Weihrauch HW 97

Neil Price works his magic on a Ger­man clas­sic

Air Gunner - - Air Gunner Workshop -

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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