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Author Topic: Gas Ram To coil Spring Considerations  (Read 561 times))

Offline Bayman

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Re: Gas Ram To coil Spring Considerations
« Reply #20 on: September 23, 2022, 09:26:52 AM »
The piston id is pretty average. What's the cylinder bore out of curiosity? What's the distance from the inside face of the piston to the rear of the piston?
Did I say pictures would help A LOT?
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #21 on: September 23, 2022, 09:52:06 AM »
The piston id is pretty average. What's the cylinder bore out of curiosity? What's the distance from the inside face of the piston to the rear of the piston?
Did I say pictures would help A LOT?

OK. I may have goofed... again.
Here is a pic of the piston
If the square hole is the sear laltch point, then the stroke is only 3 3/8", and I can indeed use a Crosman NP2 ram..
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Offline Jim-in-UK

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Re: Gas Ram To coil Spring Considerations
« Reply #22 on: September 23, 2022, 12:20:03 PM »
If the square hole is the sear laltch point, then the stroke is only 3 3/8"...

You quoted the Vortek spring at 48 lbf/in., and the stroke at 3.375"

If PS = piston stroke, PL = preload (both in inches), and SP = spring rate in lbf/in.

Spring energy to the piston in ft. lb. is ((PS+PL^2) - (PL^2)) x SR /24.

So, with one inch of preload, that would be ((3.375 + 1)^2 - (1^2)) x 48 / 24 = 36 ft. lb., which would put muzzle energy somewhere in the 12 ft. lb. range. With 2" of preload, that would rise to 49.7 ft. lb. to the piston, nearer 16 ft. lb. at the muzzle.
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #23 on: September 23, 2022, 12:27:34 PM »
If the square hole is the sear laltch point, then the stroke is only 3 3/8"...

You quoted the Vortek spring at 48 lbf/in., and the stroke at 3.375"

If PS = piston stroke, PL = preload (both in inches), and SP = spring rate in lbf/in.

Spring energy to the piston in ft. lb. is ((PS+PL^2) - (PL^2)) x SR /24.
 
So, with one inch of preload, that would be ((3.375 + 1)^2 - (1^2)) x 48 / 24 = 36 ft. lb., which would put muzzle energy somewhere in the 12 ft. lb. range. With 2" of preload, that would rise to 49.7 ft. lb. to the piston, nearer 16 ft. lb. at the muzzle.

The spring rate sill increase if the spring is shortened.......

I am going to do a partial mock assembly of the piston and cocking linkage to see if I can't get an accurate stroke dimension.
It baffles my mind that a manufacturer would spec a long stroke spring, then utilize only 70% of the available stroke.
« Last Edit: September 23, 2022, 12:31:34 PM by Ronno6 »
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Offline HectorMedina

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Re: Gas Ram To coil Spring Considerations
« Reply #24 on: September 23, 2022, 12:41:06 PM »

OK. I may have goofed... again.
Here is a pic of the piston
If the square hole is the sear laltch point, then the stroke is only 3 3/8", and I can indeed use a Crosman NP2 ram..

I think we are overcomplicating things here.

IIRC, the Re-Axis models were the first to take into account that as far as gas spring life was concerned, it was better to put the body of the gas spring into  the  piston and use the rod at a centering washer at the rear.

If so, then the main issue is not which spring to use, but how to design the two part guide that needs to guide the spring when the piston has no stem.

Yes, that square notch at the rear is what locks into the trigger sear/ramp. When the trigger breaks the sear/ramp drops and the piston flies forward.

IF the ID of the piston is 0.935" , then I would use a Titan #2 (894" ID, 0.610"ID, 0.142 WD, 30 coils, LAR -unset- 11.46")
And then adjust the rear outside guide as well as the front inside guide to match the needs.
Of course you could make a dual diameter guide and just use it at the front, but it would probably be too heavy if made of solid steel.
You can use a hollow guide and lighten the weight of the guide.

If you do this and you get too little power, then there are longer springs, but I am afraid that 3.375" for stroke is not a lot. If you use the above mentioned spring, it will compress to 80% of solid, so that is a good duty cycle for a normal life.

Remember when you have the liberty to choose the spring ALWAYS choose the largest OD you can fit into the piston.
While it is true that springs expand upon compression, it is rare that a spring expands by more than 0.015".
AND, unless you know that the spring is made of valve spring steel (usually Si-Va), it is not worth the effort.

HTH, keep us posted!







HM

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Re: Gas Ram To coil Spring Considerations
« Reply #25 on: September 23, 2022, 12:43:54 PM »
Thanks for the very specific and useful information, Hector.
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #26 on: September 23, 2022, 12:54:06 PM »
Thank you, Hector, and Peter for inviting a couple of experts into the conversation.

I am going to do a partial reassembly of the cocking mechanism and the piston so that I can nail down for sure the stroke length.
I am still asea at the thought that a manufacturer would spec a long stroke gas ram then use only 70% of the available stroke.
If this is typical, then other manufacturers must have really short strokes in their gas ram equipped rifles.
Maybe gas rams follow some of the same design considerations of coil springs??
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #27 on: September 23, 2022, 12:57:17 PM »

Remember when you have the liberty to choose the spring ALWAYS choose the largest OD you can fit into the piston.
While it is true that springs expand upon compression, it is rare that a spring expands by more than 0.015".
AND, unless you know that the spring is made of valve spring steel (usually Si-Va), it is not worth the effort.

HTH, keep us posted!

HM

Should the sleeve be eliminated?
The sleeve had an ID of about .81" IIRC.......

What is the purpose of the sleeve?
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Online mobilehomer

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Re: Gas Ram To coil Spring Considerations
« Reply #28 on: September 23, 2022, 03:36:44 PM »
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #29 on: September 23, 2022, 06:29:15 PM »
Give this palce a call.
https://www.airrifleheadquarters.com/page/page/251327.htm

Mr. James does not include a phone #, and pretty definitely states that, "If you don't see it, we don't have it."

I have talked with Tom at Vortek.
Nice guy!
I am going to provide him with data he requested to see if he can develop a PB-4 kit for the Octane.
Stay tuned.......
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Offline Privateer

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Re: Gas Ram To coil Spring Considerations
« Reply #30 on: September 23, 2022, 08:19:50 PM »
Do you have the stuff to machine a few parts?
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #31 on: September 23, 2022, 08:33:23 PM »
Do you have the stuff to machine a few parts?
Yessirree...........
Logan 820 metal lathe for starters.......
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Offline Privateer

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Re: Gas Ram To coil Spring Considerations
« Reply #32 on: September 23, 2022, 08:35:23 PM »
I'll give you a trick I use to measure actual stroke length without all the math.
I have a failed Crosman Gas piston from a Gun i fixed for a guy long ago.
I drilled a small hole in it so it travels easily.
I put that in a gun with clay to hold it in place then cock the gun.
Once taken out? I have a exact measurement of stroke and can make parts to adapt springs or Gas Rams.
And before anyone says that's Brillent?
It's just lazy.
 ;D

Work smarter. Not harder.
« Last Edit: September 23, 2022, 08:38:02 PM by Privateer »
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #33 on: September 23, 2022, 08:53:17 PM »
I have a pretty good handle on the stroke length now.
I put the piston in the compression chamber all the way forward, then measures the distance from the sear latch slot in the piston back to the sear in it's rearward position.
Using a digital caliper that dimension measured 3.25"

Now, I wish I understood why Umarex used such a long stroke ram in an application with a  much shorter stroke.....
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Offline Privateer

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Re: Gas Ram To coil Spring Considerations
« Reply #34 on: September 23, 2022, 08:54:50 PM »
Here's a image that shows some mods for adapting Gas Rams.
That's for Crosman Gas Rams to early Hatsan Spring Guns.
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #35 on: September 23, 2022, 09:02:31 PM »
Thanks, Mr. Jeff.
I adapted a Crosman NP ram into a Hatsan Striker last year, but those 2 were close in specs.
This Reaxis is a horse of a different color.......

Mr. Tom at Vortek said there was more to it than just the stroke length, but he would not elaborate....
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Offline Privateer

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Re: Gas Ram To coil Spring Considerations
« Reply #36 on: September 23, 2022, 09:09:38 PM »
A Gas Ram does not require as much preload as a Wire Spring as a start.
I've taken Gas ram guns down and rebuilt with no compressor.
I'd not suggest trying that with out a good spring compressor!
I had one get away from me once. I don't want to EVER go through that again!
So I built a Spring Compressor using a scissor jack found in many cars.
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #37 on: September 23, 2022, 09:21:20 PM »
A Gas Ram does not require as much preload as a Wire Spring as a start.
I've taken Gas ram guns down and rebuilt with no compressor.
I'd not suggest trying that with out a good spring compressor!
I had one get away from me once. I don't want to EVER go through that again!
So I built a Spring Compressor using a scissor jack found in many cars.

I made one by turning the OD of a piece of 3/4" pipe to fit 1" scope rings, and threaded a beam clamp on the end.
Works great!
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Offline Privateer

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Re: Gas Ram To coil Spring Considerations
« Reply #38 on: September 23, 2022, 09:28:12 PM »
I don't trust rings to hold a Spring with a 3 inch preload.
But that's just me.
I tried that and I have a set of rings showing a near fail so stopped using it.
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Offline Ronno6

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Re: Gas Ram To coil Spring Considerations
« Reply #39 on: September 23, 2022, 10:05:49 PM »
I don't trust rings to hold a Spring with a 3 inch preload.
But that's just me.
I tried that and I have a set of rings showing a near fail so stopped using it.

After that caveat I may machine a longer pipe so that I can put the sliding pipe clamp on the breech block end,
and use the scope rings as a guide, allowing the pipe to slide in them.
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