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CO2 power has a large following in the UK, and there are benefits over conventional air systems. A big part of the attraction comes with the fact that the power itself is contained within the CO2 bulbs, so designers have more flexibility. Where a conventional spring piston model needs a relatively heavy mainspring and piston inside, to generate power, no such cumbersome guts are required for CO2, and the result is often lighter, more manageable products; easily handled by all.

First things first though, and at this stage it makes sense to labour a general point regarding this specific power source. CO2 is directly affected by temperature. The colder the conditions, then the lower the likely power output. Likewise, cold temperature equals fewer shots per CO2 bulb. Accept that fact, and the medium has much to offer.

New Kid

When a call came in from Sportsmarketing that a new CO2 model was hitting the market, I was intrigued. Having now had a few weeks to play with the XS501, as it’s called, I can report that I rather like it! First impressions are very favourable indeed, and picking up this new model reveals a modestly weighted, wellbalanced rifle, that holds much appeal. Looks are of a small calibre hunting rifle, with that fully extended forend, and side bolt action, and the visuals get everything off to a great start. Specification includes a beech sporter stock, single shot recoilless action, automatic safety catch, fibre optic open sights, two-stage trigger, and a 22 inch rifled barrel.

As mentioned, the looks are very compact hunter and the beech sporter stock is both well-shaped and handsomely finished. Attractive grain pattern shows through the clear lacquer, and whilst the butt is rather straight line plain, it suits the streamlined feel of this rifle.

A full-length, slightly beefed up forend and comfortable pistol grip all add to the overall package, whilst that overly hard pad is basic but functional. As for the action, the large 22 inch barrel comes chemically blued to a reasonable standard. The breech block gets treated to a matt black finish, which contrasts well with the plastic trigger guard. The trigger blade itself is metal however.



Sportsmarketing (SMK) had sent this model through with one of their own branded 3-9x40 AO scopes, which meant they had removed the fibre optic rear sight from its rails, and failed to include it for inspection. Having seen the fore-sight assembly mind you, other than the fact that it’s curiously marked ‘XT501’, I’ve no reason to believe that the fully adjustable fibre optic rear sight won’t be perfectly up to the job.

With sights sorted, I just needed to get some power on board. This comes courtesy of two 12g CO2 bulbs, and the process is a little fiddly. Firstly, that front valve cap needs to be unscrewed, to allow for the CO2 bulbs to be inserted into the main expansion chamber, and this whole area deserves a little explanationsomething sadly remiss from the rather incomplete, curiously worded instructions!

That front cap needs to be carefully unscrewed ideally via the ribbed metal ring, which is the wider section of the assembly. It’s important to use this, since the front plastic section actually has a reverse thread. If you can unscrew the plastic section, then make sure that the plastic ‘screw bolt’ underneath is backed off to allow for the valving to work correctly. I managed to get the plastic cap off and check this, but it then locked on solidly, so removal was difficult. If all functions correctly, then this shouldn’t be necessary in any case.

With the valve cap assembly removed, two 12g CO2 bulbs need to be dropped into the expansion chamber, as per the photo; the first one thin neck first, then the follow up bulb rounded bottom first. The two bulbs should then be lying back to back, so that closing the front cap forces each end to be pierced, releasing the CO2 into the chamber.

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It’s important to note that when pushing that front cap assembly into place the thick ‘o’-ring needs to be firmly and quickly pushed into the neck of the chamber, then the threaded metal cap pushed down and screwed into place. The whole operation needs to be completed smoothly and quickly so as to achieve an efficient seal, containing the CO2 as it rapidly turns to a gas form. What should be simple is a bit fiddly and a dummy run with no CO2 loaded is a good idea, to get familiar. Prepare for frozen fingers if the seal isn’t good!


Action Stations

With power in place, pull that chunky bolt up and to the rear, until the hammer and trigger are heard to engage. Then roll a pellet into the loading channel, and push the bolt forwards and down to lock in position. You’re now ready to go.

The loading channel is rather cramped it has to be said, but adopt a ‘roll across from the right-hand side’ routine, and it soon becomes second nature. An automatic safety catch sits to the right hand side, and slightly high of the trigger, but its positioning makes it very easy to pull rearwards, effectively disengaging the mechanism just before a shot is taken.

Shot count with the XS501 is specified by the manufacturers as between 50- 60, when the rifle is used between 16-27 degrees C. As already mentioned, fluctuating temperatures affect CO2 as a power source, but obviously as the on-board CO2 slowly gets used up, velocity and power will drop. For a rough guide, my tests clocked energy of 9.9ft/lbs for the first 38 shots, dropping to 7ft/lbs over 50 shots. Velocity towards the end dropped by approximately 20fps each shot, but best practise would see a thorough test of a particular rifle at the start, and then work with the figures achieved – if you know you normally get 30 shots that are consistent, then stick to that number before looking to gas up. As velocity is heard to drop near the end of the charge, just cock the hammer and keep firing the mechanism until all residual gas is expended.

Velocity on test using Sportsmarketing’s own Black BS55 Domed pellets in .22 calibre showed a very acceptable total spread of 31fps over the first 38 shots. As for accuracy, I was really impressed. From a rest, I managed ¾ inch groups over 25 yards with the Black Domes, against 7/8 inch with JSBs. This all compared favourably with the manufacturer’s claim of 30mm, although over what range, those pesky instructions failed to mention!

Handling and performance overall was immensely satisfying, enhanced undoubtedly by quite the sweetest trigger for this grade of gun – wellshaped, slightly creepy, but fairly predictable nonetheless.



I really liked the XS501, and with its modest weight and easy handling fun shooting beckons for all – for a bargain asking price at that!

It just feels right in the hand, and with a pleasant bolt action, and very civilised trigger for this type of rifle, some highly creditable results are fairly easy to come by. SMK need to refine or upgrade the cylinder end cap assembly, and some half decent instructions wouldn’t go amiss, but otherwise, I can’t fail to recommend one of the nicest CO2 newcomers in a long while.

PRICE: £149.95
CONTACT: Sportsmarketing 01206 795 333

  • SMK XS501 - image {image:count}

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  • SMK XS501 - image {image:count}

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  • SMK XS501 - image {image:count}

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  • SMK XS501 - image {image:count}

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  • SMK XS501 - image {image:count}

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  • SMK XS501 - image {image:count}

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  • Name: SMK XS501
  • Type: Single shot/bolt action
  • Calibre: .177 & .22 (on test)
  • Weight: 5.5lbs
  • Overall Length: 40 inches
  • Barrel Length: 22inches
  • Stock: Beech sporter
  • Power Source: 2x 12g CO2 capsule
  • Shot Count: 30-60 shots dependent upon temperature
  • Average Velocity: 545fps using 15grain SMK Black Dome pellets
  • Variation: 31fps over first 38shots
  • Energy: 9.9ft/lbs average over 38 shots
  • Trigger: Two stage


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    07 Dec 2020 at 11:28 PM
  • Is it possible to remove the front sight block and fit a moderator?

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    Default profile image
    27 Apr 2019 at 01:42 PM
  • Hi, what are the best sights for this rifle? Does anyone know where I could pick up a lewft handed CO2 rifle?

    Default profile image
    01 Sep 2018 at 12:58 PM
  • It’s a good solid gun that packs a punch for not a lot of money. It’s probably best suited to those who don’t mind a spot of DIY, e.g. putting in proper seals and de-burring it here and there (my bolt was awful but now it’s slick). Of course, if you have a few hundred more to spare, there are much nicer guns but if you don’t or can justify it, these, or the more customisable 78’s, are well worth a look.

    Default profile image
    17 Nov 2017 at 10:21 PM
  • Hi could someone tell me the difference between smk xs501 and the smk xt501 as on box says smk xs501 but xt501 on gun ?

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    Andy Burt
    25 May 2016 at 12:43 PM
  • I have just purchased one of these.(177)
    The review is somewhat mis-leading. The plastic cap on the end of the gas chamber is to expel an unused gas before you change cartridges ( which is very easy to do).
    The cocking bolt is heavy for kids but, it`s not a kid`s gun anyway.
    I found the loading very easy with my big fingers. I fitted a 3-9x40 scope with medium mounts and still found it easy to load a pellet. They just roll straight in.
    The bolt action is positive and solid. Feels much more substantial than it really is, giving you the impression of a much heavier gauge rifle.
    The power is amazing and the accuracy is spot on. 30mm groups at 25 yards.
    It took 5 pellets to zero it in - 2 at 10 yards, then 3 at 25 yards.
    I used my first 40 shots hitting beer bottle tops at 25 yards and never missed once. I purchased it for vermin control and would recommend it for anyone who is a serious vermin hunter. This rifle packs one heck of a punch.
    My other rifles are Lee Enfield .303, Moisin Nagant sniper, Mauser 8mm, Springfield M1903, Remington 700 sniper and many air rifles, BSA, Relum etc.

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    Too Many Guns
    30 Apr 2016 at 07:58 AM
  • Bolt cocking really heavy for youngster, long travel trigger, dialing out excessive travel negates the auto safety, breech channel not really long enough to load without sometimes the pellet try to enter the barrel backwards, having worked on both its predecessor the XB78 is a better, stronger made gun.

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    Ron. T.
    14 Apr 2016 at 12:35 PM
  • Hi Paul.

    The cocking bolt has to set the trigger mechanism and cock the hammer against spring tension, so there will be effort involved. Without handling the gun it's obviously impossible to comment but it shouldn't be too hard to cock the action.

    I guess the only way you can really see if there is a problem is to go to the shop where you bought the rifle and ask to compare your rifle with the action of another XS 501.

    Let us know how you get on.

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    Troll Hunter
    09 Mar 2016 at 04:07 PM
  • I bought a 501 for my daughter we find it hard to pull the cocking lever back is this a fault on my rifle or are they ment to be stiff , overall though its a great little rifle shes had hours of fun at the range but tires at cocking it .
    Any advice much needed

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    Paul butler
    07 Mar 2016 at 09:32 PM
  • Hi, have just purchased a SMK XS501 as stated the instructions for this air rifle leave a lot to be desired, you need a magnifying glass to read the parts list!
    However as it is my first ever air rifle ( I am 74 and need to get rid of some pests) the guy from the gun shop where I bought it ran through the CO2 loading procedures with me and gave me some free targets also some CO2 cartridges. Once home, rifle unpacked, target stapled to the fence I proceeded to set up the sights ,( I'm a lefty although I write with my right hand ) perhaps this was the reason it took quite some time to set them up. Consequently this lead me to having to change to new cartridges, as in the review, and as it was my first attempt I found the procedure fiddly, and managed to lose the gas from the recharge. Having said all that the gun its self is, to my mind comfortable to use despite a little difficulty getting the pellet into the breech.

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    Phil Hunt
    10 Feb 2016 at 07:58 PM
  • The first gun as new had a air leak,after a couple of days.Took it back to the shop where l purchased it.I had a replacement gun,and that leaked air.l would l would not recommend this gun to anyone

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    m davies
    26 Jan 2016 at 06:00 PM
  • Just bought one of these. I agree with nearly all the comments except- I use a lead plain domed pellet. (Umarex smooth domed). Never got on with the Black SMK pellets-except for coating the barrel with graphite-5 pellets do it. I also find though 50 shots and the V figure falls off dramatically. I also find the pellet loading system a bit fiddly and have to watch that I dont load one back to front. Other than that and at the price i paid (£100 basic rifle). Oh yes the fibre optic sights- I find them excellent although am fitting a red dot sight.- I honestly think a scope makes it top heavy. All in all a decent rifle at a decent price.

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    Peter Colson-Osborne
    20 Jan 2016 at 11:49 PM