Canadian Airgun Forum

The #1 Community for Airguns in Canada!
It is currently Wed Nov 13, 2019 7:57 am

All times are UTC - 5 hours


The Canadian Airgun Forums are a place for people to discuss and learn about airguns and the airgunning sport in Canada. There are lots of discussions about airguns, airgun accessories, reviews, modification and repair information, airgun events, field target and free classifieds!

 

You need to register before you can post: click the register link to proceed. Before you register, please read the forum rules. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload your own pictures, and access many other special features. Registration is fast, simple, and absolutely free! To start viewing messages, select the forum that you want to visit from the selection below.








Post new topic Reply to topic  [ 126 posts ]  Go to page 1, 2, 3, 4, 5 ... 9  Next
Author Message
PostPosted: Thu Dec 31, 2015 1:05 am 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
A while back on my .30 cal Grizzly HPA I tried a new system on the hammer spring.... It rides on a guide that is adjustable in length and comes to a positive stop just before the front of it hits the inside of the hammer.... The idea is to use a long, light hammer spring, which is easier to cock, and preload it on the guide.... This increases the initial cocking force, but reduces the final cocking force, making the gun smoother and lighter to cock.... What I thought I achieved was also a reduction or elimination of hammer bounce, which reduced wasted air and increased the efficiency.... I used the same design in my new Monocoque PCP, but of course it is yet untested.... So I decided I would take a gun I was familiar with and build one of these guide stops to see if I could document any increase in efficiency.... BOY, DID I !!! ....

The gun is a 2560.... ie a 2260 converted to a PCP, with a .25 cal LW barrel on it.... The valve has been hogged out, and the gun breathes extremely well.... The standard setup is a 1.75" x 0.040" wire spring on a Challenger Power Adjuster (RVA).... I use this gun for testing because it has a small reservoir so I don't have to shoot a lot to test changes, but it is big enough at 65 cc to not lose power in this .25 cal setup which is tuned for about 50 FPE with 25.4 gr. JSB Kings.... Here is a plot of the Velocity vs Preload with the gun tethered to a regulator with a 1900 psi output (actually 1880 according to the gauge I used for these tests)....

Image

As you can see, this is pretty much the perfect spring for the gun, and the knee of the curve, where the gun starts gaining efficiency without losing much velocity, is at 4-5 turns out from coil bind.... I then chose a setting of 5 turns out and shot a string with the gun tethered but the SCUBA tank turned off.... The hoses were full, one going into the regulator and the other out, along with a gauge, so the total volume works out to 90 cc.... I got 5 shots starting at 938 fps, peaking at 950, and ending at 904 fps, and the pressure at the end was 1120 psi, so the gun used 760 psi of air, and got an efficiency of 0.85 FPE/CI.... While this in not great, don't forget that this a 50 FPE string from 1880 psi down to 1120.... I couldn't hear any hammer bounce on the first shot, but as the pressure dropped I heard more and more of that telltale B-RR-AAA-PPPP indicating it was wasting air.... I then installed the new preloaded setup, which uses a 2200 hammer spring with 0.80" of preload, which works out to over 5 lbs.... However, the maximum force to cock the gun is only 9.5 lbs. instead of over 10.6 lbs. with the original setup, which had a preload of less than 1.5 lbs.... Here are the two setups tested....

Image

You can see the guide, made from a 3" long piece of 3/16" drill rod, threaded 10-32 on both ends.... The front nut is turned down to fit inside the hammer, and at the rear are two nuts locked against each other to adjust the preload.... The 3/8" hex head bolt is drilled through for the guide, and allows you to position the front of the guide just clear of the inside of the hammer.... It is longer than needed, and if shortened 1/4", the guide could be shortened the same amount, making it more compact.... Here are photos of the gun, first uncocked, and then cocked, so that you can see what is going on....

Image


Image

The small O-ring just acts as a cushion when the guide crashes to a halt.... The hammer then carries on, coasting on its own to open the valve to the appropriate lift and dwell.... The magic occurs on the return trip.... Since the spring is not touching the hammer while the hammer is touching the valve stem, as the valve closes it does not store any energy in the spring.... When the valve closes, the hammer has to move a bit further before it touches the spring guide, but instead of having a spring with little or no preload, which is easy to compress, it hits the end of the guide, which can't move unless you push on it with over 5 lbs. of force.... so it doesn't budge.... the hammer rattles to a stop between the valve stem and the spring guide, and doesn't have enough energy to open the valve for a second time.... No hammer bounce, so no wasted air, and instead of 5 shots.... I got 7, and used less air doing it.... While the shots got louder as the pressure dropped, as expected, NONE of the shots, even the last one at the lowest pressure had that telltale burp of wasteful hammer bounce.... Here are the two shot strings....

Image

The two curves on the graph are the average of two strings each, where individual shots only varied by a few fps.... You can see that the starting velocity at 1880 psi is the same, but look at how fast the pressure drops with the original setup, compared to the new one with the preloaded guide that stops before the hammer hits the valve.... Instead of using 760 psi for 5 shots, the gun now uses only 620 psi for 7 shots, starting at the same 1880 psi and ending at 1260.... This gives an efficiency of 1.48 FPE/CI.... which is absolutely stunning for a 50 FPE gun at these pressures.... I NEVER expected to see such a huge difference.... It sure shows how much air a PCP can waste if the hammer is bouncing enough to hear it....

I shot a 10 shot string with the gun tethered at 1880 psi, and the ES was just over 1%, about 11 fps.... That is pretty typical.... One thing I noticed is how fussy the preloaded setup is to tune.... The amount of preload is the "coarse" adjustment, you have to get enough so that the average spring force, with the longer, weaker spring, is a bit more than the standard setup.... I found that the best setup for the clearance between the end of the guide and the inside of the hammer, in this case, was very close, about 0.030".... This may have to do with the rather short hammer stroke on a Disco, about 0.67" on this gun (and that is longer than stock).... It turns out that each flat on the adjusting bolt (about 0.010") is about 10 fps of velocity.... Coil bind with this spring was about 985 fps.... One thing I have done on the Monocoque PCP, which I think is a good idea, is to drill the inside of the hammer large enough that the spring and the end of the guide cannot touch the sides of the hole.... so that there is no chance of extra drag on the hammer.... It does, after all, have to open the valve while coasting....

This setup worked so well that I plan to retrofit all my PCPs eventually.... It does take a bit of extra length to accomdate the hammer spring, because you need a longer, weaker spring.... but not excessively so.... How can I pass up the opportunity to use something that, in this case, improved the efficiency by 74%.... We do need to come up with a good name for it, though....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 1:13 am 
Offline
User avatar

Joined: Fri Sep 23, 2005 2:29 pm
Posts: 6186
Location: Okanagan,BC
The Sterne Preload Wonder Adjuster

:wink:


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 3:18 am 
Offline
User avatar

Joined: Sun Jul 15, 2012 10:49 am
Posts: 6029
Location: Victoria, BC and Clarkston, WA
Drop the Wonder. Even though it is a great improvement forward!

You'll have to tell us the source of the spring, Bob.

_________________
-Rick
Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 3:19 am 
Offline
User avatar

Joined: Fri Sep 23, 2005 2:29 pm
Posts: 6186
Location: Okanagan,BC
rrdstarr wrote:
Drop the Wonder. Even though it is a great improvement forward!

You'll have to tell us the source of the spring, Bob.


Well...it's a wonder to me!

But then just about all of Bob's stuff is a great wonderful mystery to me,

:mrgreen:


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 11:43 am 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
I used a hammer spring from a Crosman 2200.... It is 2-1/4" long, made from 0.036" wire.... However, that was to replace a 1.75" x 0.040" wire spring that is stiffer and shorter than a Disco spring because of the larger valve ports for the 50 FPE .25 cal setup..... On a stock Disco, you would likely need a lighter spring, you might get away with one from a 13XX / 2289 ?.... Basically you are looking for a longer, lighter spring than whatever you are replacing.... That is because you need to preload it to at least 1/3rd of the force when cocked.... You might be able to do it by just preloading the spring you have, but that will make the gun harder to cock, not easier.... If you did that, you would have to use a larger gap between the hammer and spring guide to get the hammer strike back to where you were....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 12:17 pm 
Offline

Joined: Wed Jan 05, 2011 12:35 pm
Posts: 6000
Location: P.G. B.C.
Yeah, thanks Bob - now my brain hurts - think I'm gong to use only springers from now on.

_________________
Best Wishes
Daryl


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 2:05 pm 
Offline

Joined: Tue Jul 22, 2014 5:25 am
Posts: 361
Location: Canada
That's a very interesting mod Bob.

Maybe you could call it (SP-RVA)

_________________
Tazz


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 2:53 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
One name that comes to mind is "Slapshot" like in Hockey!.... *LOL*.... Wind that hammer up and let it fly!....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Thu Dec 31, 2015 2:56 pm 
Offline
User avatar

Joined: Mon Feb 11, 2013 12:46 am
Posts: 4116
rsterne wrote:
One name that comes to mind is "Slapshot" like in Hockey!.... *LOL*.... Wind that hammer up and let it fly!....

Bob


lol....the more curve on the stick the more it will fly.... :lol: :wink:

_________________
"A candle loses nothing by lighting another candle"

Image


Top
 Profile  
 
PostPosted: Fri Jan 01, 2016 9:39 am 
Offline

Joined: Wed Sep 10, 2014 2:42 pm
Posts: 147
Location: Ontario
This is very interesting. I already tapped mine and used a 3/8 bolt , which itself was drilled and tapped for my knurled adjusting screw. I did this to be able to unscrew the 3/8 bolt to change springs on the fly for tuning. I just wonder if your setup would benefit from a locking nut on the 3/8 bolt. My setup has the bolt tight with a locking nut on the adjusting bolt. If I build your guide I could easily change over and test it. Sounds like a project for the new year.

Image


Top
 Profile  
 
PostPosted: Fri Jan 01, 2016 11:17 am 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
I haven't installed it yet, but I will be adding a plastic plug under a setscrew as a brake to prevent the 3/8" bolt from self-adjusting.... Yes it's handy having the bolt large enough to allow changing the spring, I have always done that on every RVA I made myself....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Jan 02, 2016 12:59 am 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
I tried this idea on a regulated PCP today, and it went very well.... The gun was my QB79 Ninja, regulated at 1200 psi, that shoots 25 FPE with 15.9 gr. JSB Exacts.... I used two 1.75" x 0.040" springs on a 7/32" guide, giving a total spring length of 3.4" and a rate of about 7 lb/in.... I tried three different amounts of preload, 0.70", 0.80", and 0.90", and adjusted the position of the end of the guide from 1 turn of compression against the hammer to 3 turns of gap (24 TPI), so the total range of adjustment in position was 0.167".... Here is what happened....

Image

You can see that the maximum velocity this gun can reach is ~850 fps with these pellets.... As I increased the preload, the velocity at any given gap between the end of the guide and hammer increased, as expected.... For instance, with 2 turns of gap (0.084"), the velocity with 0.70" of preload in the spring was 760 fps, with 0.80" of preload it was 790 fps, and with 0.90" of preload it was 820 fps.... With the guide just touching the inside of the hammer, the velocities were 836, 840, and 845 fps.... and with the guide pushing on the hammer (actual preload on the hammer at rest), the velocity was within 2 fps with all preloads, about 847 fps....

The interesting part of the graph above, is the efficiency curves (the dotted lines).... With the guide pushing on the hammer, the efficiency was horrible, about 0.55 FPE/CI.... I think what is happening is that the large amount of preload is slowing the closing of the valve, and causing what amounts to a dump shot.... Once the guide is clear of the hammer, however, the efficiency is greatly improved.... With it just touching, it is 1.15 FPE/CI, which is about the same as I used to get on the knee of the curve with the original setup.... As soon as there is a gap, and it doesn't need to be much, just 1 turn (0.042"), the efficiency is great, between 1.27 - 1.32 FPE/CI at all preloads.... The efficiency at any given velocity is slightly better with more preload, which to get that same velocity requires more gap between the hammer and the guide....

I ended up using the 0.90" preload and 1/2 turn of gap (just 0.020") between the end of the guide and the inside of the hammer.... This gave me 843 fps (25.1 FPE) at an efficiency of 1.27 FPE/CI, which is better than I had with the original setup.... The ES, at 10 fps over a 20 shot string, is a bit better, and the SD is definitely better than before, with by far the majority of shots being within about 4-5 fps, with only the occasional high or low shot.... possibly due to differences in individual pellet weight or fit.... All in all, I am very pleased with the results.... It would appear that this setup does, indeed eliminate hammer bounce.... I think the efficiency graph, being so flat once there is a gap, proves that point....


Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Jan 02, 2016 1:01 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
We have dubbed this device the "Stopped Spring Guide" or SSG for short....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Jan 02, 2016 7:43 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
Yesterday and today I worked on fitting an SSG to my QB Ninja.... The gun is regulated at 1200 psi, and is modified to cock-on-open.... The best previous tune delivered 81 shots at 850 fps from a 13 CI tank filled to 3000 psi and refilled at 1100 psi.... For the preloaded spring for my "Stopped Spring Guide" modification I used two 1.75" x 0.040" wire springs on a single 7/32" guide, with 10-32 nuts both ends (the front one turned to fit inside the hammer).... The adjusting bolt is a 3/8" - 24 NF bolt drilled for the guide, and it is carried in a short piece of aluminum which is bolted inside the QB tube.... Here is the previous cock-on-open RVA, and the new SSG setup, positioned relative to each other the way they sit inside the tube....

Image

In the uncocked position, you will notice that the end of the guide is basically flush with the end of the tube, but of course it sticks out when cocked.... I cured that later, as you will see below.... There are two screws to mount the aluminum block in the tube, a short one on the bottom and a long one on top, that goes through the breech and holds it down.... Since I didn't need the back part of the bolt that normally moves the pin for the cocking block, I cut it off flush with the back of the setscrew that holds the bolt handle, and the hole for the top screw for the SSG is immediately behind the bolt when fully back.... You can see the relative positions of the parts in the photo below....

Image

In order to cover the back of the breech, I made a special bolt from a short metric flat-head screw by turning the head to 1/4" OD and thinning it slightly.... and then milled a recess in the breech cap to allow it to sit below flush, as below....

Image

The bottom SSG mounting screw interfered with the trigger, so I used a low profile SHCS and counterbored a recess in the trigger as shown to miss it....

Image

Since when cocked the guide and nuts stick out the back of the tube, and I needed something to mount the back of the trigger into, I made a cover from aluminum as shown below.... It is tapped for a 10-32 screw to attach the back of the trigger through the original hole in the back of the tube.... It does double duty to prevent the gap adjusting bolt from rotating as well.... The lip that sticks forward inside the tube has a flat milled on the top that just clears the flat on the bolt, so that once inserted the bolt can no longer rotate.... You do the adjustment with a socket wrench and then slide the cap in and bolt the trigger in place and the adjuster can no longer rotate....

Image

When the gun is reassembled, the only change in appearance is the extended aluminum cap on the back of the tube, and the head of the upper screw on top of the breech under the scope.... It doesn't interfere with my scope rings, although something to consider if yours were in a different place....

Image

During final tuning today I found a few more fps, and the gun now averages 851 fps (25.6 FPE) with the SSG one turn out from touching the hammer (0.042").... The ES is narrower than before (it was 12), only 8 fps over the first 86 shots of a 90 shot string down to 1100 psi.... Shot 91 was 838 fps.... This SSG gave me a gain of 9 shots over the previous arrangement (11%), increasing the efficiency to a pretty stunning 1.36 FPE/CI.... Here is the shot string....

Image

I am now a firm believer in the SSG system as having the potential to increase the efficiency of a PCP, even a regulated one that was already pretty good.... If you can hear the telltale BUURRRPPPP of hammer bounce in you gun, and getting rid of it has been a problem for you, considering this modification could be the way to go....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Jan 02, 2016 10:20 pm 
Offline
User avatar

Joined: Mon Feb 11, 2013 12:46 am
Posts: 4116
that's a very impressive string Bob.... 8)

_________________
"A candle loses nothing by lighting another candle"

Image


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 126 posts ]  Go to page 1, 2, 3, 4, 5 ... 9  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
News News Site map Site map SitemapIndex SitemapIndex RSS Feed RSS Feed Channel list Channel list

Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group

phpBB SEO