Just curious, what your unchoked CZ barrel prefers slug wise? I have 700mm unchoked on a katran hp x. I added transfer port restriction internally and transfer port adjustment screw externally to assist with fine tuning and to shoot lighter slugs. As a result have a good amount of hammer spring tension to maintained good es spread and gain shout count. 300cc from 250 bar to 150 bar I get 64 shots. I have it dialed for 950 fps with .217 nsa 17.5 grain slugs. Seems to like them. It also likes .217 knockout slugs at around 900fps. Seems to not like .218. Share your unchoked cz barrel slug preferences 
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Tuning What slug does your unchoked CZ barrel prefer?
- Thread starter vettebullet
- Start date
My Cricket Tactical 60 loves the Nielsen 17.5gr .216 , almost better than the JSB 18gr. My others Cricket .25 bullpup an carbine don't like slugs.....or maybe I didn't find yet the brand of slugs which could please them
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I can chime in having machined over a dozen of the 12 groove .22 CZ barrels with the 450mm twist with excellent results. They can shoot a wide variety of ammo with supreme precision. The MOST ideal of which IME has been .217 ammo with a 2-S nose, which have a sweet spot between 1090-1100FPS. Similarly with 24.8 NSAs, but I've never had consistent luck getting comparable ammo like the 25gr H&N to shoot as precise.
There are two critical factors for maximizing the precision with these barrels shooting slugs. First being chamber throat / seating depth. A 1.5-2 degree throat is ideal. You obviously want them to load square and concentric to the bore, but the depth should be set where the probe isn't jamming the majority of the slug's shank into the bore. They're more forgiving though when the throat depth is on the conservative side.
The next critical point is using higher pressure. Reason being, the CZs have tight bores with deep grooves. This makes it difficult to get slugs to obturate (making the ammo to seal quickly / completely in the bore/grooves during the shot cycle). Bore friction factors in, but not as much as obturation.
So keep in mind that slug precision in these CZs scale with power; it's just not all that efficient. An example of this inefficiency - comparing the velocity of a 600mm CZ to a 600mm FX slug A in a hot rodded Taipan Veteran shoot 40gr Griffin RBT with the 2-S nose. The 600mm FX barrel could shoot them as high as 1180FPS with that tune, but the CZ struggled to crack the sound barrier and maxed out no higher than 1115FPS with the same tune (literally doing nothing else to the rifle other than a barrel swap).
So my recommendation to most would be to use .217 size ammo (the bore will eat anything larger) and use higher reg pressure. The 24.8 NSAs. 24gr 2-S Varmint Knockers, and 40 RBT 2-S Griffin have undoubtedly stood out for me as the best of all.
There are two critical factors for maximizing the precision with these barrels shooting slugs. First being chamber throat / seating depth. A 1.5-2 degree throat is ideal. You obviously want them to load square and concentric to the bore, but the depth should be set where the probe isn't jamming the majority of the slug's shank into the bore. They're more forgiving though when the throat depth is on the conservative side.
The next critical point is using higher pressure. Reason being, the CZs have tight bores with deep grooves. This makes it difficult to get slugs to obturate (making the ammo to seal quickly / completely in the bore/grooves during the shot cycle). Bore friction factors in, but not as much as obturation.
So keep in mind that slug precision in these CZs scale with power; it's just not all that efficient. An example of this inefficiency - comparing the velocity of a 600mm CZ to a 600mm FX slug A in a hot rodded Taipan Veteran shoot 40gr Griffin RBT with the 2-S nose. The 600mm FX barrel could shoot them as high as 1180FPS with that tune, but the CZ struggled to crack the sound barrier and maxed out no higher than 1115FPS with the same tune (literally doing nothing else to the rifle other than a barrel swap).
So my recommendation to most would be to use .217 size ammo (the bore will eat anything larger) and use higher reg pressure. The 24.8 NSAs. 24gr 2-S Varmint Knockers, and 40 RBT 2-S Griffin have undoubtedly stood out for me as the best of all.
Upvote 0