Custom Bottle Mrod .25 build started

[shorty]

Sounds good and looks good. Everyone needs a name. What are ya gonna call it?

[caniborrowsomeammo]

shorty,

I made my opening .303 instead of the .25 original. I have plenty of wall. I'm going to use PTFE tubbing and compress it some so it seals.

here is a picture with the CF tube over the barrel and LDC installed.

I made my TP out of Acetal, it doesn't leak.I made a couple extras too.  Hand fitted, by parting it a little long, chuck it up and hit it with 180 grit to length. The Acetal has enough "give" to seal when fitted a little long.

Have you got any or will you have any before and after groups with the CF tube?

[Rdsail]

I have not shot groups with out. I'm waiting for the epoxy to cure well and better weather to give it a full test. I might have to go somewhere else other than my house to shoot it. It is a bit loud at 94fpe.

[SpiralGroove]

Beautiful work Rdsail ,
I can't imagine what she'd sound like w/o the LDC?  That thing is huge .
Kirk

[Rdsail]

Quick Update:

got it to shot 103 fpe at around 3000psi but it uses 150psi per shot. it is an airhog. lol

I think will tune down to about 80 fpe to up the shot count. I'm still impresses with it. I think it is wasting lots of air due to hammer bounce. you can hear it. The there is very little bounce once I reduce power.

I did my testing in the basement and had many error readings. Once the rain stops I'll test outside for more accurate readings.

[rsterne]

Pretty typical.... Do a velocity vs. preload curve and it will be obvious where to tune it.... Here is what my Grizzly did at two different pressures....



When you are up on the plateau part of the curve, the gun is an air hog.... You have to dial it back to the knee, your tune will be somewhere about there.... One way to use those curves in an unregulated PCP, is where the two pressure curves cross, for a given pellet, is where you might find a tune using those two endpoints.... For example, using the red lines (45 gr. JSB), they cross at 2.7 turns out at 930 fps.... With the preload set there, you would get a shot string that starts at 930 at 2900 psi, climb to a peak, and then drops back to 930 at 1800 psi....

Bob

[Rdsail]

Bob, My plan is to get some solid numbers as soon as it stops raining.

On another note, Travis (oldpro) made a recommendation of adding holes to the front of the hammer all the way to the back into where the spring goes in. I drilled 4 .125 holes and he also mention reducing the hammer spring length to be just shy of touching the hammer when it is in contact with the stem.

I did both things and the hammer bounce is gone. My air consumption went from 150 psi to about 50-75 psi. I did not measure it carefully. This is very impressive. I don't have power numbers but this simple mod made a huge difference.

Going back to rjorge, he was right! it is amazing how much air gets compressed by the hammer. you can feel a the air coming out of the back of the gun where you adjust the hammer spring. I made sure that the breech was not leaking air.

Thank to Travis for the suggestion!!!!

Edit: It forgot to mention that It is quieter!!!

[SpiralGroove]

Hey Bob & Rdsail,
Great tuning basics to always be thinking about -> Thanks
Kirk

[oldpro]

 Sounds like its starting to really come together! Good deal, and Please send that rain to SoCal we really need it.

[Monkeydad1969]

Bob, My plan is to get some solid numbers as soon as it stops raining.

On another note, Travis (oldpro) made a recommendation of adding holes to the front of the hammer all the way to the back into where the spring goes in. I drilled 4 .125 holes and he also mention reducing the hammer spring length to be just shy of touching the hammer when it is in contact with the stem.

I did both things and the hammer bounce is gone. My air consumption went from 150 psi to about 50-75 psi. I did not measure it carefully. This is very impressive. I don't have power numbers but this simple mod made a huge difference.

Going back to rjorge, he was right! it is amazing how much air gets compressed by the hammer. you can feel a the air coming out of the back of the gun where you adjust the hammer spring. I made sure that the breech was not leaking air.

Thank to Travis for the suggestion!!!!

Edit: I forgot to mention that It is quieter!!!

So after reducing the hammer spring length, what fps/fpe numbers are you getting?

[Rdsail]

I will post numbers once the weather gets better. It is not raining today but to cloudy and dark to get good readings. The muzzle puts out so much air that if the lighting is not right I get lots of errors. Waiting is a pain.

[PakProtector]

How did you drill the holes in the hammer? That thing is hard... I assume the .125 holes are axial, and right around the head of the striker?
cheers,
Douglas

[Rdsail]

Update:

I found that air was leaking though the stem. I added an oring on the back of the valve that compresses with a thin alum plate and two screws. This fixed the leak. Now I'm shotting 49g cast bullets at 990fps which amounts to 107 fpe. I have a few of bobs BBTs that I believe are 51 or 51 grains. I wish I had heavier  casts to try. The 55g swags I have just don't fit right in the barrel and it loose power. Does anyone have anything I can try out that is on the 55 to 65g range.

Just loving the results.

[sshewins]

Update:

I found that air was leaking though the stem. I added an oring on the back of the valve that compresses with a thin alum plate and two screws. This fixed the leak. Now I'm shotting 49g cast bullets at 990fps which amounts to 107 fpe. I have a few of bobs BBTs that I believe are 51 or 51 grains. I wish I had heavier  casts to try. The 55g swags I have just don't fit right in the barrel and it loose power. Does anyone have anything I can try out that is on the 55 to 65g range.

Just loving the results.

We're loving the results too!!

[Rdsail]

I have some numbers for you guy. I'm using hunter supplies 49g .25s.

I reduced the power top around 80 fpe and shot a full string. I'm only have 1 turn on the preload. It maxes out at 990fps if I add the full preload.

Accuracy is very good but I have an issue. I'm having some side to side wiping. The pellets start in two locations from 30 yards. I have very little vertical stringing just two POIs about 6 in apart which is odd. I think I'm going to make a barrel band to lock the barrel to the bottle. I'll have this 3D printed so there is a perfect fit.

The only other problem I found is that my fill nipple shut valve will come out if I dont face the nipple down. I can put a spring behind it but that will block flow. Do you guys have any suggesting?

here are the number.

Click to view larger

[rsterne]

Looks like about 21 shots within 4% if you start at 3000 and stop at 2200....

Bob

[Rdsail]

that is about right. I need to order more casts from hunter supply. to test at higher power. I did some quick 5 shot strings and it gets flatter as the power goes up. I think when I'm all set and done will end up with around 90 fpe. Which will be 900-920 fps. I'm very impressed that I have a range of 33pfe with one spring. I still have a small leak off the tport which blow back through the hammer. I talked to lloyd and he offered to make me a delrin tport which I hope will fix the problem. I bet I can gain a bit of efficiency if I fix that.

Next week I'm going for vacation for almost two weeks so I'll have some time to get it sorted out once I get back.

Bob,

Your BBTs 50g that you sent me shot the best. I think at some point I'll have to order a mold and start casting.

[Rdsail]

here is the barrel band ready to be printed. it uses 2 4-40 screws to tighten it.

[Monkeydad1969]

Very nice.  I might have to hit you up for some printed parts...hmmm...

[Rdsail]

I did some more shooting yesterday and found that the bullets were clipping the end of the LDC. they where actually barely touching. I think I need to order the band asap to stabilize the barrel. I check the bore alignment and it is dead on.