From what I can remember of my schooldays in the early 1960s (writes Colin Granger), at least a third of the boys in my class had an air rifle of some sort. Usually, these were ‘cheap and cheerful’ 0.177in-calibre spring-operated units that were pressurised by ‘breaking’ the barrel to compress the main spring. This provided the compressed air that powered the gun on a shot-by-shot basis.

 

Unknown to my mum, until she found pellet holes in my bedroom wall, a group of us regularly set up an indoor range, with the targets housed in a small cardboard box backed with three or four copies of the Radio Times. We could get reasonable results while lying prone in the bedroom doorway and shooting 12ft across the room, but when we go more adventurous and added the length of the upstairs landing to ‘range’. We had more than found the limitations of our rifles. Perhaps we should have got a bigger box and backed it with several copies of one of the broad-sheet newspapers.

 

My negative perception of air rifles’ accuracy was to change dramatically when a machine tool supplier invited me to visit a manufacturer of high-tech rifles. I was amazed not only by how advanced these pieces of equipment are, but also by the high levels of performance they offer.

 

Spring-operated rifles are still available from Hailsham-based Air Arms, but the emphasis is firmly on ‘pneumatic’ rifles, which are powered by a reservoir of compressed air. Compared with their sprung counterparts, the latter are lighter, less noisy and far more stable (consistent in performance) – plus there is no recoil. The only disadvantages are needing facilities for filing the rifles with compressed air at 200 bar and the fact that they cost more.

 

Just how seriously the users of these rifles take their sport and how close competition is at the highest levels is demonstrated by some of the features on Air Arms’ top-of-the-range target products: for example, a miniature spirit level that helps the shooter to maintain a consistent stance with each shot, plus a wind indicator attachment at the front of the barrel. There is even a muzzle shroud for the end of the barrel, to ensure that the pellet always exits the barrel in still air.

 

Target rifles such as Air Arms’ EV2 are serious pieces of precision engineering that are built to the very highest standards – and in significant quantities. Indeed, the company is the UK’s largest manufacturer of pneumatic air rifles, with an average throughput of some 600 units of all types a month. Moreover, each unit is individually tested and calibrated for its power (the maximum rating before a fire-arms licence is needed is 12ft-lb).

 

 

At the heart of most Air Arms rifles is the bolt housing, which is machined all over from 6082 aluminium – a grade that is particularly good for anodising and is used for non-critical parts. Parts that are subjected to air pressure are machined from 7075 aircraft-grade aluminium, which has a high zinc content and is tough to machine. When Air Arms first

started production, bolt housings were machined from solid on a Matsuura CNC vertical machining centre in a cycle time of about 30min, but demand for the company’s products increased steadily, and some six years ago it bought a pre-owned Matsuura MAM 500HF horizontal machining centre – and began using extruded material to minimise the amount of machining required.

 

Air Arms’ production manager Alan George says: “When we installed the MAM 500HF, which has a 15,000rev/min spindle, 20-bar through-spindle coolant and 11 pallets, we were planning to produce 16 bolt housings a day by loading 16 blanks at a time to a tombstone-type fixture. We knew that the horizontal would improve cycle times significantly compared with our VMC, but the gains we achieved were actually quite dramatic. These were mainly attributable to the fact that the load/unload time on the horizontal comes for free – except for the first pallet of the morning. The gains are also attributable to the fact that the time lost to tool change was now spread over 16 components – and the horizontal offered higher levels of performance than the older VMC.

 

“Demand for our products continued to grow fast and, by the start of last year, we were running our MAM at maximum capacity and looking for a second HMC. Sticking with a make and a model that we knew and were comfortable with, we bought a Matsuura H.Plus-300 PC11, which is broadly similar to our MAM, with a 15,000rev/min spindle and 11 pallets. However, it has higher rapid-traverse rates – 50m/min compared with 26m/min – faster acceleration and deceleration on the linear axes, 70-bar through-spindle coolant and some control enhancements.”

 

 

The new H.Plus from Matsuura Machinery plc, Coalville (Tel: 01530 511400), gave an immediate 30% improvement in productivity compared with the MAM. Mr George says this gain is a result of not only the faster acceleration and deceleration and the higher rapid-traverse rates, but also the high-pressure-coolant option, which allows tools to be used to their maximum capability. Furthermore, the high-pressure coolant also aids chip breakage, which is a particular benefit when machining large quantities of aluminium.

 

“With regard to programming, we bought the option of a ‘skip’ function, which simplifies the machining of parts that are similar but differ slightly in their detail – such as the bolt housings. Rather than write large numbers of programs that cover all the variants, we have a main program and switch the appropriate skips on or off as required. We do this each time we start a new batch, which is delivered to the machine with a check list detailing which skips need to be used. We could have got similar results with macro programming, but our operators find that skips are easier to use.

 

“Other options we had with our H.Plus included an increased number of ‘zero points’, to support our extensive multi-part loading. We also have Renishaw probing, which we use to probe every pallet and re-zero prior to machining. We tend not to probe individual workpieces, except when we are machining certain aesthetically critical features, such as a blend radii between two extruded forms; extrusions are only accurate to 0.15-0.20mm, plus there can be an element of twist. The accuracy of individual components is down to the machine program and the accuracy of our fixture, which we produce using the machine on which they will be used.”

 

Other key parts that accompany the bolt housing include the valve body – there are several variants, delivered to the H.Plus as turned blanks and multi-loaded to a tombstone fixture – the striker body, the trigger chassis and the trigger guard. On Air Arms’ top-of-the-range target rifles (costing more than £1,000 fully kitted), the five key components are effectively replaced by a spindle – albeit complex – machined component. In this case, the all-encompassing main body is produced on the one tombstone fixture in four stages. The same eight-sided fixture is also used to produce three other components (cocking arm, gauge mount and indicator level) – a complete family of parts off the one fixture.

 

For more information about Air Arms & their products, please visit their website at www.air-arms.co.uk

 

For more information about Matsuura Horizontal Machining Centre's, please call 01530 511400 or email sales@matsuura.co.uk

 

First published in Machinery Market October 2005