Author Topic: Tuning a Regulated PCP (Read 72327 times))

rsterne · « **Reply #80 on:** December 31, 2015, 10:58:30 PM »

Quote

The question is, can you achieve say 950fps from 7cc at 2000psi, with a 25.4gr pellet?

According to Lloyd's spreadsheet, that would require 80% efficiency (using realistic assumptions).... I've never seen that in a quarterbore.... Pressure at the muzzle of a 20" barrel would only be 607 psi maximum.... At 70% (possible), you're down to about 44 FPE.... this with a dump shot, of course.... If you eliminate all the pellet friction and transfer passage volumes, you would need 75% efficiency to get your 50 FPE.... I would say that means it's very unlikely.... Even if you could achieve instantaneous opening of the valve, the pressure pulse is far from a square wave.... After the initial pressure rise it is a steady decline as the limited reservoir volume fills the barrel....

One thing you guys may be missing.... You don't "need" a 1 cc / FPE plenum to obtain your desired FPE, you can do it with 1/2 cc / FPE, but you have to increase the setpoint pressure because the pressure drops faster during the shot.... You can likely do it with 1/4 cc / FPE as well, but be prepared to up the setpoint pressure even further.... Eventually, the plenum will be so small, you won't have a regulator (you will need full tank pressure), and you will have to keep the valve open until the pellet exits.... They call that a dump shot.... For a given starting pressure, barrel length, caliber, and volume (reservoir/valve/plenum/whatever), you will have a maximum FPE.... If you want more FPE, you can use a larger volume, to get a higher average pressure, but the efficiency will drop if you stay with that dump shot....

These are all just different versions of the same thing.... and for the most part utterly predictable using Lloyd's spreadsheet....

Bob

62hotrod · « **Reply #81 on:** January 01, 2016, 02:08:43 AM »

Okay Gentlemen, I've been toying with my 177 Challenger FT rig. I've been shooting Hunter Class with it just under 12 FPE or 780 avg. fps with 8.44grn JSB's. Needing a flatter trajectory I've changed hammer spring, and I forget the TP size(I have several to try) At the moment I'm trying to take the velocity up in FPS until loose accuracy then back up a couple steps and use that as my starting point for a Huma regulated tune. Currently I'm at 900 avg. fps. and getting very good accuracy at 55 yards(55 is my test yardage) I'd love to get in the upper 9's with a decent shot count, or lower 9's with 10.3's. After reading this and the post about the hammer spring guide it sounds as if these two tricks are something I ought to try.
Lloyd gave me a lot to think about the plenum, is there enough area there for a plenum if the guage block were drilled out?
Would a 3k fill allow for enough shot count increase to be worth while?
Could you guys please give me some ideas you how you'd go about doing this?

Bill G · « **Reply #82 on:** January 01, 2016, 09:55:50 AM »

I don't know that gun but if possible Scott's LW hammer or Bob's new hammer design. Scott has made it look like voodoo with his LW hammers and it is by far the simplest solution to increasing efficiency. Probably need a combination of LW hammer and a hammer spring. I'd contact Scott (Motorhead) and discuss it with him, he is the guru on reg'ed PCP's and LW hammers and he is into the same application.

Bill G · « **Reply #83 on:** January 01, 2016, 10:31:45 AM »

Bob yes your right on the pressure profile, it isn't square sine at all. I could have articulated that better I suppose. The time and function (Physical movements) is pretty close. The first corner a touch rounded for opening to the certain distance. The pressure profile would look close until the certain distance was met then I think it would look more like a saw tooth..? The concept I'm toying with has as close to zero dead space as I can imagine without contouring the exit side of the nozzle to match the projectile tail profile and that isn't practical at all. The nozzle profile is 60* included on the converging side and 16* included on the diverging side, with an orifice at 3/16. That will flow an unbelievable volume of air at the pressures we are working with. I think that the peak pressure spike occurs quicker than it occurs with our typical poppet valve and with next to no dead space, acceleration is quicker. I'm using 10# of break away friction in the math. the running friction is pretty darned small and even difficult for me to measure with out building a rig to do so. Even then, I cant test or measure it anywhere close to the velocities we're moving. so it is a SWAG really, 1#.

Anyway I drug this off topic far enough. the point was that there are overlapping characteristics that can be useful if applied to the regulated PCP, that will milk the system for max efficiency.

toine · « **Reply #84 on:** January 01, 2016, 10:44:15 AM »

Any thoughts or advice to share when adding an adjustable transfer port in to the mix when dealing with a regulated PCP? I've been using a combination of hammer spring preload and choking down the transfer port in order to get a PCP down from 12fpe to about 8fpe for indoor shooting, and while I know what I did works, I am curious as to whether there was a more efficient way to do so.

rsterne · « **Reply #85 on:** January 01, 2016, 01:00:09 PM »

Unregulated PCPs were very often tuned for extended strings for FT work by leaning on the hammer spring and choking up the transfer port.... You can certainly reduce the power of a regulated PCP very simply by installing a smaller transfer port, and if the gun is operating efficiently before, it will generally get even higher efficiency (in FPE/CI) when the power is reduced.... and it does get quieter in proportion to the FPE reduction.... It can be done externally with a adjusting screw, if that is incorporated into the design, such as my retracting bolt that can be restricted, or the velocity screw in an MROd valve port....

You can also reduce the power, and increase the efficiency dramatically, by reducing the hammer strike (preload) to use smaller sips of air, but if you go that route, you MUST stay above the setpoint, or you will experience a drastic velocity increase once the pressure drops below the regulated output.... Look back at the first post in this thread to see what I mean.... The great thing is this is instantly adjustable and reversible without any disassembly....

The velocity can also be reduced by dropping the setpoint pressure and readjusting to the knee of the now lower curve.... This gives more shots from the greater pressure range, and increased efficiency as well, although is more complex to do, and not as easily reversible as simply dialing back the hammer preload....

Generally, the very highest efficiency is obtained by using tiny sips of high pressure.... That means the valve is closing very early, and the air is still expanding as the pellet leaves the muzzle.... The shot will be very quiet as well.... The only drawback, as I said, is the velocity increase below the setpoint.... This likely makes using reduced preload the best method to detune temporarily, just watch the pressure guage....

62hotrod, if you haven't plotted the curve of velocity vs preload for your gun, you need to do that.... If you are already near the plateau, no amount of increased hammer preload will help, and you will just use more and more air.... Without that information, I can't offer any reasonable advice.... You can obtain some plenum space by modifying or eliminating the gauge block.... I would look for about 1/2cc per FPE minimum for a gun with an in-tube regulator (about 10 cc for a 20 FPE gun).... and make sure that volume is readily accessible to (and includes) the valve....

Bob

Motorhead · « **Reply #86 on:** January 02, 2016, 07:17:04 PM »

Bill.
What was not said 2 posts above ... is the Time/Area piece of the tuning puzzle.
It is well known as you operate at lower pressures the Area of ports must become larger than a higher pressure model operating at equal output/power.

So while I'm not stating such a small volume plenum could not be made to work in some optimized configuration,
doing so personally feel "That Tune" would be within very limited caliber & pellet weight/fit parameters.

PLEASE ... do it and share results so we can learn from it too

Optimist or Pessimist ... I'm soo conflicted !!

Just do it

lloyd-ss · « **Reply #87 on:** January 02, 2016, 07:33:14 PM »

Quote from: Bill G on December 31, 2015, 07:43:51 PM

.............
........... The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.

Bill G ,
I didn't actually answer your question, but I've got the vultures circling around it. Take a look at today's entry in this thread:
http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0

Lloyd

Motorhead · « **Reply #88 on:** January 02, 2016, 08:06:48 PM »

Quote from: lloyd-ss on January 02, 2016, 07:33:14 PM

Quote from: Bill G on December 31, 2015, 07:43:51 PM
.............
........... The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.

Bill G ,
I didn't actually answer your question, but I've got the vultures circling around it. Take a look at today's entry in this thread:
http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0

Lloyd

Not us !! .... Lol

lloyd-ss · « **Reply #89 on:** January 02, 2016, 08:58:26 PM »

We in trouble now!

ngozdex · « **Reply #90 on:** January 19, 2016, 12:54:03 PM »

another great article
must print it and labeled "the science of PCP"

rsterne · « **Reply #91 on:** April 28, 2018, 01:49:33 PM »

With time comes increased clarity and understanding (ie I'm always learning).... so I thought I would revisit this subject to add a chart that might help you understand what happens as you tune a regulated PCP with progressively less velocity than the plateau.... Here is an updated version of the chart in the first post of this thread....

The 3%, 5% and 10% below Plateau velocities are approximate only, but will give you an idea of what happens as you reduce the hammer strike, and hence the velocity, on a regulated PCP.... It will show you exactly why I like to tune 3-5% below that plateau.... because (at about 5% down) you get a few more usable shots below the setpoint before the velocity drops off.... or at the very least (at about 3% down) you save a lot of air compared to tuning up on the plateau, with very little loss of power.... The chart also shows what happens if you tune about 10% (or more) below the plateau.... Note that below the setpoint the velocity increases significantly.... and while operating in that realm gives you extremely good efficiency, for some applications (eg. Field Target, or in some countries where there is an FPE or velocity limit) that bump could put you over the limit....

Every gun is a bit different, and yours might produce a curve like the "5%" one above only 3% below the plateau, or it might be 7% below.... but to date those would be about the outside limits I have found to produce a tune that has a usable shot string (ie within a ~1% ES) extending slightly below the setpoint, which is the tune I prefer.... I hope this chart allows you to visualize what I have tried to confer in this thread....

Bob

uncle paulie · « **Reply #92 on:** April 28, 2018, 03:11:06 PM »

You have me a bit confused(easy to do).... looking at the chart, the -3% plot clearly yields the smallest ES of the four plots.Were this one of my guns, there's little doubt that would be my goal as it would offer the best opportunity for consistent accuracy. Below the chart you indicate the -10% plot is the most "efficient"; which may be the case if one only seeks maximum number of shots, but that really disregards the whole point of how much time, money and energy we put into these things just to get them to hit the target! Just sayin...

pv

rsterne · « **Reply #93 on:** April 28, 2018, 05:18:42 PM »

Even the best of regulated PCPs rarely achieve an ES of less than 1%, just from pellet variation.... That is the goal I set myself when tuning, as it is plenty good enough for shooting past 100 yards, and the -5% line on the chart above shows a total ES of 1%, from the start of the string to about 1200 psi, where the velocity falls through the starting point.... I am sure that you realize that no shot string is as smooth a curve as I have represented on the chart, as there is a shot-to-shot variation of several fps superimposed on the base curve....

As I have stated before, my tunes vary between 3-5% below the plateau velocity, depending on the purpose of the tune.... If I am after maximum power without wasting air, I will be closer to the -3% curve.... but if I am less concerned with power, and more concerned about efficiency and shot count I will be closer to the -5% curve.... In addition, if you want a smaller ES, and if the tune you choose has a bit too big a bump below the setpoint.... then stop shooting at the setpoint and you will get a few less shots with a tighter ES.... You will still enjoy greater efficiency with the -5% tune than with the -3% tune, possibly by as much as 25% higher FPE/CI and shot count....

The very best .22LR target ammo has an ES of about 2.5%, with most commercial ammo 4% or more.... Our PCPs are capable of about 1% ES under the best circumstances, and since a 2% ES is fine for 100 yard work (ie the vertical stringing is well within the MOA capability of the gun and shooter).... if I can get a few more shots and keep the ES in the 1-1.5% region I am more than happy.... I defy anyone to distinguish between a 1% ES and a 2% ES at any range within 100 yards....

I don't use the -10% tune, because although it is the most efficient in terms of air use, and will produce a ton of shots.... it has a large increase in velocity below the setpoint, where the gun shoots like an unregulated PCP, with a bell-curve.... Yes, you can simply stop shooting at the setpoint, and enjoy that efficiency.... but just like a unregulated PCP in the first part of the bell-curve, the shot-to-shot variation tends to be greater throughout the string.... This is because any slight variation in hammer strike, pellet weight, or pellet fit, causes a larger velocity variation when the valve is operating in "partial valve lock".... Therefore I stay away from those tunes, just as I stay away from tuning on or near the plateau because doing that wastes so much air....

Bob

BigBoreJack · « **Reply #94 on:** April 28, 2018, 06:15:41 PM »

Bob and Lloyd are both a rare gift to the modern airgun world; beyond reproach. Way back in the earliest days of big bore PCP airgun development, in the 1970s and early 1980s, I became friends with a machinist living in Arizona, who, as far as I know, developed the first American big bore air rifles, most of them in .44 to .510 caliber, to take big game. We tried Various barrel lengths, Various plenum volumes, various pressures, etc. We did a considerable amount of bullet design & alloy testing for use in those air rifles. Eventually, we received velocities very similar to modern day commercial air rifles. Back in those days, we knew nothing about regulators, or about shrouds. Even today, I hate shrouds---guns should be loud. One thing, among many things, that we learned, that surprised us, was that a certain volume percentage of air, affects velocity much more than the same percentage of pressure.

Nvreloader · « **Reply #95 on:** May 01, 2018, 02:01:38 PM »

Bob

Thank you, I think I have an understanding of your above posts.

Question,
I am just setting up to shoot the SSG and learning about the turn info, for the 22 cal QB 79, (OEM stock),
will 2-5 shots per turn be enough to gather valid info, on the SSG settings, with each of the different pellet weights, I want to use?

Now, that I have the compressor/tanks etc,
would it be better to shoot from the tethered 4500 psi tank > reg set to 3000 psi set point or 13/3000 psi tanks,
on each of the different reg set points of 850, 1100 and 1250 psi, of the 3 - 13/3000 Ninja tanks.

Tia,
Don

rsterne · « **Reply #96 on:** May 01, 2018, 04:06:54 PM »

I shoot 2-3 shots and record the average.... or for a quick determination of where the plateau is, just 1 shot is OK, providing you graph it out to smooth the curve.... Once you decide on where the knee is for each pressure and pellet, then you may want to shoot 10 shots or so at each setting.... enough to get a decent pressure drop so you can calculate and plot the efficiency....

You can tether your 4500 psi tank, through a 3000 psi regulator, to each of your 13 CI / 3000 psi tanks, just so you don't have to fill then frequently.... but a 13 CI tank by itself will provide a bigger pressure drop over 10 (or whatever) shots to determine the efficiency....

Bob

Nvreloader · « **Reply #97 on:** May 01, 2018, 06:03:56 PM »

Thank you, Bob

I have a very accurate psi test gauge that reads to 1/4% for the full 3000 psi range, in 20 psi steps,
with Ninja Micro bore hoses/Foster QD fittings, it is set up so I can see the psi readings on every shot fired,
when the Mag V-3 chrono is attached, along with all the SD/average for the shots fired etc.

I can shut off the 4500 psi tank and shoot from the 13/3000 tanks, then refill the 3000 tank from the 4500 tank and continue on etc.

I'll post the results for every ones view, good, bad or otherwise,
as I think I am over my head with those graphing posts you show on figuring the efficiency etc . LOL

More info later.......

Tia,
Don

Motorhead · « **Reply #98 on:** May 02, 2018, 12:41:56 AM »

Just to share another Short cut or trick we use ... here is another less done approach.

get close via hammer spring, hammer weight to @ where ya want to be .... do a pressure test by having THE PCP hooked up too an air source starting 3-500 PSI under where your regs set too.
Shoot over the chrony changing AG's tank pressure in 100# increments noting velocity.
If you note a PEAK in velocity at a pressure LESS THAN regs set point ( being higher than baseline tune ) you know that reg is set too high.

If you notice velocity keeps increasing all the way to regs set pressure you may very well be UNDER the optimum set pressure or very close to it.
* in this case, it is beneficial to up the Regs pressure far enough to see at what pressure velocity peaks & note where it starts dropping ( WITH NO CHANGES IN HAMMER SPRING SETTING or OTHER adjustments )

In doing a pressure check you get to chart what the rise or fall is in velocity under or beyond any give pressure. Then given this data you can adjust the regulator pressure just shy of the peak getting just a tad behind the bell curve.

Just another work around getting to the same place in having your PCP able to shoot at SET PRESSURE and get some more shots beyond ...

Scott

Nvreloader · « **Reply #99 on:** May 02, 2018, 03:07:25 PM »

Scott

Thank you for your info.
I am attempting to wrap my head around this info, never seen/read about this test before.

After finishing the prelim testing of the SSG and the various pellets with a 13/3000 tank,
reg set for 850 psi, logging all info etc.

Questions,
What effect does the pellet weight play in this test, or does it matter?

Note :
I have to also test the accuracy of this OEM bbl and the various pellets and hopefully the accuracy of this bbl,
will be better than the 1-1/2" groups at 25 yds, I started with, (has a new chamber/polished bore/muzzle crown).

So, I can run the psi down to below the set point of the reg, and/or fill to the required 100 psi levels to do your tests etc,
without doing a lot of extra work/wasting air etc.

Would this be an acceptable method to test with?

Suggestions/Ideas would be greatly appreciated.

Tia,
Don

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Tuning a Regulated PCP

Author Topic: Tuning a Regulated PCP (Read 72327 times))