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Lowering Barrel Friction (Project Polishing Inner Barrel)

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
Hey guys,
It's been a while, but hope all is well in OleoLand.

I have just started a new nerdy project. Nothing that will change the world, but still, I wanted to share it with you guys.

The idea is to see if polishing the standard shooting barrels will yield any performance increase big enough that it is worth doing. This of course is hard to measure, and what one man deems "big enough" wont be worth the hassle for another.
I will make this thread a work-in-progress thread as I just did the initial tests today. More to come in the coming days.

It's taken a while to find the tools needed for the polishing itself, but I finally did. I shopped around a bit online in China and found the right bits and bobs. The pics should be pretty self explanatory - there's a power drill missing, but that's about it:

OLEO_BARREL_POLISHING_SETUP_01_1200PIX.jpg

Here are the polishing bits and chucks. The chuck was the missing part of the puzzle for a long time

OLEO_BARREL_POLISHING_SETUP_02_1200PIX.jpg

I cut a 3mm steel rod to length to attach to the chuck onto

OLEO_BARREL_POLISHING_SETUP_03_1200PIX.jpg

I bought a range of different polishing pastes. I think they are used for polishing gems

OLEO_BARREL_POLISHING_SETUP_04_1200PIX.jpg
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
So, before I start the polishing, I have to have a known level of friction of the unpolished barrel.

The best I could come up with, and a pic will follow tomorrow, was to mount the barrel vertically, insert the piston, oil it well and then mount a scale on a stick which was then inserted into the piston.
I would then lay my hand on the scale and gently increase the pressure until the piston would overcome its initial friction and start moving. I guess the initial friction is higher than the friction whilst moving but this is the best I could come up.
Also, the speed of which I would increase the pressure on the scale and any wobble in my hand would influence the amount of force it took to move the piston, but I tried as well as I could to replicate my movements.
To make matters worse, I had done a test polishing for the first inch or so of the barrel, so I also had to make sure I inserted the piston in the "old" part of the barrel.

With all these disclaimers aside, after having thrown out a few outer-lying measurements and still having 10-12 readings, the average "weight" needed to move the piston was:

Standard Mares Piston: 2178g

STC Piston: 1167g

The readings are a total containing the amount of "weight" I put on the scale with my hand plus the weight of the scale, rod and base plate making up the "scale holder".
(BTW, to obtain the readings, I filmed the scale and then reviewed the footage.)

That's a 1 kilogram less to get the STC piston moving and about half the force(?). Once moving, I do not know how big the difference is and I do not know how much of a percentage wise step up in efficiency this can be said to be.

Tomorrow, I will update with a pic of the "test bed" and then I will start the polishing. As soon as that is done, I will re-do the measurements.
Stay tuned:)
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
As promised, some quick snaps of the test setup:
BARREL_FRICTION_TEST_BED_01_1440PIX.jpg

To hold the barrel, I just used what I had around, meaning a light stand. Pretty much anything will do, but good to run a spirit level on the barrel. The video light on the left was needed since I I did the test last night

BARREL_FRICTION_TEST_BED_02_1440PIX.jpg


BARREL_FRICTION_TEST_BED_03_1440PIX.jpg

A small plastic bucket is hung under the barrel to catch dripping oil. The oil can be seen on the right

BARREL_FRICTION_TEST_BED_05_1440PIX.jpg

Here is the underside of the scale showing the holder I quickly put together and yes, that's a chopstick:)
BARREL_FRICTION_TEST_BED_06_1440PIX.jpg


BARREL_FRICTION_TEST_BED_04_1440PIX.jpg

This is how I performed the test. Slowly increasing the pressure I put on the scale with my hand whilst recording the moment the piston moved. Simple as that

Next step: Polishing:)
 
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learner

Member
Mar 30, 2015
8
1
13
42
Greece
I think it will be a great project. Sorry for writing here but as a final polishing compound you may want to try FLITZ cream and for the internal oil this nano oil (its a very thin and deep penetrating oil and maybe it cant be good for pneumatic guns. You may ask the site for more information):
http://www.nano-oil.com/
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
OK, Ladies and Gents, the results are in. Drum Roll...

But first, thanks to learner for your ideas, but I wanted to do this quick, dirty and cheap. Which means with what I can find online or near me in China.
The costs of what I used to polish one barrel and to make one polishing tool which can be reused (chuck + r0d) was USD 6-7. That includes shipping which is over half the total;-)
Basically, I wanted this test to just show if it would make much of a difference at all. I do not know, how much better my results would have been if I had used better and much more expensive materials.

But back to that drum roll...:

The results for the Mares Piston:
Before polishing: 2178g
After polishing: 1470g
Friction Reduced by: 32.5%
The results for the STC Piston:
Before polishing: 1167g
After polishing: 768g
Friction Reduced by: 34.2%
Personally, I don't feel it is a huge reduction in friction, but others may disagree. I was kinda hoping for more. But in terms of my method, at least the reduction in friction was measurable and pretty much the same for both pistons.

What do you guys say? Would you do this if you had the polishing set handy? With the gun taken apart already, it shouldn't take more than 1-2 hours. Is it worth it to you?

Now, I thought about waxing the inner barrel but I don't know if eg. carnuba wax has any adverse impact on o-rings and seals or the oil? It would likely be rubbed off pretty fast anyways.

Also, I'd love to hear from Pete or Tromic, or any other engineer type out there, what my data/findings can be said to mean in more real use? Can we say that the friction whilst the piston is moving is likely to have been reduced by 1/3, too?

On a another note, I managed to verify that the STC pistons have much less friction that the standard Mares one. It is a tad shorter and lighter, too (8.9g vs. 10.6g). Going from an unpolished barrel and a Mares piston to a polished one with an STC piston gives you a 65% reduction in friction.
But they are not as sturdy as the Mares ones, it seems. I have busted one already - though at high pressure in a Mares Mirage.
 
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learner

Member
Mar 30, 2015
8
1
13
42
Greece
Interesting findings. Hope to keep the low friction when you close it. Maybe someday when i learn how to disassembly mine (cyrano mares hf) i will try to polish it.
 

tromic

Well-Known Member
Aug 13, 2007
1,635
185
153
Croatia
Great stuff, very nice images and interesting setup for polishing and measurement!
From what I read about this subject in the last time, I also have some dilemmas...

- It is not beneficial to have the most smooth sliding surface for the piston. In that case piston would wipe of all the oil. It is beneficial to have some oil that the piston would not remove while moving forward.
- Friction is much lesser on higher speed than when moving piston slowly.
- Ower polishing might remove corrosion protection of the inner barrel surface.

The only real estimation of any change on speargun would be measuring the energy/speed of the spear on the target distance.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
Great stuff, very nice images and interesting setup for polishing and measurement!
From what I read about this subject in the last time, I also have some dilemmas...

- It is not beneficial to have the most smooth sliding surface for the piston. In that case piston would wipe of all the oil. It is beneficial to have some oil that the piston would not remove while moving forward.
- Friction is much lesser on higher speed than when moving piston slowly.
- Ower polishing might remove corrosion protection of the inner barrel surface.

The only real estimation of any change on speargun would be measuring the energy/speed of the spear on the target distance.
Aha, that's a bit like in sailboat racing where for many years, the belief was that a surface that had a tiny bit of roughness would hold on to a skin of water and then the surrounding water would glide against water and not against the boat. But in later years, people have now gone to as high a mirror polish as they can get. So, it went from about something like wet-sanding with 400 grit to, nowadays, wet-sanding to 2500 and then polishing on top of that.

I get you on measuring the energy and speed of the spear - We need that test tank Omer/Sporasub has!:)

I have been talking to Dima from UBL about a possible stainless steel barrel for my Mirage. Supposedly, that has very low friction. But I am a bit on the fence because I think my gun will end up heavier (and that's not good) and the ID is 12mm. That would mean, I would have to carry spares custom made for that system as well as running the gun at even higher pressures. Decisions, decisions, decisions...
 

tromic

Well-Known Member
Aug 13, 2007
1,635
185
153
Croatia
Aha, that's a bit like in sailboat racing where for many years, the belief was that a surface that had a tiny bit of roughness would hold on to a skin of water and then the surrounding water would glide against water and not against the boat. But in later years, people have now gone to as high a mirror polish as they can get. So, it went from about something like wet-sanding with 400 grit to, nowadays, wet-sanding to 2500 and then polishing on top of that.
...
This is an interesting information, but does it applies to spear gun too? Sailboat has water all around - piston has oil only on one side...?
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
same as original
OK, even better.
Can you tell me a bit more - did you make it yourself...? Did you use the ends of the old alu barrel in the handle and nose cone area or is the whole barrel made from stainless steel? How did you solve the issue about the barrel needing to be 18mm at those areas?

Sorry for all the questions, but it is a modification I am interested in having myself.
 

MarsArtis

Active Member
Dec 20, 2013
12
1
38
46
As Tromic already stressed out the work is actually is something not so useful.
First of all polishing will result in removing the anodized protection and therefore make the aluminium barrel suffer from salt water corrosion, soon or later.

Second point is: oil spearguns works under very high pressure. When they are above 18 ATM the friction benefit tends to be equal to 0%. Both in the arrow loading action and on shooting.
It would be nice if you could measure the friction gain on a pressurized gun. But it's an hard work.

My last 2 cents: about mares vs high sliding pistons (STC, LG....), I've found that the reduced friction may be only noticeable on loading... but as said the main force to be won is the pressure.
So to me the expense is not worth.
Moreover, I've experienced air leaks with high speed pistons because of their shape and orings. The skirt shaped like oring on classic pistons grants a better sealing of the system. To me it's much more important to have a secure and always working gun.

Inviato dal mio SM-T705 utilizzando Tapatalk
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
As Tromic already stressed out the work is actually is something not so useful.
First of all polishing will result in removing the anodized protection and therefore make the aluminium barrel suffer from salt water corrosion, soon or later.

Second point is: oil spearguns works under very high pressure. When they are above 18 ATM the friction benefit tends to be equal to 0%. Both in the arrow loading action and on shooting.
It would be nice if you could measure the friction gain on a pressurized gun. But it's an hard work.

My last 2 cents: about mares vs high sliding pistons (STC, LG....), I've found that the reduced friction may be only noticeable on loading... but as said the main force to be won is the pressure.
So to me the expense is not worth.
Moreover, I've experienced air leaks with high speed pistons because of their shape and orings. The skirt shaped like oring on classic pistons grants a better sealing of the system. To me it's much more important to have a secure and always working gun.

Inviato dal mio SM-T705 utilizzando Tapatalk
Thanks for your input.
Indeed, 0% is quite low and as such I have wasted a few days...;-)
Nah, joke aside, the issue of course is that I don't really know how much friction accounts for in a normal system, but I bet it is a bit more than 0%, haha. Until the size of that factor has more thoroughly been looked into, I personally can not say whether it is worth the work to me.
But I kinda like to have 0 excuses for not catching fish. I try to be a perfectionist with my gear as then, I can not blame anyone but myself. That's just my DNA. I totally get that what I find puts me at ease and gives me a nerdy sense of pride means absolutely nothing to most other people.

I obviously can't measure the thickness of the anodizing layer, but my gut feeling is there is still a lot left. There are longitudinal scratches in the barrel from years of shooting and they have not really been diminished much by the polishing. The whole thing just looks a lot shinier.
Also, I feel the barrel is of very good quality, perhaps better than newer barrel as even at the very front where it is not really anodized well, there is absolutely 0% corrosion.

Of all the leaks I have had in my guns, I have never had any, or at least any discernible one, from a pistons. Not even when I cracked the STC piston between the two o-rings, did it leak.

Now, I'd really be curious about titanium and SS barrel in 13mm;-). There are certain benefits from living in China. One being able to source locally produced products on the cheap:)
 

MarsArtis

Active Member
Dec 20, 2013
12
1
38
46
Indeed 0% is an hyperbole.
But close to reality when you consider the precharge pressure.

I've four oleo spearguns all with dry system:
Cressi SL70 + TOMBA 700+ Mares pistón (polished barrel) last opened 3 years ago;
Mares Longsten 84 + Tomba 700x
Mares Supersten 100 + Tomba700x
Lg Manilù 90+ lg speed piston.

The LG had an air leak due to the pistons oring. I had to replace it with a wider one.

Anyway since it is a ø11, even if with dry barrel system, is quit hard during the arrow loading phase.

I do love all of them


Inviato dal mio GT-I9505 utilizzando Tapatalk
 
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tromic

Well-Known Member
Aug 13, 2007
1,635
185
153
Croatia
Regarding friction benefit of "0 %" it might be actually, in case of Mares piston before polishing (your measurement data, Diving Gecko)

2178g/10 = 0,218 kp of dynamic friction.

I've read somewhere dynamic friction might be 10 x less than static friction.

Total energy loss on friction would be than:

0,218/30 * 100 % = 0.7 %

30 - is the force on the spear during shooting, for example...

Anyway, I like what you are doing! Just keep on working that way!
 

tromic

Well-Known Member
Aug 13, 2007
1,635
185
153
Croatia
Indeed 0% is an hyperbole.
But close to reality when you consider the precharge pressure.

I've four oleo spearguns all with dry system:
Cressi SL70 + TOMBA 700+ Mares pistón (polished barrel) last opened 3 years ago;
Mares Longsten 84 + Tomba 700x
Mares Supersten 100 + Tomba700x
Lg Manilù 90+ lg speed piston.

The LG had an air leak due to the pistons oring. I had to replace it with a wider one.

Anyway since it is a ø11, even if with dry barrel system, is quit hard during the arrow loading phase.

I do love all of them


Inviato dal mio GT-I9505 utilizzando Tapatalk
Nice collection of spear guns and - Tomba!
I suppose that hard loading of LG has the same cause as the elder Tomba700 had!?
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,616
400
188
Shanghai
Regarding friction benefit of "0 %" it might be actually, in case of Mares piston before polishing (your measurement data, Diving Gecko)

2178g/10 = 0,218 kp of dynamic friction.

I've read somewhere dynamic friction might be 10 x less than static friction.

Total energy loss on friction would be than:

0,218/30 * 100 % = 0.7 %

30 - is the force on the spear during shooting, for example...

Anyway, I like what you are doing! Just keep on working that way!

Aha, very good to know. Anyways, it was a fun project and my mental spearo is happy about knowing he gained about 0.5% of efficiency, haha

From practical experience, the dynamic friction at low speeds is certainly at the least 5 times less than the static one. How do I know? Because of the way my test was set up;-).
Eg. with the Mares piston and unpolished barrel it took 2178 g to get the piston moving but as soon as it did, it would continue to move on its own - even without the force of my hand on top of the scale. The weight of the scale and "scale holder" was 415g, so that is about 5 times less than what it took to get it moving.

I think it is very plausible that dynamic friction could be only 1/10 of the static.
 
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