AC­CU­RACY MAT­TERS

Mark Camoc­cio dis­cusses the pros and cons of high-power de­liv­ery

Air Gunner - - Contents -

PRE-CHARGED PNEU­MATIC (PCP)

Whilst im­mensely pow­er­ful, pre- charged pneu­mat­ics util­is­ing fan­tas­tic brass ‘ ball reser­voirs’ were ac­tu­ally used in the Napoleonic Wars, the mod­ern pre- charged pneu­matic (PCP) has Daystate to thank, from the 1970s, as recog­nised pioneers of the sys­tem in the mod­ern age. The precharged pneu­matic sees the ri­fle built with an on-board reser­voir to hold highly com­pressed air. This cylin­der needs to be con­nected to an ex­ter­nal power source, be that a ded­i­cated air­gun pump, or a diver’s bot­tle, and then charged to a pre­scribed pres­sure, nor­mally some­where be­tween 130-250bar. Once fully charged, the shooter will then have an air sup­ply, good for a cer­tain amount of shots, which can vary dra­mat­i­cally de­pen­dent upon the gun’s de­sign. Con­ven­tion­ally-styled PCPs fol­low­ing the con­fig­u­ra­tion of straight cylin­der un­der­neath the bar­rel, typ­i­cally of­fer 50-80 shots de­pen­dent upon the model. So- called ‘ buddy bot­tle’ de­signs, where a large, ex­posed, gun-mounted air bot­tle sits at the front of the ac­tion, can of­fer far greater shot counts, in the re­gion of 200- 600 shots.

With PCPs, we then have the is­sue of non-reg­u­lated or reg­u­lated ac­tion. Many shoot­ers, par­tic­u­larly com­pe­ti­tion shoot­ers, can get hung up on con­sis­tency, and for peace of mind, a reg­u­lated ac­tion can be the way to go. The reg­u­la­tor ef­fec­tively me­ters a pre­cise amount of air for each shot – oc­ca­sion­ally, with the use of a sep­a­rate, small in­ner cham­ber within the cylin­der. Con­sis­tency should be im­proved, and with it down­range per­for­mance, due to the flat­ter power curve over the full charge. With a stan­dard pre- charged ac­tion, what’s called a ‘ knock­open valve’ is nor­mally utilised, and here the ham­mer knocks open the valve for each shot. As the pres­sure in the main cylin­der slowly de­creases, it be­comes eas­ier for the ham­mer to knock open the valve, so a slightly dif­fer­ent pulse of air might be re­leased over time. This can cause quite a marked ‘power curve’, which is when the ve­loc­ity rises and falls.

FILL PRES­SURE

With this style of air­gun, it is vi­tal to mon­i­tor care­fully the pres­sure to which the gun is charged, and re­search so that you know which par­tic­u­lar ac­tion likes a cer­tain fill pres­sure. Charge an ini­tial fill pres­sure too great, and the ham­mer can come up against more re­sis­tance from the valve at the start, caus­ing lower ve­loc­i­ties, set­tle into the smoother, flat­ter part of the charge (com­monly known as the ‘sweet spot’), and then as the resid­ual air pres­sure drops, so fi­nally, will the ve­loc­i­ties. There are no such con­cerns over the fill pres­sure with a reg­u­lated ac­tion, and for this rea­son, many shoot­ers put great store by pay­ing a premium for a fit­ted reg­u­la­tor. Many man­u­fac­tur­ers of­fer non-reg­u­lated and reg­u­lated mod­els, but pre­ci­sion reg­u­la­tors can also be pur­chased as af­ter-mar­ket add- ons, from such spe­cial­ist out­lets as Air­mas­ters, who are highly re­garded within the in­dus­try. With a ‘ reg’ fit­ted, shot count would nor­mally in­crease too.

The up­side of PCPs is easy load­ing by just pulling back a small bolt or lever, and of course, re­coil­less shoot­ing be­cause the gun hardly moves on fir­ing. The down­side is the gun’s reliance on that ex­ter­nal power source, a pump or diver’s bot­tle, and the ini­tial cost of that charg­ing gear.

SIN­GLE-STROKE PNEU­MATIC

To my mind, the sin­gle-stroke pneu­matic is the holy grail of air­guns, but whilst the sys­tem has proven suc­cess­ful for pis­tols, de­sign­ers have still strug­gled to achieve full power in .177 cal­i­bre, cer­tainly in pro­duc­tion mod­els. The de­sign sees a large lever mounted on the ri­fle, that needs to be pulled all the way back. On the out­ward stroke, air is sucked into an in­ter­nal cham­ber. On the re­turn stroke, that air is com­pressed. That vol­ume of pre-com­pressed air then pow­ers the pel­let. A con­sis­tent cock­ing stroke is needed to keep the vol­ume of air the same each time, but with care, ve­loc­i­ties with this style of gun can be phe­nom­e­nally con­sis­tent. Re­coil­less shoot­ing is the prize, but these guns are in­evitably heavy.

MULTI-STROKE PUMP-UP

Amer­i­can man­u­fac­tur­ers were al­ways keen on this style of gun, with Ben­jamin and Sheri­dan per­haps the best known. Here, an on- board pump­ing sys­tem al­lows for be­tween 3 and 10 pumps to be com­pleted to achieve full power, with a blow- off valve nor­mally in place to keep ev­ery­thing le­gal. Again, this style of air­gun of­fers re­coil­less shoot­ing, and can be fairly light, but the down­side is the ef­fort re­quired to com­plete those last few pumps. Pop­u­lar in the late ‘ 70s and ‘ 80s, this style of gun isn’t of­ten avail­able in the UK, pre­sum­ably due to lack of de­mand.

VA­RI­ETY

So as we can see, there’s an in­cred­i­ble se­lec­tion of hard­ware out there! Next month, we’ll look at choos­ing the right model for the right ap­pli­ca­tion.

“The reg­u­la­tor ef­fec­tively me­ters a pre­cise amount of air for each shot”

The mod­ern PCP is a su­perb tool, and eas­ier to shoot than some other types

Multi- pumps need a fair bit of in­put ef­fort

Don’t for­get, charg­ing gear is needed for a precharged air­gun

The FX In­de­pen­dent is unique

A bolt ac­tion is the most com­mon type of PCP

A typ­i­cal fill­ing valve con­nec­tor on a PCP

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