Regulator for BAM B51

[Taso1000]

Bob,

I was looking for 500 - 550 fps with 7.9 grain pellets.  I have been tuning with spring length and washers.  Clipping portions of coils and adding washers to the side of the spring opposite of the hammer.

Taso

[BigTinBoat]

Bob,

I was looking for 500 - 550 fps with 7.9 grain pellets.  I have been tuning with spring length and washers.  Clipping portions of coils and adding washers to the side of the spring opposite of the hammer.

Taso

If you want 500-550 you should lower the regulator pressure

[Taso1000]

I pulled apart the original regulator.  It looks like brand new.  I checked that the bevel washers were oriented like this ()()()()() and they were. 

While I didn't initially see it I did find that the top small oring was not in it's groove but jammed in the top of the adjuster.  I have included pictures.  All the times I had inspected the regulator the small oring was in it's groove.  What would cause the oring to pop out of place and how would the regulator function if the small oring was out of place?

When I removed the regulator 5 or 6 times to adjust it I didn't have a way to pull it out of the air tube so I would put pressure with my air compressor on the valve output to push the regulator out.  Could this 100 psi of pressure move the oring out of place?

Taso

[Taso1000]

Rob,

It was suggested I try the unmolested 2nd regulator I had with a setpoint of 1500 psi because it was thought the first regulator may be wonky.  I just inspected the first regulator and found the upper oring was not where it was supposed to be.  I don't know what effect this would have.  So I will try the first low setpoint regulator again when I've tested out the high pressure setup.

In reply #102 I have a graph of the low setpoint shot string.  I don't know what pressure it is currently set at as I lowered it to tune velocity and I have no way to see the output pressure.  I also don't know at what point in time the oring came out of place.

So I'm still collecting data and troubleshooting.

Thank you Sir,

Taso

[rsterne]

I would expect that with the small O-ring out of place, the regulator would not regulate, merely bypass the full tank pressure to the outlet, or leak, if the tube is vented between the two O-rings....

If you want 500-550 fps, I would lower the regulator setpoint to less than 1000 psi and see what you get for a shot string.... I'm guessing you may need even less than that, probably less than 850 psi, and maybe as low as 400-500 psi.... I set up one gun for under 500 fps, and it was only 400 psi....

Bob

[nervoustrigger]

Sorry for the belated reply, I had the following typed up and then our internet connection went down and I've been on the phone with Comcast trying to get it working again.  So anyway here goes...

A few options to tighten the ES:

Approach 1
Goal:  Keep velocity at ~550fps without monkeying with the regulator setpoint
Approach:  Increase hammer strike and try a very small transfer port (wild guess: 1.0 - 1.2mm).  Adjust the aperture as needed until you hit the desired velocity.

Approach 2
Goal:  Keep velocity at ~550fps
Approach:  Reduce the regulator setpoint to, say, 600 - 700psi.  Then adjust the hammer spring preload until you find the max velocity.  If that happens to be pretty close to your 550fps goal, enjoy.  If it's too slow, increase the setpoint and/or enlarge the porting if that is feasible.  If it's too fast, reduce the setpoint further and/or choke off the transfer port as in Approach 1. 

Approach 3
Goal:  Higher velocity (800fps), lower shot count, louder report
Approach:  increase hammer strike (more preload, stronger spring, heavier hammer or some combination thereof)

In my opinion, #2 is the right way to do it but #1 can work well and may in fact have the softest report because of how we perceive loud sounds.   A loud, quick burst isn't as obtrusive as a softer but longer burst.

[Taso1000]

Bob,

I think the first regulator is set around that setpoint more or less.  I have no way to test the output pressure of the regulator.  In reply 102 I have a shot string with that regulator but I don't know if the oring was out of position at that time.  I will replace the orings and try it out again after I'm done testing the current 1500 psi regulator.  Would polyurethane regulator orings provide any benefit over the buna orings?  I have to check the sizes I currently have.  Or I can order some.  Poly comes in 70 and 90 durometer.  What durometer would be best for the regulator?

Jason,

I think I'm going to try approach 1 at this point in time and collect the data from the shots since the 1500 psi regulator is in the gun.  Then I can compare high and low setpoint shot graphs, pick the best one and start shooting the rifle for accuracy, finally lol!

All,

So the consensus to flatten the shot curve of the current setup is to add hammer spring rate/pre load?

Thank you,

Taso

[nervoustrigger]

So the consensus to flatten the shot curve of the current setup is to add hammer spring rate/pre load?

I would say so, yes.  For better consistency (low ES), you need to knock open the valve with a little more authority.  You have a rifle operating at a pressure and with porting sufficient for much more energy than you want to use.  You'd rather not reduce the regulator setpoint right now so it looks like your best option is to give the valve a good whack and choke off air flow to keep the muzzle velocity down.

Regarding the type and durometer of O-ring, polyurethane will have a slight edge in longevity because of its improved abrasion resistance.  There isn't much movement of the regulator spool but there is some.  Polyurethane's weakness is with high temperature and compression set leading to extrusion failure, neither of which should be a concern here.  Also, a higher durometer will tend to wear better provided you can reassemble the reg without damaging the O-ring and I suspect that won't be a problem either.   With that said, I would not hesitate to use a Buna-N.  Either type will last a long, long time.

[rsterne]

I'm not an O-ring expert.... I would ask Tim @ Mac1 Airguns what he recommends.... I think he supplies MilSpec. 90D Urethane with all his Ninja regs, but I'm not sure....

Bob

[Taso1000]

Hello All,

I have an update on my project. 

Number 1, I calculated the plenum area wrong.  My spacer is 1.425 inches long and the air tube internal diameter is 2.65 cm.  When I convert all to centimeters a calculate the volume of a cylinder I get 19.96 cubic centimeters.  Way bigger than needed for a 5 fpe gun.  I know I need to deduct the volume of the spacer and add the volume inside the valve to have the exact plenum volume but I think they even each other out.  I can calculate the spacer volume but does anyone know the volume of the rear chamber of the valve where the poppet and light Hillman spring are?

Could this be causing the regulator weirdness where the plenum is too big and the regulator is not getting enough drop in pressure to react/regulate?  I could try to take up 15 cc's of space in the plenum to see if it makes a difference.

Number 2, I filled the brass transfer port with molten silver solder and drilled a .075 hole.  Velocity was throttled to around 580 fps if I recall correctly.  I'm going to verify the numbers by shooting and then try a .070 hole and see what that does.  The next smaller drill bit I have is .0585 which may be too small.  Hopefully I will do a lot of shooting over the holiday and record the results for all three.

After that I am torn on whether to retain and research this configuration further because I recently got a good deal on an FWB 601 match rifle. 

I definitely know that at this moment I don't want to drill an air tube for a 5 cc plenum.

Thanks,

Taso

[Taso1000]

Last night I put the low, unknown Taso lowered, setpoint regulator and spring setup back in the rifle.  I pumped the rifle up to 1600 psi and shot down to where it dumped all pressure.  I am using the same pellets, Crosman Premier Lights from the brown cardboard box.

It will be the first graph I post.  My chronograph did not record about 25 shots for some reason. No errors were displayed, just no speed was reported.

The arch I had in reply # 102 seems to be gone.  Second attached graph.  NOTE:  This graph started at 3000 psi.  So figure for comparison the last 200 shots.

It seems the regulator is working better now except for the larger jumps in the first 99 shots.  The remaining shots in the second string are closer together. 

The third attachment will be the first 99 shots and the forth will be the remaining shots.

I reshot a 99 shot string from 1600 psi down this morning to see if the regulator settled down.  The velocities seen more erratic at the higher pressure in the first half of the string compared to the end.  I hope that makes sense.

I have two more things to try unless anyone has any suggestions.  First, I'd like to try a restricted transfer port to squash the peak velocities and see how that works.  Second, I'd like to reduce the plenum volume to see what effect it has.  I'll have to hunt for smaller diameter tubing to fit inside each other like the wooden Russian dolls. lol

Thank you All for your help and patience!

Taso

[Taso1000]

I had an idea.  I think I may be able to kinda figure out what my regulator setpoint is.  I was thinking I could remove the check valve out of the foster fill fitting.  I could pump the rifle to a pressure above the setpoint and monitor the shot velocities on my chronograph while the pump is still attached.

I could then see the tank pressure drop as I shoot.  When the shot velocity starts falling I can see the current tank pressure on the pump gauge.

Does anyone see any problems with this?

Thanks,

Taso

[nervoustrigger]

No need to remove the check valve.  Simply shoot until the velocity begins to fall off, then attach the pump and pump it until you hear the check valve open and look at the pressure on the gauge.  That will give you the same result.

It won't be exact (you did say "kinda figure out...").  For example, if it is tuned to the knee, the actual setpoint will be somewhat higher than what you read on the gauge.

[Taso1000]

Thanks Jason!  I don't have a rise in velocities when it comes of the regulator so I think I'm on the knee or shin lol.  I ended up concurring pretty much on your Approach 2 you suggested a while back.

Less hammer spring so lighter cocking effort.

Taso

[David Mccann]

great info here.. thank you all. cheers