Heat shrink tubing

[Mossonarock]

I'm trying to learn about heat shrink tubing on spring guides to reduce spring twang. I'm wondering which materials are best for this purpose and how to evaluate the tubes for the thickness of the tube wall after it shrinks or if that's even a thing to consider. Mcmaster-Carr has quite an assortment: https://www.mcmaster.com/heat-shrink-tubing/
I don't really even know where to begin. What do you suggest?

[Roadworthy]

I suggest determining the clearance between your spring and the guide.  If the fit is too close you may find you can't slip the spring onto the guide with the shrink tubing in place.  Be advised the tubing is much softer than the guide.  When selecting shrink tubing it must be large enough to fit over the guide before you shrink it, obviously.  If too large it will not shrink tightly onto the guide.  There should be guidance on how much given tubing will shrink.  Lacking guidance figure the tubing will shrink to roughly half its original diameter.  When cutting the stuff to length be sure your cut is clean.  It can split when shrunk if the cut is uneven.  Lube it well before attempting to slide a spring onto it.  Of course a better fix is simply having a better fitting spring guide made.

[Artie]

Most guides I've done on springers require 1/2" heat shrink. It comes in different thicknesses. The Harbor freight stuff is usually fairly thin and good to experiment with.
There is adhesive lined heat shrink you can order or may find at a local electronics supply if you are fortunate enough to have one in the area. It is much thicker than the HF shrink and more durable.
You can spray the guide with 3M adhesive or something similar and use regular heat shrink (gotta be quick about it). If it's a fail, just cut off the shrink material and clean adhesive with acetone.
Speaking of acetone, clean the guide before applying heat shrink or adhesive so the shrink anchors better.
The trickiest guides are the plastic/delrin guides. Almost certainly need adhesive in that case. I recommend lightly sanding the guide before applying the adhesive and shrink.
If it's a tight fit before heat shrink is applied it may not work. The spring may grab and squish back the heatshrink or even shred it. Using adhesive makes the heat shrink even thicker.
Some folks don't heat shrink the entire length of the guide. They only do the first third to half closest to the trigger block.

[Jeff Marshall]

I have done "shrink tunes" to many guns; probably 30 or more.

15ish years ago I purchased ordinary polyolefin heat shrink tube in bulk; it is the only type I have any experience with. The only type of adhesive I have any experience with is silicone sealer. My heat shrink tube is probably 5/8" inside diameter unshrunk, but it may be 3/4".

The adhesive needs to fully coat the guide, and must be applied very thinly. Shrink the tube on in an oven;
300ish degrees for steel guides, and 250ish for plastic guides.

The most common type of tube like I use will increase the guide diameter about .030". The spring can be quite tight....tight enough that the spring must be twisted on to the completed guide, and tight enough that the spring will not just pull off the guide. The fit of low powered guns needs to be just a bit looser to avoid a power loss.

The end of the spring needs to be prepped to remove sharp corners etc. so that the tube isn't damaged when installing the spring.

Cut the tube long and cut to length after installation so that it rolls over the tip of the guide.

The tube may be applied two layers thick if necessary. I have used electrical tape on the guide and installed tube over that to get a "half size".

A shrink tuned guide will usually last for years. It it is going to fail it usually does so quickly.

I have a couple of professionally tuned guns; the shot cycle of many of my "shrink tuned" guns is just as good.

[Mossonarock]

Thanks for sharing your experience, everyone. I won't get to it soon but at least trying this out is cheaper than getting a lathe.
I'm sure McMaster-Carr has something that is suitable. I'm particularly wondering if the abrasion resistant tubing made of polyolefin will work.

[nced]

I'm trying to learn about heat shrink tubing on spring guides to reduce spring twang. I'm wondering which materials are best for this purpose and how to evaluate the tubes for the thickness of the tube wall after it shrinks or if that's even a thing to consider. Mcmaster-Carr has quite an assortment: https://www.mcmaster.com/heat-shrink-tubing/
I don't really even know where to begin. What do you suggest?

I don't know the correct way to install "heat shrink" however I do know there are incorrect ways judging by a gun I worked on that had wads of slipped heat shrink jammed between the coils!

[Artie]

I'm trying to learn about heat shrink tubing on spring guides to reduce spring twang. I'm wondering which materials are best for this purpose and how to evaluate the tubes for the thickness of the tube wall after it shrinks or if that's even a thing to consider. Mcmaster-Carr has quite an assortment: https://www.mcmaster.com/heat-shrink-tubing/
I don't really even know where to begin. What do you suggest?

I don't know the correct way to install "heat shrink" however I do know there are incorrect ways judging by a gun I worked on that had wads of slipped heat shrink jammed between the coils!

Yep, happened to me before I started using adhesive.

Now about adhesive...
I had a guide I sprayed with 3M and layered with heat shrink. After shrinking it the fit was too tight for the spring so I cut off the shrink. The guide was sticky from the 3M spray and for whatever reason I did not clean the 3M off with acetone. I left the adhesive on, installed the spring, assembled the gun and test fired. No twang.
Still shooting twangless after many, many pellets down range. So that is an option to experiment with... The adhesive was enough to kill the vibration/resonance. The adhesive stays on the guide, does not harden or ball up, does not transfer to the spring or rest of the chamber far as I can tell. I will say the test was on a HW95 with a delrin guide that was neither tight fitting or sloppy loose. The 95 was a hard gun to eliminate the twang on, about the hardest gun I have.

[Mossonarock]

That's interesting, Artie. Did you notice any difference in FPS from the adhesive? I can't imagine there'd be much but what do I know?
I haven't yet opened up my Terrus. So I don't know how much of a gap there is between the guide and spring but I can hear it.

[Artie]

I didn't chrony afterward, I doub't it had much effect on a 95 frankly.

[DanD]

That's interesting, Artie. Did you notice any difference in FPS from the adhesive? I can't imagine there'd be much but what do I know?
I haven't yet opened up my Terrus. So I don't know how much of a gap there is between the guide and spring but I can hear it.

The Terrus guide isn't cylindrical like most guides.  It is a long X shape so there are only 4 linear contact points along the spring. I'm not sure if spray adhesive alone will have enough contact area to work, but I suppose it wouldn't hurt to try. I shrink tuned my Terrus with non-adhesive tubing from the local electronics store and I can't believe how well it works.

[Artie]

That's interesting, Artie. Did you notice any difference in FPS from the adhesive? I can't imagine there'd be much but what do I know?
I haven't yet opened up my Terrus. So I don't know how much of a gap there is between the guide and spring but I can hear it.

The Terrus guide isn't cylindrical like most guides.  It is a long X shape so there are only 4 linear contact points along the spring. I'm not sure if spray adhesive alone will have enough contact area to work, but I suppose it wouldn't hurt to try. I shrink tuned my Terrus with non-adhesive tubing from the local electronics store and I can't believe how well it works.

My Gamo Accu had a similar plastic x-shaped guide (looks like "+" when viewed from the spring end). For that guide I cut 4 equal length pieces of insulated wire and placed them in each quadrant. Then I slipped on a slightly longer (long enough to cover the end of the guide and wires) length of adhesive lined heat shrink and heated till all was tightly wrapped. Works like a charm.

[prosportfan]

FWIW, try the old plastic or aluminum can piston liner first. I have only used the aluminum can version but I can honestly say that it made a heelva difference in sound.

[Artie]

Piston liners are all that's needed on many guns but not all guns, my HW95 for example.
I have also been told that a small piece of plastic liner at the end of the guide by the trigger block works too. Basically a tight fitting shim,  it doesn't have to cover the whole guide, two or three coils should do it. Obviously, it has to be thin enough for the spring to "screw" on over it. The tight fit is supposed to keep the shim plastic from moving or coming out.

[Mossonarock]

Thanks for the tips guys. I just put in an order for round tuits and as soon as I get them, I'll see what I can do with my gun.