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The Theoben Evolution Air Rifle
By Brad Troyer
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When a lot of guys catch the airgun bug they tend to fall into the deep morass of tuning and customizing their airguns. A good tune is probably the most common upgrade performed on a piston gun. Nearly all benefit from a spring kit or a full out tune to reduce the vibration and recoil while increasing the power and lock time. I have owned and shot a lot of untuned piston guns over the years and nearly every one of them suffered from spring twang and added vibration because of the loose manufacturing tolerance required for mass production. That changed recently when I had my first chance to shoot a Theoben Evolution.
A good number of airgunners are familiar with the fine airgun line produced by Theoben. Their piston guns use a patented High Efficiency (HE) gas ram system that replaces the metal spring with an air spring. The overall affect is that all spring vibration, twang, and torque are removed from the shooting cycle. On top of this a patented inertia weight is used inside the piston. It slides with the piston and helps to eliminate piston bounce. All this translates into quicker lock time and a shorter recoil period. The new HE gas ram is reported to improve consistency and reliability over previous gas rams. This was accomplished by improving the seal material, moving the seal placement, and modifying the cone angles of the inertia weight to produce a smoother movement.
The origin of the gas ram idea reportedly came to Ben Taylor one day when he was rebuilding a spring gun that he and co-founder David Theobald had built. While in the process of working on the rifle Ben noticed that the forks on a Suzuki GS1000 motorcycle were air assisted. The wheels began to turn in Ben's head and the idea for an air piston was born. He made a rough prototype for his spring gun to see if the idea would even work. It did and after a few years of tests and prototypes he patented the original gas spring. It took a couple of more years before Ben and David officially formed Theoben on July 4th 1982.
Theoben started in the corner of a factory owned by Anglia Circuits Engineering in St. Ives Cambridge. The made their first gas spring rifle, the Sirocco, at this facility. They made about 400 Siroccos the first year and it was during this time that they employed an apprentice named Martin Rutterford. After about 18 months the company moved to a new facility on Stevenson Road and quickly grew to include some office space next door. While in this facility Theoben produced a variety of gas piston rifles including Eliminator/Crow Magnum, Sirocco Grand Prix, Sirocco FT, Sirocco Countryman, SLR 88, HW90, Fenman, and Taunus. They also produced gas ram conversion kits for a number of spring guns that were popular at the time.
In 1995 they move to a larger facility in Somersham, which is just outside of St. Ives, where they are located today. It was at this facility that the Olympus, Fenman Profile, Sirocco 2000, Dual Magnum, SLR98, Crusader, and Evolution were and are produced. Theoben also makes the fine Rapid series precharge air rifles that spans a good bit of this history. In 2001, the one time apprentice and then general manager Martin Rutterford became a junior partner. Then in 2003, when Ben and David decided to sell the company, Martin and Jonathan Radford purchased the company and are continuing the great Theoben tradition.
The Evolution was first introduced in 2002 and was designed to be an entry level gas ram rifle that was built to the high quality standards of Theoben. From what I saw on the test rifle, they certainly accomplished their goals. The Evolution is a commercially produced air rifle that is actually hand built. The parts for all the Theoben rifles are machined on CNC machines but the final assembly and fitting are done by hand. The bluing on the test rifle was flawless and everything fit very precisely. I am an engineer by trade so I could really appreciate that!
Evolution in Walnut (top) and Beech (bottom).
The Evolution is available with several stock options, the standard beech, left or right hand walnut, and a recently announced thumbhole sporter. The standard beech stock is a bit less ornate than the walnut design but it offers both right and left handed shooting from a single design. The walnut stock is a much more custom looking design that is bought for either a left or right handed shooter. I had a walnut stock on the test rifle and it was beautiful. I thought the stock design was ideal. When I pulled it into the shoulder if fit right and felt good. The forearm flared out to be a bit thicker than the breech area. It filled the hand comfortably and the laser engraved checkering was positioned so that the hand could grip it in most normal shooting positions. Since the gun doesn't have any iron sights, the cheek piece was set a bit higher than most rifles to accommodate the use of a scope. The pistol grip had a nice steep curve to it and more laser engraved checkering. The grips spacing back from the trigger was just right so that my hands could hold the pistol grip and still reach the trigger comfortably.
The rifle uses the Theoben trigger unit by the same name, the Evolution trigger. It is a two stage trigger unit that is adjustable for second stage travel and weight. The weight can be adjusted down to just 1 ½ lbs. The rifle I tested was given to me by David Slade of Theoben USA. David had adjusted the trigger unit perfectly so I didn't mess with any of the settings myself. For a sporter rifle, the Evolution trigger works great. It was adjusted to a safe weight for hunting or plinking purposes yet had a very predictable, crisp let-off. I didn't detect any creep in the second stage. The trigger on the test rifle was top notch.
Cocking the Evolution is akin to starting a finely made automobile. A gentle slap released the barrel from the barrel latch. The cocking stroke was smooth and precise with a satisfying click at the end of the stroke indicated that the rifle was cocked and ready for action. The whole cocking action made me feel like I had a thoroughbred in my hands. Once the rifle was fired, it pretty evident that the gas ram system has a shorter shooting cycle. I didn't have a way to really measure the lock time but it seemed like the shot occurred quicker with the gas ram than in a spring gun like my R9. It may be that the air under pressure in the gas ram may have a faster expansion coefficient than a metal spring. I do know that the recoil period stopped much quicker than a conventional spring gun. After releasing the shot, the image of the target came back into focus faster than with a conventional spring gun.
Like any piston airgun, the Evolution has a piston that moves forward to compress the air behind the pellet. However, unlike other spring power plants, the gas ram doesn't have a spring that torques the rifle and vibrates as it expands. This gives the gas ram an advantage over the spring and makes the Evolution a bit easier to shoot consistently. One thing I noticed though is that the recoil, while quicker, is also sharper. The recoil hit faster and harder than a comparable spring gun but it didn't hurt accuracy or rifle control. After shooting the Evolution for a while I felt that the overall shooting cycle was superior to a typical spring powered rifle.
Well, all of this is fine but it isn't worth a hoot if the rifle doesn't shoot. Well, don't worry about that, the Evolution is plenty accurate. It came to me with a 5x scope mounted on top. From a bench I was able to shoot 5/8" groups on average at 35 yards. The tightest group I shot was ½" and the biggest was 7/8". These are pretty good groups for a 5x scope and I bet I could have shot tighter groups if I had used a higher mag scope. Either way, the rifle can shoot. I shot the majority of my test groups with the Crosman Premier .22 pellets but also tried JSB Jumbos, Daisy Pointed, and Crosman Pointed pellets and all shot well. The Crosman Pointed pellets performed comparably to the Premiers which surprised me. The others were a bit less accurate but all shot under an inch at 35 yards.
Part of the accuracy is due to the consistency of the power plant. The test rifle averaged 650 fps with the 14.3 grain Premiers for an average 13.4 fpe. The highest velocity was 657 fps and the lowest was 643 fps with an overall standard deviation of 3.60. That is pretty darn good for a piston gun, I don't care who you are!
Shooting the Evolution for an extended plinking session was very enjoyable. The cocking effort of 21 lbs. was low enough so as not to tire quickly from repeated cocking. The rifle weights in a typical 7.5 lbs. so holding and carrying the rifle for an extended time was no problem. The Evolution uses a 10.5" barrel that reduces the overall length to just 38 1/2". It was pretty apparent that the rifle was shorter since the overall balance was excellent. It didn't feel nose heavy at all and pointed very well. Theoben uses Anschutz barrels for the .177 and .22 calibers and a Walther barrel is used for the .20 caliber.
I spent some time shooting the Evolution both in the back yard and back woods. It handles extremely well and feels good when it is pulled into the shoulder. It took a little time to get used to the firing cycle since it is different from a conventional spring gun. I really liked the quicker lock time and shorter recoil. In most cases when I did my part on the shooting discipline, the recoil calmed down quickly enough for me to see the reaction of the target when the pellet hit it. The trigger was not set to match grade levels but it was very smooth and predictable. That enabled me to hit what I was aiming at the greater majority of the time and usually when I missed I did something wrong.
The Evolution is a commercially produced custom airgun that is ready to shoot right out of the box. The shooter doesn't have to tear into it to install a tune kit or send it to an airgunsmith for a makeover. It is ready to go as is and will shoot for years with little maintenance. This test has made me seriously consider a gas ram for my next purchase, perhaps in a field target configuration. The Evolution is a top notch airgun that some may wonder if the quality is worth the money spent but won't regret buying one after many years of proud ownership.
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Theoben Evolution Specs
| Model | Evolution |
|---|---|
| Manufacturer |
Theoben Ltd., UK www.theoben.co.uk |
| Importer |
Theoben USA www.theobenusa.com |
| Type | Break Barrel, Gas Piston |
| Caliber | .177, .20, .22 |
| Energy | 13.5 ft. lb. |
| Weight | 7.5 lbs. |
| Overall Length | 38.5" |
| Barrel Length | 10.5" |
| Cocking Effort | 21 lbs. |
| Sights | None |
| Stock | Ambidextrous Beech Right or Left Handed Walnut Thumbhole Sporter |
| Length Of Pull | 14" |
| Safety | Automatic |
| Trigger | Two Stage Adjustable |
| Suggested Retail Price |
$646 Beech $746 Walnut |
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© Copyright 2006 by Brad Troyer & American Airguns