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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Stopping Spring Guide vs the Korean Cliff

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jackssmirkingrevenge:
I'm in the process of resto-modding a Korean 0.22" Duk Il "King Hunting Master" sidelever pneumatic, and I'm interested to see how an SSG would influence the typical velocity curve.

This is the first SSG iteration, due to the fact that the receiver is closed and the rod cannot stick out of the rear, it needs to be a telescopic design:



Here it is disassembled:



A quick first test with 14.3 grain Crosman hollowpoints, 10 shots with the stock hammer setup and 10 shots with the SSG.  For each 10 shot string pressure started at 1600 psi and dropped by about 200 psi:



Not a very encouraging start, less energy for the same pressure drop and a non-linear variation in velocity compared to the stock setup.  I suspect the bolt thread is snagging and launching the hammer with inconsistent force.  I will make a new pin with a female thread, held by a bolt inside the spring guide.

rsterne:
IMO, to get rid of the Korean Cliff, you have to reduce the hammer strike at the beginning of the curve when the pressure is the highest.... If as in many of the Korean guns the hammer is striking a stop on the back of the valve that limits the valve stem lift, you will have great difficulty getting rid of the cliff.... Lift has to vary inversely with pressure to achieve a bell curve....

Bob

jackssmirkingrevenge:

--- Quote from: rsterne on June 18, 2023, 12:17:17 PM ---If as in many of the Korean guns the hammer is striking a stop on the back of the valve that limits the valve stem lift, you will have great difficulty getting rid of the cliff...
--- End quote ---

On this model there is a Hi/Lo power setting where if I understood correctly the low power setting puts a stop in the path of the hammer, but the synthetic material had degraded and crumbled and I did not replace it, I'm not even sure what it originally looked like.

I've improved the SSG in the meantime with an aluminum telescoping pin that is held by a screw inside the spring guide, along with a series of Delrin rings that fit between the screw and the spring guide that effectively limit the spring travel:



I've done some testing and the results I got are rather interesting, all starting from 3000 psi and using 14.3 grain Crosman hollowpoints:



The first column is using the stock hammer setup and there doesn't really seem to be a "cliff" at all.

Using the SSG with minimal precompression (still using the stock spring), I'm somehow getting higher velocities, although I fired 15 shots rather than the 25 for the stock setup so one can't really make a direct comparison.  Pressure drop is also in the same range.  I did a side 5-shot string with this setup using 30.1 grain Eley Magnum slugs and got an average velocity of 1005 feet per second, average energy of 67.5 ft lbs and a standard deviation of 6.54   

Limiting the SSG travel a little more drops the energy but still 2 ft lbs more average muzzle energy compared to the standard, and massively increased efficiency with an average of 36 psi pressure drop per shot compared 60 psi.  The difference in noise is also palpable.

Limiting the SSG travel even further drops the average energy by about 30% compared the standard setup, but that seems like a small price to pay for an astonishing 73% drop in air consumption!

jackssmirkingrevenge:
The SSG has been slightly modified to better stabilize it:







I tried it as is for 25 shots with 14.3 grain pellets starting from 3000 psi, and for another 25 shots with a 4mm spacer added to further limit the SSG travel, here are the results respectively compared to the same parameters with the stock standard hammer setup:



In terms of ft lbs muzzle energy per psi the difference is quite dramatic:

Stock: 0.71

SSG: 0.91

SSG + 4mm: 1.27

I think I will keep the last configuration, air consumption is just 60% of the stock while still giving about 7% greater muzzle energy

One caveat is that of course 14.3 grains is far too light a projectile for this level of energy, and those proportions will probably change with a projectile around twice the weight, but generally I'm extremely pleased with the result, it really demonstrates how much air is wasted with hammer bounce.

rsterne:
Good job, Jack!.... Once again showing how great the SSG is at conserving air....

The increase in velocity when you added the SSG may have been because the hammer was bouncing off the back of the valve in the stock configuration.... I have seen that reduce the dwell before, where reducing the preload on the hammer spring (no SSG) actually increases the velocity a bit....

Bob

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