S&W 79G Question
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S&W 79G Question
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Topic: S&W 79G Question (Read 1068 times))
Airjason
Plinker
Posts: 267
yes
S&W 79G Question
«
on:
July 26, 2022, 01:55:34 AM »
My S&W 79G air pistol in .177 shoots very poorly. I have been trying to find what I can do to make it shoot better. Took it apart several times already, changed all the seals. On firing, I can feel some CO2 gas blast out on to my hand. I suppose the leak is at the valve and barrel connection. I am wondering if there is supposed to be a small o-ring at this connection, otherwise it is just a metal to metal fit. My groups with the gun at 25 feet is a horrible 4 inches shooting from a rest.
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Hawaii, Honolulu
Beeman/Weihrauch 50S,77,35,R1 all .177
Many CO2 pistols
Jonah
Marksman
Posts: 433
yes
Real Name: Lionel
Re: S&W 79G Question
«
Reply #1 on:
July 26, 2022, 08:02:23 AM »
Can you tell where the blast of air comes from? It may be the transfer port seal or from the bolt o-ring.
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Bluffton, Texas
VN CO 59th Engr (Land Clearing) '69-'70
JayDee24ca
Shooter
Posts: 76
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Real Name: John
Re: S&W 79G Question
«
Reply #2 on:
July 26, 2022, 10:49:35 PM »
Its toast. You should sell it to me.
JD
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Canada, BC
brewbear
GTA Senior Contributor
Posts: 2338
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Real Name: Brewbear
Re: S&W 79G Question
«
Reply #3 on:
July 26, 2022, 11:27:05 PM »
Quote from: JayDee24ca on July 26, 2022, 10:49:35 PM
Its toast. You should sell it to me.
JD
Real funny! HA HA!
$450 and it's yours!
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USA, CA,
Roboslug
Plinker
Posts: 181
yes
Real Name: Floyd
Re: S&W 79G Question
«
Reply #4 on:
July 26, 2022, 11:48:22 PM »
OP, if it holds gas it's probably not one of the three screws that hold the valve in the frame. It probably is a result of the genius (read God-awful) barrel/transfer port/valve connection.
I presently have a 78G that needs a new valve and am scratching my head as to "how to seal the transfer port again?" Previously, I have used layers of electrical tape and pierce the TP hole. This provides some cushion as an o-ring that allows the barrel screw to tighten while still maintaining barrel/bolt alignment.
Most folks use some sort of silicone tubing, but I haven't had much luck with that.
Please let us know what you end up using.
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USA, LA, Baton Rouge
brewbear
GTA Senior Contributor
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Real Name: Brewbear
Re: S&W 79G Question
«
Reply #5 on:
July 27, 2022, 01:21:54 AM »
I have a couple of 78g, the .22 big brother but in all honesty, I have no clue on assembly/ disassembly of the things.
Following this thread.
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USA, CA,
Airjason
Plinker
Posts: 267
yes
Re: S&W 79G Question
«
Reply #6 on:
July 27, 2022, 06:49:32 AM »
Hey Roboslug, I used a couple of layers of electrical tape over the valve port and punched a hole through it. Works great, no gas leak at the transfer port now. Gun shoots quieter too. Did a quick test group that was about 1.25" at 25 feet. I think I can do better later.
As to your needing a new valve, what is wrong with the old one? There are o-ring kits on ebay for the S&W 78 and 79 that may get the valve working well again.
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Hawaii, Honolulu
Beeman/Weihrauch 50S,77,35,R1 all .177
Many CO2 pistols
Wayne52
GTA Senior Contributor
Posts: 31841
Gone but not forgotten!!!
Real Name: Wayne
Re: S&W 79G Question
«
Reply #7 on:
July 27, 2022, 07:56:31 AM »
I've redone a couple of the 78G's and to be honest after replacing all the o rings I don't feel any gas leakage at all from either one of them. I did do a complete restoration of everything in the gun which includes everything needed for the valve (new poppet is a must) to all the o rings everywhere in the guns. I did make sure that all the o ring spots were very clean before reassembling the guns. These guns are really nice when working like they should, I even bought a holster for them which wasn't cheap but well worth it.
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USA, MI, Grand Rapids
HHDSUPCOM Cam Rahn Bay VN 71-72
My F10 Shoebox rocks
Roboslug
Plinker
Posts: 181
yes
Real Name: Floyd
Re: S&W 79G Question
«
Reply #8 on:
July 27, 2022, 10:59:18 PM »
AJ, you'll know you have a leaky valve when you hear gas coming out of the barrel or open bolt. I've installed a Mac1 valve on one 78G and will try a white plastic valve from the big "E" auction site on the second 78G. There is nothing wrong with the Mac1 valve. It is lighter and smaller than the original so the performance is better. I can't back that up, but fuel economy is better. About 75 shots with three turns of the hammer screw. I don't have a chrony at this time.
The auction valve is even lighter than the Mac1 valve, so I'm real curious how this one will run.
BTW, the Mac1 valve has had well over 200 Co2 cartridges and 20,000 pellets since I installed it less than three years ago. I shoot it almost every day. The last cartridge went 83 shots in a 91F garage.
As far as leaks go, try the "tissue" test by laying tissue over the bolt/grip area and watch to see if the tissue moves when fired.
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USA, LA, Baton Rouge
brewbear
GTA Senior Contributor
Posts: 2338
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Real Name: Brewbear
Re: S&W 79G Question
«
Reply #9 on:
July 27, 2022, 11:49:51 PM »
These are my two S&W 78G. Due to lack of knowledge and time and also fairly close proximity to Mac1, they will go to Tim in the near future.
Roboslug, what you are saying about the Mac1 valve is encouraging both for performance and fuel economy, thank you.
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USA, CA,
45Bravo
Self confessed addict of anything with a trigger..
GTA Senior Contributor
Posts: 2953
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Real Name: Ian
Re: S&W 79G Question
«
Reply #10 on:
July 28, 2022, 01:20:29 AM »
This series has some good information in it.
When daisy started making the 780 & 790 pistols, they replaced the metal to metal transfer port with a plastic affair that would seal the area better.
https://www.pyramydair.com/blog/2019/06/smith-wesson-78g-and-79g-target-pistols-part-4/
«
Last Edit: July 28, 2022, 01:22:35 AM by 45Bravo
»
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Houston, Tx.
I make 2 predictions;
ON THE DATE WHEN US TROOPS ARE ISSUED AN Energy Pulse Weapon,
1. The US Soldier will have on his person a version of the Colt 1911.
2. He will be aiming the NEW Weapon at someone carrying an AK47.
TerryM
Expert
Posts: 1559
yes
Re: S&W 79G Question
«
Reply #11 on:
July 28, 2022, 07:40:10 AM »
I had a 78G for a while, put new seals in it. They are a different animal. I really liked the balance and feel of the gun. Couldn't get mine to group well, sold it.
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TX
Crosman model#
101, 108, 110, 112, 113, 114 (x2), 118,
140, 180 (x3), 187, 400, Mark II, 1377, 1322, 150, 122CG, Sears 126.19311, Ted Williams Match Rifle (2nd variant 160) Self made 180-400-114 hybrid carbine
Benjamin model#
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Sheridan:
Blue Streak (x2: '64, '67)
F model CO2 Blue Streak (converted to bulk fill)
Roboslug
Plinker
Posts: 181
yes
Real Name: Floyd
Re: S&W 79G Question
«
Reply #12 on:
July 28, 2022, 08:46:20 AM »
I can only guess that Tim tried plastic valves over the years but chose to stick with machined brass valves that he sells now for either performance or longevity issues. I have at least one spare Mac1 valve for my c600's and 78G.
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USA, LA, Baton Rouge
Airjason
Plinker
Posts: 267
yes
Re: S&W 79G Question
«
Reply #13 on:
July 31, 2022, 04:54:47 AM »
Just a follow up on my original post. While the electrical tape bushing worked on my first S&W 79G, it didn't work on my second pistol as the original bushing was too worn out. Today I was busy trying to work something out. I made a new valve bushing using delrin and it worked to stop the gas leak at the transfer port. Now both guns have no puff of gas on my hand as I fire them. They both shoot about an inch group at 25 feet. Note, the new delrin bushing is made high and is to be trimmed to fit. The hole through it is smaller so as to give it strength.
«
Last Edit: July 31, 2022, 05:21:11 AM by Airjason
»
Logged
Hawaii, Honolulu
Beeman/Weihrauch 50S,77,35,R1 all .177
Many CO2 pistols
Airjason
Plinker
Posts: 267
yes
Re: S&W 79G Question
«
Reply #14 on:
July 31, 2022, 03:28:08 PM »
There is another concern with the S&W 79G. While you have the gun apart, check the inside of the barrel at the transfer port hole. My guns had burrs that could damage the pellets as they were fed into the breech. I took a piece of 400 grit sand paper wrapped around a drill bit to remove the burrs.
Logged
Hawaii, Honolulu
Beeman/Weihrauch 50S,77,35,R1 all .177
Many CO2 pistols
Roboslug
Plinker
Posts: 181
yes
Real Name: Floyd
Re: S&W 79G Question
«
Reply #15 on:
July 31, 2022, 10:14:31 PM »
Wow AJ, that's a great idea. Yes, chamber burrs were standard on SW air pistols.
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USA, LA, Baton Rouge
Airjason
Plinker
Posts: 267
yes
Re: S&W 79G Question
«
Reply #16 on:
August 01, 2022, 01:31:30 AM »
Hey Guys, my delrin bushing failed, just had to say this to dispel false hopes to anybody trying it. I went to making a bushing out of brass today and it is back to a metal-metal fit at the gas transfer port. The gun with the electrical tape over the original bushing is still holding up, well it's been only a few days so far. Did a test shot group with each gun, photo shows results.
Logged
Hawaii, Honolulu
Beeman/Weihrauch 50S,77,35,R1 all .177
Many CO2 pistols
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