Power trimming - expert help please

Power trimming - expert help please

Joined: June 2nd, 2002, 10:34 pm

October 11th, 2010, 6:34 pm #1

<p>I've a post running on the UK Chinese forum, I'm copying it here in case one of the members has a better way to Trim the FPE.</p>
<p>The thing to note is that because of the UK 12 FPE limit Im after 10.5 fpe not 11 +, I feel 10.5 gives a decent sort of safety margin to allow for temp changes and so on  One more limitation externally accessible power adjusters (unless they just reduce the power) <span> </span>are problematic at best.</p>
<p><strong>Quote :- </strong></p>
<p><span class="postbody"><em>I'm finding it very fiddly to fine tune the power of the 79 I'm setting up.

As far as I can tell opening up the Co2 flow path to get the maximum efficiency makes it very very sensitive.

<span style="text-decoration:underline;">Relevant Mod's.</span>
The exhaust port/transfer port is wider than standard and the and the hole into the barrel is about 4mm (it's a 0.22) wide and slightly over that in length. The valve has a longer softer spring fitted replacing the original one.

Taking out just one thin washer (0.45mm 0.020) from behind the hammer spring dropped the fpe from 11+ by a good 1fpe.  

I can get fine adjustment  by elongating the trigger block bolt holes  and sliding it back or forward but I'm wondering if I'm doing something fundamentally dumb and just making things hard for myself.

So am I doing this wrong, is there a better way?

If you have a better way of fine trimming the fpe please let me know. </em></span></p>
<p><span class="postbody"><strong>End Quote.</strong></span></p><span class="postbody"></span><p><span class="postbody">I know I could make a new spring guide/block that would give some adjustment but its a chunk of work when I only need the adjustment during set up.<span>  </span></span><span class="postbody">Any better ideas, is there some simple way to achieve this? <span> Have I overlooked anything?</span></span></p>

One of the members has posted this one :http://ukchineseairgunforum.myfreeforum ... php#109240 it's good but I only want to adjust at set up time so I'm after something easier.

Many Thanks          Ora


My Websithttp://www.ora8i.rivington-riflemen.org
Last edited by ora8i on October 11th, 2010, 6:54 pm, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

October 11th, 2010, 9:16 pm #2

... I'd like to hear about it as well. Are some complicated ways, but with a specific power goal you only need to do it once, so if the mod fro external adjustment is a lot of work, it's easier to just keep taking the rifle apart and adjusting to that goal.

Ways to adjust power (but none lend them selves to external adjustment without a good bit of work).
I'm going to assume CO2 power (think I remember the pic. you published...this is a co2 tanker, right?)


#1. Smack the valve harder or lighter.
A. Striker spring tension can do this, but with the cock on closing system, can't just tap the end cap for an power adjuster.
B. Striker weight. No easy adjustment here.
C. Striker stroke. Your trigger moving system can give you a small adjustment in this area, but getting the trigger unit to stay put is a pain.
#2. Strangle off the transfer port.
A. Making different sized port seals is the easy way, but no external adjustment.
B. Not enough room for a variable restrictor screw in a standard QB breech... a one-piece riser breech does have the room to add a restrictor screw.
#3. Limit the valve travel.
A. Can limit the amount of valve stem that sticks out of the valve to be smacked by the striker.
(that gets complicated. Changing the valve stem length also changes the striker's stroke).
B. Changing the valve return spring tension.
C. Making a positive stop for the valve stem's travel.

Personally, I'd just take the gun apart a few times, fiddle with whatever seemes easiest to fiddle with, and test it along the way until you get where you want to be. but with co2, temperature plays a big part in energy, and if you tune it up on a 70F day, but "they" test it on an 85F day, you might be faster than you planned on.
-------

took me awhile, but for some on-going tests, got a .177, 20, and 22 QB (these are HPA tankers) all running at about 12 foot pounds. No power limit here, so i just stopped fiddling around when they were between 11.8 and 12.4 foot pounds. So I know the ping-pong game it is to hit a goal..a little fast...a little slow...little fast...etc.

For my tests, I just increase the range a bit for the 12.4 foot pound versions to get impacts to work out very close to equal.
Last edited by gubb33ps on October 11th, 2010, 9:19 pm, edited 1 time in total.
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Joined: June 2nd, 2002, 10:34 pm

October 11th, 2010, 9:25 pm #3

just bite it and do the mod, I dont like moving the trigger block and messing about with washers, stripping the rifle each time just ruins the transfer port sealsd.


Thanks Ora

My Website -http://www.ora8i.rivington-riflemen.org
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Joined: November 17th, 2006, 3:51 am

October 11th, 2010, 11:15 pm #4

..hase been posted here, and that would allow a simpler power adjuster (striker spring pre- tensioner) that might let you dial it into the energy level you need.
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Joined: May 12th, 2001, 1:29 pm

October 11th, 2010, 11:20 pm #5

<p>I've a post running on the UK Chinese forum, I'm copying it here in case one of the members has a better way to Trim the FPE.</p>
<p>The thing to note is that because of the UK 12 FPE limit Im after 10.5 fpe not 11 +, I feel 10.5 gives a decent sort of safety margin to allow for temp changes and so on  One more limitation externally accessible power adjusters (unless they just reduce the power) <span> </span>are problematic at best.</p>
<p><strong>Quote :- </strong></p>
<p><span class="postbody"><em>I'm finding it very fiddly to fine tune the power of the 79 I'm setting up.

As far as I can tell opening up the Co2 flow path to get the maximum efficiency makes it very very sensitive.

<span style="text-decoration:underline;">Relevant Mod's.</span>
The exhaust port/transfer port is wider than standard and the and the hole into the barrel is about 4mm (it's a 0.22) wide and slightly over that in length. The valve has a longer softer spring fitted replacing the original one.

Taking out just one thin washer (0.45mm 0.020) from behind the hammer spring dropped the fpe from 11+ by a good 1fpe.  

I can get fine adjustment  by elongating the trigger block bolt holes  and sliding it back or forward but I'm wondering if I'm doing something fundamentally dumb and just making things hard for myself.

So am I doing this wrong, is there a better way?

If you have a better way of fine trimming the fpe please let me know. </em></span></p>
<p><span class="postbody"><strong>End Quote.</strong></span></p><span class="postbody"></span><p><span class="postbody">I know I could make a new spring guide/block that would give some adjustment but its a chunk of work when I only need the adjustment during set up.<span>  </span></span><span class="postbody">Any better ideas, is there some simple way to achieve this? <span> Have I overlooked anything?</span></span></p>

One of the members has posted this one :http://ukchineseairgunforum.myfreeforum ... php#109240 it's good but I only want to adjust at set up time so I'm after something easier.

Many Thanks          Ora


My Websithttp://www.ora8i.rivington-riflemen.org
...adjustment I cobbled up sees roughly 2fpe change in ME for every 1/32" change in preload (i.e., each whole turn = 0.031" of the 32tpi adjusting screw. That's pretty darn close to the 0.02" = 1fpe that you're seeing.



Steve
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Joined: January 9th, 2005, 1:46 am

October 12th, 2010, 1:54 am #6

<p>I've a post running on the UK Chinese forum, I'm copying it here in case one of the members has a better way to Trim the FPE.</p>
<p>The thing to note is that because of the UK 12 FPE limit Im after 10.5 fpe not 11 +, I feel 10.5 gives a decent sort of safety margin to allow for temp changes and so on  One more limitation externally accessible power adjusters (unless they just reduce the power) <span> </span>are problematic at best.</p>
<p><strong>Quote :- </strong></p>
<p><span class="postbody"><em>I'm finding it very fiddly to fine tune the power of the 79 I'm setting up.

As far as I can tell opening up the Co2 flow path to get the maximum efficiency makes it very very sensitive.

<span style="text-decoration:underline;">Relevant Mod's.</span>
The exhaust port/transfer port is wider than standard and the and the hole into the barrel is about 4mm (it's a 0.22) wide and slightly over that in length. The valve has a longer softer spring fitted replacing the original one.

Taking out just one thin washer (0.45mm 0.020) from behind the hammer spring dropped the fpe from 11+ by a good 1fpe.  

I can get fine adjustment  by elongating the trigger block bolt holes  and sliding it back or forward but I'm wondering if I'm doing something fundamentally dumb and just making things hard for myself.

So am I doing this wrong, is there a better way?

If you have a better way of fine trimming the fpe please let me know. </em></span></p>
<p><span class="postbody"><strong>End Quote.</strong></span></p><span class="postbody"></span><p><span class="postbody">I know I could make a new spring guide/block that would give some adjustment but its a chunk of work when I only need the adjustment during set up.<span>  </span></span><span class="postbody">Any better ideas, is there some simple way to achieve this? <span> Have I overlooked anything?</span></span></p>

One of the members has posted this one :http://ukchineseairgunforum.myfreeforum ... php#109240 it's good but I only want to adjust at set up time so I'm after something easier.

Many Thanks          Ora


My Websithttp://www.ora8i.rivington-riflemen.org
Ora,

I'm glad you're posting something like this "back home". UK shooters can be sailing rather close to the wind - in my opinion - by using probe-tipped bolts and free-flow breech seals without possibly taking appropriate steps to throttle back performance somewhat in their QB78s.

And I'm not so sure how widely understood is the significance of temperature on muzzle velocity when it comes to CO2-powered air rifles.

Just published on my blog (link below) is some test data I've put together showing how just piercing 2 x 12Gram Powerlets reduces the gun temperature by 10 degrees F - that's 20fps! Especially when there is the need to keep muzzle velocity (and energy) below a certain limit, it's a good idea to stress that the gun's temperature should stabilize for at least 3 minutes before testing, and then shoot not more rapidly than one shot every 30 seconds, or better once a minute when running a test. Otherwise the muzzle velocity will be lower than expected due to the cooling effect of CO2 use. If trying to keep muzzle energy below 12 ft/lb, this is, of course, not a good thing.

Stephen Archer
Archer Airguns Inc.
Website http://www.archerairguns.com
Videos http://www.youtube.com/ArcherAirguns
Blog http://www.archerairguns.info
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Joined: June 7th, 2010, 12:14 am

October 12th, 2010, 2:18 am #7

Did your testing include a direct correlation between CO2 chamber temperature and muzzle velocity? The question is, does the self regulation feature of the knock open valve fail to accomodate changes in CO2 pressure due to temperature?
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Joined: June 7th, 2010, 12:14 am

October 12th, 2010, 2:21 am #8

... I'd like to hear about it as well. Are some complicated ways, but with a specific power goal you only need to do it once, so if the mod fro external adjustment is a lot of work, it's easier to just keep taking the rifle apart and adjusting to that goal.

Ways to adjust power (but none lend them selves to external adjustment without a good bit of work).
I'm going to assume CO2 power (think I remember the pic. you published...this is a co2 tanker, right?)


#1. Smack the valve harder or lighter.
A. Striker spring tension can do this, but with the cock on closing system, can't just tap the end cap for an power adjuster.
B. Striker weight. No easy adjustment here.
C. Striker stroke. Your trigger moving system can give you a small adjustment in this area, but getting the trigger unit to stay put is a pain.
#2. Strangle off the transfer port.
A. Making different sized port seals is the easy way, but no external adjustment.
B. Not enough room for a variable restrictor screw in a standard QB breech... a one-piece riser breech does have the room to add a restrictor screw.
#3. Limit the valve travel.
A. Can limit the amount of valve stem that sticks out of the valve to be smacked by the striker.
(that gets complicated. Changing the valve stem length also changes the striker's stroke).
B. Changing the valve return spring tension.
C. Making a positive stop for the valve stem's travel.

Personally, I'd just take the gun apart a few times, fiddle with whatever seemes easiest to fiddle with, and test it along the way until you get where you want to be. but with co2, temperature plays a big part in energy, and if you tune it up on a 70F day, but "they" test it on an 85F day, you might be faster than you planned on.
-------

took me awhile, but for some on-going tests, got a .177, 20, and 22 QB (these are HPA tankers) all running at about 12 foot pounds. No power limit here, so i just stopped fiddling around when they were between 11.8 and 12.4 foot pounds. So I know the ping-pong game it is to hit a goal..a little fast...a little slow...little fast...etc.

For my tests, I just increase the range a bit for the 12.4 foot pound versions to get impacts to work out very close to equal.
How about adjustable or replaceable probe tip apertures?

Brass valves from the carburetor spares bin anyone? Or the camping gas lamps?

With suitable bolt modifications this could be quite simple.

CalG
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Joined: June 7th, 2010, 12:14 am

October 12th, 2010, 2:23 am #9

... I'd like to hear about it as well. Are some complicated ways, but with a specific power goal you only need to do it once, so if the mod fro external adjustment is a lot of work, it's easier to just keep taking the rifle apart and adjusting to that goal.

Ways to adjust power (but none lend them selves to external adjustment without a good bit of work).
I'm going to assume CO2 power (think I remember the pic. you published...this is a co2 tanker, right?)


#1. Smack the valve harder or lighter.
A. Striker spring tension can do this, but with the cock on closing system, can't just tap the end cap for an power adjuster.
B. Striker weight. No easy adjustment here.
C. Striker stroke. Your trigger moving system can give you a small adjustment in this area, but getting the trigger unit to stay put is a pain.
#2. Strangle off the transfer port.
A. Making different sized port seals is the easy way, but no external adjustment.
B. Not enough room for a variable restrictor screw in a standard QB breech... a one-piece riser breech does have the room to add a restrictor screw.
#3. Limit the valve travel.
A. Can limit the amount of valve stem that sticks out of the valve to be smacked by the striker.
(that gets complicated. Changing the valve stem length also changes the striker's stroke).
B. Changing the valve return spring tension.
C. Making a positive stop for the valve stem's travel.

Personally, I'd just take the gun apart a few times, fiddle with whatever seemes easiest to fiddle with, and test it along the way until you get where you want to be. but with co2, temperature plays a big part in energy, and if you tune it up on a 70F day, but "they" test it on an 85F day, you might be faster than you planned on.
-------

took me awhile, but for some on-going tests, got a .177, 20, and 22 QB (these are HPA tankers) all running at about 12 foot pounds. No power limit here, so i just stopped fiddling around when they were between 11.8 and 12.4 foot pounds. So I know the ping-pong game it is to hit a goal..a little fast...a little slow...little fast...etc.

For my tests, I just increase the range a bit for the 12.4 foot pound versions to get impacts to work out very close to equal.
nt
Last edited by CalG on October 12th, 2010, 2:23 am, edited 1 time in total.
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Joined: June 2nd, 2002, 10:34 pm

October 12th, 2010, 8:13 am #10

Ora,

I'm glad you're posting something like this "back home". UK shooters can be sailing rather close to the wind - in my opinion - by using probe-tipped bolts and free-flow breech seals without possibly taking appropriate steps to throttle back performance somewhat in their QB78s.

And I'm not so sure how widely understood is the significance of temperature on muzzle velocity when it comes to CO2-powered air rifles.

Just published on my blog (link below) is some test data I've put together showing how just piercing 2 x 12Gram Powerlets reduces the gun temperature by 10 degrees F - that's 20fps! Especially when there is the need to keep muzzle velocity (and energy) below a certain limit, it's a good idea to stress that the gun's temperature should stabilize for at least 3 minutes before testing, and then shoot not more rapidly than one shot every 30 seconds, or better once a minute when running a test. Otherwise the muzzle velocity will be lower than expected due to the cooling effect of CO2 use. If trying to keep muzzle energy below 12 ft/lb, this is, of course, not a good thing.

Stephen Archer
Archer Airguns Inc.
Website http://www.archerairguns.com
Videos http://www.youtube.com/ArcherAirguns
Blog http://www.archerairguns.info
I the uk we pretty much HAVE TO get the maximum number of shots per-fill.

An example Co2 of at "good prices" :-

88g screw in bottle (airsource type not crossman) $ 7.92
12g capsule $ 0.67

less if you buy in bulk but still a reason to screw every last shot from them.

I agree that too many UK shooters set up their 78/79s too close to the limit it's just plain risky, I did some temp/vel testing when I set up a 2250 some years ago and again with a 78 which convinces me that 10.5 is the maximum that I should set up to.

[/img]


Using the 2250 I also measured the effect of rapid shooting on vel :-

[/img]


ATB Ora

My Websihttp://www.ora8i.rivington-riflemen.org
Last edited by ora8i on October 12th, 2010, 9:04 am, edited 1 time in total.
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