Airgun World - - Conversion Test -

The cylin­der in­sert works very well in my TX200 at 85mm of pis­ton stroke, so some might be tempted to try it with rather shorter strokes, which I’d strongly ad­vise against, for a va­ri­ety of rea­sons.

First, a longer cylin­der in­sert would eat into avail­able spring room, and might ne­ces­si­tate us­ing a stiffer spring, as would re­duc­ing the avail­able pis­ton stroke, which would sharpen the re­coil, and might in­crease hold sen­si­tiv­ity.

Sec­ond, fit­ting my 11mm cylin­der in­sert ef­fec­tively in­creased the length of the trans­fer port from 9.8mm to 20.8mm, which caused a slight re­duc­tion in en­ergy ef­fi­ciency, al­though it was so slight that it was a price well worth pay­ing. Fit­ting a longer plug, say 16mm, to re­duce the stroke to 80mm, would in­crease the ef­fec­tive trans­fer port length to 25.8mm, which will cause a fur­ther re­duc­tion in en­ergy ef­fi­ciency; ex­actly how much of a re­duc­tion I can’t say with­out fit­ting a longer in­sert and test­ing, but what I can pre­dict is that it would ne­ces­si­tate sig­nif­i­cantly higher peak cylin­der pres­sure and tem­per­a­ture to main­tain muz­zle en­ergy, and I don’t know whether the ac­etal would stand up to that.

In ad­di­tion to the in­creased pres­sure and tem­per­a­ture ne­ces­si­tated by the longer trans­fer port, a po­ten­tially much larger in­crease could be needed to com­pen­sate for the re­duc­tion in swept vol­ume, and con­se­quent air mass avail­able to ac­cel­er­ate the pel­let. Taken to­gether, the nec­es­sary in­creases in tem­per­a­ture to com­pen­sate for the in­crease in trans­fer port length and re­duced air mass would take us into un­char­tered ter­ri­tory, just as I was 12 months ago when I fit­ted the 11mm cylin­der in­sert. It might work fine for a while, but un­til it has pow­ered 10,000 shots, it might not turn out to be re­li­able.

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