Inner barrel modifications. Somedays I have some odd ideas.

[Iceni]

I was thinking about inner barrels and what could be done and has been done to them in attempts to make them more accurate.

I put a madbull 6.03 into a stock gun a few years ago, I've never noticed an improvement in terms of accuracy and less flyers over the 6.08 JG barrel it replaced. In fact the hop window is so much smaller than the stock barrel it tends to be far harder to setup and get right. Having just picked up a new gun and not wanting another barrel as I feel does nothing for my gun I wanted to try something else.

It got me thinking this weekend what I could do to a 6.08 to make it better.

I've gone ahead and polished it but not in a regular way, I have access to a range of tolerance'd sharpening stones for my straight razors. These stones are about as accurate as you can get in terms of micron grading on a consumer product.

The stones I have,
Naniwa Chosera/Professional 1000 grit.
Naniwa Super/Speciality 3000, 5000, 8000, 12000 grit.

Very high quality chrome oxide pigment powder.

I built a slurry on the stones, Transferred it to a cut down 10mm felt dremel pad, And pushed it through the barrel. I started  with the 3000 grit slurry knowing how much material a 1000 grit stone can remove I didn't want to rebore the barrel!

The 3K ran smooth after about 20 passes, So I redid the 3K stage for another 20 passes.

I then moved up the grits to 5K then 8K and did about 15 passes on each. The scratch pattern was all but gone at 8K.

The 12K I only did 5 passes, Then lapped it out with the chrome oxide powder on a swab.

Currently that barrel is internally pristine,  It has a mirror finish for the full length.


Once I'd lapped  the barrel I got thinking about the Magic box barrels and how they work. Then I did the math on the size of the platforms they must have internally.

6.06-5.95= 0.11
0.11/2=0.055mm

Allowing for bb tolerance those pads can only be 0.05mm high. And you can get film/metal tapes that thick.

JG
6.08-5.95= 0.13
0.13/2= 0.065mm

Slightly more play in the JG stock barrel and enough that a 0.1mm film PTFE tape could be used if the hop was set a little lighter. In fact a 0.1 film in that barrel for the initial hop stage would still give 0.03mm clearance to the top of the barrel. Perhaps enough to actually attempt it since a 6.01 only has 0.015 top clearance  this would still be more than double that.

So what I'm thinking is this.

I take a section of low friction PTFE film cut it at about 4mm wide and long enough to clear the hop window, As well as wrap past the barrel end and sit under the bucking. This overwrap + the self adhesive should keep it in place well enough to test it at home.

If it works it should reduce the friction on the bottom of the barrel, Allowing more hop pressure, and more backspin. If I'm right and I can get a way to make it safe it might be a simple mod to increase hop efficiency on heavier BB's and weak hop units.

Shoot this down before I go and do it please! I have enough bad ideas!

You guys are working too  slowly... I just found and bought this....

https://www.ebay.co.uk/itm/3M-60-PTFE-Film-Electrical-Tape-25MM-X-33M-1-034-x-36Yd-Ex-MOD-/282635932394?hash=item41ce6a12ea%3Ag%3A~~IAAOSwLlpZqxSE&nma=true&si=fBy4xJQf%2FIt88lKE%2BI7dSYT51sU%3D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

 

[Hangtight]

Just as a thought exercise, I'm not sure having the BB run on a strip of tape under the hop will increase the effectiveness of the hop, but it may centre the BB in the bore,so instead of the air pressure around the BB lifting it into that position once it's cleared the hop it'll already be aligned along the axis.

It may make things better, worse or have no measurable effect at all, but there's no harm in trying.

 

[Iceni]

I'm not sure having the BB run on a strip of tape under the hop will increase the effectiveness of the hop

The reason I think it might help is the hop pushes on the BB, And the BB pushes on the lower part of the barrel. For a normal barrel the bucking has to beat the friction at the bottom of the barrel (the lower part of the BB needs to rotate forwards), I already know that I can't lift a 0.3 BB with my setup, It simply can't generate enough backspin to hop well or it jams. Lapping alone might actually be enough if done to a high enough standard, But I want to see if it can be pushed.

I also need to do a slip test. I have some brass bar kicking about, so I can lap one section, and apply PTFE tape to another. Then hold a BB and rub it as hard as I can and see what surface produces the lowest friction. It should be the PTFE, but it might also show that the tape doesn't have the adhesion to the brass that I need.

 

[Iceni]

Update:

My roll of tape has arrived. I don't need to do a slip test. The tape is slick, insanely slick. If you hold the roll on the sides gravity pulls it out of your fingers. I tried cutting some with a sharp knife and it just skips over the surface. Using a  lot of cutting force was needed to get it to cut.

The section I cut has been stuck to some brass plate, I'm going to try damage it in a bit and see if the glue holds up. The fact it has taken paint off my desk leads me to belive the glue might be decent, but I won't know until I've cured a bit with heat onto that brass.

I did go searching for another roll out of curiosity, The cheapest I could find the same roll for was £166... So I might have the deal of the century if this is a winning solution.

I have a car to fix this morning but as soon as I get chance I'm going to cut a section and put it into the barrel I lapped. I might not be able to test it right away however as I'm going to have to put a few K's of bb's over it on a range to see how long it lasts, and if it improves the hop.