Question about pcp tuning and lower muzzle report.

[Taso1000]

Has anyone performed and experiment with changing valve opening dwell time and muzzle report loudness on a pcp? 

My thinking is that a shorter valve opening dwell time will produce the least report.  But unless the short dwell is accompanied by higher pressure the pellet velocity will drop.

I have read that shorter valve dwell times are more efficient or was it consistency (ES)?  Is efficiency and muzzle report interrelated?

Say that after a lot of testing we find that a rifle is most efficient and quieter when the valve closes when the pellet is 1/3 down the barrel.

I know that longer barrels can produce more power.  Does the efficiency and muzzle report also follow the 1/3 barrel length?

The reason I am asking is that I'd like to replace the 18 inch barrel on my BSA R10 with a 15 inch barrel to make the rifle more compact.  I know I will lose velocity but will the rifle be louder and less efficient since the pellet will be closer to the end of the barrel when the valve closes than it was with the longer barrel?

I hope that wasn't too confusing to read.  I remember an Audi engineer stating that a louder car is a less efficient car.  It was in an Audi Le Mans documentary.  I was wondering if that holds true with air rifles.

Thanks,

Taso

MODS:  I wasn't sure if this was an appropriate thread for the "Bob and Lloyds Workshop" gate.  If it is or will get more attention there could you move it for me please?  Thank you!   

[Rob M]

ive experimented with long barrels , and the report can be reduced to almost nothing while keeping the muzzle velocity.. finding that balance is tough, and often luck.. and yes, shorter barrels are wayyy less efficient

[mann]

I know the ss valve closes fast and is efficient . Has a short dwell time and puts out propper amount to keep your speed up . But it is definitely quieter compared to the stock valve in my 25 synrod

[rkr]

I was getting 945 fps from a 15" barrel in my .22 Scorpion so you shouldn't loose much if any in velocity. Efficiency will drop of course.

[rsterne]

Muzzle report is proportional to residual muzzle pressure.... The longer the barrel and the shorter the valve dwell, the more the HPA released by the valve will expand in the barrel, so the lower the pressure, and hence the report.... Starting with a higher pressure will increase the report, of course.... Using a small plenum (or in the case of a dump valve, a small valve), will decrease the muzzle pressure and report....

If the valve closes when the bullet is only 10% of the way down the barrel, then the residual pressure will only be about 10% of the operating pressure (eg. start with 3000 psi, end with 300).... If the valve closes when the bullet is halfway to the muzzle, the pressure at the muzzle would be half the starting pressure, but only if the reservoir is of infinite volume.... If the plenum/valve volume is equal to half the barrel volume (ie quite small), and the valve closes when the bullet is halfway down the barrel, at that instant the pressure is already down to 50% of what you started with.... so by the muzzle it is only 25% of your operating pressure( eg. start with 3000, down to 1500 at valve close, residual muzzle pressure only 750 psi).... If you had an infinite volume, and the valve was open until the bullet left the muzzle, the report would be VERY loud, because full operating pressure was there when the bullet leaves....

In simple terms, yes, efficiency and report are closely related.... Shortening a barrel will lose power, and increase report, from the same air released by the valve.... Less FPE, same air = lower efficiency....

Bob

[Motorhead]

We ( some of us ) are well versed in the lower dwell & lower noise equation.
As you gain AMPLITUDE in delivered air to pellet while also reducing the dwell time, muzzle reports go from a BLAP to a SNAP.
There are multitudes of posts speaking of such within many of the more in depth tuning posts made in past years.

[nervoustrigger]

Has anyone performed and experiment with changing valve opening dwell time and muzzle report loudness on a pcp? 

My thinking is that a shorter valve opening dwell time will produce the least report.  But unless the short dwell is accompanied by higher pressure the pellet velocity will drop.

Correct.  And fundamentally, what you have described here is the first portion of any unregulated rifle's bell curve.  I suspect you've noticed the first few shots after being filled are noticeably quieter, and it's because the high reservoir pressure produces a shorter dwell.

I have read that shorter valve dwell times are more efficient or was it consistency (ES)?  Is efficiency and muzzle report interrelated?

Yes, it is perhaps easier to understand why long dwell is inefficient.  Taken to the extreme where the valve remains open even after the pellet leaves the barrel, it becomes obvious how this scenario is wasteful of air, and is louder because it expels an excess of air.

So short dwell is preferred for both better efficiency and a softer report.  And in fact, tuning for ever shorter dwell--even below the "1/3 of the barrel" guideline that Bob has spoken of--will produce ever better efficiency but eventually you will reach a point where the ES begins to climb.  That's because you get to a point where the valve is just barely being knocked open, and that magnifies slight variations in the mechanics of the system.

[Taso1000]

Thank you everyone for your responses!

Scott, could you point me to some other threads so that I can read more?  I searched and did not find anything.  Maybe I needed to use different search terms.

Mr. Sterne, so we need the residual muzzle pressure to be low.  Optimally we would like the tune to be on the high side of the pressure curve versus the low side.  I know standard procedure is to tune a regulated rifle on the low side of the pressure curve for a longer consistent shot count.  So we're kinda stuck with a longer dwell.  Correct?  Barring getting rid of the regulator, is there anything else we can do or are we stuck in that dwell constraint?

Jason, yes, I have noticed rifles being quieter on the high side of the pressure curve and then recently when I was tuning my .25 Sentry.    I hadn't heard that in a while since I've been tuning regulated rifles.  I didn't understand why till I read one of Scott's  responses in one of my threads that rifles tuned to the high pressure side of the curve are more efficient.  So I assumed they were related.

Thank you All,

Taso

[rsterne]

You are mixing up the "low side of the pressure curve" (of an unregulated PCP) with tuning "on the knee" of the curve (in a regulated PCP).... With a regulated PCP, tuning on the plateau is similar to the low pressure side when unregulated (because you have more dwell than necessary at that pressure = loud and inefficient).... Tuning a regulate PCP on the downslope is similar to being on the high pressure side when unregulated (which is why the velocity rises below the setpoint).... When you tune on the knee with a regulated PCP, you are tuning to what would be the top of the bell curve when unregulated....

Bob

[mackeral5]

This is a very informative thread.  I don't have much to offer on this topic other than some limited recent experience in getting the valve to open faster with extremely light hammers (solid peek) and peek poppets.  My guns are much quieter at the same velocity as they were tuned to with steel hammers and delrin poppets.  one particular gun increased shot count by 12.5% (increase from 40-45 shots) at 1fpe higher tune.  The report was quieter as well.  Much more crisp/sharp report.

However, I do notice that ES is higher when tuned at the knee or lower.  ES seems to tighten up as I tune closer to the plateau.  I believe this to be more apparent with smaller plenums, along the lines of .5-.75cc/fpe.  This is based on a very limited dataset and I am just now trying to learn how to make use of these new tools. 

[oldpro]

We ( some of us ) are well versed in the lower dwell & lower noise equation.
As you gain AMPLITUDE in delivered air to pellet while also reducing the dwell time, muzzle reports go from a BLAP to a SNAP.
There are multitudes of posts speaking of such within many of the more in depth tuning posts made in past years.

You showed them how to make a Cobra high lift short dwell valve and as of yet I haven’t seen anyone do it and it’s easy to do. You want to hear what a snappy short dwell sounds like follow Scott’s thread on Cobra tech He and I worked on a few years ago. Talk about a quiet report! You can lead a horse to water as they say

[Frank in Fairfield]

All I know is right after Scott tuned my Marauder (4 years ago now, I think), we were shootting at Ione in an FT match. The two fellows I was shooting with couldn’t hear it at all. I knew I had I had fired cause I saw the target fall down (a rare occurance so easy to remember ).

[Gerard]

You showed them how to make a Cobra high lift short dwell valve and as of yet I haven’t seen anyone do it and it’s easy to do. You want to hear what a snappy short dwell sounds like follow Scott’s thread on Cobra tech He and I worked on a few years ago. Talk about a quiet report! You can lead a horse to water as they say

I'm intrigued, and puzzled at the same time. The ONLY thread yielded by a site search for 'cobra' is this one - https://www.gatewaytoairguns.org/GTA/index.php?topic=126118.0 - and there are no images in that thread showing how one works. Rather there are a few references to the tech being secret, pending a patent, and a lot of performance reports which sound amazing. Looking on the WAR store page I see a Cobra valve for WAR Flex or WARP rifles, and a more expensive upgrade kit also for WAR stuff, but nothing about buying a Cobra valve for other air rifles. I've got a QB78D with a short barrel (13.4") in .22" delivering close to 130 shots at about 19fpe, using a 13ci regulated Ninja bottle. I've got a carefully tuned SSG in there and loads of other mods, very light hammer etc, but hey, I'd be game for more tinkering.

But not if I'm just outright guessing as to what a cobra valve actually is. Can't really see how anyone "showed them how" so I really wouldn't know where to start in constructing such a valve. The images on the WAR store page show a chunk of aluminum with a few holes in it, so no real clues there. Any chance there's actually a QB78D version on the market and I just can't find it? Or is the tech open source now? I'm happy to pay for a plug-and-play valve if it's going to mean a quieter moderate power shooter, or to build something with my lathe if the information is available. But if this is just a tease, well, I'll carry on shooting what I've got.

[Motorhead]

You showed them how to make a Cobra high lift short dwell valve and as of yet I haven’t seen anyone do it and it’s easy to do. You want to hear what a snappy short dwell sounds like follow Scott’s thread on Cobra tech He and I worked on a few years ago. Talk about a quiet report! You can lead a horse to water as they say

I'm intrigued, and puzzled at the same time. The ONLY thread yielded by a site search for 'cobra' is this one - https://www.gatewaytoairguns.org/GTA/index.php?topic=126118.0 - and there are no images in that thread showing how one works. Rather there are a few references to the tech being secret, pending a patent, and a lot of performance reports which sound amazing. Looking on the WAR store page I see a Cobra valve for WAR Flex or WARP rifles, and a more expensive upgrade kit also for WAR stuff, but nothing about buying a Cobra valve for other air rifles. I've got a QB78D with a short barrel (13.4") in .22" delivering close to 130 shots at about 19fpe, using a 13ci regulated Ninja bottle. I've got a carefully tuned SSG in there and loads of other mods, very light hammer etc, but hey, I'd be game for more tinkering.

But not if I'm just outright guessing as to what a cobra valve actually is. Can't really see how anyone "showed them how" so I really wouldn't know where to start in constructing such a valve. The images on the WAR store page show a chunk of aluminum with a few holes in it, so no real clues there. Any chance there's actually a QB78D version on the market and I just can't find it? Or is the tech open source now? I'm happy to pay for a plug-and-play valve if it's going to mean a quieter moderate power shooter, or to build something with my lathe if the information is available. But if this is just a tease, well, I'll carry on shooting what I've got.

https://www.gatewaytoairguns.org/GTA/index.php?topic=139401.msg1402661#msg1402661

[Gerard]

Ah, thank you for that. I'll study it carefully and see if I'm up to doing such work.

---------------------

Okay, read through the thread, struggling at times with the written descriptions but eventually figuring out how everything works from that plus the pictures. Seems unlikely to deliver anything close to a desirable result by guessing the various dimensions and throwing it into a QB78, especially considering the critical venting parameter which must be fine-tuned to achieve sufficient ease of opening for it to even open enough for a shot. More likely would take at least a handful of trial and error setups, perhaps making a couple of versions and testing each a half dozen or more times before getting it right. If I'm not totally off base with that, one would be well served to have a scuba tank or compressor to fill from. As a hand pump only guy (the old FX still going strong after six years with multiple airguns) and knowing it takes at least 250 pump strokes to get the Ninja bottle filled enough to make testing worthwhile, I can see running out of patience rather too soon to get something like a cobra valve working. Especially considering the particulars of my reversed bottle setup... which, well, isn't the most dismantling-friendly, shall we say. So I'll chicken out and give this valve a pass. It'd be nice to have a more efficient, quieter valve, but if there isn't a drop-in version for sale it's just not practical for me to try and re-invent the wheel.

[skorec]

Muzzle report is proportional to residual muzzle pressure.... The longer the barrel and the shorter the valve dwell, the more the HPA released by the valve will expand in the barrel, so the lower the pressure, and hence the report.... Starting with a higher pressure will increase the report, of course.... Using a small plenum (or in the case of a dump valve, a small valve), will decrease the muzzle pressure and report....

If the valve closes when the bullet is only 10% of the way down the barrel, then the residual pressure will only be about 10% of the operating pressure (eg. start with 3000 psi, end with 300).... If the valve closes when the bullet is halfway to the muzzle, the pressure at the muzzle would be half the starting pressure, but only if the reservoir is of infinite volume.... If the plenum/valve volume is equal to half the barrel volume (ie quite small), and the valve closes when the bullet is halfway down the barrel, at that instant the pressure is already down to 50% of what you started with.... so by the muzzle it is only 25% of your operating pressure( eg. start with 3000, down to 1500 at valve close, residual muzzle pressure only 750 psi).... If you had an infinite volume, and the valve was open until the bullet left the muzzle, the report would be VERY loud, because full operating pressure was there when the bullet leaves....

In simple terms, yes, efficiency and report are closely related.... Shortening a barrel will lose power, and increase report, from the same air released by the valve.... Less FPE, same air = lower efficiency....

Bob

Bob, THANKS again,
Your explanations  are always  easy comprehensible  and  I hope  also  clear  for all.

[Ribbonstone]

Really only three things that decide noise:

1. How much air is released at each shot.
2. The pressure of the air at muzzle exit (when the pellet "uncorks).
3. The volume/design of any LDC/Shroud attached to the barrel.

And they are kind of interelated.

#`1. seems like it would stand alone as efficiency. But it is possible to release so little/short a blast of air that friction becomes a MINUS before the pellet exits a long barrel.

#2. Seems like it would be decided by the starting pressure.  BUt the exit pressure is  not really decided by the starting pressure....it;s more about how long the valve stays open and how long the barrel (which is the cylinder that containts the air pressure released by the valve.  A .16" .25 barrel runs about  .8CI in volume...a 24" barrel is about 1.2CI in volme.

#3. A shroud or an LDC acts like a gas condenser back in Physics lab...it gives volume and back-flow (by way of baffels) to slow the gas down before it exits.   "Good" ones work better than "average" ones.


So take your pick...but keeping the same energy might be hard, depending on how high upo you cranked it

Generally, when I'm seaking quiet, I go for a reductioin (although it does NOT have to be a bunch) in energy and a big increase in air use per shot (efficency).


One way to look at it is this:

1. The MOST air per shot you'd use, with the MOST noise is to fire a ""blank" (charged PCP/ and no pellet).  There is energy exiting (or we'd not be able to blow apart wasps/roaches with just the air exiting), but it does use the most air per shot and the hardes enery per shot to figure out(As you can't chronograph air without a solid projectile)>

2. The LEAST noise per shot would be to plug the barrel with something heavy enough/tight enough to NOT be ejected.

3. Betweet the two extreams, will find that lighter weight pellets are a touch lounder than heavy weight pellets (even with the same tune-settings).


So at this point, some logic should kick in.   The ONLY energy released at a shot is the air being ejected. That air can use up it's energy in transmitting energy to a pellet, to vibration of the barrel, to heat, to friction (which is pretty much linked to heat), or to noise. 


The energy to create those things has to come from somewhere, and the only energy release is the air ejected during the shot....and that energy is going to be used up by moving air/vibrating the barrel. moving the pellet, or making noise.

[Taso1000]

Thanks Ribbonstone!

This quot of your got me thinking of something else:

So at this point, some logic should kick in.   The ONLY energy released at a shot is the air being ejected. That air can use up it's energy in transmitting energy to a pellet, to vibration of the barrel, to heat, to friction (which is pretty much linked to heat), or to noise. 

Are there any sound waves propagating down the barrel from the valve cracking opening or slamming closed?  Kind of like the ping that is heard on some rifles?  If yes, I would think they are much lower decibels than the sound of the air flowing after the pellet clears.

Thanks,

Taso

[Ribbonstone]

Conventional thought is that ping is the sudden movement of air from one side of the cylinder to the other, which "rings" the air cylinder.   Suddenly drop pressure on the valve end, and the air moves quickly from the front end to ever things back out again.

Have not done in in depth study of it..."we" know how to sloe that movement down to remove the sound, but do not know if we actually eliminate it or move it to another frequency that humans can't hear.

[skorec]

YES,
 

Only  by using SS balance valve with  H@N Piledriver .177/21gr the power is two times higher but the noise is lower however I am shooting at 3000 PSI  .
Interesting also is that  via much better BC the ballistic curve is better however the speed is slower.