Author Topic: A New Method for Increasing the Efficiency of a PCP - the SSG (Read 373403 times))

cilami · « **Reply #180 on:** January 06, 2016, 08:39:56 PM »

Quote from: oldpro on January 06, 2016, 08:38:33 PM

Next on the list will be the Prod.

That's good news!

oldpro · « **Reply #181 on:** January 06, 2016, 08:44:28 PM »

Douglas I'm using a smaller OD spring so it both fits threw the end cap and never touches the sides of the hammer. http://i.imgur.com/LeCpnrth.jpg this is a cassette style that allows for easy spring changes.

rsterne · « **Reply #182 on:** January 06, 2016, 10:03:03 PM »

I've been using a large enough RVA bolt that I can change the spring from the back ever since I built my SECOND one in 2008.... It is just sooooooooooo much easier to not have to pull the end plug off the back of the gun.... With the SSG, they end up being a cartridge that just screws in, in one piece, with the preload already adjusted.... I'm guessing if you choose the correct length and wire spring, and get the preload so that it will reach the velocity plateau the gun is capable of.... all that will be needed will be to adjust the gap for different velocities by how deep you screw in the cartridge.... Travis, I think you have the right approach.... Are you going to make a screw-on cover that threads onto the end plug?....

Bob

oldpro · « **Reply #183 on:** January 06, 2016, 10:40:55 PM »

Im going to make a screw on half shell that covers the top of the SSG it will block any misplaced fingers but not require the stock be ground to fit so its reversable if one wants to sell their gun or put back to stock.

rsterne · « **Reply #184 on:** January 06, 2016, 10:43:38 PM »

Makes sense.... I just Googled Airgun SSG, and there are several hits on it on the various Forums I post on.... That didn't take long !!!

Bob

tefloncoated · « **Reply #185 on:** January 06, 2016, 10:44:49 PM »

A Russian airgun enthusiast created a piston gas/air version. Same exact idea of a free floating hammer.

http://forum.guns.ru/forummessage/25/1662795.html

and a video:

The device is filled with an air compressor or a hand pump. A fill of 9psi gives you a pre load of 4kg or about 9lbs.

Due to Russian regulations on air guns (similar to UK regulations) he also added the "anti cop device" - a finger tight nut to quickly release the air pressure inside the piston and render the air gun inoperable.

rsterne · « **Reply #186 on:** January 06, 2016, 10:54:06 PM »

I don't understand a word of Russian, but it looks like he is using a small Gas-Ram.... It would work in the same way, providing it was adjusted to have a small gap with the hammer free floating.... We discussed this concept in the thread on the XS-60C PCP Repeater last July, which led me to building the first SSG for my Grizzly.... to emulate a Gas-Ram using a preloaded spring.... It all started here.... http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.1040 with full credit to stalwart for asking the question in the first place.... Post #1047....

Bob

rkr · « **Reply #187 on:** January 07, 2016, 01:07:13 AM »

Quote from: oldpro on January 06, 2016, 08:44:28 PM

Douglas I'm using a smaller OD spring so it both fits threw the end cap and never touches the sides of the hammer. http://i.imgur.com/LeCpnrth.jpg this is a cassette style that allows for easy spring changes.

While looking at that picture I started to wonder, is that rod actually guiding the hammer as it goes - i.e. is it rigid enough to keep the hammer centered in the bore and thus giving you the zero fps spread?

oldpro · « **Reply #188 on:** January 07, 2016, 02:03:54 AM »

No its not rigid at all actually. I went first with a very rigid strait push SSG that ran in a tight bore but wasnt getting enough fps so I took the bushing out of the rod carrier and thats when my FPS came up and I started getting real good numbers. What I think is happening is that a hammer is held at the bottom by the sear and this cocks the hammer slightly down with the spring pushing from the center. By allowing the SSG to free fly and self align to the off center hammer it actually is faster and has less drag plus the hammer being cocked isnt putting a side load on the free floating rod. This of course is all conjecture and further testing needs to be done. I believe not having any spring contact on hammer walls and no contact of spring on spring adjuster allows the spring to function in a almost perfect state. So the only thing that can now effect velocity is fill pressure and hammer drag. I polished the hammer bore and lubed hammer to make it as close a constant as possible, so now we mainly have just fill pressure to deal with and because there is no hammer bounce and no spring drag the psi used per shot is very consistent thus the 5 shots in a row with no fps difference but that only happened once to be honest but still only seeing a few feet difference per shot in the sweet spot of the curve. More testing and more changes to SSG will help answer some questions I have now.

Motorhead · « **Reply #189 on:** January 07, 2016, 02:26:40 AM »

Quote

By allowing the SSG to free fly and self align to the off center hammer it actually is faster and has less drag plus the hammer being cocked isnt putting a side load on the free floating rod.
I believe not having any spring contact on hammer walls and no contact of spring on spring adjuster allows the spring to function in a almost perfect state.

Yup, completely agree

Gerard · « **Reply #190 on:** January 07, 2016, 02:46:26 AM »

Yup, same here. Working on one of these for my 2240 I found that the rod was binding just slightly as it was an easy but minimally wiggly fit through the larger bolt. Running some 150-grit sandpaper on a rod through it on a drill for a little while opened the hole enough so it's still a decent fit, not sloppy, but slack enough that the tilt to the striker when cocked doesn't cause it to bind at all.

oldpro · « **Reply #191 on:** January 07, 2016, 02:51:03 AM »

Fantastic Gerard its nice to have data to back up a theory. I also found a slightly larger pin head on rod contacts lower on hammer forcing it up and strait into bore faster. Ill take pics Im not sure if im explaining it well.

Gerard · « **Reply #192 on:** January 07, 2016, 02:54:49 AM »

After threading the nut on the fixed end and peening it out, I ground the nut into approximately the same shape as the inside end of the Crosman hammer recess. So a very shallow cone. Wasn't trying for a super-exact fit or anything, it just seemed sensible that it should square up against the end of the hole more or less. A flat end makes sense to apply to different shaped holes in different hammers.

Motorhead · « **Reply #193 on:** January 07, 2016, 02:56:50 AM »

Something that may be relative to keeping hammer traveling straight and true in spite being held at full cock tilted.

BY PUSHING ON IT on the broadest diameter practical, which would be very close to the spring bore diameter of the hammer.
Once hammer released the push of the spring VIA THE STOP RODS END is full perimeter and NOT just a central contact point.

oldpro · « **Reply #194 on:** January 07, 2016, 03:05:43 AM »

Ok so imagine striker rod inside bore of hammer as you can see if the hammer is cocked slightly down in the bore by the sear the contact spot will be low on wide head of striker forcing it to become concentric to bore http://i.imgur.com/1nbJJw3h.jpg like this http://i.imgur.com/SC6aCKxh.jpg thus less drag on hammer down bore. with stock spring set up the spring just deflects more causing more cocking and more spring drag.

Motorhead · « **Reply #195 on:** January 07, 2016, 03:24:49 AM »

What you need to keep mind of is that spring directly IS NOT DRIVING THE HAMMERS MOTION .... The end or Hat of stop rod is.
If Hat and rod are rigid traveling in alignment with hammer bore within main tube the only cant spring can have is some side to side motion. By virtue of Hat & rod traveling straight and true having contact between hat and hammer on a large contact diameter, once hammer is released the force across there contact point squares them up and propels them as one towards poppet stem with minimal or any tilt present.

rkr · « **Reply #196 on:** January 07, 2016, 04:14:15 AM »

Quote from: Gerard on January 07, 2016, 02:54:49 AM

After threading the nut on the fixed end and peening it out, I ground the nut into approximately the same shape as the inside end of the Crosman hammer recess. So a very shallow cone. Wasn't trying for a super-exact fit or anything, it just seemed sensible that it should square up against the end of the hole more or less. A flat end makes sense to apply to different shaped holes in different hammers.

I'm wondering if a delrin nut at the rear cap would withstand the forces here, it would provide much less friction.

Tomg · « **Reply #197 on:** January 07, 2016, 09:44:04 AM »

I dont use a delrin cap. But I am using a delrin stop nut. And it works good.

Bullfrog · « **Reply #198 on:** January 07, 2016, 10:12:02 AM »

Quote from: oldpro on January 07, 2016, 02:03:54 AM

By allowing the SSG to free fly and self align to the off center hammer it actually is faster and has less drag plus the hammer being cocked isnt putting a side load on the free floating rod.

Does this mean you are running your SSG without an insert in the gun's end cap to keep the rod centered?

Tomg · « **Reply #199 on:** January 07, 2016, 10:30:37 AM »

Pictures of mine, with the delrin stop plug on my Discovery.

I realized the cocking effort was suffering a little bit since I used to use the end of the rear tube for my thumb leverage. Which I fixed by making a thumb recess:

Ps. Before anyone asks, the thing on the cocking bolt is an spring loaded adjustable depth pellet seater.
The first prototype of this can be seen here: http://vid54.photobucket.com/albums/g97/renderbrandt/20150704_205527.mp4

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

Author Topic: A New Method for Increasing the Efficiency of a PCP - the SSG (Read 373403 times))