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68 special uncontrolled fire
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mestapho View Drop Down
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    Posted: 12 September 2014 at 10:43pm
My buddy gave me his old 68 special to play around with.
I bought a new CO2 tank and some paintballs.

It had a gas leak that was easy enough to fix with a couple of new o-rings in the gun valve.

At first it had uncontrolled fire, then it seemed to sort itself out and was firing great.
Unfortunately it started having uncontrolled firing again.  I pull the trigger and it
keeps firing until I stop it by the linkage arm.  Seems like it's not recoiling enough
for the sear to catch the rear bolt.

Any ideas of what needs to be done to correct this?
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Lightningbolt View Drop Down
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Points: 5055 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Lightningbolt Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2014 at 10:46pm
Check to see if the sear is worn out. Additionally if you have a leak somewhere maybe there isn't enough blow back pressure to reset the sear.

Edited by Lightningbolt - 12 September 2014 at 10:48pm
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Thx for the quick reply.  

The rest of the seals looked good and I couldn't hear any hissing, but I'll recheck them and the sear.

I read that not using a siphon tank could cause issues as well, is that true?
This is the tank I purchased.
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Tippmanns are the best in the business for handling liquid co2. Another potential issue could be a bent guide pin that can occur from a runaway gun which could create resistance.   I bent one once cycling my rt 98 at insane speeds.
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Points: 9906 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mack Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2014 at 12:20pm
OK, it's been a long time since I messed with one of these, but I thought the 68 Specials were among the last markers that Tippmann made that were designed for liquid CO2 so required a siphon tank.

Where's OS when you need him?
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Originally posted by Mack Mack wrote:

OK, it's been a long time since I messed with one of these, but I thought the 68 Specials were among the last markers that Tippmann made that were designed for liquid CO2 so required a siphon tank.

Where's OS when you need him?

Yeah, from poking around I believe that is true. 
Can you still buy siphon tanks?  Couldn't find one online.
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If I remember os seminar he stated that the anti siphon was for consistency problems particularly when it's cold.   Another option is to run the tank vertical with a coiled remote.   I don't think that this is the problem with a runaway gun but maybe it's possible.
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Three options:

1. Worn sear, or bolt recess. File sear to a 'square' where it engages bolt recess. File recess in bolt to square. If these edges become rounded and they do, bolt will 'bounce' over sear and a runaway.

2. Recoil spring. With age it weakens and will not hold enough forward pressure on bolt to secure lock it on sear.

3. Valve spring too weak, not allowing enough blowback to get the bolt to move far enough back in cycle to engages sear.
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Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mestapho Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2014 at 1:59pm
Originally posted by oldsoldier oldsoldier wrote:

Three options:

1. Worn sear, or bolt recess. File sear to a 'square' where it engages bolt recess. File recess in bolt to square. If these edges become rounded and they do, bolt will 'bounce' over sear and a runaway.

2. Recoil spring. With age it weakens and will not hold enough forward pressure on bolt to secure lock it on sear.

3. Valve spring too weak, not allowing enough blowback to get the bolt to move far enough back in cycle to engages sear.

Thanks for the tips.  I refilled the CO2 and its working fine again.  I just have to keep the velocity
adjuster screw nearly all the way in.  I think it was runaway firing last time due to the CO2 being low.
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Points: 5055 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Lightningbolt Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2014 at 7:44pm
I was laughing thinking that may be the problem. Glad it's working
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