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Airgunshooter10
26-04-2005, 01:58 AM
PART 1

The CZ Slavia 631 Air Rifle

By Ian Pellant

The search for a low cost, well built air rifle for indoor and backyard target shooting is not an easy one !

My BSA rifles equipped with 'scopes are just too heavy and powerful for 10 m target shooting. The Benjamin -Sheridan 397 is too tedious to pump up over long shooting sessions, plus it doesn't have a target rifle feel, balance or trigger. So... start looking for something else. I deliberated for over six months before noticing the Slavia 631; actually it took most of time to realize what "type" of rifle I should be looking for.

As way of explanation:- to me it seems that contemporary air rifles fall into several types or categories:


youth pellet and BB rifles - usually low cost, small and of low power and accuracy;

a variety of made pump-up pneumatics and CO2 guns which in recent years seem to have drifted towards reduced manufacturing costs in preference to advancing the breed;

magnum sporting spring rifles - usually mid priced guns of 12 fp. (foot pound) (16.27 J.) muzzle energy or above; my BSA Supersport is such a rifle;

magnum Field Target rifles - can be rather expensive and are intended for shooting at ranges from 10 m to 50 m; there's a large variety of recoiling spring, gas ram, recoil-less spring, gas and PCP (pre-charged pneumatic) rifles in this group of 12 fp. to 24 fp. (32.54 J.) guns such as my BSA Superstar;

"super" magnum PCP rifles - these rifles are of fire-arm capabilities; definitely not intended for indoor target use;

Match air rifles - usually very heavy, exquisitely built and of exceptional accuracy and quite expensive; they usually produce 6 fp. (8.13 J.) muzzle energy - very quiet and safe for 10m target shooting; available in spring (usually recoil-less), CO2 and PCP powerplants.
For indoor and outdoor close range (10 m) target shooting, 6 fp. is all that is required. In fact, any more power simply adds noise, requires a heavier target back stop and must be treated with more regard to safety.

Perhaps because my first airgun was a Webley Junior - a spring gun - to me, an airgun is not an airgun, unless it is a spring gun. We all have romantic attachments to certain types of airguns, for me, springs are it.

So, finally I started looking for a low power (8 fp. muzzle energy or less), accurate spring air rifle with which I could do a lot of 10 m. shooting. True Match air rifles were eliminated from my search criteria, not so much because of cost, but because of weight. A rifle of 10 lb. or more is a mite too heavy for me to enjoy snapping off a 100 pellets from a standing position. My Superstar weighs close to 10lb with scope, it gets heavy after a while... I wanted a rifle in the 6.5 to 7.5 lb. range to fit my aperture sight to.

In late May 1998, I revisited the Compasseco web site (http://www.compasseco.com) and took greater notice of the CZ Slavia 631 rifle. The picture of the rifle with a match style plastic stock caught my interest. I phoned Compasseco, and discovered that somehow that model had never been imported; perhaps the web author had made a mistake; so I inquired about the wooden stock model and was told that a shipment was due the next week.

My wife was born in Czechoslovakia (actually her birthplace is now in the Slovak Republic). I consulted her opinion on whether or not an inexpensive Czech air rifle was worth considering, and got a "go for it."

A week later I placed an order; but an unexpected delay caused another 3 weeks to slip by before I finally took delivery. The price had dropped from $115 when the order was placed, to $95.99 on the shipped invoice. Can't complain about a price reduction, but isn't that getting a little too cheap if you want some quality?

Upon opening the box, my impressions were a little mixed because 2 long scratches on the top of the air cylinder were very noticeable. The cardboard box did not look as if it had been opened... but would the factory ship such a blemished gun? Closer examination revealed several other small scratches and nicks in the metal work and there were some rough cross-grain sanding marks in the timber stock. Okay, so it looked a little rough in the finish department... but I could always tidy it up later. I then lifted the rifle to the shoulder, and puzzlement set in. This rifle "feels" just right (at least for me); it just begs to point at a target. That chunky, deep stock really works.



Slavia 631 (aperture sight is after-market).

However, before shooting a new airgun, a quick read of the instructions is always in order. I became concerned when I noticed a Caution note about how the gun should be dry fired to remove a preservative from the piston and air chamber before first use... reach for the tool kit now !

Just what is this gun all about?

The action is held in the stock by the traditional two fore screws and one through the trigger guard. Lift the action out and... oops the cocking lever swings free. It is held in place by a flat spring in the stock... a bit unusual. The trigger blade is very long and slender and the first stage tension is by a flat spring in the trigger guard... another surprise. The main spring looked very dry, as were the cocking lever links and the trigger spring. So lubrication was called for; but first a little cosmetic work.

The deepest scratch on the air cylinder was sharp edged but not very deep. So a rub back with 1200 wet paper was needed before cold blueing. Then a rub with fine steel wool and Beeman MP5 rust inhibiting oil brought all of the steel work up to an acceptable finish. Not in the BSA class, but certainly equal to any gun for the money.

The stock is oil / wax finished. So sanding the rough spots and following it with some stain and a fresh waxing is actually a fun thing to do. I'd much rather work on an oiled stock than one daubed with a lacquer finish.

A few drops of spring oil in the spring slot and on the pivot pins; a smear of white grease on the trigger spring and the contact surface in the trigger guard spring and a dab of moly grease on the flat cocking lever spring in the stock, then reassemble. It now looked neater and the all the working parts moved fairly smoothly... but what about that dry firing to remove the preservative from the air chamber? After due consideration, a few drops of air chamber oil were inserted through the port, an oiled cleaning pellet was pressed into the breech and the gun was fired for the first time. Another surprise, that's one light trigger ! The owners' manual states that the trigger is adjustable in the 3 - 10 N (0.6 to 2.2 lb.) range. It comes set to mid-range - about 1.4 lb. A few more felt pellets, a pull through with a few cleaning patches and off to the garage shooting range.

The sights on the rifle are quite sturdy and of all steel construction. The first shot was low and off center. Try again. The pellet went through the same hole; so did the third... it soon became obvious that this is an accurate rifle !

Whilst the open sights are quite good, my original intention was to fit the aperture sight. I looked at the rear sight and found that does not look like it is intended to be removed easily. It is retained by a split drift pin that is only accessible when the action is open. Okay... leave it on for the first photo session... crank it down with the large thumb wheel and see how it works with the aperture fitted.



Rear sight.

It then became apparent that the front sight was canted to the right. The hooded foresight is a robust "one piece" unit consisting of an inverted "U" shaped base with hood welded on top. The post is a rod welded to the base, that projects up into the hood. Very solid, very non-adjustable. The unit is clamped by two screws onto a dovetail groove on top of the barrel. Somehow, mine had been knocked to one side. It was a simple matter to remove the sight, de-burr the clamping surface, slide it back on the dovetail and screw it in place.

Having a rear sight and an aperture sight is an unusual configuration. Surprisingly it works very well. With the rear sight adjusted all the way down, it hardly intrudes in the sight picture through the aperture. After sighting in through the aperture sight, the rear sight was adjusted to be centered in the view through the aperture sight... and was found to be in the exact center of it's own adjustment scale. This is a testimony to how straight this rifle is.

Airgunshooter10
26-04-2005, 02:01 AM
PART 2

Now some "serious" target shooting was done. What a delight ! The rifle is very nicely balanced, very quiet and very accurate. The more I used it, the more its' "peculiarities" became "natural".

One thing that seemed a potential nuisance is the breech lock. If you wondered what the triangular thing is under the barrel in the photo of the rearsight... that's the breech lock.


To open the gun ("break the barrel") you need to slide the breech lock forward to release the barrel catch. In the photo with the breech open, the catch can be seen as the small wedge shaped pin just under the breech opening.

In practice, it soon becomes second nature to thumb the breech lock forward, open the action, then slide the hand down the barrel a little ways before pulling back to cock the gun.

This is a very easy gun to open and cock. It became obvious just how easy it is to operate when I had a shooting session with my BSA Supersport, just after using the Slavia. Not only does the Supersport require a hefty pull to break the action open, the spring in the Supersport is a lot more powerful than the Slavia's.

I'm now becoming quite fond of that breech lock because it makes opening the gun a pleasure rather than a wrestle.

Incidentally, in this photo, the pressed checkering on the stock can be seen. On my rifle, the checkering on the LHS of the stock is deeper than on the RHS... The next cosmetic improvement will probably be to hand cut the checkering.

The Slavia is equipped with an automatic trigger safety. Perhaps I have had too many air rifles before safety catches became commonplace; I am generally skeptical of automatic safety devices on airguns. They either get relied upon too much by careless users, or they become a nuisance to experienced shooters.


The trigger safety on the Slavia is a knurled knob that pops out a few millimeters from the rear of the cylinder when the gun is cocked. It is very easy to push in by thumb when ready to shoot. I like it.

The safety can be re-applied at any time by pulling the knob back out.

The gun is not fitted with an "anti-bear" device, which means that the safety can be pushed in whilst the barrel is pulled back beyond the cocked position and the barrel can then be eased back to the closed position and the gun un-cocked. I like to be able to un-cock a spring gun without the need to fire it, so I appreciate this capability on the Slavia.

In this photo, the Beeman aperture sight, fitted with a Merit Iris Disc can be seen. This sight combination works very well, but it costs slightly more than the whole Slavia 631 air rifle !


Finally, the rear sight was removed. Being nervous about tapping around the breech with a hammer and drift on a cocked rifle, I removed the action from the stock, which disengages the cocking lever and allows the barrel to be opened without cocking the mainspring. The pin holding the sight was only a firm fit and didn't take much force to remove it and the sight.

The breech block has a radial slot cut into it for the sight elevation screw to seat into. Remove the sight and the slot is exposed. It looks quite neat; there are none of the threaded screw holes usually seen after removing a rear sight from an air rifle.

Before extolling the shooting merits of the rifle, let's cover some of the technical details of the Slavia.

"Slavia" was the trade name of Antonin Villimec who produced pistols in the town of Kdyne, Bohemia, prior to 1938. In 1938, that factory disappeared. CZ was founded in 1936.

CZ is Ceska Zbrojovka (pronounced "Cheska Broyoka") in Uhersky Brod (Czech Arms Factory Uh. Brod). Uh Brod is located about 80km east of Brno in the Czech Republic. I do not know what the connection is, but in the 1970's CZ was a trade name for a Czech motorcross motorcycle. My father bought an agricultural model CZ - it was tough and reliable. BSA also once made motorcycles; odd coincidences.

The instruction booklet for the Slavia states they "are break-barreled air rifles with a sporting stock and adjustable trigger pull. The weapons are designed for sporting and practice shooting and are equipped with a rear sight adjustable for elevation and windage. The front sight is interchangeable. The safety locks the trigger mechanism." That's a very succinct summary ! The remaining specifications are given as:

Caliber (mm / in) 4.5 / .177
Weight (kg / lb.) 3.1 / 6.8
Overall length (mm / in) 1160 / 45.7
Barrel length (mm / in) 530 / 20.9
Sight radius (mm / in) 500 / 19.7


There is no indication of muzzle velocity or energy.

Note the overall lengths of the rifle. The Slavia 631 is 4.7" (120 mm) longer than the BSA Supersport; the barrel is 1.9" (48 mm) longer than the BSA. The Slavia is a long rifle.

More details are:

Construction materials: Practically all steel; the only plastic rifle parts are the piston seal, the trigger guard, the breech seal "O" ring and the knob on the breech lock.
Trigger Single stage. Adjustable from 0.6 to 2.2 lb. Coin slot adjustment screw in trigger guard.
Front sight Hooded post.
Rear sight Wheel adjustable for elevation; coin slot adjustable windage screw.
Dovetailed receiver (for scope) 14mm wide dovetail, 100mm (4") long; transverse scope stop pin grooves.
Barrel locking Positive thumb operation release catch.
Stock Deep profile, darkly stained and waxed wood. Very tight and even grained timber.
Stock Butt plate Hard plastic. Mine had rough sanding marks in it.
Stock Checkering Pressed checkering on forearm.
Barrel rifling Very fine grooves. (See comments later)
Price $95.99 from Compasseco (June 1998)
Warranties 30 day money back from Compasseco. Manufacturer's 12 month guarantee.


From the overall design of the rifle, I would tend to classify the Slavia 631 as a target / Match trainer rather than a sporting airgun. The Slavia is not a powerful air rifle (advertised at 700fps (213 mps.)) by modern standards. The scope dovetail is a short 100mm - too short for most one piece mounts, but just fine for an aperture sight. This is not a "Magnum" air rifle, but then, neither are the expensive 10 m Match rifles... it's the accuracy and ease of use that count when paper punching.





Sometimes airgun manufacturers package a test target with their guns. One such target was included with the Slavia. The 3/4" (19mm) grouping of ragged holes is rather unimpressive and no indication is given of the range it was shot over. I was concerned that the rifle would be a mediocre paper puncher...

The first shots fired were rather informal. I was more concerned about getting the "feel" of the rifle - primarily the trigger and recoil characteristics, and at that time, I was using the factory fitted rear sight.

The first thing I noticed was the very clean holes that RWS Hobby pellets were punching in the paper. Those ragged holes in the test target had had me worried that the rifle was a slow performer... at 280 fps (85 mps.), Hobby pellets tend to tear rather than cut the paper. There was no evidence of tearing, so I immediately knew that it was spitting the Hobby's out at a respectable clip.

With the open sights, the pellets were striking a bit high and to the side, but in repeatable tight groups. Time to fit the Beeman aperture sight !


Then the true accuracy of the rifle became apparent when sighting in after fitting the aperture sight (10 m. targets shot over 6 m. range).

The first string of pellets fired were a surprise. They were punching a vertical worm trace as I adjusted the sight for elevation... I've rarely seen that before. (Windage adjustment for the aperture was set by centering it on the still installed rear sight picture.)

My hopes that the Slavia really has potential as a target trainer soared.




The more I shoot the rifle, the more I appreciate its' inherent accuracy. Any stray shots are my fault, not the rifles'. Five shot groups are usually very tight - shot at 6 m off hand. The Slavia certainly seems to be as accurate as I can shoot. When I drift off target on trigger release, the pellet strikes at the point the rifle was last aimed.

The trigger is becoming crisper and more predictable the more I use it. It has a single stage pull that has creeps a few millimeters before the resistance increases, then a crisp release follows at 1 lb. pull. (I have unscrewed the adjustment by a complete turn from the factory setting. It can adjust lighter, but there's hardly any need - it works very nicely at 1 lb.)

Subjectively, I had guessed the rifle was producing something over 600 fps. (180 mps.) with RWS Hobby pellets... subjectively by the neatness of the holes punched in the paper and the noise made on the steel backstop. So, after about 100 shots, I set up the chronograph.

Airgunshooter10
26-04-2005, 02:04 AM
PART 3

Initial chrony results with Hobby's were 670 fps. (204 mps.) average, an extreme spread of only 7 fps. (2.13 mps.) with an average of 6.93 fp. (9.40 J.) of energy ; quite nice. Then I tried my favorite RWS Super Mag pellets and got a poor 520 fps. (158.5 mps.) average for 5.64 fp. (7.6 J.) That's a loss of over 20% in muzzle energy ! And the rifle sounded like it was suffering a hernia !

Since the rifle was still smoking a little from the factory "preservative" and my oil mixtures, it was premature to pass judgement; more shooting was required before the gun could settle down to a "normal" state.

Special airgun "Air Chamber" oils are of high flash point and usually act as a combustion dampener. In sporting airguns, where power is paramount, the spring chamber is often lubricated with an "active" oil that migrates in minute quantities past the piston seal and is burnt in the firing cycle. Adding chamber oil directly through the transfer port usually causes a drop in velocity because it suppresses the other lubricants from combusting.

After another 200 or so shots, I set up the chrony once again and began more intensive testing. During this series of tests, the average velocity for Hobby pellets had dropped from 670 fps. to 645 fps (196 mps.)... why was that? Was the gun wearing out so soon?

I then added a few more drops of chamber oil. Immediately the average velocity for Hobby pellets dropped to 620 fps. I then tested other pellets and received even poorer results. Then I started a long test of 60 shots with Hobby's and saw the average velocity climb back up to 645 fps.

Further experiments with adding a drop of chamber oil, then measuring the velocity with Hobby pellets showed an initial drop to an average velocity of 625 fps, then a slow climb back up to an average of 645 fps. This profiles the Slavia as typically producing between 6.0 and 6.5 fp. of muzzle energy, with a maximum of around 7 fp. when lubricated with an active oil. Remember: 6.0 fp. is the norm for modern expensive Match air rifles; 25 years ago, the Slavia 631 would have been considered a powerful air rifle. It is power enough for eliminating small animal pests.

Many of the pellets tested in the Slavia gave lower velocity and energy results than expected. By far the worst pellet was the RWS Super Mag; which yielded only an average of 4.61 fp. (6.25 J.) at 471 fps. (143.56 mps.) The Super Mag is my favorite pellet in the BSA Superstar, so something is amiss ! In the same test series (same state of lubrication), Hobby pellets were averaging 6.44 fp., so this was a monster loss of almost 30% in efficiency. The second best performing pellets were Crosman 7.9 gr. Wad Cutters... I normally don't use Crosman pellets in spring airguns because they have a smaller skirt diameter than most of the RWS and Beeman pellets. The good results from the Crosman pellets indicated that the Slavia has a "tight" barrel.

Close examination shows that the barrel is finely micro-grooved. The instruction booklet for the rifle states: "insert a pellet or BB shot". This indicates that the barrel is bored for pellets and the European lead rounds, with the shallow rifling intended for good sealing with lead balls. A simple test was made by inserting an oiled Hobby pellet in the breech and then pushing it through the barrel with a nylon rod. It pushed through with a only a few pounds. The same test with a Super Mag pellet was extremely difficult. It took a lot of force to get the pellet moving and then still a considerable amount of pushing was required to get it all the way down to the muzzle. This clearly showed that large diameter pellets with stiff skirts will absorb a lot of the Slavia's potential energy, just getting down the very long barrel.

Next, testing was performed with Hobby and Crosman pellets sized down to .1800" (with a Beeman die). Shooting sized pellets through the chrony, immediately followed by unsized ones showed some energy loss to the sized pellets. The sized Hobby's lost 1.5% energy; the Crosman's lost 1.7%. (The unsized Crosman's attained 98.11% of the unsized Hobby's.) It seems that the ideal pellet diameter for my Slavia is something a mite larger than .1800". Most sporting / magnum pellets have skirt diameters of 0.185" to 0.188", so therein lies the problem with pellet choice for the Slavia. H&N Ultra Match pellets are nominally 0.184" skirt diameter; so they probably would perform well; most other pellets are probably too tight for the bore and will perform poorly without being sized. Guessing the probable results for different pellets is one of the fun challenges of airguns.

Now I turned to a closer examination of the test target that came with the rifle. The ragged holes are surrounded by a peculiar, circular puckering. They were certainly not made with a flat head pellet. I shot some RWS Super Domes and some Crosman Pointed into paper and compared the results. The Super Domes punch a small round hole, that, when the paper is flattened, are smaller than the holes in the test target. The Crosman Pointed pellets cut a slit more than a round hole that almost disappears when the paper is smoothed flat. My best guess is that the test target was shot with BB lead shot and not pellets. BB size lead shotgun fodder is a bit over 0.1800"... a trip to the local gun shop seems in order... BB's are not as accurate as pellets, but are easier and quicker to load and a bag of lead shot will last a long time. (Steel BB is definitely NOT suitable - it will not match the bore diameter and may cause damage to both the barrel and spring / piston.)

It's difficult to assess the durability of a rifle from a sampling of only one. CZ have been making airguns for a long time, and my rifle, except for a few blemishes in the finish, is very well made, so I trust it will give many years of service before requiring mechanical attention. The Slavia 631 is, after all, a modestly powered spring gun compared to today's "magnums", so it is not highly stressed. For the money, I really doubt that a more durable, accurate and satisfying to use adult sized air rifle can be found !... well... perhaps the El Gamo Sporter 500 is comparable in price / performance.

If you are looking for an inexpensive, well designed and built paper punching air rifle, have a close look at a Slavia 631.

Postscript:

Experience has shown that the 631 can be troublesome to equip with a telescopic sight. The scope grooves are wide (14mm) and shallow on top of the air cylinder. Many scope mounts will not fit correctly because of the wide spacing and the need to bridge over the curved surface. The underside of the scope mount base may need to be filed to clear the air chamber. Another potential problem is that break barrel rifles may be "droopers" - that is the barrel locks up slightly below a straight line projected from the air chamber; hence the term "drooper". The long barrel on the 631 accentuates the affect such that a scope must have sufficient vertical reticle adjustment to compensate, or the rear scope ring may need to be packed. I generally do not recommend fitting a scope to the 631 becasue of the potential problems and also, it is such a modestly powered air rifle that it is most suited to fine 10m shooting which does not need a scope.

The trigger is quite good with a light pull, but it does have a rather long take up before release. This can be reduced substantially by simply leaving the safety engaged, point at the target, pull the trigger until it hits the stop, then thumb off the safety and complete the aim and shoot. Please do this carefully and ensure the technique is safe on your rifle; it works well on mine and improves the trigger action substantially.