeing what it was doing over what thought was a VERY WIDE pressure range, as I seldom recall threads over the years of non regged rigs where the sweet spot was generally seen within 500-800 psi min/max.
 
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Motorhead said:
The share was deliberate in seeing what it was doing over what thought was a VERY WIDE pressure range, as I seldom recall threads over the years of non regged rigs where the sweet spot was generally seen within 500-800 psi min/max.
Click to expand...

This is very true, and I didn't even notice. Your 55fps spread is over a much larger pressure window than typical for unregulated PCPS.
My USFT is 1500-1250
1720t is 2600-2000
Both Condors have been around 2200-1800fps.

The way you balanced all the parameters out to be fairly consistent over a 1500fps fill/refill pressures is quite impressive.
 
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Sergey1972 said:
Much easier to tune ES at home than travel and practice shooting. Tuning ES works well with my ADHD and OCD. Congrats on your skills and hard work.
Click to expand...

Thanks. I was just trying to point out that really tight ES is overrated, and much greater emphasis than warranted is often placed on single digit extreme spreads.
 
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Motorhead said:
In reference to my Kral Super Duty project.
See: Kral Project

Lightened the hammer, changed hammer spring and some minor trigger work sense last time.

Here is what the shot profile is looking like with a 1500 psi spread going from 3000 down to 1500 psi.
* Actually done on a fill stopping at these pressures and chrony testing.

1500 psi is 849 fps
2000 psi is 903 fps
2500 psi is 880 fps
3000 psi is 845 fps

So we have an ES of @ 55 fps in this unregulated 1420 cc capacity air beast as currently tuned.
I'm thinking for the quantity of shots there is going to be that it is very doable for an open field 100's of shots per day squirrel whacker !!!

So for you unregulated guys .... how is this tune ? ( I'm a regulator tuner and this was very time consuming )

Thanks,
Scott
Click to expand...
I own two, and wouldn't call myself particularly proficient at it. My mrod got hammer and transfer adjustments until shot 1 was as similar to shot 16 (25 cal and looking for most useable power). I would say your tune looks pretty good if poi shift isn't a big problem.

My aea, I stumbled on something. I don't fill it as far as others do because that gun gets left in the hot sun pretty often. I bottle converted it and turned the transfer closed maybe 40% and just having more air fixed a lot of what I hated about that gun. Back fired pellets, short shot count with a lot of data movement. 330cc bottle fixed all of that. For the guns intended purpose, I can handle a consistent slow downtrend and the shot count is 1 fill with acceptable poi shift for its job(ground squirrels)

Your numbers look like something pretty good to me that could be refined over time as you notice more of its personality. Nice work op!

Screenshot_20250505-072745_FX Radar.jpg
 
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Every time I dive into an unregulated gun, when I’m done I go get a blood test to check my lead levels. I’ve learned some shortcuts for figuring out my starting pressures, but I still wind up getting punch drunk from all the shooting. In the end it’s worth it. And like the guys have mentioned, I have my start and stop pressure marked on my gauge, but I also know the pressure range for when I want to show off.
 
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Franklink said:
This is very true, and I didn't even notice. Your 55fps spread is over a much larger pressure window than typical for unregulated PCPS.
My USFT is 1500-1250
1720t is 2600-2000
Both Condors have been around 2200-1800fps.

The way you balanced all the parameters out to be fairly consistent over a 1500fps fill/refill pressures is quite impressive.
Click to expand...
With as much air onboard as Motorhead's rifle has he could tune it to an ES of 5fps for lot's of shots if that was what he wanted out of it.
 
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Most of mine are regulated now, thanks in no small part to your assitance over the years. But I love my unregulated Air Ranger and tune it differently every now and then - it has a custom built internal SSG I made for it so it functions well over a broad pressure range too so I have lots of experience with tuning it.

I agree with most of what has been posted, except I feel you need to do a few more velocity checks in the 2500-2000 psi range (especially around 2200 or so) -, as I expect you have not found your true peak speed off those four data points. While the tune is clearly great, I bet your true ES is higher than 55 fps, but you won't know how much until you test it in that area to find that peak speed (I strongly suspect the point at 2000 psi is coming down off the peak).

But other than that small point, kudos to a great tune!
 
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BBGunn said:
With as much air onboard as Motorhead's rifle has he could tune it to an ES of 5fps for lot's of shots if that was what he wanted out of it.
Click to expand...
It is ... "A work in progress"
But it absolutely IS NOT a competitive set up ... Run it on a fill and kill stuff ... Basic simple PCP with little fuss once set up.
 
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Motorhead said:
It is ... "A work in progress"
But it absolutely IS NOT a competitive set up ... Run it on a fill and kill stuff ... Basic simple PCP with little fuss once set up.
Click to expand...
I agree, and understand your goal. With the way my squirrel hunts go I could shoot for several days without a fill using your rifle! :cool:

My point was that the key to low ES and lot's of shots from an unregulated rifle is having a large air reservoir.
 
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