2400 2K PCP build

[threesuns]

initial results with “0” hammer spring adjustment,
                          “0” hammer striker adjustment,
                           1/16 tp installed,
                           2k fill
                           10.5gr CP ultra mags

shot 1) 386, 2) 390.3 … 10) 414.8

refill & add 1/4 turn to hammer spring

shot 1) 414.7, 2) 419.7, 3) 425.1 … 10) 449.8, 11) 448.3 12) 434.1 

gonna refill & add another 1/4 to the hammer spring & run it to empty

[Ribbonstone]

Following...just don’t have a lot to say about it yet. (although I did clean up an old 2300 tube and reseal an old HiPac unit, just in case I get the urge again.)

Totally new parts in an old frame equates to a new airgun...and like any new PCP,  it’s going to self-change (break in).  No matter how nicely you adjust it now….will be readjusting 100 or 200 shots later as parts mate up, the poppet takes its final seat, and friction decreases.

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Did come out nice looking...prefer the 1701 front sight, but that’s just me,,,how close you can get it to zero would be more important than style points.

Short Al. Breech (and a lefty at that) works with an iron sighted pistol...no need for the extra length/weight.

Best location for a barrel band on a pistol using the 2240 type breech design.  Mitigates the poor breech retention.

One of the ones with a dovetail cut for the 2260 type rear sight.  Real PIA to get zeroed (like a long ping-pong match)….don’t sweat getting it dead-zero for testing.

Even at 450fps, likely has a quick/sharp “snap” sound.  Not irritating, just unexpected  (does tend to PO my wife when I shoot inside the house).

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Thinking in reverse, one of the self-tests for air use is what I find comparing lighter and heavy pellets.

Pretty much a given that heavier pellets would earn more energy, even at lower speeds.

But if the heavier weights (10ish) earn a “bunch” more energy than  standard weights (8ish), pretty good indication that the valve dwell is a bit long (“slow” would be a better adjective).

Down in the .177 low power world, a ”bunch” doesn’t seem like it when it’s only 1 foot pound.   But considering 5 foot pounds of energy, 1 foot pound is a “bunch”...even ½ a foot pound is significant.

[threesuns]

2k fill

1) 423.7          11) 459.8          21) 463.7          31) 458.2           41) 422.6
    425.3.               462.1                466.2                458.2           
    438.9                465.1                467.8                457.2
    445.5                463.                  463.4                449.8
5) 447.2          15) 462.6           25) 461.6         35) 454.3
    449.8                470.2.                529.6               440.9
    447.8                467.3                 462.5               439.1
    453.8                463.                   455.                 434.8
    450.6                467.6                 458.2               430.2
    462.3                466.3                 457.4         40) 428.7


musta gotta std weight pellet in the tin for shot #26 (good data though)

Average 442.9fps           standard deviation 13.4          FPE 4.56           (substituted 460 for shot 26 to get results)

shot count exceeded my expectations. I think there is still room to play. Since mechanically same as a P-rod, 1701 & 1720 maybe B Staley buffer would be better than SSG.

dB read on 1rst floor above where I shoot in bsmt.

not too confident in my abilities to hack up a LW barrel but including a pic of what I was envisioning for a final result + the performance trade off. ??
   
   

[threesuns]

forgot to mention ending pressure was around 750-800 psi by my pump gauge

[Ribbonstone]

Just a couple of thoughts.


Barrels:

When I had the shop and tools, wanted a shorter barrel, but was happy with the accuracy of the long barrel….would shorten it from the breech end and treat it like a re-barrel.  Normally, the accuracy stayed real close to what it was as a long barrel.

Shortening from the front removes any choke /  requires a new crown...it’s more of a “do over” so far as accuracy.   Can make a good crown, but if you miss the choke, can’t really duplicate it.

As for velocity loss….don’t believe the simple “this much per inch” rules.   It’s more related to the parentage of change.  2” off a 10” barrel will be worth more than 2” off a 24” or 20” barrel.  Ballpark guess it as ½ the percentage of change.  Do have a low power tune working for you, so might see less.

Velocity variation:

Got use to be strict about 4% percentage of velocity change over a rifle’s shot string.  Those limits got carried over to PCP pistols….and that might have been a mistake.

Real limit for open sight pistols is the shooter’s eyesight. Am not open iron sight shooting a pistol at little targets at nearly the distance of a scoped rifle.

Even if you sit down at 20 yards bench rested and seriously try to detect when the groups are low only due to velocity variation, it takes a larger % of change to notice it.

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Referring to the “4% variation rule above”….and considering it’s your first full shot string…really close to the 30 shot original goal.

[threesuns]

Ribbonstone, thank you, I really appreciate your input.

I’m really happy with the end result. Atleast initially, I think I’ll just drop my fill pressure down to 1900-1950psi & go from there. This barrel is more accurate than I am, even with cheap pellets. At 30ft in my basement I got 1 ragged hole about the size of a nickel during the 40 shots.

Regarding the 1701 site … the post is too tall for my application & I ran out of elevation adjustment but that could easily be remedied. However, taking a closer look, there is a little too much material for it to clear the tube with a shorter barrel.   

Who knows maybe my 2300s will fall victim to a PCP upgrade in the future.

[threesuns]

just took some measurements for future reference … to get the look I was initially going for, could get a stock 1740/2240 barrel, drill out the front brake 1/4” deeper (there is 1 inch of material there to play with) & shave the bottom of the brake to clear the pressure tube. That should allow the barrel & fill cap to be flush at the end.

I don’t think I could shoot a good 1740 barrel any better than this LW with open sites.

Better start compiling another list of parts to justify crosman’s flat $4 shipping charge. 😃

[threesuns]

Curiosity got the better of me … added 4) 19x2.4mm 70 duro O-rings & added a bit more hammer spring

Fill pressure 1950psi + same CPUM 10.5 pellet

1) 433 fps          11) 464.4           21) 457.6           31) 456.9
    431.                    464.6                 459.1                 452.6
    445.9                  467.1                 458.8                 441.7
    434.2                  468.6                 462.1                 440.3
    445.5                  462.8                 458.8                 434.
    449.1                  463.4                 461.7           36) 436.1
    451.1                  463.1                 454.8                 
    456.4                  462.7                 455.9
    457.1                  463.9                 457.6
    456.4                  463.                   458.

Average 453.9fps      FPE 4.8      SD 10.6       ES 37.6       Pressure 850ish

It got better but lost a handful of shots.

Tried higher pressure & spring adjust + hammer throw to get 40 shots but ES got real bad. Not really sure why, other than I like round numbers.
As is, it is still more accurate than I am, super easy to fill & gets more shots than anticipated. Ultimately I think I will chop or swap the barrel to get the look & size I wanted but that’ll be a while. Time enjoy while I contemplate the next project.