A New Method for Increasing the Efficiency of a PCP - the SSG

[rsterne]

My guess is that the guide and spring assembly will travel as a pair with the hammer and add to the impact.... Don't forget that they are still together when the guide hits the (very light) stop, at which time the gap begins to open to about 0.020" (or whatever you set it at), and even if they came apart over that distance, the hammer then hits the valve and immediately slows down, and the guide catches up with it again.... before the poppet even has a chance to decompress and leave the seat would be my guess (it has to travel a few thou just to decompress).... The entire round trip for the valve (dwell) from beginning to end is only about 1 mSec (plus or minus) during which time it has to lift 1/16-1/8" and then close again.... so I don't think there is any question the guide will be travelling with the hammer from the time the valve opens until it closes.... After that, you are correct that you have two pieces rattling around loose, the hammer and the spring/guide assembly....

Bob

[Bobbieone]

Hi Bob , just an idea to run past you, been thinking down these lines for a while , but as I am now retired I have no access to machines to try it ,,
If we were to drive the hammer using two strong opposing magnets cotained in a plastic sleeve so little friction ,  the rear magnet could be on a adjusting rod ,
 once out of raange of the rear magnet this would act like the slingshot idea but no spring to bounce it back,
what you think ?  , also thanks to you and other members for some great ideas and reading, it keeps the grey stuff ticking over  ,

[rsterne]

I think that since magnetism drops off so quickly with distance it would not be suitable for the hammer stroke we need.... Also, it would be extremely hard to cock that last few millimeters.... Electronic solenoids have been used in lower powered guns, but they have an actual stroke distance under power.... I'm not so sure that if you had a permanent magnet strong enough to do the job if it wouldn't be just as prone to bounce as a spring anyway....

Bob

[zaphod621]

Original .25 Mrod was tuned BLT @ 2500 to 1800 fill avg 760fps 24 shots @4% spread and very evident hammer bounce burping. Not having the tap to thread end cap I drilled out the original spring tensioner to 1/4" the size of the bolt used for the spring guide. Used steel brake tubing as a sleeve to center original 6# spring. Removed stroke screw and installed set screw flush with hammer face and not protruding into hammer cavity. Shaped bolt head and polished guide for smooth cocking. Its about as simple as it gets and very effective, not to mention cheap.

Now @ 2300 to 1600 fill avg 750fps 40 shots @4% quieter and no burping, nice sharp pop sound. I fill with scuba or hand pump so this is perfect for me. I use it for small game and varmints so 31fpe is even overkill. Trajectory is predictable with a mil-dot scope.
Cat skinned successfully.

[musquat]

Hi guys, new to the forum and relatively new to modding, so please forgive my limited understanding.
I keep going back to bstaley's idea of the guide rod going through the hammer.  What if the striker on the front of the guide rod were large enough in diameter- say, half the diameter of the hammer- that when the hammer is at rest, the striker being flush and sprung against the front of the hammer would be enough to keep the guide rod aligned.  Then you wouldn't have to have a long channel to keep it aligned.  You could literally use a prod hammer drilled through for the guide rod.  True, you would loose a little hammer travel to the thickness of the front of the striker, but it wouldn't have to be that thick... maybe 0.1".  You could gain that in other places, like taking it off the back of the valve stem, or maybe if the front of the hammer is meaty enough you could countersink the striker into it.  The step inside the hammer only needs to be strong enough to retain the spring at full cock-it doesn't have to sustain any impact.  When you cock the hammer, the rear cap and the small hole in the hammer will keep the guide aligned. 

On my 2250 I am using a disco hammer spring and an RVA from a 2300S.  With the RVA adjusted all the way in, plus about .050" worth of lip on the spring guide, it's still not at coil bind.  There should be plenty of room for a stop nut in there.  I don't know how much preload that gives me, but I know it's enough to hold the valve open when not charged.

Besides being compact, with no rod out the back to pinch fingers, it also allows you to adjust the spring tension without affecting the gap.  If your RVA was large enough, you could screw it out, slide the guide rod out the back, adjust the spring tension nut, and re-set the RVA(which now is the gap adjustment) without further disassembly. True, you would loose some velocity when the hammer picks up the guide and spring, but you gain their momentum.  In the original design you loose velocity by accelerating the guide rod/spring/nuts and then loose their momentum before the strike.  It would be interesting to see how the two hammer strikes compare.  And you would have to mod/replace the hammer, but many of us have to do that anyway when we put a better trigger group on our 22xx or discovery.

Brandon

[rsterne]

Not sure how you can adjust the preload without affecting the gap.... To increase preload, you have to shorten the distance between the front and rear stop nuts, so you then have to screw the RVA / gap adjuster back in by the same amount to compensate.... unless I'm not understanding something....

EDIT: I understand now, it is the end of the guide that hits the RVA, the stop nut can be anywhere ahead of that, so changing the preload won't affect the gap....

Bob

[aPpYe]

Just read the thread and pick up on the earlier thoughts shared on WEIGHT that hammer spring must move tho have no effect on actual strike energy, and the need for enough strength of the stop rod being able to tolerate repeated impacts of decelerating the stop rod components.  ( Think small jack hammer ) and build accordingly.

Have fun !!

Heh...  I found this thread when the conversation was already two weeks in...  I am reading through from the beginning, but am only at post 100 or so, and this thread is on fire!  I want to absorb as many ideas as I can before doing this, as I see that a lot of variations on this idea have been put forth.  I got a lot of reading to do!!!

Here are all the major variations of the SSG that have been invented so far....

... Aaaand once again, thanks to Bob for being a heckuva guy!!!

[musquat]

In this setup, the front "stop nut" is actually the striker, which is actually just the end of the guide rod.  The other end of the guide rod goes all the way back to the RVA which sets the gap.  You could actually get away without an RVA- just measure from the valve stem to the rear cap, subtract the gap, and cut it to that length.  One drawback to this system is you can't independently adjust the preload and cocked spring tension.  As one goes up, so does the other.  Hope I'm not missing something obvious LOL!

Brandon

[zaphod621]

Bob, your not missing anything,
Since I  used the original spring tensioner and drilled it out with a 1/4" bit some of the original apex flats remain, enough to still be able to adjust the pre tension but I   have to take out the end cap and remove the guide to make adjustments, a pita to be sure. I just happened to luck out and can adjust the length with the jam nuts and still be at my chosen speed before hammer bounce occurs, but its close I can increase speed by backing out jam nuts to about 770 fps before i begin to hear the tell tale burp. When I backed jam out all the way was getting about 825fps and all kinds of bounce.  Have not tried increasing preload yet to see where that takes things. I am just thrilled with how it shoots now, for now. Never leave well enough alone.

[rsterne]

I went back and included the bstaley suggestion in the compilation in Post #356.... my apologies for missing it the first time around.... 

Bob

[BigTinBoat]

Now @ 2300 to 1600 fill avg 750fps 40 shots @4% quieter and no burping, nice sharp pop sound. I fill with scuba or hand pump so this is perfect for me. I use it for small game and varmints so 31fpe is even overkill. Trajectory is predictable with a mil-dot scope.
Cat skinned successfully.

So you are over 31FPE with an efficiency of 2.0 FPE/cuin? Doesn't seem possible, Mrod's in .25 will be flying off the shelves

[shorty]

Zaphods 2.0 efficiency is plausible.

Heck, I am already hovering around 1.8 efficiency with a 25 to 30 fpe tune in .22 cal using a short stiff spring with a few other changes.

Add a sort stiff hammer spring or SSG, a heavier than stock poppet return spring and port correctly will get you in the efficiency range of 1.5 and greater.

And you are right,
Mrods should be flying off the shelf with that kind of marketing/perfromance. Unfortunately, crossman doesn't have mad scientists like us working at their facility.

[clgraham82]

Tons of great info on this mod (tons of it over my head  ) wondering when the YT videos are gonna start popping up on how it's being done and results...

[zaphod621]

I  correct my speed, it is 750fps peak not average. Low was 720 and average was 740 with a total of 43 shots. I got over 5 magazines with this fill. Another correction my fill was 2500 down to 1500, I  wrote down the guns gauge instead of the tanks correct gauge. Gun is about 200psi off. I wrote down 2300psi when i was within 2% of peak for 30 shots down to 1600psi. Sorry for the confusion but still an impressive improvement.

[moorepower]

Before a mfgr makes this available it will have to be be pleasing to the eye and hand. I love the idea and will implement it, but most of what I have seen are not attractive.

[BigTinBoat]

I  correct my speed, it is 750fps peak not average. Low was 720 and average was 740 with a total of 43 shots. I got over 5 magazines with this fill. Another correction my fill was 2500 down to 1500, I  wrote down the guns gauge instead of the tanks correct gauge. Gun is about 200psi off. I wrote down 2300psi when i was within 2% of peak for 30 shots down to 1600psi. Sorry for the confusion but still an impressive improvement.

OK so now it's 1.47...........a bit more believable to go from 1.24 to 1.47 and not 1.24 to 2.0

[PakProtector]

 I really like the idea that all the work the spring does gets to smack the hammer, instead of a large percentage of it going to waste....
Bob

Bob,
How much is required for this weight to be, 'large'? With an AL guide( that is at present waaay to long), and two 10-32 nuts, I have 120 grains, or roughly 8 grams....about 10% of the marauder hammer.
cheers,
Douglas

[rsterne]

I have only used steel guides, that are as large as I can get to slide freely in the spring.... so they are a pretty big percentage of the total weight.... Obviously with the original version, the less the guide assembly weighs, in relation to the hammer, the better.... That is one of the reasons I want to try the last version I drew in Post #356.... I frequently use spring guides that ride with the hammer, with a front the same as we are using now, captive between the hammer spring and hammer.... and those add to the weight of the hammer, increasing dwell, which in the more powerful guns I am often chasing, helps.... That version will share that advantage....

Bob

[Motorhead]

On that note ... As i'm tweaking original small screw diameter stop rods have incorporated Acetal Spring I.D. guides.
It is nothing more than a fitted to spring I.D. sleeve with a shallow shoulder spring seats against.  Placed at REAR against end cap so it remains stationary.  It's length adjusted so upon spring compression during being cocked it does not interfere with hat holding spring at hammers end.
This has fully controlled spring cant and vibration allowing stop rods size/mass to remain very small.

[PakProtector]

I got the .224 running with the SSG. Plastic rear nut to the end cap, and 2x 1.5", .059 springs at .420 OD. Without going nuts on preload it shoots quite consistently at 960 fps using 225107, 40 gr slugs. It is more accurate than I remembered; few sighters, and I drilled a 9V battery right in the middle at 50 yards. Going to try it on the squirrel population reduction program tomorrow...

I will also run a string and see how the numbers look with a 23" barrel.
cheers,
Douglas