tuning discusson

I'm no expert, but I start shooting the heavier pellets I'm going to be shooting, at a higher power setting, and go down from there. Then I look at a medium weight pellet, and start shooting it a bit higher than what the heavy pellet was lowest at. Repeat with a low weight pellet. That way I have an idea of what power range to shoot each weight class. Understanding that your gun will like certain pellets and throw others all over the place is paramount. 

"Kitplanenut"Thought I might learn so figured on bring up this topic. When tuning a PCP is it better to set the reg as low as possible and then slowly increase the hammer spring tension until the desired fps is reached? If the fps can't be reached then decrease the hammer spring tension, increase the reg slightly and start increasing the hammer spring tension again until the desired fps is reached. Keep repeating until successful. Or set the reg above pressure needed to obtain desired fps and adjust the hammer spring up to desired fps? All guns will be different, these are a couple of basics to start form. What are your thoughts. Sylvan

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That's the way to do it with most airguns to acieve the lowest ES
The idea behind this is to dump the complete plenum volume all at once.
One exeption is the impact, with the valve stop adjustment, you can achieve a very low ES too by making use of this end stop.
This doesn't mean other way's don't work, but to me, the way you descibe it is the perfectionists way
With my LG110 I can achieve good results with a tight ES by running a bit higher reg. pressure, and dial the speed up/down with the external v0 adjuster.

This is a good question, especially for someone adding a regulator to a non-regulated original equipment gun (Marauder as an example). An experiment could be run on one of the FX products that include both regulator & hammer spring tension adjusters to determine the impact on accuracy, shot count/efficiency, or report. I wonder if higher regulator pressure and lower hammer spring tension results in lower report & higher efficiency due to partial valve lock.

Have any Impact or Crown owners noticed trends?

This discussion is pointless without first clearly defining the objectives and acceptable trade offs.

Gotta agree with Inde - what purpose? 100 benchrest? Hunting? Power? accuracy? economy? you name it, there's a tradeoff.

First thing you need to do is plot a velocity curve and determine if your V starts going up or down when you go off the reg at the hammer tension and velocity you are targeting. You could be maxed out on plenum volume too if trying to move heavy pellets into the high 8's or low 9's. Reg pressure may get you there but at some point your valve will not allow enough dwell (too much reg pressure) to reach the target V due to hammer spring tension/hammer weight. Its all related! 

I adjusted my Mutant .22 reg down to around 130b and shot count, consistency and velocity were much more consistent and easier to control with HST but there is a limit as indicated above. Depends on what your goals are. 

Here is a clinic on this subject: 

https://www.gatewaytoairguns.org/GTA/index.php?topic=74919.0

Hope this helps.

Rgds,

DT

Hello.

I look at it from force on pellet perspective. 
work=force x travel
If you have higher pressure(150bar) and close valve after lets say 4inches of pellet travel, the air will expand till end of barrel to some pressure.
if you set at 120bar, for same work you will have to close valve later, lets say after 7inches. This air will too expand until end of barrel, but you will have higher pressure then, so more wasted air.

I own cricket .25 with proper size ports, and pressure behind pellet only rose for aprox 60 bar during shot, with 130 bar on regulator. Co it seems flow i still not fast enough.

i plan on doing propper research on exactly this topic soo i hope, will inform

No problem. Once you get the hang of it it is a fairly simple process although it can be painstakingly slow if you are messing with your reg on a regular basis. Shot curve should get you in the ball park. 

I have an Edgun .30 that will sling 44gr JSB at 880-890 all day long at 140b reg pressure with a fairly flat velocity/shot curve before dropping off. Reason is hammer weight, HST and plenum volume. Its not really working hard to be honest but its dialed in and fairly efficient at the current settings. 

Have fun man! 

Regards,

DT

I'm in the process of tuning my Crown to attempt to use the JSB 34gs at EBR 2017 this year. So to define my goal, is very predictable pellet placement at 75 and 100 yards. Just as everyone else, my crown came shipped at 125 Bar moving 25.4s at around 890 and 34s around 790. Average ES was about 16-20 fps when I got it. EBR 2017 typically is very windy so I believe if I want my best chance of success shooting in the wind, I need to get the 34s shooting well if the Crown is going to come with me. Otherwise, I'm going to use the Boss. It moves a 50g 30 cal at 830 with an ES around 9. 
First, I'll say the crown is a laser beam with no wind at 50 yards with the 25.4g pellets at 50 yards. It litterally makes a single hole in the paper as everyone claims. But the ES shows up at 75 yards. Using a chronograph, I can literally tell within 5 fps what the chrony reads from where the pellet hits the target.
So my process started with increasing the hammer spring to increase the velocity of the 34g to about 825 fps before further increasing the adjustment of the hammer spring no longer yeilded an increase in velocity. I then increased the regulator pressure to 130 bar and not much happened. It seemed that very little increase in velocity happened but ES went crazy. I was getting 823 one shot and 850 the next shot.
I then decided to test moving the reg to 140 bar to verify that I could move the pellet in the 860ish fps range and where would the hammer spring need to be set to accomplish that and what would that mean for group size and ES with the 34s? 
So, today I did that and got that configuration worked out and the gun seems to like it as the group sizes are okay with a few fliers but ES measured at 22 during a 13 shot string. Verticle group size is smallerat 860 vs 830 at 75 yards. I'm pretty sure ES will be exagerated at 100 yards so I'm still concerned that I haven't found the sweet spot to get the ES down under 10. I'm worried that with the crown's lack of the valve adjustment, I may not be able to have confidence in the gun with this high ES condition.
Anyone else with a crown got the 34s figured out? I'm currently at 140 bar and 858fps average. Anyone else having high ES issues with the crown? 



Here are a few groups for comparison on 1 in grid paper.
50 yard crown groups as advertised..


75 yard groups with 25.4s no wind.


75 yards with 34g at 860ish fps (notice how the groups grow vertically)

and considerably more fliers. These are my better groups from the 34s.

...Still in search of the sweet spot.

I think I will also follow the prior suggestion and move down the regulator and start at about 130 bar and sneak up the hammer spring a little at a time and measure ES through the range of hammer spring tensions. Move up 5 bar and do it again and see if I can find a spot with low ES and an acceptable velocity and hope the gun likes it.

Any input is welcome. Hope this helps someone out.

Thanks for the info. I have a similar project with 34g in different gun. Non adjustable Renegade ( LW barrel ) shoots 34g at an Ave. Of 952 fps. Have only tested at 50yds. and accuracy is about the same as yours. Will be stretching it out in about month when the weather cools a bit.
Btw. Suggest you do not get hung up on ES. SD is statistically a much more accurate measure of repeatabilit. 

Kitplanenut, thanks for confirming there is nothing wrong with my crown es and sd numbers. I was thinking i might need to send it back. Im with you in thinking the 1:28 twist barrel may be the ticket on realing the flyers in but how do we fix the sd? Missing vertically is just as bad as missing horizontally at 100y. My impact and boss are both outshooting the crown at 75 as well. Don't have 100y in the back yard unfortunately but loguc says it only vets worse with distance.

you going to ebr?

For a regulated pcp that ES is very large. Why have a regulator if you still have an ES of 29 fps. A good regulated pcp tuned properly will be 15 fps or less across the whole string. For long range shooting the ES is very important and needs to be at a minimum especially if you are competing and not just shooting for fun. If you want to tune the pcp for efficiency and low ES there is a simple way to do it. 
Most pcp rifles perform best when on the knee of the regulator setting. You have two points: the plateau and the knee. The plateau is exactly what it sounds like. The plateau is the highest velocity you will get with the current reg setting regardless of hammer energy. Its fairly easy to understand. Once you hit the plateau the only thing that happens when you increase hammer energy is wasted air. So the best performance is tuning the pcp to have just enough energy to be just under the plateau. That is referred to as the knee of the reg setting. Most people see the best results in ES and efficiency being tuned on the knee not the plateau. I dont think there is an answer as to how far down the knee is best and takes experimenting to see where on the knee that particular pcp performs best at.

Its easy to see if you are on the knee or plateau.

#1: Make a note of the reg setting, and hammer spring setting. I would also say you should have the TP fully open while tuning the regulator to be balanced properly.
#2: Shoot a few shots across the chrony and note the velocity.
#3: Adjust the hammer spring to have more tension. Dont make a huge adjustment you only need to adjust it enough to increase velocity. What you are trying to do is see if you are on the plateau with the current reg setting. 
#4: Shoot a few shots over the chrony with the new setting. If the velocity does not increase you are on the plateau. If the velocity increases you are on the knee.

At this point if you are on the plateau you will need to decide if you are getting the velocity you desire. If the velocity is 10 - 20 fps above what you want you can start to decrease hammer energy to get down on the knee. At that point you will need to do some shooting to see how far down the knee gives you the best performance. If you are on the plateau and below the velocity you want then you will need to increase the reg set point to get the plateau 10 - 20 fps above the velocity you want. Once the plateau is above your desired velocity you can start testing different points on the knee to see where it performs its best. 

LDP, thank you very much for the detailed explanation. I understand, however, one question. What do you mean by TP in step #1?

You are welcome! The transfer port. I believe the crown has an adjustable transfer port much like the AA S510. When doing the tune you should have it wide open. Once you get it tuned where you want then you can use the transfer port to choke down the velocity for the times you may want less power. If the pcp does not have an adjustable transfer port then you can disregard that comment.

Thank you for the clarification. By Boss has an ES of about 9 and an SD of about 3. My Impact has an ES of about 6 and an SD of about 2. I know this is a new gun so there is not a lot of data out there on it. What do you think I should expect for those specs from the crown? I want to be realistic.

I think you should expect very good ES numbers. I believe the crown is considered one of their flagship rifles. If the other FX rifles can get single digit ES numbers out of the reg the crown certainly should as well. Having an ES of almost 30 would not be acceptable to me and I would have to say the rifle probably just needs tuned and it should be right there with the others you have. The crown has allot more adjustments and flexibility so it may be that it needs to be finely tuned once bought to get the lower ES numbers you get from the other FX rifles. The problem you run into by having a pcp that can change so many factors and use different caliber barrels is that in order to get the best with each setup it will require tuning and its not as plug and play as some think. It shouldnt be an issue and the tune should be repeatable when you change back and fourth. The owner just needs to know how to properly tune the crown for each caliber used and if there are different length barrels as well. Once tuned for each setup if the data is recorded you should be able to switch back and fourth and easily adjust the settings to what is needed for the best performance.