That is an ISSUE ..... It is a Known issue with polyurethane 0-rings that they can and will take a set ( As in if forced to take a slightly different shape they lack the shape memory ) when compared to Viton, Buna o-rings we typically see in PCP air guns.Always leave pressurized! Why do you think it makes a difference?
So WHY are they using Poly o-rings .... tough question that many asked when these rifles first came to market. With SKOUT ( Smart Parts in Paintball ) the use of POLY in markers was a durability thing I was told by them & it has been carried over to there PCP development. Personally wish then had not as I've too seen flattened & deformed poly o-rings in my skout and well a few other manufactured PCP's .... yea there tough as nails but there shape memory not so much.
My take away in a PCP such as SKOUT that has such awesome engineered parts and pieces threw out the entire system bottle to regs to valve heavily using Poly rings on near every air control / sealing surface, The use of poly o-rings is GREAT in some locations but falls short of ideal in others ... Thus the "Why For" your seeing state of tune shifts as you have shared / stated. JMO
Upvote 0