I know there is probably not a one size fits all answer for this but is there a general rule of thumb for velocity gain per psi increase on regulated guns? FWIW I'm working with a huma regulator and 25 caliber marauder.
Velocity increase vs psi increase
- Thread starter Cbourbeau32
- Start date
Nope its going to be different for every barrel length and even same length barrels will have different internal dimensions that effect velocity. Then you have lot to lot variations in projectiles that will also cause inconsistent results lot to lot. You can get a ball park idea and a window of expected velocity with a regulator setting of say 130 bar but thats it. You have to shoot thru a chrony to get the actual fps. Hammer spring variation, variations in the valve and moving parts all influence the fps in every pcp at the same reg setting even model to model. You can give us the velocity you are looking for and if your rifle is stock and we can give you a starting point then you have to shoot and fine tune it from there.
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I should have said that I know what my velocity is at the current reg setting for my marauder and asked if there was a way to predict the increase of velocity with the increase in psi.
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I agree with LDP. There are a lot of variation and areas of impact that effect overall velocity. Basically increasing psi may or may not increase the FPS; the pressure increase could surpass the hammers capability of opening the valve fully. This intern will lower your FPS..is no short answer to your question. I've been tuning M-rods for minute or so and I've seen a few things. I have my own little formula for accuracy, FPE, and FPS. It's like a puzzle, all the pieces have to fit and complement each other from start to finish. Just doing one thing may hinder something else, there has to be continuous balance within the system.
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Any mathematical model would necessarily contain many assumptions of dubious accuracy.
A practical empirical approach would get you much closer. If my knowledge of the Mrod is correct, it's fairly easy to replace the barrels.
You could start with a number of barrel blanks of minimum 24" length.
1. Set your regulator to a "low power" position.
2. Fire a group with your preferred pellet/slug, record the velocities.
3. Next cut an inch off the barrel and re-crown it.
4. Shoot another string and record the data.
5. Rinse and repeat cutting an inch at a time until you reach a minimum practical barrel length based on your airgun configuration.
Then install a second barrel and increase the regulator output up by a known amount. Repeat the shoot/record/cut an inch.
Do the same with more barrels(s) at additional regulator settings to develop more data.
Yup, a lot of work but you'll get graphs of real data that you can generate empirical formulas from.
A practical empirical approach would get you much closer. If my knowledge of the Mrod is correct, it's fairly easy to replace the barrels.
You could start with a number of barrel blanks of minimum 24" length.
1. Set your regulator to a "low power" position.
2. Fire a group with your preferred pellet/slug, record the velocities.
3. Next cut an inch off the barrel and re-crown it.
4. Shoot another string and record the data.
5. Rinse and repeat cutting an inch at a time until you reach a minimum practical barrel length based on your airgun configuration.
Then install a second barrel and increase the regulator output up by a known amount. Repeat the shoot/record/cut an inch.
Do the same with more barrels(s) at additional regulator settings to develop more data.
Yup, a lot of work but you'll get graphs of real data that you can generate empirical formulas from.
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Not really. Theres more than one adjustment that gets the velocity at a given psi. Also one would have to know if you are tuned below the knee on the knee or the plateau. Theres enough variables that I dont believe theres one formula that will say increasing 50 psi reg pressure will give you 30 fps increase in speed. Working with valves, valve timing, hammer weight and energy, transfer port and plenum size are much different than working with smokeless powder to get a specific fps or calculate the amount of fps gain you will get by increasing powder charge.
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What are your settings for hammer pre load, hammer travel and transfer port size? Are you tuned below the knee if so how much? Are you tuned on the knee? Are you tuned on the plateau? Those are all needed to have any idea how much fps you may gain or lose by increasing the reg pressure alone.
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What I have confirmed is that the hammer needs an optimal preassure to open the valve.
If preassure increases over that optimal, then the hammer may not open enough the valve and fps decreases.
So regulator has to be set at optimal preassure to allow the hammer to open the valve adequately.
If preassure increases over that optimal, then the hammer may not open enough the valve and fps decreases.
So regulator has to be set at optimal preassure to allow the hammer to open the valve adequately.
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As I see it, there is a problem with trying to approach your tuning focused on reg pressure. Assuming you have a well balanced tune, if you change the reg setting more than a little, then you really need to adjust hammer tension accordingly also. Otherwise, you will quickly lose air efficiency and high-consistency shot count, diminishing the advantage of a regulated rifle. I'm no expert, but that's my perception from the tuning I've attempted.
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Pressure and fpe are pretty closely proportional. For example if you want a 15% increase in fpe, increase the pressure by 15%.
Also I recommend heeding Ed’s advice regarding a well-balanced tune. With regulated airguns, the relationship between the setpoint and the hammer spring tension is really quite simple. There is only one hammer spring setting for a given regulator setpoint that will yield the best consistency (extreme spread or standard deviation).
To find the optimal hammer spring setting, keep increasing the tension until the velocity no longer increases. Then back it off until the velocity is somewhere around 95% - 97% of that maximum. So for example, if your max velocity was 900fps, dial the hammer spring back until the velocity drops to about 855 - 873fps.
When adjusted in this manner, your airgun will be somewhat insensitive to the little inevitable variations in pressure or hammer strike. It is akin to how an unregulated PCP operates in and around the top of its bell curve (the sweet spot).
If the resulting velocity isn’t what you want, increase or decrease the setpoint and readjust the HST.
Also I recommend heeding Ed’s advice regarding a well-balanced tune. With regulated airguns, the relationship between the setpoint and the hammer spring tension is really quite simple. There is only one hammer spring setting for a given regulator setpoint that will yield the best consistency (extreme spread or standard deviation).
To find the optimal hammer spring setting, keep increasing the tension until the velocity no longer increases. Then back it off until the velocity is somewhere around 95% - 97% of that maximum. So for example, if your max velocity was 900fps, dial the hammer spring back until the velocity drops to about 855 - 873fps.
When adjusted in this manner, your airgun will be somewhat insensitive to the little inevitable variations in pressure or hammer strike. It is akin to how an unregulated PCP operates in and around the top of its bell curve (the sweet spot).
If the resulting velocity isn’t what you want, increase or decrease the setpoint and readjust the HST.
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