CZ 452 Varmint .17 HMR bolt stripdown and Lockdown maintenence.

May 25, 2020 at 12:19 am

The easing of the UK Lockdown for fieldsports, including fishing and shooting, took most of us by surprise, at least expecting limited mileages to be maintained, putting a block on many activities, but no, we are free to roam and able follow our sporting passions without the fear of a fine from the authorities.

Assuming that I still had a week or two to get round to my final rifle in the Lockdown maintenence series, I had left my CZ 452, 16 inch barreled Varmint .17 HMR rifle until last, but a phone call from one of my farmers to say that he was cutting the spring growth of grass around a large rabbit warren this week, soon had me changing my plans.

The Varmint is a heavy rifle due to it’s barrel, which tapers up from 16 mm up to 26 mm, the purpose being to absorb the heat generated from the tiny 0.17 inch plastic tipped magnum round, which produces 245 ft lb of energy and a velocity of 2,550 feet per second at the muzzle. At a hundred yards, the 17 grain bullet still carries 137 ft lb of energy with a velocity of 1,755 FPS, being dead on accurate at this range. Firing from the bipod on a windless evening, I once decimated a rabbit warren at ranges varying from 90 to 140 yards, taking over twenty bunnies in ten minutes, the two, five shot magazines needing to be reloaded at intervals being the only limiting factor. My rifle above, equipped with a Hawke 40 x 4-12 parallax scope, Harris HB25CS bipod, extending from 13.5 inches to 27 inches and the Swift silencer, bring the overall weight up to 9.6 lbs, a bit of a lump to carry around the fields, but the weight also gives stability for those extra long shots well beyond a hundred yards.

The main job today was to dismantle the rifle bolt, basically the engine of this extremely reliable weapon.

In line for carbon blowback, when each bullet is fired, carbon builds up around the firing pin and more importantly the ejection claws. The bolt slides forward and is locked in the breech by a cam action, when the arm is pushed forward and down. Lifting the bolt arm activates the cam that unlocks the bolt, allowing it to be drawn backward over the top of the spring loaded magazine. Pushing the arm forward again causes the bolt to push a bullet forward into the breech, pushing the arm down activates the cam lock, pulling back the firing pin, while the spring loaded claws in the bolt are then forced over the rear of the bullet, clamping over the rim. When the trigger is pulled, the firing pin strikes the side of the bullet rim, igniting the powder and sending the bullet on its way. The bolt absorbs the full reactive force of the bullet. When the bolt is raised and drawn back, the empty case is pulled from the breech by the claws. The right hand claw has a sharp gripping edge, while the left hand claw has a radiused edge, which tilts the case to the right as it is drawn back, the effect of both spring loaded claws being to eject the case out of the gap between the bolt and the breech. Considering that this all takes place in parts of a second, it is important that the bolt mechanism is kept clean and oiled.

To gain access to the firing pin for cleaning, the bolt is removed and the bolt arm rotated to ease the cam on the spring loaded firing pin. The thumb lever shown is held in position by the force of the firing pin spring, a pin on the lever passing through the bolt. To remove the thumb lever, the black hardened button has to be pushed in against the force of the spring and the thumb lever pin pulled out through the the hole.

To ease the spring, I use a 1/4 inch pin punch with a shrader valve dust cap fitted over the end. This allows a better grip than metal to metal contact. I have the scars to prove it. The punch is held firmly in a vice, the bolt is gripped in the left hand, while the button is located over the dust cap and forced downward. As the button is forced upward, the thumb lever becomes loose and can be pulled away by the right hand. Care must be taken to ease the pressure on the button once the thumb lever is removed, gently releasing the firing pin and it’s spring to avoid parts being scattered.

These are the parts that make up the firing pin mechanism, all held in by the thumb lever pin.

At the other end of the bolt are the case ejector claws. These fit into holes in the sides of the bolt and are held in place by a C clip. The clip is easily levered out of position using a small instrument screwdriver.

I sprayed WD40 into all the holes and surfaces of the bolt parts, the residue clearly visible in the container. Each part was individually cleaned and wiped down with absorbent kitchen towel. The container was emptied and cleaned, before the parts were sprayed by WD40 again and left to drain.

Reassembly is the reverse of the strip down. Care must be taken to fit the sharp ejector claw on the right hand side of the bolt, as fitted to the rifle, the rounded claw on the left. See the image below.

Although WD40 has lubricating properties, all parts of the bolt were sprayed with Bisley Gun Oil on assembly. While the bolt was out of the rifle, I lubricated the front wire brush end of my .17 HMR Boresnake and dropped the brass weight through the bore from the breech. Once through, I turned the rifle round to face me, pulling the cord and and the cleaning brushes through in one stroke, avoiding putting pressure on the crown at the muzzle. Without oiling the brushes, I pulled the Boresnake through again for good measure.

With the bolt and a full magazine fitted, I checked that the bullets were loading and that the ejectors were working perfectly. The Swift silencer was screwed back on and the rifle is ready for another busy season.