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packrat · Senior Member

for a job EXTREMELY well done on the Discovery air rifle... I built a gun using a new 2260 action , new .177 caliber barrel from Crosman. Everything else is new, Discovery stuff from Crosman. The gun is 100% stock, EXCEPT I did Bob's mods on the trigger, I shortened the hammer spring 1 1/2 colis, and I put a Crosman 2300kt PA on it..Aduster was completely out for this string...NO tension on hammer spring whatsoever.
I built this, wanting something I could get long shot strings with minimum air use, which is why I trimmed the spring...Keep in mind that the string below is shots #31 through # 62 !!!

I am a Crosman fan now for sure, I had NO IDEA it would turn out this good Mr. Green

I forgot --I did also add a Crooked Barn Ultimate Breech and bolt..

rsterne · Moderator

Nice string.... I assume the first 30 shots were slightly less velocity?.... What did the velocity start at?....

Bob

packrat · Senior Member

Low 740's IIRC -- I turned the chrony off without thinking what I was doing, so didn't get a printout..first 3 shots were a bit low..after that the next 59 showed no POI change.. this at 50 yards.....I had no idea it would be this good..it's exactly what I wanted.. ..2 of the 5 shot groups could be covered with a US quarter....BTW, I installed the trigger-over travel screw today..should have done it back when I changed out the spring...makes a nice difference to have trigger stop the instant it breaks....
How high on PSI do folks regularly go on re-fills? Can it safely be filled to 2400?, even though amount is in the yellow zone?? Thinking about trying higher pressure and testing different turns IN on PA, just to see what I can get Mr. Green

although what I have now is WAY more than I expected!

rsterne · Moderator

It sounds like you are already filling it a bit too high if the velocity is down nearly 100 fps from the peak.... More pressure will result in LESS velocity in an unregulated PCP.... unless of course, you crank in the hammer spring quite a bit....

If you are shooting at 50 yards, I would recommend you stay within about 4-5% total velocity variation within the string.... that will give you about 1 pellet diameter vertical dispersion at that range (depending on pellet and velocity).... That means use a fill pressure and refill pressure that keeps the shots between, say, 800 and 760 fps....

It woudl appear that your shot string has continually increasing velocity for about the first 45 shots or so and then a decrease over the last 15.... If you increase the hammer spring tension, you will increase the velocity and get a more balanced string.... but shorter of course....

It all depends on what you are trying to achieve.... Generally, if you are after lower velocity (and more shot count).... you will fill to a lower pressure.... and refill at a lower pressure also....

Bob

packrat · Senior Member

That's what I had in mind...more pressure and turn in PA some..as in this string I had backed out completely...ZERO tension on spring..and was just curious as to how much effect another 200-300 psi would have with say 4 to 6 turns IN on the PA....Actually I'm perfectly content with the results of this string- it's what I was hoping for..long shot string..which is why I did not use the barrel that came on the 2260.....but went with .177 instead .
I'm gonna refill to 2100 and see what velocity was (for sure) at start of string.

BTW-what about my question concerning filling gun to 2300-2400?? I know it's in the "caution" zone..just wanted your thoughts on using that pressure..I'm sure there's a large safety factor designed into the tube. From what you told me I probably can use 1800-1900 psi and still have the long shot string that it's now producing....

edited to add--didn't mean to go into a long discussion, sorry ! I just wanted to brag on what a great job Crosman has done!! I am amazed by the performance of the 22XX guns.. Mr. Green

rsterne · Moderator

RE safety at 2400 psi.... Crosman's only warning about going over 2000 is that the velocity will drop.... I've done it.... I needed a heavier hammer spring to dump the air, though....

What you do is up to you, of course.... I certainly wouldn't go into the "red" zone....

Bob

packrat · Senior Member

Thansk Bob, that's what I needed to know....I think I'll leave it as is, with the shortened stock spring. Rather than use 2100psi as fill point, I'm going to use 1900....May lose a few shots, but it should make the ES a little less... Heck, even 50 shots at average of 800 is fine with me.. and BTW....I DID get 3 five shot groups yesterday, at 50 yards, that could be covered with a quarter Mr. Green

Just wish all that wood didn't weigh so much Crying or Very sad

rsterne · Moderator

Playing with the balance between hammer spring and fill (and refill) pressure is one of the cool things about PCPs.... You can get almost anything you want.... Cool

If you are satisfied with quarter sized groups at 50 yards.... even a 5% velocity range will hardly make any difference to POI.... about 3/8" difference in drop between 820 fps and 780 fps....

Bob

packrat · Senior Member

For now, the accuracy is OK with me.....I did run about 100 pellets through just it to see what kind of groups it was doing..I feel confident it can do "nickels" or "dimes" For now though I'm gonna play with hmr. spring(s) and fill pressures. I shortened the spring because at 2000psi the first few shots were in 840/860 range and were peaking at 950..more than I wanted so I cut it....(I have lots of Crosman springs, for all different models) ..I had in mind 750 to 800fps,and hoping for ~ 50 shots before having to refill..that would be 10-11 fpe and for just shooting at pine cones in top of trees, cans and goofing off, I figured that that would be sufficient..Have not messed with PA at all so far, still at ZERO tension Cool

BTW..i had a BRAINSTORM today, instead of holding and aiming gun while resting, I secured it in my Winchester shooting vice and have it aimed at target. NOW it's just load and pull trigger, load and pull trigger,,,etc,etc,etc, takes no time at all now to do 60-70 shot strings...what an idiot I am for not thinking of doing that much sooner Embarassed