Regulator PSI + Volume VS VALVE BREECH GAP
Because a Regulator works with a Charge Chamber the Reg can’t put out as much air as would come from a tank without Reg but at the same working PSI. Of course, only one shot at the specified PSI is available without a Reg.
Therefore, the Regulated AF Rifle initially puts out less FPS at a given PSI BUT is more consistent over a number of shots.
But, there is one more piece to the puzzle, the air chamber between the Valve Body and the Pellet also effects the FPS. As WOK pointed out, if you seat the pellet deep, the FPS is reduced. I found that to be true with my Regulator also.
It is evident that decreasing the Breech Valve Gap can gain FPS by getting the pellet moving sooner with the volume of air provided by the Reg Charge Chamber. So, I am thinking that if I move the barrel to the rear to decrease the Breech Valve Gap, can I gain FPS before I run out of enough space to easily insert a pellet?
Has anyone tried decreasing this gap?
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Viewing 9 replies - 1 through 9 (of 9 total)
Hey guys,
The Brits have been doing the breach volume reduction thing for a while as they have the 12 ft lb rule .They do it by making a top hat with a longer breach insert section ,this does the same thing as moving the barrel back ,and they have found more consistency .
My thoughts are in the line of not only reducing volume ,but also getting the pellet closer to the air supply/ valve so there is less latent delay ,this can be done with moving the barrel backward .the breach dimensions can be modified so it does not run into the barrel step while loading .I also thought that if this is done the loading of pellets can be made easier by cutting part of the barrel away at the rear and recutting the breach seat,Kind of like a short ramp into the breach seat .
I am waiting for a barrel blank from LW to do this very mod and will give an update when complete .
Moving the barrel toward the tophat reduces “chamber” volume. The barrel is filling the open area of the breech, so the area between the valve seal and the skirt of the pellet has been reduced. Upon a discharge of air, the pellet starts moving sooner with all other things being equal.
My rifle is not regulated.
If you make the breech larger, you wont be reducing that volume at all.
Ive had my barrel about .25″ closer for quite a while, any closer makes my fat thumb unable to start a pellet. When I remove the barrel, I can see a ring of silicone grease there the breech o-rings stop, I still have .25″ to go before the breech would hit the larger section of the barrel.
This reduced volume seems to have the same affect as crimping a centerfire cartridge, the beginning of the pressure curve is more consistent provided you seat the pellet the same each and every time.
My results havent been so much improved velocity, rather its been more consistency in velocity which as we know improves accuracy at longer ranges.
YRMV of course.
Maw,
I didn’t read your post throughly before typing mine, and then saw what you wrote as I was going out the door. You can put poor reading comprehension on my report card along with does not play well with others. 😆
When I am talking abut volume, I mean the volume between the Airforce Valve and the regulator.
So far there has not been enough volume in regulated Condors to get true Condor velocities and keeping the stocks egonomically usable. There seem to be two approaches to remedying this, one like dyotat100 is doing and welding an additional reservior on it, or like I am contemplating which is to make the Airforce tank a reservior and supply it with pressurized air from a regulated exteral tank.
Probably before either of us get this accomplished Marmotmilitia will come up with a way to solve it, but it is fun trying in the meantime.
Roachcreek
The breech seal riding on the barrel would not make a difference, why do we need one, I just heard that it was bigger maybe cause the barrel is bigger in diameter. If you guys want to talk about volume then maybe the breech should be bigger.
Maw,
Do you mean where the rear of the breech rides on the barrel, if there are o rings there it should not make a difference. About the hammer and the end of the barrel step. One of the machinists here could fix that fast.
On the regulated tank set up I am considering, I will use a aluminum breech with perhaps two orings on each end, a custom valve and a remote tank that is 4500 PSI and feeds into the short canted ETAC nipple.
The plan is to make the Condor tank the reservior and the remote tank will be regulated from 4500 PSI and the regulated pressure will supply the Condor tank with whatever pressure I want.
I am not sure I need a regulator just yet. If I fill the remote tank to say 3400 PSI instead of 4500 PSI and use it to keep the Condor tank at 3400 PSI longer due to increased volume, I can experiment with pressure and velocity. I use 3400PSI as an example, I can fill it to any pressure I want, the object of the experiment is to see how high I can go on the pressure at a safe level or until accuracy with the heavier slugs starts waning.
Once I can find the sweet spot with the pressure, then I can buy a regulator to put on the tank, either a fixed one set at the pressure I found to work best or an adjustable one like AirHog sells so I can still play around. Then I can worry about shot count.
Some questions I have are, why do the Stealths have a 250 bar rating and our tanks only rate at 210 bar? Is it the same tank with just a lower rating stamped on it for safety? Also has anyone ever learned what pressure the safety burst disks release at?
Lurker, I think this breech gap is indeed another avenue that needs to be explored.
Roachcreek
That is interesting, I wonder why I never thought of this, Plus what about the rear barrrel seal, does it leak alittle?
Therefore, the Regulated AF Rifle initially puts out less FPS at a given PSI BUT is more consistent over a number of shots.
But, there is one more piece to the puzzle, the air chamber between the Valve Body and the Pellet also effects the FPS. As WOK pointed out, if you seat the pellet deep, the FPS is reduced. I found that to be true with my Regulator also.
It is evident that decreasing the Breech Valve Gap can gain FPS by getting the pellet moving sooner with the volume of air provided by the Reg Charge Chamber. So, I am thinking that if I move the barrel to the rear to decrease the Breech Valve Gap, can I gain FPS before I run out of enough space to easily insert a pellet?
Has anyone tried decreasing this gap?
Hmmmmm, interesting…… :popcorn:
I decreased the gap as much as I could but your limited by the movment of the hammer hitting the step in the barrel. I don’t have a chrono yet, but for sure there is less dead space/wasted air.
The only downside is that getting the pellets in is a little more fiddly, and the really long slugs would be a no go.
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Thanks for the comments fellows. Although my point was that velocity can be improved with a smaller air chamber for the breech, RiffRaff has already discovered that the ULTIMATE GOAL OF ACCURACY can be improved at long range by reducing this breech chamber by moving the barrel 0.25″ to the rear.
I noticed that some accurate air rifles with a multi-shot cartridge have a very small breech space. Without a multi-shot cartridge option we may not be able to reduce the breech gap that much but it looks like we can gain some ground.
Today I got to the range and tried a combination of things we have been discussing. I adjusted the Top Hat to 0.102″ to nearly snug to the latched breech knob and I punched a hole put a 0.070″ innertube patch behind the Top Hat.
Mind you, this is not a test of my 2500 PSI E-TaCReg so much as it was an experiment to learn the relationship of Regulator volume to velocity. Shooting my choice 21.14 grain H&N Baracduda Match pellets at only 20 yards.
Fill PSI 3150/Reg.2500
Top Hat = about 0.102″ but space taken up by 0.070″ rubber patch o-ring
One Shot per Power Wheel Setting
PW = 0…FPS = 431…POI down 3 1/2″
PW = 2…FPS = 544…POI down 2 1/2″
PW = 4…FPS = 657…POI down 1 3/4″
PW = 6…FPS = 790…POI down 1 2/3″
PW = 8…FPS = 890…POI down 1″
PW = 9…FPS = 959…POI down 1″
PW = 10…FPS = 979…POI down 1″
PW = 11…FPS = 988…POI down 1″
ENDING PSI = 2600
AVG. PSI USED 18.75 (not actual useage)
But compared to a 20 shot string at PW = 11 of 27.5 psi per shot it shows the direct relationship of air used per PW setting.
Surprisingly the last 4 shots stacked at 20 yards.
Re-Filled to 3150 and moved target to 30 yards. 10 shots of 2 diagonal lined groups from about 0.9″ to 0.25″ low. Well, there seems to be some consistency to my poor shooting skills.
On to target at 50 yards. Again roughly 2 diagonal patterns but 2″ low 1/3″ to left to 1″ low 1 1/3″ low for the better diagonal.
With this setup it appears that the Baracuda Match pellets like the velocity of 890 to 989+ at 20 yards. I said (+) plus because I didn’t continue past PW = 11 with 989 FPS in this test. Possibly at PW of 12 or 13 it could reach or exceed 1000 FPS. But why go there when the sweet spot for Kodiaks and Baracudas is around 980 FPS.