Umarex Notos tune, the beginning

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From all my tinkering and mods done to my 3 KRAL NP-O3s I have some left over barrels. The KRAL barrels are 16 inches long. I replaced them with the AKELA, KRATOS longer 19 inch barrels in those builds. Almost direct fit except where barrel goes into breech it has a shoulder that needs to be turned down a little to fit all the way into breech. On my NOTOS the .25 KRAL barrel needed about 3/16 turned to get barrel all the way into breech. Easy to do. Waiting on my bottle and .25 mags to test it out. Also made carbon fiber shrouds with crossman NP TRAIL baffle installed. Images to follow once completed.
 
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Drilled out barrel port- valve port - the bottle block- the connector from breech to bottle and the breech itself. Swapped bottle from my .22 NOTOS reg set to 2000 psi. Hand loaded 20 gr .25 and shot at 775 fps. Once I get the reg and new bottle set at 2400-2600 psi and start adjusting hammer spring I think there is more there.

NOTOS .25.jpg
 
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rdpjr6504 said:
Nice work. I put a 2200 psi reg on today and with hammer spring all the way backed out I get 785 fps with 20. gr pellets. Still playing. Also doing up a .177 version. Have you given any thoughts to making a biathlon style lever with t handle ?
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My gun is at the factory reg setting. I have no idea what it's really set at. I'll know this afternoon. Did you open up the air tube adapter? Made a remarkable difference with the plenum. It was shooting at over 28 ft lbs. I think I'll bore the valve body and make a peek valve along with a little larger ports. Certain it will exceed 30 ft lbs. It'll get interesting
 
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New revelations. I installed the guage block and am using a Huma guage....only reading 135 bar. Seems low and it's a brand new guage. I'll switch it out with a digital tomorrow and see.

Regardless, the reg has not changed so the following is a direct comparison. Had a bit of spare time so did the following.
Took all ports from .154 to .167
Bored the valve to .247
Made a peek valve.

These changes made it even more evident that it was at the limits of the set pressure for that barrel.
With JTS 18.1, adjuster flush
844 846 846 845 852 852

Backed the adjuster out five full turns
844 847 847. Zero change as the gun was still at the plateau.

15.89 JSB
892, 887 885 889 884
FIVE OUT
883 888........

In or out, very little change. To gain velocity it will need a higher set point and likely much less hammer as it is just wasting air after the pellet is gone.

Digging through my sprig cache I found a shorter one from Gauntlet tuning
These results were using JSB 15.89 only. Appears ideal for this tune.

Flush 735 734
1 in 809 808

2 in 861 855

3 in 881 877

3 3/4 in, maxed 890 882.

Tomorrow, higher set point testing.

20230908_160519.jpg
 
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Replaced the guage with another new Huma, read the same. 135 bar.
Set reg to 148 bar, soft spring
JSB 15.89. Adjuster flush 568. Two turns out 372. Two turns in 584.

Installed factory spring @ 148 bar.
Adjuster flush. JSB 15.89. 915, 913. 29.5 ft lbs. One turn in or two out, virtually no change.

Adjuster flush. JTS 18.1 882, 878, 878. 31.1 ft lbs
Four turns out. 861

NSA 17.5 slugs. .2175 diameter, tight fit.
875, 875. 29.7 ft lbs

Heavy pellets are slower, making best use of excess air so I tried JSB 25.39s. 778, 776, 780,782. 34.2 ft lbs with the factory barrel shortened a half inch.

At this point, I'm done with porting and valve work. time to focus on air use. Will try lighter hammer to reduce dwell. Motorhead and others have seen same velocities with much more efficiency in some builds.

Going to find a 14 in barrel in .22 and .25.
 
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Rohmpm said:
Machined the valve body down to the valve seat line. Valve, transfer, barrel drilled to .154.
Some would drill .186, 20% of bore.......I question the valve area and at this point, I cannot bore my valve body any larger. I could have had I not machined the valve for possible increased flow. I'll order a new valve.
View attachment 386138
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how do you get that brass seat out of the body?
 
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