Weihrauch HW 97
Neil Price works his magic on a German classic
Afriend asked if I could improve the performance of this lovely Weihrauch HW97 rifle in .177 calibre that he had recently acquired. He said that he was very satisfied with the accuracy and that he was getting good groups at up to 30 yards. He did think that the firing cycle was harsher than he had expected, though, and that the recoil and muzzle flip could be improved.
First thing to do is to put it over my Skan chrono using JSB Exact 4.52 pellets straight from the tin to see how it is performing.
A 14 fps variation is not bad for a rifle of this build quality. There was quite a bit of felt recoil on firing, and I thought that the action was a little harsh. It was also coming too close to the UK absolute limit of 12 ft.lbs.. for my liking.
If your chrono’ only gives a muzzle velocity reading, then to find the muzzle energy in ft/ lbs, use the formula (FPS x FPS x Pellet weight in grains, divided by Weight in Grains)/450240, i.e. (777 x 777x 8.44) = 5095472.76, divide by 450240 = 11.32 ft.lbs..
The owner decided that he wanted a V-Mach tuning kit fitted. This is a full tuning kit and has a replacement highquality mainspring with much better dynamics than the original; a tight-fitting mainspring guide and top hat, a power seal, a spring sleeve, power-adjusting washers and spacer, and his own special moly grease and oil.
The HW77/97 rifles had a compression cylinder bore diameter change from 25mm to 26mm, from rifle serial number 1446049, so you must choose the correct kit for your rifle by checking the serial number. Also, the mainspring is different for the varoious calibres because the .22 calibre rifle is more air efficient than .177 calibre. Fitting the incorrect mainspring could cause the rifle to be either under- or over-powered. As can be seen by the packet that the kit came in, this kit is for a HW77/97 with a 26mm diameter bore and to be below 12 ft.lbs., so it is the correct kit for this rifle.
Remove the two slotted screws from the front of the stock and the two screws in the trigger guard. The stock can now be removed from the action.
With a 13mm AF open- ended spanner, remove the pillar nut that holds the anti-bear trap mechanism in place. Make sure that you find the small spacer that is beneath the pillar nut.
With a pin punch and hammer remove the two cross pins retaining the trigger mechanism in the trigger block. When removing the trigger mechanism from the trigger block, keep one finger over the safety button to stop it flying out and the
spring being lost. This was a fairly new rifle and these pins were very tight. The lengths of the retaining pins are different; the longer one is at the front of the action and the shorter one to the rear.
With the pins removed, the trigger unit can be withdrawn from the trigger block slot. Notice that the safety hasn’t flown out because I held it in, as described before.
Take out the safety button and return spring and put safely away so that it can be found again for reassembly.
Drive out the cocking arm cross pin with a pin punch and hammer and slide the cocking arm ‘ears’ down from the barrel block. Again, I found that this pin was extremely tight to remove.
Rotate the whole cocking linkage downwar, and disengage the cocking link from the slot in the compression tube. The anti-bear trap assembly can be left in position on the cocking link.
To remove the trigger block from the compression cylinder, I insert a length of flat bar of a suitable thickness into the slot, and then whack the end of it with a soft mallet whilst holding the action with the other hand. This usually moves it. If it doesn’t, then I keep whacking the bar until it does.
Before carrying on any further, I always look inside the cocking slot to make sure that the original spring hasn’t been replaced with an aftermarket square section spring with an excessive length of pre-load on it. If it has, then removing the trigger block should be carried out in a spring compressor, for safety.
9 Here is the trigger block removed, and you can see how small an amount of pre-load the mainspring had.
With the trigger block removed, the mainspring and guide, compression cylinder and piston assembly can be removed from the action.
The piston seal can be prised off the end of the piston with the blade of a small screwdriver. 12The replacement V-Mach seal can be fitted onto the piston, using the same small screwdriver blade to ease the internal lip over the retaining diameter of the piston.
Remove the adhesive tape and let the sleeve spring out to its natural position.
Inside the piston at the top, there will be packing washers held in place with an ‘O’ ring. By tapping the piston latch rod sharply down onto a hard surface, the washers and ‘O’ ring can be removed. Failure to remove these will result in the rifle unable to be cocked.
Squeeze the sides of the spring sleeve together and insert it into the piston, with the split of the sleeve opposite to the cocking slot.
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