AirMaks Arms Katran velocity unstable?

[Rabbit's foot]

Hey there.

First, as a basic setting theory, set the spring tension so that the speed is slightly lower than the maximum velocity, i.e., 95-97% of the maximum velocity.
This is a standard rule of thumb.

On the other hand, based on my experience, Katran and KRAiT use a special hammer system, and I feel that a range of 97-98%, which is slightly different from the standard rule of thumb, tends to stabilize the speed.

Looking at the data Ericf has compiled, the maximum muzzle velocity is 1045 fps. At 97%, this would be 1014 fps, so if the current setting is around 950 fps, the spring tension is too weak.

As far as I recall, the factory settings for the KATRAN-L (.22) were REG: 110/MV: 920–935 fps (16 gr).

Based on this, I suspect that ericf's Katran was delivered with the regulator set too high due to some error.
(It is likely set to around 120 bar.)

If you set the REG to 110 bar and adjust the hammer spring to approximately 97–98% of the maximum muzzle velocity at that pressure, stable shooting should be possible. (And that would be 920–935 fps.)

The KATRAN is an excellent gun, and your choice was spot-on.

Best of luck.

 

[ericf]

I consideration of the details, would it be plausible to just increase the hammer tension to maximum and check velocity over several shots. Accuracy would be nill, but velocity should be constant. Is this a correct assumption?
It would give me insight into a regulator issue if velocity changes are as dramatic, or hammer tune issue.
I could be incorrect in my thinking, I usually am. Just ask My wife.

 

[ericf]

Going on maximum hammer strike and a velocity recording I could begin reducing spring pressure till velocity changes with a slight reduction. At that change perform the 97% reduction rule and set velocity with slightly reduced spring pressure. Would this approach be workable?
It would appear the above would be a more viable possibility since lower hammer spring pressure causes such wild swings. But again, maybe not.

 

[Rabbit's foot]

All wives in this world are always right.
And we are always wrong.

Well, I think your theory is correct.
When firing at maximum velocity, the velocity itself is almost always stable.
However, if too much air is expelled, it causes the pellet to move unsteadily the moment it leaves the muzzle, and also reduces fuel efficiency.

I usually check this velocity by firing two shots at a time, rotating the screw by 1/4 turn each time.

However, at around 95~97% spring tension, the adjustment becomes very precise, and the final adjustment rotation is only a very small amount.

 

[Rabbit's foot]

Going on maximum hammer strike and a velocity recording I could begin reducing spring pressure till velocity changes with a slight reduction. At that change perform the 97% reduction rule and set velocity with slightly reduced spring pressure. Would this approach be workable?
It would appear the above would be a more viable possibility since lower hammer spring pressure causes such wild swings. But again, maybe not.

I think HAM's article provided detailed information about HST settings.

An Introduction To The PCP Regulator. Don’t Ignore The Plenum!

Producing constsnt FPS in a PCP with varying air pressure is tough. Instead why not use a PCP regulator to produce a constant pressure at the valve?

hardairmagazine.com

However, this theory is a method that applies when the regulator is equipped with an appropriate power spring and hammer, and there are exceptions.
But Katran is fine.

AMA air guns strike the valve with a pendulum-like arm, which is equipped with a spring, so when the spring tension weakens, the speed suddenly becomes unstable.
Therefore, personally, I recommend a setting of 97-98%.

Additionally, structurally, immediately after turning the screw, the contact surface between the spring and hammer is unstable, making it difficult to record accurate speed.
Performing about 10 decocks each time you turn the screw should stabilize it.

 

[RoosterCogburn]

"The katran. Even a superb gun like mine was/is. Will have giant spreads if the hammer is set incorrectly. The katran is very sensitive to this."

So I can better understand, If the hammer setting is the issue, and I am able to get a decent setting on the hammer, the velocities should stabilize far better than what I'm seeing. Is this a correct interpretation? Then, with the hammer set at this designated point giving me stability in fps, the only way I can reduce velocity (if needed) is to use a heavier pell or disassemble it and adjust the regulator. And adjusting the regulator will cause the whole process to start over. Is my understanding correct? I apologize again for my lack of knowledge in this matter.

Yes. So if the hammer is set too low for the given pressure. Its not applying enough force against the valve stem. Giving you poor shot to shot consistency. Typically on low hammer. You'll start low and crawl high, with intermittent wild numbers here and there. Depending where the plenum is as far as refilling itself and equalizing after each shot.. the same happens.when you're far too.high on hammer. You'll go low high high low high and will use a ton of air. Youre looking for 2 things in a good tune. One Is consistent velocity with minimal shot to shot velocity change. My Katran when carefully tuned might have a 2fps spread.. if I went a half turn in either direction. 30FPS or more sometimes..

The other is usually a side effect.of the 'sweet spot' efficient air use.

 

[RoosterCogburn]

I think HAM's article provided detailed information about HST settings.

An Introduction To The PCP Regulator. Don’t Ignore The Plenum!

Producing constsnt FPS in a PCP with varying air pressure is tough. Instead why not use a PCP regulator to produce a constant pressure at the valve?

hardairmagazine.com

However, this theory is a method that applies when the regulator is equipped with an appropriate power spring and hammer, and there are exceptions.
But Katran is fine.

AMA air guns strike the valve with a pendulum-like arm, which is equipped with a spring, so when the spring tension weakens, the speed suddenly becomes unstable.
Therefore, personally, I recommend a setting of 97-98%.

Additionally, structurally, immediately after turning the screw, the contact surface between the spring and hammer is unstable, making it difficult to record accurate speed.
Performing about 10 decocks each time you turn the screw should stabilize it.

Exactly.

This is why we say "1 shot is not enough to know"

 

[ericf]

Update,
I talked quite a long time with UA. I was advised that the "HP" version is factory set up for heavier slugs. I knew it had a larger plenum but I am not sure what else is done for that "Setup". He advised to try heavier slugs. I inquired about heavier skirted pellets and he wasn't able to comment except to repeat the slugs suggestion. So I ordered 25.x grn and 28.x grn slugs to see what can be done for better consistency. Meanwhile I'm just going to attempt to set the trigger for an average chrono velocity of 890 with 18.2 pells and just enjoy it.

 

[RoosterCogburn]

Update,
I talked quite a long time with UA. I was advised that the "HP" version is factory set up for heavier slugs. I knew it had a larger plenum but I am not sure what else is done for that "Setup". He advised to try heavier slugs. I inquired about heavier skirted pellets and he wasn't able to comment except to repeat the slugs suggestion. So I ordered 25.x grn and 28.x grn slugs to see what can be done for better consistency. Meanwhile I'm just going to attempt to set the trigger for an average chrono velocity of 890 with 18.2 pells and just enjoy

You cannot set for 890 at that pressure if it's shooting 960. The inconsistent velocities will be soul crushing.

The hammer spring on that gun.. IF you set to 100b it HAS to be within a certain SMALL window of adjustment or you'll get terrible results.


If you set to 110 You'll have to slightly adjust upward.


If you set to 90 You'll have to LOWER the stroke of the hammer. this is a regulated gun. You are at the mercy of the set pressure. The hammer spring MUST be within that window for whichever pressure you use. YOu MUST find that window, which is why we've recommended you Make incremental adjustments up. fire 5-10 shots per adjustment UNTIL you come to a point where the next adjustment starts to drop in average velocity. So you know the gun is capable of sending 18s well over 950 FPS. Find the peak. Then Dial back until the velocities are Consistently within a few fps of eachother. Yes you can shoot Skirted pellets. Suggest JTS or AEA 25.3 or fx 25.4, OR JSB 25.39 or JTS 28.55. if you attempt to shoot 18.1 gr pellets when the gun is trying to shoot 18grs at near 970 You're going to have an awful time.

Visualize a seesaw. And you're trying to have it not tilt to either side, you place equal force or weights on both ends. to have it balanced.. Well that is what you're doing with the valve and hammer.

 

[ericf]

OK. to summarize all this information that you guys have given me (very much appreciated) and videos and reading articles. The regulator , hammer spring tension (setting) and Pell size all have a direct correlation on each other. The perfect "Tune" places everything in a static balance. If regulator output increases, then hammer tension would need to be changed (probably increased) to rebalance, If pell weight changes, an Over vel or under vel. can result requiring regulator changes which then require hammer changes to rebalance the system. It Cannot stay in tune with simple hammer changes to maintain velocity if pell weight changes.
Is this summary correct?
I believe I'm getting a perspective on this process. However, what I'm not happy with is that a simple pellet change for the day, for whatever reason, can cause all kinds of havoc with velocity and accuracy. But I guess it is what it is.
Does the Plenum have any involvement in this equation ? Or is it more only for air volume availability for the desired target velocity?
I'm going to spend the morning sampling velocities and making hammer adjustments to see where it ends up in this balance using a 20.xx pellet
I'm not going to concern myself with the accuracy or velocity, but only with getting the "chrono velocity extreme spread " as minimum as possible.
UA told me that this "HP" version was designed and setup (factory) for slugs. I hope that isn't a huge issue, I just would rather use lighter weights in the mid and low 20's . I'm hoping to achieve this without having to guesstimate a regulator pressure change which would probably require (rinse and repeat) to hit that target velocity .
Growing old isn't for Puss***. Sometimes understanding a topic comes slowly. Other times "no explanation is needed."
I apologies again for my "slowness" in this area. But thanks to all that helped.

 

[ericf]

As per UA, In the enclosed "shot" information with my new Katran, they were shooting an AEA 25.3 grn. pill and getting 915fps average.
It's still a little fast, I think.
Why can't manufactures just put an external adjustment for regulators on these rifles. It would make life so much simpler.

 

[ericf]

ok, just for information. After shooting 40 pells through the rifle, I came to these figures. I think the final would be much better because the last shots had reached 150 bar in tank and I'm sure that is where it is set to. These pellets were 21.14 grn H&N Baracudas which is heaviest I have right now. Spread looks more like where it should be. Especially if last two shots were thrown out
1 1000.5............ hi- 1006.9
2 1002.6 ............ lo- 999.5
3 1001.8 ............ SD- 2.6
4 1006.9 ............. ES - 7.4
5 1004.5
6 1004.7
7 999.7
8 999.5

 

[Rabbit's foot]

OK. to summarize all this information that you guys have given me (very much appreciated) and videos and reading articles. The regulator , hammer spring tension (setting) and Pell size all have a direct correlation on each other. The perfect "Tune" places everything in a static balance. If regulator output increases, then hammer tension would need to be changed (probably increased) to rebalance, If pell weight changes, an Over vel or under vel. can result requiring regulator changes which then require hammer changes to rebalance the system. It Cannot stay in tune with simple hammer changes to maintain velocity if pell weight changes.
Is this summary correct?
I believe I'm getting a perspective on this process. However, what I'm not happy with is that a simple pellet change for the day, for whatever reason, can cause all kinds of havoc with velocity and accuracy. But I guess it is what it is.
Does the Plenum have any involvement in this equation ? Or is it more only for air volume availability for the desired target velocity?
I'm going to spend the morning sampling velocities and making hammer adjustments to see where it ends up in this balance using a 20.xx pellet
I'm not going to concern myself with the accuracy or velocity, but only with getting the "chrono velocity extreme spread " as minimum as possible.
UA told me that this "HP" version was designed and setup (factory) for slugs. I hope that isn't a huge issue, I just would rather use lighter weights in the mid and low 20's . I'm hoping to achieve this without having to guesstimate a regulator pressure change which would probably require (rinse and repeat) to hit that target velocity .
Growing old isn't for Puss***. Sometimes understanding a topic comes slowly. Other times "no explanation is needed."
I apologies again for my "slowness" in this area. But thanks to all that helped.

I think that's a perfect understanding. Excellent.

So the KATRAN you have is the HP model.
With 25.3gr pellets at 915 fps, it's likely that using 23gr slugs would achieve around 930 fps, and 20gr slugs around 960 fps.

While an externally adjustable regulator could open up more possibilities for fun, it also complicates the structure and increases the risk of air leaks.
Furthermore, the regulator itself would inevitably need to be miniaturized, potentially leading to drawbacks like reduced durability.
One of the KATRAN's strengths is its very simple, robust construction.

However, adjusting the KATRAN regulator is straightforward: just bleed the air and unscrew the air tube to access it.
Since it's a HUMA regulator, it also has a pressure indicator seal (though this number is completely unreliable lol).

These kinds of challenges are part of the fun of the hobby, aren't they?
Have a good day.

 

[ericf]

Any idea regarding how far to adjust? I have read that to reduce pressures it should be screwed in, Increase - unscrewed. But how far?
One guy on YT vid says that one full turn is equal to about 30 bar. I'm not so sure about YT vids.
The pressure appears to be about 140- 150bar setpoint. Any guesses how much reduction would be needed? Reduce about 15 bar? Or start with about 45* turn for reduction ( just under 1/4 turn)? I have no idea how to interpret this without just trial and error which doesn't sound very appealing.

 

[JimD]

I like to use digital calipers to measure the height of the regulator for a reference of it's setting. I have done this a few times on my SPA regulators and now know about where to turn the adjustment screw to (what length) to get an acceptable setting. My Huma has a paper tape on it but the markings were faded last time I had it apart. I wouldn't say they were inaccurate but they were only a rough reference point (still a lot better than nothing). If you can still read the tape on yours you might even want to make a little table of length versus paper tape indication. Then you could shoot it down once and know how far the tape is off. The distance between settings should be pretty accurate but the tape may have moved making the absolute value not very accurate. Wth an accurate table you could forget about the tape or even just take it off.

I don't think the situation relative to the need to retune each time you change pellets is as bleak as you suggest but it depends on where you set the gun and what you change to. My Bullshark is set up to shoot 18.3 grain AEA (which are really 18.1 grains) about 860 fps. It will also shoot 14.3 Crosmans as accurately as I have ever shot Crosmans at the same settings but they are going about 930 fps. If I increased the 18.1 grain up to 890 fps or something in that range it would push the 14.3s up were you are now in your Katran and they would not be accurate. But if I was at 880 with 18.1 my guess is 16 grain would still be fine. And when I increase pellet weight it normally doesn't require a retune unless I don't like the velocity. I believe velocity is at most a secondary factor in accuracy as long as you don't go far over 900 fps. The primary factors are whether the gun likes the pellet and having the hammer spring properly set a little under or possibly even slightly over the peak velocity for the regulator setting (over is inefficient but can be accurate). Once you have a good tune you should be able to shoot a reasonable range of pellets pretty well. The Bullshark I referenced gave me my first 200 this year on the 30 yard challenge and my P35-22 gave me my second yesterday even though the 21.9 grain AEA pellets I was shooting were only going about 835 fps. 880 is typically recommended by my Caiman likes to shoot 18 grain H&Ns about 930 fps. It gave me a 200 last year. I'm not sure there is a floor where accuracy gets bad, in England they are limited to 12 fpe without a special license and commonly shoot well under 800 fps but they are still accurate. It seems to me to be more a question of having an acceptable trajectory. 800-930 have all worked well for me and my little Prod only does about 750 but is quite accurate.

At least for now I stopped shooting slugs in my Caiman X. It was not as accurate with them as it is with pellets and the barrel leaded up (it is a CZ like your Katran I think). If you do start shooting slugs you may want to invest a few dollars in a bore scope to check for leading. It can be difficult to remove.

 

[Rabbit's foot]

The KATRAN HUMA regulator has a pressure reference sticker affixed to it.

The HP model's settings are unknown,
but the factory default settings for the KATRAN-L (.22) should have been REG: 110 / MV: 920-935 fps (16gr) (Sorry, I might be wrong; I don't have the data on hand right now.)

Adjusting the regulator simply involves aligning the top notch with the 110 bar value on the sticker.
For details, search for “HUMA Regulator Adjustment Method”.

However, as mentioned earlier, this sticker is quite rough. For extremely precise measurements, you must use the regulator tester sold by HUMA.

The setup performed after regulator adjustment follows the same procedure as the method I tried previously.

 

[bchannell]

I haven't read it all, so forgive.
The plenum, if overly large, "can" be hard to tune down. Then add a second reg, and more confusion. Believe me I had trouble getting my head wrapped around tuning my Wildcat.
The Katran should be easier, but I'm not sure what changes were made to the HP version. Big plenum with low speed tunes, sips so little air that the reg doesn't always replinishes after every shot.

Here's where I'd start. Leave your reg at factory setting. Lower your hammer a bunch. Shoot 5 shots over the chrony, increase hammer 1/2 turn, shoot 5 more, rinse and repeat til velocity stops rising. Now go back and refine. Say velocity stopped rising between 3 and 4 turns, then go back to three and work up in 1/4 turns.

If es doesn't settle down then you've got mechanical problems, assuming you're not too light on pellets. UA is correct that you may need heavy pellets. My WC mk3 has an 89cc plenum and doesn't play well with pellets less than 18gr or so. I had troubles until I started shooting 25gr MRDS and BINGO, I got in it's sweet spot.

All non balance valve regulated guns are tuned the same way, it is just adding different plenum, hammers, springs, reg's etc that complicate the process.

Even though it's probably a tuning problem. I wouldn't be surprised something else mechanically is wrong, because the Katran I had was rock solid and one of the most consistent rifles I've ever had with es well below 10fps almost every time, and that's for full strings.

 

[RoosterCogburn]

ok, just for information. After shooting 40 pells through the rifle, I came to these figures. I think the final would be much better because the last shots had reached 150 bar in tank and I'm sure that is where it is set to. These pellets were 21.14 grn H&N Baracudas which is heaviest I have right now. Spread looks more like where it should be. Especially if last two shots were thrown out
1 1000.5............ hi- 1006.9
2 1002.6 ............ lo- 999.5
3 1001.8 ............ SD- 2.6
4 1006.9 ............. ES - 7.4
5 1004.5
6 1004.7
7 999.7
8 999.5

GREAT NUMBERS (spread and consistency) wayyyy high for pellets.

I haven't read it all, so forgive.
The plenum, if overly large, "can" be hard to tune down. Then add a second reg, and more confusion. Believe me I had trouble getting my head wrapped around tuning my Wildcat.
The Katran should be easier, but I'm not sure what changes were made to the HP version. Big plenum with low speed tunes, sips so little air that the reg doesn't always replinishes after every shot.

Here's where I'd start. Leave your reg at factory setting. Lower your hammer a bunch. Shoot 5 shots over the chrony, increase hammer 1/2 turn, shoot 5 more, rinse and repeat til velocity stops rising. Now go back and refine. Say velocity stopped rising between 3 and 4 turns, then go back to three and work up in 1/4 turns.

If es doesn't settle down then you've got mechanical problems, assuming you're not too light on pellets. UA is correct that you may need heavy pellets. My WC mk3 has an 89cc plenum and doesn't play well with pellets less than 18gr or so. I had troubles until I started shooting 25gr MRDS and BINGO, I got in it's sweet spot.

All non balance valve regulated guns are tuned the same way, it is just adding different plenum, hammers, springs, reg's etc that complicate the process.

Even though it's probably a tuning problem. I wouldn't be surprised something else mechanically is wrong, because the Katran I had was rock solid and one of the most consistent rifles I've ever had with es well below 10fps almost every time, and that's for full strings.

I found that for every 12th of a turn you'd gain about 5-7Bar, there should be a blue stamped Set pressure on the back of the regulator when you first separate the plenum/valve/bottle from the gun and pull the plenum off the reg.

On the Katran L 177 90b was stock set, it was marked. ~890-900 with 10.3gr pellets. I turned CCW from 1:00 to 11:00 and was now shooting at 940-960 depending on pellet and where the in sweet spot i had the hammer. Tuning to JUUUUST the left of peak on the curve got me 100+ shots with 10.03 mk3s at 935. Wasn't enough, so i adjusted again from 10:30- 9:00. That's where it sits today. at about 115-118b. shooting 10.03' slugs at 966 groupling single hole patterns and STILL in excess of 80 shots per fill.

 

[ericf]

More information. The regulator in this rifle has no sticker nor identifying marks. I marked the factory setting and turned it 90* inward. The average velocity after re-tuning the trigger to the new setpoint dropped to 946fps. still using the H&N 21.14. The setpoint drop-off is now about 125 bar. So, it appears that a quarter turn averages about 25bar change. I'll wait till I receive the 23 grn slugs and recheck velocities after adjusting trigger,,,Again.
One thing, the "ES- " now is 2.9 over 8 shots using the same 21.14 pell. Not bad for my intentions. Actually far better than the starting point.
I'll need to put up a target to check for accuracy. Even though it's a little too high velocity.
I have edit this, 1/4 turn inward (tightening)=25 bar reduction on my reg.

 

[RoosterCogburn]

More information. The regulator in this rifle has no sticker nor identifying marks. I marked the factory setting and turned it 45* inward. The average velocity after re-tuning the trigger to the new setpoint dropped to 946fps. still using the H&N 21.14. The setpoint drop-off is now about 125 bar. So, it appears that a quarter turn averages about 25bar change. I'll wait till I receive the 23 grn slugs and recheck velocities after adjusting trigger,,,Again.
One thing, the "ES- " now is 2.9 over 8 shots using the same 21.14 pell. Not bad for my intentions. Actually far better than the starting point.
I'll need to put up a target to check for accuracy. Even though it's a little too high velocity.

Inside of 50-60 950 will probably fly. Going up 1-2grns would put you in the perfect slot.