Beeman P17 "backdraft" mod?



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Offline Stinger177

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Beeman P17 "backdraft" mod?
« on: February 15, 2019, 05:45:54 PM »
Yeah, I know, yet another P17 topic.

I believe I have done my diligence in searching the net for the answer, but haven't yet found it.

I want to add a longer barrel and TKO to my P17, but obviously the piston then wouldn't clear the intake hole. I keep reading about the "backdraft" mod, but no where is there a clear explanation of how to do this. I understand the principle (I think) and that it involves holding the trigger back while cocking to draw air in through the valve. And yes, I am also aware that this is generally a bad idea, especially since I have removed the auto-safety mechanism, but I am a responsible shooter and I know which is the dangerous end of a gun.

I also understand that the shortened piston draw (due to the longer barrel/trigger guard interference) will lessen the power from a full draw, but a longer barrel should restore some of that lost MV (at least that's another thing that I've read).

I have tried holding the trigger on my stock (except for the safety) P17, but it does not open the valve to let air in.

I could drill a new intake hole further rearward on the compression tube, but it appears that there is a different way.

Can someone please explain how this is done?

Thank you.


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Offline Roadworthy

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Re: Beeman P17 "backdraft" mod?
« Reply #1 on: February 15, 2019, 06:05:21 PM »
You may get some insight here:  https://www.gatewaytoairguns.org/GTA/index.php?topic=80474.0  or you can try You Tube.
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Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #2 on: February 15, 2019, 06:13:05 PM »
You may get some insight here:  https://www.gatewaytoairguns.org/GTA/index.php?topic=80474.0  or you can try You Tube.

Thanks Thomas. I read that one, and every other thread I could find. It was actually that thread that gave me the idea of the TKO. I PM'd silent_airman about his full mod, but he never replied.

In that thread is where it says to "remove the auto safety so that you can pull the trigger when opening to back draft the air thru the exhaust port" (which is why I did that to mine). That alone does not do it. I think there must be some adjustment to the valve/trigger engagement or something.

Thanks though.  :D
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Offline mr007s

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Re: Beeman P17 "backdraft" mod?
« Reply #3 on: February 15, 2019, 07:59:22 PM »
Did you find this thread? https://www.gatewaytoairguns.org/GTA/index.php?topic=49115.msg639814#msg639814

You can also do the backdraft mod, and change it at will.

If you simply drill a hole into the face of the piston, it will de-comp. If you go too deep, a bit of epoxy will refill to a depth that works for you.

I highly recommend backdrafting with a 117 ring. The rings last, and the ESs drop to amazing levels.

Good job TomRob! LOL... Tom is right... slug it often as you sneak up on your choke... you'll feel when you are close. Try shooting it before you go the last little bit, you may already be where you need it.
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Offline tkerrigan

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Re: Beeman P17 "backdraft" mod?
« Reply #4 on: February 15, 2019, 08:05:25 PM »
I'm confused here, what does the barrel length have to do with the piston?  Any extra length sticks out the front of the gun.  Regards, Tom
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Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #5 on: February 15, 2019, 08:16:36 PM »
I'm confused here, what does the barrel length have to do with the piston?  Any extra length sticks out the front of the gun.  Regards, Tom


This. The moderator hits the trigger guard before it is fully cocked, thus reducing the full pull of the piston and allowing it to get past the air intake hole. In the position it is in this pic (borrowed from the thread that Roadworthy linked to) there is still about 1/2" of throw left if not for the moderator hitting the trigger guard.
So this is my question - How does he get any air inside the comp tube to even compress it? Supposedly there is a way for air to be drawn in from the rear valve, and that requires holding the trigger back while cocking. THAT is the unknown (for me)

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Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #6 on: February 15, 2019, 08:24:15 PM »
Did you find this thread? https://www.gatewaytoairguns.org/GTA/index.php?topic=49115.msg639814#msg639814

You can also do the backdraft mod, and change it at will.

If you simply drill a hole into the face of the piston, it will de-comp. If you go too deep, a bit of epoxy will refill to a depth that works for you.

I highly recommend backdrafting with a 117 ring. The rings last, and the ESs drop to amazing levels.

Good job TomRob! LOL... Tom is right... slug it often as you sneak up on your choke... you'll feel when you are close. Try shooting it before you go the last little bit, you may already be where you need it.

Well Eric, I saw that thread as well. Just didn't feel like reading through 28 pages of tit-for-tat to try to find the real answer, if it even lies within that thread. The page that your link goes to directly talks about de-comping, which is not what I want to do, so dishing the piston face does not apply to my question.

I'll read that thread in full I guess, right after I re-read the Bible.

Funny thing though about your #117 o-ring comment. I happen to be right now doing just that. I just got in a bag of 50 pcs. #117 o-rings (anybody need one?) and now I'm putting a Band-Aid on my knuckle from pulling out the piston and hitting the upper shroud.

Am I the only one who cuts themselves EVERY TIME I open up a gun?
« Last Edit: February 15, 2019, 09:16:27 PM by Stinger177 »
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Offline tkerrigan

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Re: Beeman P17 "backdraft" mod?
« Reply #7 on: February 16, 2019, 02:14:45 AM »
Looks like it's time for a missing and or shortened moderator and a modified trigger guard.  Regards, Tom
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Offline tkerrigan

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Re: Beeman P17 "backdraft" mod?
« Reply #8 on: February 16, 2019, 02:17:29 AM »
I have a 13.5" barrel on my Alecto and it works just fine. +50fps.  Regards, Tom
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Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #9 on: February 16, 2019, 02:26:55 AM »
I have a 13.5" barrel on my Alecto and it works just fine. +50fps.  Regards, Tom

I have the extended threaded barrel with a TKO on my own Alecto/Zoraki HP-01 but on that pistol, there is enough travel to obtain a full cocking throw.

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Offline stalwart

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Re: Beeman P17 "backdraft" mod?
« Reply #10 on: February 16, 2019, 09:18:58 PM »
Did you find this thread? https://www.gatewaytoairguns.org/GTA/index.php?topic=49115.msg639814#msg639814

You can also do the backdraft mod, and change it at will.

If you simply drill a hole into the face of the piston, it will de-comp. If you go too deep, a bit of epoxy will refill to a depth that works for you.

I highly recommend backdrafting with a 117 ring. The rings last, and the ESs drop to amazing levels.

Good job TomRob! LOL... Tom is right... slug it often as you sneak up on your choke... you'll feel when you are close. Try shooting it before you go the last little bit, you may already be where you need it.

Well Eric, I saw that thread as well. Just didn't feel like reading through 28 pages of tit-for-tat to try to find the real answer, if it even lies within that thread. The page that your link goes to directly talks about de-comping, which is not what I want to do, so dishing the piston face does not apply to my question.

I'll read that thread in full I guess, right after I re-read the Bible.

Funny thing though about your #117 o-ring comment. I happen to be right now doing just that. I just got in a bag of 50 pcs. #117 o-rings (anybody need one?) and now I'm putting a Band-Aid on my knuckle from pulling out the piston and hitting the upper shroud.

Am I the only one who cuts themselves EVERY TIME I open up a gun?

If you think it takes a long time to read... imagine the time I put into writing and illustrating it. lol

And, no... you're not. I de-burr everything I work on, so the next time in, it can't hurt anyone.

Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #11 on: February 16, 2019, 09:35:44 PM »
Eric, I wasn't making a slam on your very thorough thread. It's just that I still couldn't find the answer to my question.

I'm beginning to think that the backdraft thing does not exist, and that the only way that silent_airman got that setup to shoot is to remove and replace the TKO in between shots (which I did read somewhere in all my searching).

Still a nice article though. Wish I had all that access to machining.

Nice job!! :D
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Offline stalwart

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Re: Beeman P17 "backdraft" mod?
« Reply #12 on: February 16, 2019, 09:52:59 PM »
Eric, I wasn't making a slam on your very thorough thread. It's just that I still couldn't find the answer to my question.

I'm beginning to think that the backdraft thing does not exist, and that the only way that silent_airman got that setup to shoot is to remove and replace the TKO in between shots (which I did read somewhere in all my searching).

Still a nice article though. Wish I had all that access to machining.

Nice job!! :D

 Not taken as a slam, bud! I hear it all the time! And, I write a succinctly and briefly as I possibly can. Best I can do...

Backdrafting does exist... I developed the concept. With a long barrel (or a set screw "stop" in the nose), some will not open far enough to pull air through the inlet. A new hole, that clears, will also work, but another benefit to BDing is that the o-ring is not dragged over a hole. About the time a normal rig has ruined the ring this way, the modded ones are settling in for a seriously small ES (some as low as a couple percent, no vertical stringing... ever), and they last many times as long as stock.

When I shoot mine, I put a tiny drop of oil into the exhaust port (opened just enough to do so) and it gets drawn and evenly distributed throughout the air system as I open it the rest of the way (release trigger before closing, holding it open will allow the air to escape before it can cock). I dry fire it into a rag, to get rid of any excess, and it's ready to go.

Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #13 on: February 16, 2019, 10:25:06 PM »
I was hoping that at some time "The Man" (you) would appear!!

Please explain to this Simpleton what I am doing wrong. I pull and hold the trigger while pulling the upper cover back, stopping just short of exposing the hole (and trying to line up the barrel where I think an ldc would touch the trigger guard. Still holding the trigger, as I return the piston back down there is no build up of air in the tube to compress. I've tried holding the trigger only until the start of the return stroke and still nothing.

What am I doing wrong, or is there an adjustment inside, around, or on the valve stem that needs to be made?
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Offline stalwart

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Re: Beeman P17 "backdraft" mod?
« Reply #14 on: February 16, 2019, 10:34:10 PM »
Only hold the rigger during the opening.  If the pistol is still holding a vacuum when nearly fully opened, your valve spring is too strong (saw this one time) to allow drafting. Remove and compress it slightly... it should open within the upper's opening arc.

For anyone trying this, removing the auto safety is easy... pull the pin in front of the trigger, open the gun and dump out the spring and lever. Replace the pin (to cover the hole).

Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #15 on: February 16, 2019, 10:43:05 PM »
Quote
If the pistol is still holding a vacuum when nearly fully opened, your valve spring is too strong

OK, that explains why it didn't draw air in. My spring is stock. I didn't compress it or anything when I tuned the trigger (I did stretch the trigger spring a bit though - It's as light as my Alecto now  :D).


Quote
Replace the pin (to cover the hole).

Mine kept falling out, so I left it out.

Thank you Eric. I'll give it a try next time I'm inside it.
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Offline stalwart

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Re: Beeman P17 "backdraft" mod?
« Reply #16 on: February 16, 2019, 10:55:10 PM »
YW. My pleasure.

"knurl" one end of the pin, with wire cutters, and it will stay put.

Offline Stinger177

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Re: Beeman P17 "backdraft" mod?
« Reply #17 on: February 16, 2019, 10:58:37 PM »
"knurl" one end of the pin, with wire cutters, and it will stay put.

Good idea. Looks better than scotch tape, but mine's now in a little baggie with the safety lever (somewhere)  ???.
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