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PostPosted: Sun Oct 08, 2017 2:44 am 
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Joined: Wed Dec 21, 2005 11:27 pm
Posts: 2078
Location: Toronto
I got my hands on my second HW70 (older version with no safety).

I chronied it at 220 fps so I decided to take it apart. I can see that the breech seal has turned to mush and ordered a new one. The other cause for the low velocity could be the piston seal.

The endcap of the compression chamber requires a special tool to unscrew it as it has slots carved onto the surface. I used a watch case opener with two opposing bits that is adjustable to fit the endcap slots.

The spring is under some considerable pretension. I removed all the components and cleaned out all the old grease and debris from compression chamber.

The spring seemed fine with only a minor sign of fatigue so I had it cleaned and the end polished to a reasonable smoothness. Dimensions are 184mm OD, 12.7mm ID, 2.9mm coil thickness. The length spanned 20.5cm long with 31 coils.

The piston seal was also in good condition so if wasn't necessary to replace it. Should it need replacing in the future, I'm sure there are some good substitute seals for it. The OD is 25 with an ID of 10mm and a height of 5mm.

While I had it disassembled, I polished the trigger and sear components and used some moly grease on all the metal to metal contact areas. I dabbed some lithium grease on the piston and reassembled. The most difficult process was getting the endcap on without any specialized tools. I removed the 2 bits from my watch case opener and countersunk them upright into a block of wood (holes measured and drilled to hold the bits in the right position for the endcap slots). I then pushed the main body of the gun down onto the endcap, which was now resting flat against the wooden block with the bits securely in the grooved slots. It took a few tries of pushing downwards precisely while turning clockwise to screw the endcap back, but i did it. After that the rest of the steps are simple.

The breech seal was scraped out from the breech groove and a replacement seal I ordered from http://www.airrifleheadquarters.com was a perfect fit for it.

Now it shoots ~350fps with 7.4gr Crosman Wadcutters, which is about the same as my other HW70 (360fps). These springer pistols are not powerhouses, but sure are smooth and accurate.

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PostPosted: Sun Oct 08, 2017 11:05 am 
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Joined: Mon Feb 11, 2013 12:46 am
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