Disco hammer adjustment

[Rickey]

I've ordered the Discos R Us hammer for my .22 Disco but I need some pointers on just how to adjust it.  I think this is how it goes.  The shorter the travel length the less air that is released by the air valve and with that the shot count goes up.  In adjusting with a Chrony the object is for the extreme spread and standard deviation is supposed to go down but with that being said does the accuracy go up?  The last time I put the disco across the Chrony I was averaging about 869 fps and I've read the sometimes since the new hammer is I think lighter the fps will drop some any way.  This I can handle but how much will the adjustment out with the extension lower it as well and what is a good place to start on the screwing out to get the process started?  O I forgot I also have the heavy spring.  I'm looking for an increase in accurate shots.  I ought to know most of this but sense I've been using the stock hammer I haven't had ant reason or ability to make adjustments of this kind so any pointers will be greatly appreciated.  O, Norm if you happen to read this THANKS . 

[Ribbonstone]

Kind of.

Think of it this way:

On one side we have the force of the air holding the valve closed.  The more air pressure, the firmer it’s held closed.

On the other side we have the force of the striker hit opening the valve.

So the harder the striker hit, BOTH the higher the air pressure it will open AND the longer the valve will be open.

So by just cutting back the striker hit to the valve, the point where it fully opens the valve will be at lower pressure.  It basically moves the “sweet spot” down in pressure, which does make for lower speeds.


So with a weak striker hit, might see a lot of slow shots at first, but would notice a trend where they keep going faster and faster.  What’s happening is that the air pressure holding the valve closed is decreasing with each shot, so the striker hit is opening the valve a little “better” each time.


Eventually it kind of levels off (the closing force of air pressure pretty much balancing with the opening force of the striker hit) and you get a string of shots at about the same velocity.


After that, the air pressure just can’t keep the balance, and velocity starts to decline with each shot.

So with a 2K filled Disco, if the shots start off fast and decline, then the opening force (striker hit) starts out stronger than the closing force.

If the velocity starts low and slowly increases to a peak, then a decline, then the opening force (striker hit) is too low for the pressure.

IDeal for the most good shots would be for the velocity to be a little low, quickly coming to a plateau, then decreasing in speed.

[CptMoonlight]

^^
Excellent explanation, I've never heard it explained that way and it really helps a lot since I'm currently modding my hammer spring.

From my understanding (reading LOTS AND LOTS of posts on here), for a more consistent POI, you would want a shot string that is relatively consistent. This makes sense. If you have a quickly falling shot count, your POI, over longer distances, will change as the speed of the pellet decreases. At 869 fps, not knowing what grain you're using, I'm assuming you are getting less than fifteen good shots before reaching your lower limit of 1k PSI? I saw a post from Tommy in which he had a shot string of 30 per fill and was getting an average of 775 fps with a 14.3 cphp, giving him right at 19 fpe. He also added a power adjuster and can get 20 shots at an average of 850 fps with 14.3 cphp giving him right at 23 fpe. Again either of these will give him sufficient energy to ethically kill any small game with good shot placement. His procedure and a good thread on the subject is here:

http://www.gatewaytoairguns.org/GTA/index.php?topic=77272.0

[tjcib]

If your goal is an increase in accurate shots per fill, I am able to get 34 shots per fill with JSB 18s shooting about 685 fps...which is plenty to dispatch a squirrel. Those 34 shots were all with 3% extreme spread.

http://www.gatewaytoairguns.org/GTA/index.php?topic=82722.msg792108

I did this with everything stock except I cut three full coils from the stock spring and added a power adjuster. Did nothing to the hammer other than cleaning it.

[Tater]

Kind of.

Think of it this way:

On one side we have the force of the air holding the valve closed.  The more air pressure, the firmer it’s held closed.

On the other side we have the force of the striker hit opening the valve.

So the harder the striker hit, BOTH the higher the air pressure it will open AND the longer the valve will be open.

So by just cutting back the striker hit to the valve, the point where it fully opens the valve will be at lower pressure.  It basically moves the “sweet spot” down in pressure, which does make for lower speeds.


So with a weak striker hit, might see a lot of slow shots at first, but would notice a trend where they keep going faster and faster.  What’s happening is that the air pressure holding the valve closed is decreasing with each shot, so the striker hit is opening the valve a little “better” each time.


Eventually it kind of levels off (the closing force of air pressure pretty much balancing with the opening force of the striker hit) and you get a string of shots at about the same velocity.


After that, the air pressure just can’t keep the balance, and velocity starts to decline with each shot.

So with a 2K filled Disco, if the shots start off fast and decline, then the opening force (striker hit) starts out stronger than the closing force.

If the velocity starts low and slowly increases to a peak, then a decline, then the opening force (striker hit) is too low for the pressure.

IDeal for the most good shots would be for the velocity to be a little low, quickly coming to a plateau, then decreasing in speed.

I don't even own a PCP but one day hope to afford one (Disco) but I'm always reading about them and trying to learn. That is the best explanation of the relationship between the striker, valve and air pressure that I've read.
Thanks for putting it all into an easy to understand format. Great post!

[Rickey]

Yes Matt I'm using Premier 14.3 grain Ultra Magnum domes.  But what I'm needing is with the adjustable Marauder stile hammer what would be a good starting point to screw the screw out for the adjustment process of getting the extreme spread and the standard deviation down?  What 2 or 3 turns in the outward direction to shorten the stroke length?  This is a learning process that I don't know anything about.   

[clgraham82]

Yes Matt I'm using Premier 14.3 grain Ultra Magnum domes.  But what I'm needing is with the adjustable Marauder stile hammer what would be a good starting point to screw the screw out for the adjustment process of getting the extreme spread and the standard deviation down?  What 2 or 3 turns in the outward direction to shorten the stroke length?  This is a learning process that I don't know anything about.   

Here is how Norm explained it to me:

I would go a full turn on the power adjuster each time and keep records of the number of turns you move it as well as the results. This way if you go too far you can back up to the one you like.
A good way to go about it is to screw the Power Adjuster all the way in as that gives you a very good repeatable spot to work from. That may be at coil bind and you may need to back it out to be able to cock the gun. Also you should make a mark on the PA’s adjustment head to you know exactly how much you are turning it.
As an example let’s say that when the adjustment all the way in does put you at coil bind and backing it out 2 turns takes you out of the coil bind situation. Now you know that is the highest power you can get with that spring and you can get back to that exact setting by screwing in the PA all the way and backing it out 2 turns. SIMPLE!
 
Now let’s say you have two shot strings that you like, one being for hunting and one for target.. It is very easy to get back to each of them by screwing the PA adjustment all the way in and turning it CCW the recorded # of turns for whichever one you want
 
Norm
Discos R Us

Once you get it out of coil bind and you are able to cock and shoot the gun, get the pellets, air and chrony out and start recording shots for each CCW turn of the PA.  Since all guns are different this is the best way to find out how much to adjust the PA for your gun to get your best ES/SD.

[Monkeydad1969]

Yes Matt I'm using Premier 14.3 grain Ultra Magnum domes.  But what I'm needing is with the adjustable Marauder stile hammer what would be a good starting point to screw the screw out for the adjustment process of getting the extreme spread and the standard deviation down?  What 2 or 3 turns in the outward direction to shorten the stroke length?  This is a learning process that I don't know anything about.   

You can get the modded P-Rod hammer from http://discosrus.net/disco/

Joe

[Rimshot]

I just bought the combo stroke adjuster, PA ,and Mrod trigger group from Norm, just to finish off my disco mods.

I understand the PA adjustments but how do you incorporate the stroke adjuster. I have a nice 30 shot string at about 20fpe using a pa from elsewhere that I am going to change out.

I would like to fine tune that by incorporating the stroke adjuster. I am thinking it is like tuning a Mrod? What results have everyone else had?

Rim