Alignment of homemade piston in the barrel

[Zahar]

Having a front cover, a handle and a native sear, I decided to pile a full-fledged gun with a 12mm stainless barrel and a stainless receiver! Piston combined caprolon + titanium with one O-ring and a segment valve for pumping through the barrel with a pumping piston! As a centering of the piston in the barrel applied a split bushing of graphite-filled kaprolon! Excessive backlash of the piston when arming the platoon removed the length of the piston skirt in which to facilitate the hole made longitudinal! Backlash became 1.5mm! In general, nothing new except a split bushing of the piston and a split bushing in which the piston is fixed with a sear for centering the piston skirt!

 

[popgun pete]

You should post this thread on the pneumatic gun sub-section as then more people will see it. I only saw it because I put a thread on the Demka BR internal; rubber pipe guns here and just decided to look at what else was here.

 

[Zahar]

I find it difficult to navigate! If you have the opportunity, then I authorize to place My Solution in any Theme you need on this site. Thank!

 

[popgun pete]

I find it difficult to navigate! If you have the opportunity, then I authorize to place My Solution in any Theme you need on this site. Thank!

I don't have the authority, but you can ask foxfish to move this thread to https://forums.deeperblue.com/forums/pneumatic-spearguns.110/ as he is a forum administrator. In fact he may look at this thread now there are new posts. https://forums.deeperblue.com/members/foxfish.7596/

 

[foxfish]

Done....

 

[popgun pete]

Very Interesting design! So this gun is pressurised or pumped up through the muzzle as say in a Zelinka, but uses a separate pumping piston while the main piston is caught by the sear lever and contains a valve within the piston that allows air to enter the gun. Is that correct? A single seal piston will travel very fast as friction is low, but single seal pistons tend to rock or wobble in the barrel, especially during muzzle loading for the next shot. I assume the split bush on the piston behind the single "O" ring seal stops this wobbling, but how does air flow through the piston during pumping or does it have a tiny hole running right through it, but with a one-way check valve.

The white plastic object mounted on the wire is a line release I assume, the wire acting as a torsion spring. What pressure level do you use in this 12 mm diameter inner barrel gun?

The metal piece that flanks the sear lever and helps centre the cocked piston while stopping the mushroom tail jumping the sear tooth is very similar to what Mares used when they had a rocking piston in their very early “Sten” gun, only it was made from plastic. Mares omitted this piece when their next piston had much more widely spaced seals.

 

[popgun pete]

This zipped file shows the "Sten" diagram with an annotated parts table, Mares never named the parts originally so I wrote them in, guessing the names.

 

[Zahar]

 

[Zahar]

Segment valve - valve Alexander Migachev (Mechanics)! What is the publication date of the MARS centering piston bushing?

 

[Diving Gecko]

Wow, so simple - like in some bicycle handpumps. A small cut out of the o-ring flange lets the o-ring "leak" on purpose in the direction of the cut-out. Am I understanding this correctly?
I like the trigger sear, too. Looks well made and better surface finish than the ones I have. Looks to be MIM molded? What brand is that trigger sear? Pelengas?

 

[Zahar]

Trigger Pelengas - Trigger Yuri Pastushenko!

 

[Zahar]

http://www.fishgun-master.ho.com.ua/oglavlenie.htm -
Yuri Pastushenko!

 

[popgun pete]

Segment valve - valve Alexander Migachev (Mechanics)! What is the publication date of the MARS centering piston bushing?

Mares included the plastic bushing in 1968 or 1969. The very early "Sten" (1967) lacked this bushing (part no 163315 or 15 as indicated on the parts diagram) and this could cause problems with the short and prone to wobble piston, so the bushing was added. When Mares changed to a 3 seal piston, 2 cup seals and a centre "O" ring, then they eliminated the bushing. The 3 seal metal piston was used for many years, but made the gun slightly less powerful than it had been originally with the short piston and its back to back one-piece cup seal. The plastic bushing affected the air flow in the inner barrel, but it was not too dramatic as I put a bushing that I made in my early "Sten" and it still shot OK. However the biggest change was when I had to replace the piston with the 3 seal version, then there was a noticeable drop in performance as judged by the jerk when the spear hit the end of the shooting line, but the reliability of the gun increased as previously during muzzle loading some air escaped the gun if the piston rocked in the inner barrel.