Question Spring Gun Tuners

Question Spring Gun Tuners

Joined: November 21st, 2011, 1:41 am

March 24th, 2012, 1:34 am #1

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
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Joined: June 22nd, 2010, 12:49 pm

March 24th, 2012, 1:47 am #2

But I don't mess with the port because some how the engineers that design the guns are a lot smarter that me. As long as the ports look clean, I don't mess with them. If I find the breech is rather tight, I might champher it a tad. That's about all I do in that categories of 'tuning'. Hth's.

Theoben H.E. Gas Rams,..Shock the system!!!
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Joined: October 21st, 2000, 9:30 pm

March 24th, 2012, 1:54 am #3

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
Some brands are already done, and other makes aren't. The primary reason i did it was to reduce possible hot spots that can fry piston seals and it can help reduce detonation due to hot spots. I doubt you get much if any velocity increase unless you are trying to push the powerplant pretty hard for max power. I did note that I got less evidence of seal burning from chamfering/radiusing the port.

"The Universe is comprised mainly of two things.. hydrogen and ignorance."
John Dobson
Inventor, astronomer and metaphysical thinker.
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Joined: May 15th, 2011, 4:13 pm

March 24th, 2012, 1:55 am #4

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
Probably not much to be gained, and is a PERMANENT mod. You´ll gonna have to throw the receiver (main part of the gun, and most expensive part along with the stock)if this doesn´t work.
Maybe some guns that are produced in all calibers with a same transfer port, and your example is a .25, might benefit from this. No proven mods out there for transfer ports.
I´ll be happy to bore mine out, probably by a machinist friend, if this were a proven mod for my guns.
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Joined: March 15th, 2005, 12:43 am

March 24th, 2012, 2:51 am #5

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
That transfer port, if you will, serves two purposes. It routes the air to the rear of the pellet and restricts the speed with which the piston bottoms out. ie. You are creating some slight back pressure as the piston moves forward. Make the hole bigger and you'll increase the force with which the piston bottoms out against the front of the compression chamber. You will shorten the length of the firing cycle. Not a good idea.

Now, if you wish to improve the movement of air into the chamber, you can polish the inside of the hole with some fine media. That will improve the flow of air similar to the polishing and porting in a custom built engine. Just don't make the hole bigger. Make it smoother. Who knows, it might make the gun more accurate by a thousandth or so.
HTH
John
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Joined: March 23rd, 2012, 5:27 pm

March 24th, 2012, 3:16 am #6

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
First of all, you really dont want to go there.
With that out of the way, I personally chamfer just a touch and\or polish, but that depends of the state of the gun in the first place. But I do not do this for any speed gain. If it's power you want from this, better just buy another rifle or leave it alone. I've seen really nasty coarse chamfers from the factory, and really horrible porting jobs from over-ambitious previous owners, both of wich are bad and promote inconsistency, poor handling and faster self destruction.
Bigger hole equals more pressure, but lower speed, and vicaversa according to Bernoulli. Sounds simple doesnt it? Trust me, it's NOT that simple, not in springers anyway, as soon as you put a projectile in the way, it's another science. A chamfer and a smoother hole reduces turbulence, which in turn will promote consistency and accuracy out of the barrel. But again, put a projectile in front and a heavy piston at the back..... There's still a whole lot of ifs ands buts hows and whys to the matter, so, you really do not want to go there. Overdo a chamfer and\or a port and you can end up with serious piston slam\bounce, a horrible shooting experience and a really deep but slender ashtray to mention a few things.

The dont go there part especially applies to porting, just leave it or I'm pretty sure you'll be unhappy with the next chrony numbers. For example I have fixed a couple of guns that had over ambitious owners that thought porting was a good idea because they probably thought Bernoulli made airrifles, well if only he did... It can be fixed by gluing in tubes and put the port back to original spec, wich by the way it turns out, is ALMOST always pretty much ideal for pelletspeed and handling.
Last edited by El-Joppo on March 24th, 2012, 3:20 am, edited 1 time in total.
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Joined: October 21st, 2000, 9:30 pm

March 24th, 2012, 3:18 am #7

Probably not much to be gained, and is a PERMANENT mod. You´ll gonna have to throw the receiver (main part of the gun, and most expensive part along with the stock)if this doesn´t work.
Maybe some guns that are produced in all calibers with a same transfer port, and your example is a .25, might benefit from this. No proven mods out there for transfer ports.
I´ll be happy to bore mine out, probably by a machinist friend, if this were a proven mod for my guns.
I have opened up transfer ports and have achieved performance increases. The big question I just how much to ream the port out? The answer is: it varies with the make and model..and if you go too big..you lose not just power but the gun can become more harsh. With less backpressure the piston tends to slam. I'll give and example: the Beeman R9 (hw95) comes from the factory with a 3mm (.118") port. I get best results with a .121" port that also gets radiused at the back. I do not use a drill, but rather a precision ground .121" reamer. Drills have a tendency to drill slightly oversized holes if not done with a perfectly sharpened/centered bit and done in a machine.

"The Universe is comprised mainly of two things.. hydrogen and ignorance."
John Dobson
Inventor, astronomer and metaphysical thinker.
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Joined: October 21st, 2000, 9:30 pm

March 24th, 2012, 3:29 am #8

My computer has been messed up in recent weeks so I've been posting via my phone. The problem with these andriods is that they sometimes assume you're trying to spell or say one thing and it seems to prioritize its decision over what you're really trying to type out. Plus..I'm still learning this contraption..LOL.

"The Universe is comprised mainly of two things.. hydrogen and ignorance."
John Dobson
Inventor, astronomer and metaphysical thinker.
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Joined: September 1st, 2001, 6:38 pm

March 24th, 2012, 3:36 am #9

Do you port or chamfer the transfer hole and what fps gain?That is in front of piston seal leading into the barrel.
1. By porting I gather you mean change the port size. It's risky as mentioned. Consider those replies you got with all due weight. If you want to experiment with changing port sizes (Danger, Will Robinson), leave yourself a way to return the port to its original size if performance decreases in any way.

2. Now, as to an actual chamfer, don't do it. Just nicely-smooth or roll a sharp edge if there is one so it does't cut the breech seal or distort the airflow. That's it and you're done. If you actually chamfer the port you increase the air that's held inside the chamfer when the rifle is fired. That's air that could have/ should have been put behind the pellet instead.

The above are two of those areas where less is almost-always better. The exceptions as applied to spring piston air rifles are very-few and far between.


Happy Shooting!

Ed, The Airgun Tune-Meister


"We can rebuild the squirrel. Make him stronger, faster...We have the technology"---Skyler M.
Last edited by ekmeister on March 24th, 2012, 3:38 am, edited 1 time in total.
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Joined: April 3rd, 2008, 10:15 am

March 24th, 2012, 3:44 am #10

First of all, you really dont want to go there.
With that out of the way, I personally chamfer just a touch and\or polish, but that depends of the state of the gun in the first place. But I do not do this for any speed gain. If it's power you want from this, better just buy another rifle or leave it alone. I've seen really nasty coarse chamfers from the factory, and really horrible porting jobs from over-ambitious previous owners, both of wich are bad and promote inconsistency, poor handling and faster self destruction.
Bigger hole equals more pressure, but lower speed, and vicaversa according to Bernoulli. Sounds simple doesnt it? Trust me, it's NOT that simple, not in springers anyway, as soon as you put a projectile in the way, it's another science. A chamfer and a smoother hole reduces turbulence, which in turn will promote consistency and accuracy out of the barrel. But again, put a projectile in front and a heavy piston at the back..... There's still a whole lot of ifs ands buts hows and whys to the matter, so, you really do not want to go there. Overdo a chamfer and\or a port and you can end up with serious piston slam\bounce, a horrible shooting experience and a really deep but slender ashtray to mention a few things.

The dont go there part especially applies to porting, just leave it or I'm pretty sure you'll be unhappy with the next chrony numbers. For example I have fixed a couple of guns that had over ambitious owners that thought porting was a good idea because they probably thought Bernoulli made airrifles, well if only he did... It can be fixed by gluing in tubes and put the port back to original spec, wich by the way it turns out, is ALMOST always pretty much ideal for pelletspeed and handling.
I am no expert, not even a novice, LOL!!
However, this conversation reminds me that bigger is not always better (shhh, don't tell that to your girlfriend or wife, LOL!!), of course, depending on what you are trying to accomplish.

When I was at Ft McClellan I had a 280ZX and wanted a larger exhaust for "better air flow", so, had one installed, it was several sizes larger AND had some other "stuff" removed as well that would get you in a lot of trouble now.

I "thought" she should really run now with it getting a lot of air flow...- WRONG!!!
Low end (back pressure) was gone and it was slower off the line. At very high speeds it was better, however, you do not drive at very high speeds every day without getting a bunch of tickets and the worse thing they did years ago was the "point system" when you get a ticket. At one time, you could get 3 tickets a day and no big deal as long as they were paid on time and they used to be $10, $15, $20 and $25. Today you get "points" and after so many "points", your license is pulled AND tickets are no longer $20. My last ticket was well over $200. Yeah, times have changed.

So, unless you are experimenting, the gun does not shoot well anyhow, you just want to experiment, etc, I would leave size alone. Polish it- Yes, but no more than that.

Just my novice opinion from experiencing this with a car (and now a truck) when something was on the road at night and it got hit as the truck sits low and whatever it was literally flattened the Y-Pipe. I HAD to get it repaired and should have ordered the correct part, but got a deal on a guy making one, so I said no smaller than what I have on it now (it was a new stainless steel exhaust), and when he was finished, it SURE was NOT any smaller, it was huge. I wish a million times I would have just bought a new Y-Pipe as I was still working. Even though the truck is modified and supercharged it is too big and once again, it is slower off the line, but high end is fine, but now I can not afford tickets either, LOL!!

Hope this get's you to thinking about size, air flow and power...
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