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Old 05-07-2013, 03:44 AM   #1 (permalink)
Join Date: Jul 2006
Location: Czech Republic (middle Europe)

Sterling CA efficiency tunning

This heavy modified Sterling Bronze, I will using like "CA training rifle", instead of my Stock Class Sheridans - I have modified him to get similar sight picture and ergonomy like with P68SC/PGP (

In the past 14 days I have dryed some efficiency mods on this marker to get the best posible ratio between quietness / gas consuption / power / velocity consistency. Bassicaly I will have similar shoot feeling like is in my best performance tunned SC Sheridans and preferably with similar avelerage velocity (there are most of the consistent shoots between 248-265 fps).

On this Sterling have been already performed these mods which affecting performance:
- lightened (20g) hammer (= no boncing)
- stronger hammer spring (combined shortened Spyder hammer spring with inserted unknown spring - combined str. 8.1 Kg)
- lighter valve spring (weak conical valve spring from 32 spyder spring set - strenght in setup 0.2-0.8 Kg cl./op.)
- new valve body (with big 9mm ID central hole and one radial elyptical oppening 10x7mm on diameter) and chamber
- entlarged air passage in the frame and bolt (small cylindrical => big elyptical).
- SS custom barrel (ID .683", lenght 9.5"), hand polished / flexy honned

Like powersource Im using half-filled 12oz Catalina CO2 tank, with Smartparts valve with build-in micro expansion chamber and anti-siphon tube. I have chosen the 12oz instead 9oz because he fits better in shoulder and he has larger vertical space for the antisiphon tube. With the ability be deeply under-filled (I really do not need having 340g of CO2 in tank with this pump), it is perfect setup for liquid/gas CO2 separation.

The current tunning was step by step work, with 8 following chrono tests. The same paint was used for the all tests (one year old RPS Evil, size 17.0-17.6mm / .669-.693" , avelerage weight of ball was ~3.25g), the ambient temperatures have been nearly the same (15-22C), tank was filled on nearly same level. During tests I have fired 20 shoot strings trough chrono.

At first I have worked on the flow modifications to make the flow more laminar and less turbulet. With modification of the cupseal shape (rouned back spaces facing to the valve chamber) and rounding of the 90 turn in bolt and valve body the result was:

- the avelerage velocity raised for 44.2 fps, from 229.7 to 273.9 fps (= kinetic energy gain +35%)
- 20 shoot velocity (in)consistency has been changed from +/- 25.5 fps to +/- 9.5 fps (!)
- the avelerage shoot to shoot velocity deviation has been reduced from 10.1 fps to 5.0 fps (!)
- ~0.3g of CO2 per shoot consuption (before it was somehere between 0.20-0.25g - Im not sure by the exact value)

With these flow mods, valve dwell should be been not affected (the same hammer and the same springs were used), but because of the flow improvement (in the entire dwell), there was then muzzle blast clearly visible, which was been not here before the mods. The CO2 consuption has been raised likewise, evidently...

Because the hammer was pretty light already and the actual valve spring was very light, I have dryed reduce the dwell a little with little stronger valve spring. With the first spring (conical 0.4-1.0 Kg)) I have not luck, but with the second (cylindrical 0.9-1,7 Kg) it was better:

- avelerage velocity droped to 256.9 fps (nearly exactly on the optimum for me)
- 20 shoot (in)consistency raised to +/- 13.5 fps (but is still only +/- 10 fps in the first half of the string)
- avelerage shoot to shoot deviation raised to 6.15 fps (but is still only 4.9 fps in the first half of the string)
- air consuption droped below 0.22g of CO2 per shoot
- so the avelerage kinetic energy in shot droped for ~12% but the air consuption droped for ~26%

...the marker consumes now less gas per shoot, he is more silent and the muzzle blast is nearly invisible now. The consistency is little worse, but the accuracy looks be not affected, the marker looks be even more accurate on medium range (25m/75ft). Without the one 242 fps shoot the inconsistency will be +/- 10.5 fps and the avelerage shoot to shoot deviation 5.72 fps.

The paint what I having now is really not perfect, so I was not sure how are the results limited / affected by the paint quality... The best 20 shoot (in)consistency which I have get with this sort of paint in this year was +/- 9 fps, but the best avelerage shoot to shoot velocity deviation for 20 shoot strings was between 3.9-4.3 fps...

To find the paint limitation I have performed two tests with sorted better/worse paint.

There was only small difference in consistency: +/- 13.5 vs. +/- 17.5 fps but the avelerage velocity raised a little (avelerage kinetic energy +4%).

The setups with the stronger valve spring looks be simply a little less consistent - perhaps is the closing force of the spring less consistent than the force or the pressured gas or the stronger spring reducing the flow in the valve chamber. Perhaps I will try reduce the dwell trough the hammer lightening instead of the stronger spring...

But Im curently satisfied with the performance of the marker - he shoots now with decent velocity and consistency, is quiet and accurate. In comparsion with the same marker before 14 days, he shoots now with bigger velocity but with smaller dwell and he is a lot more consistent - some things are not visible on velocity graph.

I think that the informative test of this marker on 12g will be follow - it is simply hard to resist. Best know Steling gives 388 J per 12g. When this uses 0.22g per shoot with avelerage velocity 257 fps (9.5J), the he can theoreticaly get ~500 Joules per powerlet.

In future I will concentrate myself mainly on other than performance mods (small feed mods, better trigger work).
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Old 05-09-2013, 04:23 AM   #2 (permalink)
Join Date: Jul 2006
Location: Czech Republic (middle Europe)

Test on powerlets:

Ambient temperature: 23C

Paint: one year old RPS Evil, dimensions between 17.0-17.6mm (0,669-.693"), avelerage paintball weight 3,26g (50 balls = 163g).

Powerlets: No Name, with measured real powerlet fill 12g (full/discharged difference - 40=>28g ...measured only by common kitchen weight = 1g accuracy).

Common Brass Eagle Q-changer was used in bottomline ASA.

At beginning of the test, I have really not the best feeling - the paint was really crap and there was leak after piercing of the powerlet, up to ~ thrid shoot (I have disasembled the valve before the test, so the cup seal need "find thier proper place" perhaps..)... but the shooting was great:

I have get ~43 "good shoots" (avelerage velocity of them 249.5 fps, and without few shoots with lower velocity - caused imho by bad paint - they were all above or very close to 240 fps) and then perhaps 4 "emergency", close-range shoots around 200 fps.

The avelerage shoot to shoot deviation in the first 20 shoots was 7.3 fps and in the second 20 shoots 7.5 fps. Without the weak shoot no. 8 and no. 14 (imho bad paint) the avelerage shot to shot deviation for the first 40 shoots will be 6.74 fps (with them 7.45 fps).

I have been not concentrated on accuracy testing, but on ~23m / ~75 ft I was able with ~90% of the first 43 shoots hit mask-sized target... and at least half of shoots having really pin-point accuracy! Really amazing with the non-perfect paint.

In the 50 shoots were stored total 421 Joules of KE, in the shoots in 235-300 fps range total 363 Joules.
...that is better than my best result with P68SC and nearly the same, like with my best tunned old style PGP (total 429J... with hi-flow internals and excessive light 8g titanium hammer for very short dwell).

With more lightened hammer instead the stronger valve spring, Sterling will be imho performing even better on powerlets and there are still reserves in shawing of the valve stem and shape of the slipway in the valve body...

Im interested how good it could be without the leak on beginning and with perfect paint... but momentaly I do not will spend the paint and time to find that out. I likewise do not plan further efficiency mods on this Sterling now - it should be CA marker.

Altrought I have not tunned this marker for powerlets, it looks so that he handles with powerlets very, very good... Im very satisfied with him. With q-changer he is very confortable and it is pleasure to shoot with him.

...the good is question, why do not use him even like primary Stock Class marker. The main disadvantage opposite my lowed Sheridans is size and weight (with q-changer, without paint and powerlets he weights now 1320g - that is for 30% more than oldstyle PGPs). On the other side, the main advanages are imho: non-corosive materials only and easy field cleaning of the bolt & barrel.
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