Author Topic: SSG and results  (Read 18597 times)

oldpro

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Re: SSG and results
« Reply #15 on: January 19, 2016, 10:26:30 PM »
 I had and interesting thing happen tonight when high power tunning the SSG that I havent quite figured out I hope Bob Sterne chimes in and bails me out here. Anyway I wanted to set the SSG at a very high power tune and was shooting 25.4 grain pellets around 990fps and wanted to back it off a bit to get it to 950ish(I have my reasons) instead of taking the guide clearence rod adjuster off and resetting the tension adjuster I just gave the clearence adjuster more free play and instead of going slower it climbed up 30 fps so Im thinking maybe im above the knee of the curve but nope It stayed right there till It fell off the knee. So I refilled and did it again same results HHHHMMMM Im missing something or im just tired its late.

rsterne

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Re: SSG and results
« Reply #16 on: January 19, 2016, 10:46:14 PM »
You may have a slight misalignment problem, and a half turn on the adjuster caused some drag.... and then another half turn got rid of it.... well vice versa, actually.... When you backed of the gap aduster, the hammer ran more freely, and the velocity increased....

Otherwise, I got nuttin'

Bob
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oldpro

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Re: SSG and results
« Reply #17 on: January 19, 2016, 10:53:20 PM »
Its a very loose fit so not likely and the numbers where to constant threw the string both runs...Im missing something.

oldpro

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Re: SSG and results
« Reply #18 on: January 19, 2016, 10:56:09 PM »
 Is it possible that the added clearence let the rod build more momentum and acted like a heavier hammer? Im using the internal SSG like above. Dammit im going back out and try it again or I wont sleep.
« Last Edit: January 19, 2016, 10:58:55 PM by oldpro »

Motorhead

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Re: SSG and results
« Reply #19 on: January 19, 2016, 11:08:20 PM »
Just came in from the shop redoing my .25 cal BAM 50 hammer configuration / SSG devise for a second try.
Increased hammer weight from 30 grams to 38 grams, made spring cavity 1/4" shallower to get more spring preload with the same spring used previously.

Wala we got MAJOR POWER with rifle going from 890 fps with 25.4 kings to 925 fps now.
Rifle really seems no more effecient ( Same as first SSG attempt in this particular rifle ) but at least now were at and exceeding previous power level.   48 ft lbs with a JSB king at 925 fps is moving right along  ;)
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oldpro

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Re: SSG and results
« Reply #20 on: January 19, 2016, 11:22:52 PM »
That will get a squirrel out of a tree!!! I had to shoot a gray 3 times today with the .22 to get him to fall, dam there tough animals. Might have to do a carbine .25 for squirrels around here. The SSG is a billion times easier to tune than standard spring pocket gun dont you think Scott. I was going to go out to the shop but decided id drink a beer instead plus its DAM cold out there lol. Tomorrows another day Ill figure it out.
« Last Edit: January 19, 2016, 11:28:53 PM by oldpro »

rsterne

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Re: SSG and results
« Reply #21 on: January 20, 2016, 10:01:38 AM »
After a nights sleep (I do my best work in bed)  ;) .... I have an idea what might be happening....  It's possible that with the style SSG you are now using (where the hammer slides on the guide, and it is the front of the guide that strikes the valve).... that if the gap is really small the guide doesn't have a chance to really get moving before it strikes the valve stem.... so what the hammer sees is in effect just a really heavy poppet (the weight of the poppet and guide combined).... As you back it off a bit, the guide has a chance to get moving faster, and there is a point where the velocity peaks.... and then as you increase the gap further it drops as you would expect because you are compressing the spring less, reducing the peak cocking force, and storing less energy in the spring....

In the extreme case with, say 1/8" preload on the guide instead of a gap, the guide and poppet move as one heavy chunk, being struck by the hammer only.... instead of a very light poppet being struck by the heavier combination of hammer and guide.... It only makes sense it would react differently in the two situations....

Bob
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oldpro

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Re: SSG and results
« Reply #22 on: January 20, 2016, 10:19:22 AM »
 Thats it my friend. I just finished testing and if I go back further with rod gap it slows so there is a sweet spot at around 40-50 thou. I had it around 20-30 thou. before. The string looks good either way it just is faster at 40 thou clearance.

rsterne

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Re: SSG and results
« Reply #23 on: January 20, 2016, 10:55:51 AM »
We may not know for sure the exact mechanics of what is happening.... but at least have a plausible theory that supports the facts.... I would assume if you use a different preload, the maximum velocity reached at the peak will be different.... Too bad you can't come up with one adjustment that will leave the gap at the ideal 0.040" and just change the preload.... hmmmmmmmmmmm....

How about if the barrel you use for adjusting the gap had a socket in the end that simultaneously turned the preload nut?.... If they were the same thread pitch, the gap would remain the same and only the preload would change.... If you needed to change the gap independently, you could remove the end cap, turn the gap barrel (but not the preload) and slide it back together again.... All you need is some "simple" socket arrangement that will turn the preload adjusting nut as you adjust the barrel, and the same pitch on both parts.... You would have to hold the guide to prevent it from turning, of course....

Bob
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Windmeister

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Re: SSG and results
« Reply #24 on: January 22, 2016, 12:52:06 PM »
I've been doing some testing (500 rounds worth) on the "standard" SSG configuration, where the stop nut is in the back, and separate from the hammer.
When I increased the spring force to where I wanted the power to be, I noticed my accuracy went down. I removed the obvious variables, LDC, Baffles, Stripper, checked for alignments, etc etc. Barrel is a nail driver, so I know that's not it, and it's CF sleeved, I did check the crown, and such.
But the trouble remained, on the "brick" my rest, at 30yds, it would shot 2-3 even 5 shots in one single hole left from the first pellet, then all of a sudden strays, with no real pattern to it. As mentioned I started to chase the problem in the usual places, but couldn't find a solution. went back to a regular spring setup and problem disappeared.
After looking at the mechanics of it, it's kinda obvious now.
The regular SSG using the rear tube as the backstop for the spring guide, meaning there is a good jolt inflicted on the chassis, before the hammer hits the valve and releases the shot. This jolt/vibration propagate through the gun as the shot is released, which is not optimal for accuracy.

My latest design combat this by moving the mass and mechanics onto the hammer instead. The rear "Pink" delrin stop piece never move until the spring is almost to it's full travel, so there is virtually no drag. It has the added benefit that by threading the rear of the guide, you can still have all the adjustments to compression rate available without taking anything apart. Only when you have to replace the spring, for whatever reason, do you need to remove the rear cap and undo the spring guide from the hammer.

Uncocked:

 
Cocked:

rsterne

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Re: SSG and results
« Reply #25 on: January 22, 2016, 03:21:52 PM »
I haven't done any accuracy testing, we are up to our knees in snow right now.... but for a different reason I am working with a newer version of the SSG as well.... I am using a version which effectively does the same as yours, but the guide is not fastened to the hammer.... It looks like this....



Think about is as the way you are doing it, but without the guide fastened solidly to the hammer, it just pushes against it.... The weight of the guide travels with the hammer, and no energy is wasted accelerating it and then having it crash to a halt against the end of the tube.... All it does is pick up the weight of the very light collar just before hitting the valve stem.... In addition, it doesn't stick out the back anywhere near as far, nothing to catch your fingers with, but you can still get a cocking indicator if you wish.... The added advantage is that you don't need as high a cocking force, as no energy is wasted.... The first time I used this, I had a choice of less preload or getting more energy from the hammer and being able to use a heavier pellet (guess which I picked)....  ;D

Bob
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Windmeister

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Re: SSG and results
« Reply #26 on: January 22, 2016, 04:37:53 PM »
Looks good Bob, only concern I have, and this might be negligible. When the hammer pulls fwd, it could have some variable friction drag caused by the nature of the loose guide.

rsterne

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Re: SSG and results
« Reply #27 on: January 22, 2016, 06:14:23 PM »
I think there is a lot less chance of that than the hammer cocking in the tube and causing a rigid guide to drag at the back.... I have built rear-cockers, and they are a PITA to get to run freely.... Besides, the guide and hammer move together until the hammer reaches the gap, which is only 0.020-0.040", at which point the guide picks up the light collar.... a few microseconds later, the hammer hits the end of the valve stem, and the guide catches up with it again (if it ever in fact left it).... and all of the moving weight opens the valve....

Bob
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oldpro

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Re: SSG and results
« Reply #28 on: January 22, 2016, 10:22:19 PM »
Ive built a few now and many ways to boot and the best results have been with very loose fitting sliders. I now do not put any kind of sleeve but simply use and over sized hole and let the spring and plunger align on their own under tension. The least amount of contact the slider has on the follower the better under load.

rsterne

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Re: SSG and results
« Reply #29 on: January 23, 2016, 04:40:14 PM »
I pulled apart my 2560 today and swapped it over to the new style one with the internal stop.... Here are the old and new parts....



I am now using a 10-32 machine screw with a piece of 7/32" OD tubing slid onto it for the guide.... Then you slide on the spring and an aluminum collar that hits the end of the gap adjusting bolt when cocking the gun and compresses the spring.... The stop nut is turned from a piece of 5/16" rod, drilled and tapped 10-32 and tightened against the end of the brass tube.... I start out a bit longer than I need and keep shortening the tube until I can get the gun shooting on the plateau with no gap.... Once I get the right length, I install the stop nut with a drop of blue Loctite, tightened against the end of the tube.... The stop nut has a slot in the end for this purpose.... The gap adjusting nut is drilled just over 5/16" because the stop nut has to slide through it.... The end cap is tapped 7/16"-20NF for the adjusting bolt, and then counterbored just over 7/16" to miss the cocking collar.... At the bottom of the photo is the original SSG I made.... You can see how much shorter the new guide is.... Below is the new SSG assembly, ready for installation....



When the gun is uncocked, the stop nut is recessed about 1/2" inside the gap adjusting bolt, so you can't see it.... Compare this with the one above, where the stop nut and bumper O-ring (no longer required) are outside the gap adjusting bolt.... Below is what the gun now looks like when cocked....



This installation is much cleaner, and there is no way you can pinch your fingers like could happen with the old one.... However, you still have a cocking indicator because the stop nut (the part with the slot) is visible when cocked.... With no gap I had about 985 fps, which I could adjust down to whatever I wanted.... At 1-1/2 turns out the velocity was just over 900 fps and the gun was very quiet.... I ended up about 1 turn out, with a average velocity of 960 fps, the same as I had before.... I might have lost a couple of shots compared to the first SSG, but I have still gained about 40% more shots per fill than without the SSG.... and I no longer have to worry about pinching my fingers and I can wrap my thumb over the wrist of the stock again because is it so much more compact.... The efficiency is around 1.40 FPE/CI....

Bob
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