Power tuned .257 condor shot string and pics

[MrP]

I have the chronograph going and have been collecting some shot string data. 

This was a modified condor shooting from 4000 psi down to 3000 psi with the power wheel at ~8.75 shooting 70 grain boat tails from an Accurate Mold I had ordered. Powerful gun and that looks like a nice string at least for my needs. I will check 3000 down to 2000 eventually.

Doug Noble made the guts:
.257 tj barrel, 27”.
Heavy hammer (115 g)
Heavy spring
Custom breech slide
High power valve 

I made a shroud with a 3d printed core that has a reflex air stripper and pushes a lot of air back into the whole volume behind the airstripper. The baffles are streamlined “Tesla diodes” of my own design and work great especially at higher power levels. It is made of PLA+ and has handled hundreds of shots without a crack. I would show the structure but maybe that is forbidden here - I am talking about the shroud not a detachable moderator though. 

It is a 27” barrel so most of that aluminum tube is empty space, with about the last 6” being baffles (if I remember right - I made a variety of these when testing). I kept it as short as I could thinking the air stripper and volume behind would divert the brunt of the blast. No venting in the tube - I see vented moderators but I’m never sure if that’s a good idea or not.

It is difficult to cock when the spring preload is high so I 3d printed an oversized bolt that makes it much easier

. .

 

[Airgunmann]

Looks like original bottle on the pics I wouldn't fill that to 4000 psi if it is I had a talon that I had a Doug valve on and tj 30 inch barrel with 3600 fill and 85 gr slugs with power wheel on 6 and 6 it was pushing them over a 1000 fps they are power houses I also got all of it from Doug ended up trading it because I didn't use it like I thought I would 

 

[MrP]

It isn’t - it’s a thick walled 4500 psi aluminum bottle. 20% volume more or less because of the thick walls.


and yes, I can see this flinging 85 grain slugs at 1000 fps with the hammer at max preload. Would have thought you would have to go over 3600 though. 6 on the PW you say? That last 3” of barrel seems to help! I will gradually learn more of what this gun is capable of, have never really “opened it up” so to speak. Something else to look forward to. 

 

[Long_Gun_Dallas]

Man, that looks like a lot of fun! Power curve looks very nice. Good work on the mod as well. Venting does help, but I do worry about lead dust being blown back toward me. One of my mods I printed is only about 3.5" in length and it is vented at the first baffle. Only has 2 baffles, but it is extremely effective for it's size. 

 

[Airgunmann]

Yeah your shot string looks good on that definitely will reach out there 

 

[MrP]

Man, that looks like a lot of fun! Power curve looks very nice. Good work on the mod as well. Venting does help, but I do worry about lead dust being blown back toward me. One of my mods I printed is only about 3.5" in length and it is vented at the first baffle. Only has 2 baffles, but it is extremely effective for it's size.

Thanks. It took a while to figure out how to make it work and hold up. 


The way I put it together it’s easy for air vent out the back and th your face so I had to seal that up carefully because like you I don’t like getting a puff of air with lead dust in my face every time I shoot it.



I got a little carried away and assembled two other “noblized” guns, both .250, i will get a string for those shortly. They have the same baffled shroud design but shorter barrels and thus shorter tubes.

One has a 24” tj’s .250 which is perfect for my needs, shoots over 100 fpe. I love this gun as it handles all my cast slugs perfectly. It needs heavy projectiles or very low hammer preload to shoot pellets at subsonic speeds. Jsb 33.9 grains can be shot in the 900-1000 fps range with no hammer preload.

The other currently has an 18” heavy LW .25 barrel, and it is a great compact shooter. 300cc bottle so not too bad to hand pump, shoots in the 50 - 80 fpe range and doesn’t seem pellet-picky. [EDIT: the 50-80 fpe gun does not have a noble valve - it has a TT polished / ported condor valve with TT top hat so I shoot it closer to 3000 psi]. 

 

[MrP]

Here is the full string from 4000 down to 2000 psi. Didn’t mean to leave the best fit lines on there - I was just using those to estimate slope overall and meant to delete them


It looks like the right side of a bell curve with a couple of outliers, and I am wondering how to shift that all to the right and get more shots on the upslope to look at and have the peak come a bit later in the string. The velocity changes pretty predictably once you’re past the peak, and there are 24 shots there in the middle that lie right along their descending trend line. I like this region because it can be flattened by adjusting the power wheel.

My understanding is I have two ways to shift this curve:

I can decrease the hammer preload, which yield a few (?) several (?) more shots on the upslope before the peak for that fill pressure.

On the other hand, I could leave the spring preload alone and increase the pressure in the tank so it isn’t so easy to knock open, again resulting in more “upslope” shots. 

I know there are experienced tuners here so I’m hoping someone can tell me when it is best to add more spring load, and when it is best to add more pressure. 


Since the tank can hold more air, I may first try filling it up to 4100 or 4200 psi and leave the hammer as-is. Running low on those projectiles and it is too cold out (for me) to cast more.

 

[MrP]

Here is a shot string from a .250 24” tj barrel in an airforce frame with Doug Noble hammer and valve setup. 


I should mention that the combination of Doug Noble’s hammers and breech slides really make the action much nicer - just feels like tighter tolerances and smoother movement. I got them for the combination of weight and durability - didn’t expect the smoother cocking. 


Love the airforce guns, as I keep saying. I hope this platform evolves slightly but without losing its utilitarian and interchangeable design.

 

[MrP]

Here is a shot string from a .250 24” tj barrel in an airforce frame with Doug Noble hammer and valve setup, shooting 55.5 grain NSA, pw on 8.5. I did not collect accuracy data but I was able to surgically disassemble a steel can away that makes me feel very good about the trajectory across a lot of that range. 

no idea what caused those odd low power shots! Nothing had physically changed with the gun. Makes me think I need to open it up and clean it all out around the mechanism.



If anyone has any thoughts on what they might do upon seeing that curve, I would love to hear them. 


I should mention that the combination of Doug Noble’s hammers and breech slides really make the action much nicer - just feels like tighter tolerances and smoother movement. I got them for the combination of weight and durability - didn’t expect the smoother cocking. 


Love the airforce guns, as I keep saying. I hope this platform evolves slightly but without losing its utilitarian and interchangeable design.