Regulator for BAM B51

[Motorhead]

So I got the rifle all together and roughly adjusted to shoot around 550 fps with 7.9 grain Crosman Premiers.  I have never had or shot a regulated rifle before and the prior configuration didn't have 50 pellets through it to break in.

Later I will try tuning it for better efficiency via striker length and maybe an ssg.

I know things should smooth up and settle down.  My question is how is a regulator supposed to work?  The reason I ask is right now the rifle with the regulator starts at a lower velocity, 490's, and then comes up to the 540's after 5 or 6 shots and pretty much stays there.  I pumped it back up to about 2900 psi and it did the same thing. 

I also think if I let it sit for an hour and then shoot it I get the same pattern.  Is this normal?  Does the regulator need to break in?  I asked Milo74 to set at 1200 psi.

Thank you,

Taso

The Up/Down velocity when starting out or stopping for a spell is SET POINT CREEP & not typical or wanted.
Pending hammer weight, spring rate, stroke in any combination etc ... has valves poppet react differently to the pressure within plenum changing.

What the specifics are in your case can't say other than this "general regulation profile" of operation ....

As a regulator creeps MORE air is put into plenum until reg stops finally resulting in HIGHER than set point pressure.
So generally this higher pressure makes the opening of poppet take more energy.

In this case I see this as hammer strike being too soft overall and when plenum pressure is up from the set point creep poppet is NOT opening sufficiently resulting in a lower velocity.
* It can also create a Spike in velocity in cases where hammer strike is on the heavy side and easily overcomes a rise in plenum pressure and releases the higher pressure to pellet resulting in a higher speed.

It is a dance of finding the balance .....

* Your regulator may be just fine being they ALL creep a little ... just in your case as set up the incremental change in plenum pressures messing with your velocity excessively.

[Taso1000]

Scott,

"SET POINT CREEP"??   Is there a cream for that???   

All joking aside, I just did some educational reading on set point creep.  The regulator was built by Milo74 and this is it's maiden voyage.  I get what your saying that plenum pressure is increasing over the 1200 psi regulator set point over time and harder on the poppet opening thus reducing shot velocity until the plenum comes back down to 1200 psi.   

Do you think the regulator is defective or maybe an oring in the regulator is leaking and could be replaced?  There were extra orings in the zip lock with the regulator and they look like buna black orings.  Would polyurethane work better?

Thanks,

Taso

[Taso1000]

I degassed the gun and pulled the regulator out.  I took the regulator apart and checked for any foreign objects or damaged orings.  As far as I could tell I didn't see anything wrong.

Taso

[Taso1000]

I put the regulator back in the rifle and pumped it up to about 1525 psi, I think.  I'm 95 percent sure but I could be wrong.  Then I shot 50 7.9 Crosman Premier pellets.  Velocities shown below:

1     550          26   568
2     569          27   563
3     595          28   564
4     601          29   566
5     580          30   566
6     569          31   568
7     567          32   579
8     574          33   580
9     563          34   575
10   573          35   561
11   583          36   578
12   580          37   579
13   568          38   582
14   575          39   579
15   581          40   586
16   575          41   557  first shot after 5 minute washroom break, sorry lol
17   570          42   574
18   553          43   601
19   577          44   586
20   574          45   586
21   572          46   598
22   562          47   593
23   575          48   594
24   564          49   599
25   567          50   605

Hi   605
Lo   550
Av   576
ES   55
SD   12

Ending pressure was around 1325 psi.  Somehow that doesn't seem right that it only used 200 psi.  I may be wrong about starting pressure. 

I would have thought the regulator would give me a tighter ES.  Do you think there is something wrong with the regulator or am I doing something wrong?

I'm going to pump the rifle to 2000 psi.  Tomorrow morning I will check to see if the rifle held air and I will shoot 10 shots to see if above set point pressure crept into the plenum overnight.  I'll report the results.

Thanks,

Taso

[Motorhead]

You need to Reread my post and try & wrap your mind around hammer strike, pressure & variances in velocity.

Stated was regulator may be fine ... hammer strike is too light, heavy bias hammer strike with a plenum pressure change higher raises velocity.

as your currently set, way to define if reg is stable and/or other factors are at work ... is, raise hammer strike energy with a heavier spring
& go after a shot string ( At what ever energy it is stable at ) getting into the mid range of adjustments where slight differences in plenum pressure really have minimal effect on velocity.  * as in the reg creep ( small if present ) really in not an issue.
Ideally even tho regulated, valve when getting more balanced should reflect attributes of a self regulated valve being pretty stable in output even tho digesting subtle changes in operating pressure. 

If the tune at this juncture is stable, then more or less velocity is best controlled by transfer port size calibration.

[Taso1000]

Scott,

My brain wants to think "if" the regulator is giving me a constant 1200 psi and my springs and hammers remain the same I "should" have a shot string that may vary + or - a couple feet per second due to variation in pellet weight and seal.

I get that in a non regulated gun, like an FDPCP for example, you fill to 1500 psi and say we have a goal of 900 fps with a rising and then decreasing velocity curve.  At 1500 psi you are not in your hammer sweet spot and the valve is harder to open so you're only getting 800 fps.  As you shoot and use air pressure, the valve becomes gradually easier to open, we get to our sweet spot pressure and the velocity climbs to our 900 fps goal.  As we keep shooting valve is even easier to open but we're almost out of gas and velocities drop off.

Don't some of these laws of physics transfer to regulated rifles?  I'm not being a smart aleck, I really do want to understand what is going on.  I have no experience in tuning air rifles.  That is why I am asking experts for help.  Scott, are you saying to compensate for the regulators variance in pressure I should increase hammer spring force?  When I increase hammer force velocity goes up.  Then to decrease velocity you need to increase pressure or striker length or decrease transfer port.

Initially after I installed the regulator I started with a cut down Menards spring that had very little to no preload and the shortest nylon hammer I got from you.  Velocities started at 136ish and went up to the 300's.  This was probably the overnight creep you explained.  I then removed that spring and installed the WAR 10# Marauder spring you suggested.  The velocities were in the 900's and I could hear air screaming out of the barrel after each shot.

I then took another brand new Menards spring and cut coils till I was in the 700 fps range.  Then I installed the middle length nylon hammer I got from you and velocities were in the 550 - 600 range.  This is where I want to be velocity wise.  I planned on fine tuning the striker length to find the knee eventually but my velocities were jumping around.  Thus my present dilemma.

I guess there's more to learn and a regulator doesn't really eliminate the pressure variable in my equation like I thought.  I am on here to learn, have fun and make friends.      Can you help me understand?

Thank you Scott,

Taso

[Taso1000]

Hello All,

This morning I checked the pressure in the rifle and it's at 2000 psi, according to my Xisico pump gauge, so it may be leak free.  I'll have to watch it over a week or month. 

So I shot another quick 20 shots this morning with no changes in the rifle from last night:

1    457
2    477
3    502
4    512
5    534
6    544
7    570
8    582
9    585
10  582   
11  579
12  585
13  592
14  588
15  592
16  603
17  594
18  596
19  588
20  591

I'm probably premature but it looks like it's settling down.  The last 13 shots are reassuring    I would like to get 50 or 100 more rounds through the rifle today.  I will use cheap Crosman milk carton pellets just to break in the rifle and then shoot a 20 or 30 shot string with the Premier Lights to see the effects.

If you have any suggestions or comments please feel free to post.

Thanks to everyone for your help! 

Taso

[Taso1000]

Tonight I put about 100 7.4 grain Crosman Hunting pellets, from the milk carton, through the rifle.  I took a break for about an hour and then shot 30 7.9 grain Crosman Premier domes, from the cardboard box.

1    567          16  604
2    592          17  605
3    601          18  618
4    600          19  616
5    607          20  614         
6    609          21  615
7    606          22  596
8    620          23  615
9    608          24  590
10  593          25  610
11  601          26  606
12  602          27  599
13  599          28  616
14  601          29  610
15  616          30  608

HI  620
LO  567
AV  604
ES  53
SD 10

If I remove the first shot, 567 fps:

HI  620
LO  590
AV  606
ES  30
SD  8

Does anyone have any thoughts or an explanation on what's going on?  Average velocity crept up but that may be due to the breaking in.

Thanks,

Taso

[rsterne]

Most of your strings show an increase in velocity towards the end of the string.... That indicates that the hammer strike is too light for the regulator setpoint.... That setup typically causes a rise in velocity below the setpoint.... Increase the hammer strike (gives higher velocity) or reduce the setpoint....

Bob

[Taso1000]

Bob,

Thank you for your input!  My goal is right around 575 fps with 7.9 grain pellets.  I just re read your post on tuning regulated pcp's and I finally understand what the knee is.  I have not done the spring preload testing to find it yet.  Should I do that first and see where my velocity ends up?  Or should I reduce setpoint and then try to find the knee?  It would not be terrible if my velocities are less than 575 as this is just going to be my offhand trainer.  So accuracy is first, shot count a close second and velocity to maximize accuracy and shot count.

Thank you All for your help!

Taso

[Taso1000]

Scott,

I found this picture when I re read Bob's post "Tuning a Regulated PCP"  Is this behavior what you were talking about?

Disclaimer:  This picture is Bob's, not mine.

Taso

[Motorhead]

While Bobs graph shows an upswing in velocity ... reason for, BOTH of us have elaborated on already.

[Taso1000]

Hi All,

Just a little update.  I went and lowered the regulator setpoint.  It was initially set at 1200 by Milo.  Half a turn only brought velocity from 920 to about 800 fps. Another 3/4 turn brought it down to 300 fps. So I went back and now I'm basically 3/4 turn CW from the original setting.  I have no way to measure the output pressure to verify the setpoint.

Milo says a 1/4 turn is between 190 and 250 psi.  So if I did 3/4 turn I should be between 630 and 450 psi.  Does that sound right?

So now at this setpoint the rifle was shooting 630 on the plateau.  I adjusted coils and shims to around 580 fps if I remember correctly.  I wasn't able to shoot much yesterday.  I will try again tonight.

So I have a question.  In Rsterne's post on tuning regulated pcp's he explained that the knee velocity is around 3% lower than the plateau velocity.  If my plateau is about 630 fps and with adjusted hammer stroke and spring tension I'm down to 580 fps goal which is 8% below plateau velocity.  I think that puts me on the shin lol. 

I will probably increase hammer stroke/spring tension to bring my velocity up to within 3% of plateau so I don't get the velocity spike when I come off the regulator. 

I guess I'm at the 80% performance point with 20% effort lol.  That was a lot of effort for that 80%.  I have learned a whole lot though.

Do I need the last 20% performance?   

I still need to shoot a couple long strings to see ES but I think I'm close to having met my goal for this rifle. 

Hopefully I can shoot some strings tonight.

Thank you to everyone that has helped!

Taso

[SpiralGroove]

Hey Taso,
Do you have a RVA?  Otherwise, shorten your striker (assuming adjustable on your set-up) to get velocity up to about 600/610 fps.

Good luck

[Taso1000]

No.  I have the medium length nylon hammer Scott made me.  I have so far been adjusting with shims in the endcap and spring length. 

I could cut some off the front of the hammer or substitute the nylon hammer with the shorter nose.  I don't recall how much shorter it is but I submitted pictures in this post earlier.

I had made a cheat sheet with what certain adjustments affected but that's at home and I'm at work.     I didn't sleep well last night and I had plumbers come real early to fix a slow drain.  So my brain is mush today.  lol

What are the pros and cons of adjusting hammer stroke from the nose versus shimming at the endcap?

Thank you!

Taso

[SpiralGroove]

Yeah Taso,
Don't cut the hammer; it would just add more shims to increase spring tension

[Taso1000]

I was able to put some rounds through the rifle this morning.  With the two washers installed in the end cap I got:

587    636
617    637
640    635
643    638
641    639
639    638
637    633
637    640
637    638
646    638

Which calculates to ave 634, es 59, sd 12.  If I remove the first two shots it calculates to ave 638, es 13, and sd 2.

I also wanted to verify the plateau so I added more washers. 

3 washers gave me:

677
665
659
668
664

ave 666.6

and 4 washers gave me:

672
663
663
663
665

ave 665.2

So with 3 and 4 washers installed the setup is on the plateau.  With two washers installed the average velocity is 4.2% down.

I want to bring the velocity down another 80 or 90 fps hopefully to quiet report further for back yard use too.

What velocities are usually the quietest out of .177?

Should I try and 1/8 or 1/4 turn on the regulator set screw? 

Thanks,

Taso

[Motorhead]

Tighten up ( decrease ) the transfer port size now to get on the target velocity .... IMO.

You can screw with Reg output ... but lower the pressure within valve becomes, greater the dwell likely will be as well.

[Taso1000]

Scott,

Thank you for the guidance.  I am currently using the original brass transfer port.  Mike Melick had sent me two delrin rod pieces drilled with 3mm and 2mm holes respectively.  I can try those but I'm gonna need to figure out how to "slice" them and keep them flat.  Do you think they will be ok flat or do they need to be shaped like the original?

It may be easier for me to fill the original transfer port with JB Weld and drill the port out in increments and test in between.

Would that work Scott?

Thank you,

Taso

[Motorhead]

Scott,

Thank you for the guidance.  I am currently using the original brass transfer port.  Mike Melick had sent me two delrin rod pieces drilled with 3mm and 2mm holes respectively.  I can try those but I'm gonna need to figure out how to "slice" them and keep them flat.  Do you think they will be ok flat or do they need to be shaped like the original?

It may be easier for me to fill the original transfer port with JB Weld and drill the port out in increments and test in between.

Would that work Scott?

Thank you,

Taso

In principal YES ... Sadly a 1000 PSI PULSE hitting a restriction is very similar to the resulting pellet being somewhat the same being it may blow the weaker JB right on out ... If not there ya go.

In brass, given the need to, personally would SOLDER it closed, drill it far under size and then open size till at wanted velocity.
Once done ... get one made of a billet material and be done.

JMO ...

PS,
This tune which is taking a platform typically making 3-4X the power is really non typical & readers need to understand how those of us helping the process may say things contradictory to common tuning practices.