My 99% complete custom 2240...

[eyebull]

Whilst the shot count is impressive the set velocity is also quite low...at 100 m/s it probably won't punch clean holes at 10m.
I've never had a .177 co2 Crosman so I can't compare it to anything I've owed - but by way of comparison my Tau-7 is .177 and 12g co2 powered and at about 120 m/s it'll do just under 90 shots on a single cartridge.
I normally run it at about 150 m/s and it'll do around 70 shots to a cartridge.
It'll be interesting to see what it does when you wick it back up to the 5 ft/lb mark as the gun was doing previously as at the moment it's difficult to gauge the improvement in efficiency.
Keep up the good work....this is interesting stuff

I'll probably split the difference and add perhaps another ft/lb or so. I haven't loctited the nut yet so I can go in there quite easily and add a bit more preload.

One thing I noticed on the GTA forum (where this subject took off last year) was that people were measuring efficiency by adding the total ft/lb generated per cartridge, So if you got ten shots at 10 ft/lb you'd be getting 100 ft/lb from each capsule. Not a bad way to look at it if you think about it.
So in terms of this particular pistol, if it was getting 35-40 shots at 5 ft/lb, that would be 175 to 200 ft/lb.
Now it is getting (lowball estimate on both parts) 180 shots at 2ft/lb, that is 350 ft/lb total. So there is a clear increase in efficiency, not just the total shot count.

I have a suspicion that somewhere in between these two extremes I can find a nice compromise between shot count and power that may well breach the 400 ft/lb barrier. If I can run it at 3 to 3.5 ft/lb and still get 100+ shots I will be chuffed as nuts.

[eyebull]

I completely sympathise with Terry D and his stance on chrono string tests - it is a deathly dull process!

Two experiments tonight -

First, I tried to bring the power up to about 5 ft/lb, where it was originally.
I did do this, but it doesn't look like I got the full benefit of the SSG. Super-boring shot string follows. Again, all in metres per second, with an 8.44 gr JSB pellet, dry fires denoted by *.

two shots to confirm cartridge pierced, and then
151.2
149.6
152.8
157.2
157.1
156.2
156.7
157.1
158.5
159.1
159.3
157.2
157
157.7
157.6
158.1
159.2
159.9
158.7
159.7
158.8
159.7
160.9
159.2
158.2
158
158.2
159.3
161.4
160.9
160.3
161.8
159.2
161.4
160.7
161.2
158.9
161.5
160.4
160.1
159.2
159.3
160.4
159.3
160.4
159.3
160.5
159.4
159.5
159.9
160.4
160.2
159.7
158
159.8
158.1
158.6
156.4
154.4
153.5
152.5
152.1
151.7
149.5
146.3
141.4
142.2
139.5
137.2
133.2
134.5
127
123.9
120.2
116.5
110.9
107.8
103.8
98.4
93.6
87.8
82.9
77
70.3
64.9
59.6
*****
*****
*****
(empty)


I reckon about 60 shots before a steady decline sets in. Back-of the envelope, I make that about 300 ft/lb generated in total from the usable shots. So, more efficient than the stock spring, but less efficient than my first SSG set up.
What's interesting about this string is the long tail off of about 35/40 shots, when the SSG is meant to get a more sudden decline in power after a relatively flat power curve. I suspect that another design of SSG could get better results at this power level. There really is no standard for these and they are all different.
As this was pushing, at peak, 5.25 ft/lb at room temperature, I wasn't really comfortable leaving it at this power level. So onto experiment number two, splitting the difference.


My patience for recording Combro results was waning rapidly at this stage (and pellets cost money!), so there were a lot more dry fires for this string, which were taken in rapid succession:

**
130.2
129
*****
*****
128.5
*****
*****
*****
*****
129.5
*****
*****
*****
*****
132.7
133.3
*****
*****
132.6
133.7
*****
*****
*****
*****
128.1 (gun was getting quite cold at this point so I had a fag break)
*****
*****
133.9
*****
*****
131
*****
131.8
*****
***** (noticeable sound difference here)
108.5
*****
85.2
*****
*****
*****
*****
(empty)


An average of about 3.5 ft/lb for 120-ish shots before drop off, makes 420 ft/lb generated in total - so I broke the 400 ft/lb barrier, making this the most efficient set up so far! It's good to be right sometimes....but then even a broken clock is right twice a day
I could drive myself mad tweaking this forever and a day, but I am (as I said I would be) chuffed as nuts with 120 shots at 3.5 ft/lb so will leave it here, at least for this gun.

I would be interested to see what our resident engineers can make of this concept, because if a ham-fisted bodger like me can get these kind of results then the sky is the limit for someone with actual skill.
There is a 40-odd page thread on the GTA forum for the interested - it's called "Re: A New Method for Increasing the Efficiency of a PCP - the SSG". Loads of different designs on there - some very intricate - but it can be as simple as my set up of a 4mm hole in the rear plug, a screw, an o-ring (optional!), a spring and a nut.

Please give it a try.

(and yes, this 2240 is officially complete now, promise....)

[harvey_s]

Thanks for posting this it's been a most enlightening thread...

[AIRGUNNERMO]

That is a very impressive piece of artillery. Great job.

[988396]

Very nice setup.
I have been looking at the companies you mentioned.
Makes me want to do one of my own now.

[David22]

Great job - looks awesome !
I'm building a 2300T from scratch, essentially a 2240 with the 10" .177 barrel.
I've gone for the "hidden screw" type of breech as I've found the lighter .177 take a "nose dive" into the barrel screw recess hole.
I'd be very interested on your thoughts on the Alliance front globe sight. Any more pics ?
Cheers David