Springers give lower power in the win­ter. Is it the same for PCPs? Our guru knows

Air Gunner - - Contents -

QI like to check the muz­zle en­ergy of my ri­fles reg­u­larly, and over the last cou­ple of years it seems to me that it varies with the sea­sons, not by a huge amount. Whilst I un­der­stand this is nor­mal with springers, my PCPs tend to give lower power dur­ing the win­ter than they do in the sum­mer. Is this nor­mal? Should I just re-zero and carry on, or do I have a prob­lem?

AGURU SAYS: It is per­fectly nor­mal for airgun muz­zle en­ergy to vary ac­cord­ing to the sea­son or, to be more pre­cise, ac­cord­ing to the tem­per­a­ture. Co2 guns show the great­est vari­ance, be­cause the pres­sure at which Co2 changes from a gas to a liq­uid drops as tem­per­a­ture falls, so there is sig­nif­i­cantly less pres­sure in cold weather, so much so that I would strongly ad­vise al­ways check­ing zero be­fore shoot­ing a Co2 if the tem­per­a­ture has changed more than per­haps 10 de­grees since it was last ze­roed. Spring airgun muz­zle en­ergy varies with tem­per­a­ture for a va­ri­ety of rea­sons that can see en­ergy climb or fall at lower tem­per­a­tures, and to make mat­ters worse, pel­let point of im­pact (POI) changes can be out of all pro­por­tion to ac­com­pa­ny­ing changes in muz­zle en­ergy, or even go in the ‘op­po­site’ di­rec­tion, so that lower muz­zle en­ergy can give a higher pel­let POI. Things seem to hap­pen if the tem­per­a­ture ap­proaches zero, or rises by around 20°C since ze­roed, so check zero if there is a sig­nif­i­cant tem­per­a­ture shift. The PCP should be least af­fected by tem­per­a­ture, although it is by no means im­mune to changes. As in spring air­guns, low tem­per­a­tures can thicken lu­bri­cants, which would take en­ergy from the ham­mer, so the valve open­ing could be less, or of a shorter du­ra­tion. As in spring air­guns, dif­fer­ent ma­te­ri­als ex­pand and con­tract at dif­fer­ent rates with changes in tem­per­a­ture, again al­ter­ing fric­tion and im­pact­ing on muz­zle en­ergy. In my ex­pe­ri­ence, changes in muz­zle en­ergy due to thick­en­ing lu­bri­cant or fric­tion are far less in the PCP than in the spring airgun. Even though the PCP is least af­fected by tem­per­a­ture fluc­tu­a­tions, it is al­ways worth check­ing zero be­fore a shoot­ing ses­sion, if for no other rea­son than pel­let POI can change for other rea­sons, such as the bar­rel or scope ac­ci­den­tally get­ting a knock in tran­sit. Fi­nally, don’t worry so much about changes in muz­zle en­ergy as changes in muz­zle ve­loc­ity. What seems a sub­stan­tial change in en­ergy can be just a few fps, and far too lit­tle to change pel­let POI.

Frosty win­ter morn­ings are a great time to hunt ... if you’re pre­pared

Small sea­sonal changes in PCP muz­zle en­ergy are noth­ing to worry about, but check zero fre­quently, re­gard­less

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