FWB 300 Tech Info Needed

Joined: September 1st, 2016, 2:30 pm

May 27th, 2017, 10:13 am #1

I'm planning on making a jig to determine the tension ( pound weight ) on FWB 300 springs.

I want to compare the difference between new springs, old springs, old springs and new springs, difference between double springs and a single spring and also how much of a difference, ( if any ) if I leave the spring loaded overnight, like leaving the gun cocked.

To make the jig isn't a big deal, what is important is having an exact measurements of how much the spring is compressed before it's cocked and the distance after it's cocked.

Although not the only factor, I'm interested in knowing how close new springs are to each other. I'm curious to know if this can be one of the reasons Chrony number vary when replacing new springs even on the same gun.

Does anyone know this compressed measurement on the FWB 300 springers ? Thank guys.
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Joined: November 28th, 2010, 2:13 pm

May 27th, 2017, 12:54 pm #2

I just overhauled a 40 year old FWB 300S Match. I replaced the original spring with an OEM spring. I assume it was original because of the type and condition of the seals. After repair, there was no significant change in velocity. The OEM spring shown in the picture includes the spacer between the two springs. The new ARH spring shown is one piece from Macarri. After 40 years, the original spring didn't seem to change much. JSB 7.33 gr velocity increased from 639 to 649 fps. I expect the new spring will take some set after a while.

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Joined: December 18th, 2015, 10:18 am

May 27th, 2017, 6:30 pm #3

I'm planning on making a jig to determine the tension ( pound weight ) on FWB 300 springs.

I want to compare the difference between new springs, old springs, old springs and new springs, difference between double springs and a single spring and also how much of a difference, ( if any ) if I leave the spring loaded overnight, like leaving the gun cocked.

To make the jig isn't a big deal, what is important is having an exact measurements of how much the spring is compressed before it's cocked and the distance after it's cocked.

Although not the only factor, I'm interested in knowing how close new springs are to each other. I'm curious to know if this can be one of the reasons Chrony number vary when replacing new springs even on the same gun.

Does anyone know this compressed measurement on the FWB 300 springers ? Thank guys.
as far as information searched here and the vintage airgun forum....

I recall that the stroke of the piston is about 65mm or roughly 2 1/2 inches...with about 90 mm of length room for a compressed or "cocked" spring...don't hold me to those numbers they're just what I remember...

I've rebuilt about 15 300s with the intention of "hotrodding"...without changing the stroke or swept volume 12 of 15 guns ended with JSB 7.33 velocities around 660 to 670....with JMs 300/150 spring or his universal mini spring...and would not respond favorably to an altered HW55 spring...but...

3 guns did like the HW55 spring and shoot the 7.33s in the 695 to 710 fps range (RWS 7gr pistol and RWS 6.9 hollow points shoot between 725 and 740fps acceptably well but are not tack drivers like the JSBs 7.33s and 7.79s)

Virtually every 300 preferred the AA 7.79gr or the JSB 7.79 gr as its favorite pellet with the JSB 7.33 equal to or a very close second favorite.

These three fast guns have one thing in common that I observe and that is when I hold my thumb over the breech seal to test for compression by pushing the piston forward, each one seems to have no blow by at all past the piston ring and seem to actually stop the piston with compressed air until I release it with my thumb...also...

I've moved one of these tight "chamber/piston" to a different barrel/ action but the speed was not there so I concluded that a particular barrel/breech and pellet fit therein also contributed to achieving the higher speeds....

Seems there are many variables to a spring guns performance...with all my fiddling no loss of accuracy after a 300 settled in its new components at the higher speeds.
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Joined: September 1st, 2016, 2:30 pm

May 27th, 2017, 7:24 pm #4

Very interesting info. I appreciate your willingness to share the knowledge you have in this field and always enjoy your posts on the subject.

I have done a lot of searching and will continue to do so. Some may feel I am wasting my time but I do not. Although I'm not looking to "hot rod" any of my 300s', I really want to know how much of a difference there is with these springs and how close the tolerances really are . To do so I need the exact two measurements . I will eventually fine the information I'm looking for and I'm in no rush.

I hoping someone has the information I'm looking for, you never know if you don't ask.
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Joined: December 18th, 2015, 10:18 am

May 28th, 2017, 1:02 am #5

are what was given in the forum discussions...I never actually took an exact measurement of these...the OEM spring dimensions are 20mm OD, 14.7mm ID, a 2.65 mm wire thickness , 210mm length per individual spring with 15 coils each wound in opposite directions. This could be the total length of both springs....that comes from a list of spring dimensions for individual makes and models of spring airguns.

Useful if you must substitute a different spring to power up or down or what ever...

from experience I put in a 31 coil spring with a wire diameter of .110...the gun would not cock because the spring was coil bound completely compressed...31 x .110= 3.42 inches or roughly 87 mm.

I recall trying to measure the piston stroke and I recall it was very close to the 65mm (67mm sticks in my mind because I shave down the piston bumper flat and to a minimum to gain swept volume and still cushion the piston.)

You have about 6 inches total to put in a 8.5 to 10 inch spring with 29 coils of .108 wire.
I hope this helps ...
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Joined: September 1st, 2016, 2:30 pm

May 28th, 2017, 10:05 am #6

...that's exactly what I was looking for. Thanks again.
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