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Walther LG400 - Power Mod from 7.5 to 16J

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#1 Walther LG400 - Power Mod from 7.5 to 16J

Fri Jul 28, 2017 12:39 pm

credit: https://airgunaccuracy.wordpress.com/in ... her-lg400/

Prior Installing, you require:
1. Walther LG300 Reg. 16J
2. Adapter (contact Sven)

"I made another adapter for Frédérik to mount the Walther 16 Joule LG300 regulator to the Walther LG400 to convert it from 7.5 to 16 Joule. To show how to install the reg and adapter I made the pictures below."

WARNING: WHEN YOU USE ANY INFORMATION FROM ANY PAGE ON THIS WEBSITE YOU DO THIS AT YOUR OWN RESPONSIBILITY.

"The LG300 16Joule (or LG300 Dominator) regulators are factory set at about 75 to 78 bar output pressure. Some of these regulators are marked with 83, 84 or 85 with a pencil or marker. But I have checked four of these regs on two and three different manometers. And all of them had an output pressure of 75 to 78 bar.
The maximum velocity you will get at this pressure is 232 to 236 m/s (761 to 774 fps) or 14,5 to 15,0 Joule (10,7 to 11 FPE) with 8,4 grain JSB Exact. My rifle shot very accurate with this setup. If you think you need to get closer to 16 Joule / 12 foot-pound the reg output pressure needs to be set higher. The best way to do this is with a reg tester. If you do not have a reg tester you may try to increase the reg pressure by adjusting the regulator and testing the velocity. Be carefull when opening the reg and make very small steps on the set screw. It only needs 1/16th to 1/8th of a turn to increase the pressure to 85 bar. At 85 bar I got to a maximum velocity of 240 m/s (787 fps).

For opening and adjusting the Walther regulators see this page: https://airgunaccuracy.wordpress.com/wa ... egulators/

Preventing Point Of Impact Shift / POI shift: What you also need to do is to remove the o-ring / plastic ring under the barrel holder and adjust the barrel holder so the barrel is fully free floating. It takes some fiddling to get it right. The method I use now is to wrap a strip of printer paper in a double layer around the barrel. Loosen the both bolts on the barrel holder. Slide the paper over the barrel until under the barrel holder and tighten the bolts again. Then remove the paper and check by eye if the barrel holder does not touch the barrel."
Attachments
001.jpg
1. Remove the air cylinder
002.jpg
2. Remove the top of the barrel holder
003.jpg
3. Use a 3mm allen key to move the fore-end forward and also to release the single system bolt
004.jpg
4. Lift the systemblock up until the cocking lever assembly clears the stock
005.jpg
5. Slide the systemblock forward until the regulator bolt heads clear the stock
006.jpg
6. Lift the system block out of the stock
007.jpg
7. Dry fire the rifle without air cilinder to make sure there is no air pressure left in the regulator
008.jpg
8. Unscrew the regulator Allen bolts a quarter turn each with a 4mm Allen key
009.jpg
9. Unscrew the other Allen bolt a quarter turn. Keep unscrewing each bolt a quarter turn at a time
0010.jpg
10. You will see the regulator moving away from the system block
0011.jpg
11. When fully unscrewed you can take out the bolts by hand
0012.jpg
12. Remove the regulator and the valve return spring
0013.jpg
13. Shake out the distance ring for the valve return spring. You will NOT need this for the 16J regulator
0014.jpg
14. With help form the spring you can pull out the valve
0015.jpg
15. You now have disassembled the LG400 7.5J regulator, valve return spring, distance ring and valve
0016.jpg
16. Here you see the green o-ring and black valve seat
0017.jpg
17. Insert the adapter with the stepped side facing you and the angled side towards the valve seat
0018.jpg
18. Adapter inserted
0019.jpg
19. Push the 9.25mm ID x 1.78mm o-ring in with your fingers
0020.jpg
20. Use the new regulator to push the o-ring in all the way
0021.jpg
21. Remove the regulator again and insert the valve and spring
0022.jpg
22. Insert the 16 J regulator. Do NOT use the distance ring that was in the original reg.
0023.jpg
23. Insert the original bolts and screw them both in by hand for the first few turns
0024.jpg
24. Alternately give quarter turns on both the bolts to fasten the regulator
0025.jpg
25. Make sure the reg moves straight back and does not angle
0026.jpg
26. Do not overtighten the bolts. You are screwing steel bolts into aluminum
0027.jpg
27. With the bolts fully tightened you screw a filled air cylinder onto the installed regulator and listen for air leaks
0028.jpg
28. Remember the pressure in the cylinder and put the assembly away overnight to check for leaks
0029.jpg
When checking the pressure drop remember that a cylinder will always show a higher pressure directly after filling because of the heat generated when filling it. When you find no leaks you can set up your chronometer and check the velocity. Adjust the striker spring preload, 1/8 of a turn at a time, until you reach 16 Joule or 12 fpe (max 245 m/s with 0.54 gram pellets / max 800 feet per second with 8.4 grain pellets). You may now put the system back in the stock. Follow pictures no. 5 to 1. It is not possible to lift the system in or out of the stock by lifting it straight up. You need to slide it in backwards because the bolts from the reg will interfere with the topside of the stock.
0030.jpg
LG400 breech block rear side. The screw with the red paint is used to adjust the velocity. Clockwise gives a higher preload on the hammer spring.
0030.jpg (9.46 KiB) Viewed 216 times

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