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General Discussion To Gateway To Airguns => The Shop => : ezman604 March 01, 2010, 02:40:50 PM
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I have a question for and need advice from the pros here. I just got a used (like new) Benjamin Super Streak .22 barrel in. It was a complete barrel assembly minus only the cocking lever and pin. It even had the breach seal but man, is it toast. I have some spares so that's no biggie. I posted a picture below of the old seal that came off the USED barrel I received. This seal had 2 spacers behind it. Too many???
Here's my question. The SS has spacers behind the seal. The parts breakdown shows 3 spacers (total available) to put behind the seal. HOW many spacers should be installed and just HOW far should the seal protrude from the breach? With the new barrel I just installed, I did not install any spacers. The seal protrudes from the breach just slightly. I thought that would be enough to make a good seal. And the gun is putting out 800fps with .22 cal CPHPs. Should I drop 1-2-3 spacers in behind the seal to get a better closed system and more fps? Here too is a shot of the barrel with a new breach seal with 1 spacer.
Thanks ya'll and Happy Shooting!!!!
Dave
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To my eye, that seal is standing a little proud. The seal alone, no spacer would probably do it. The only thing shimming a proud seal would do is cause barrel droop and faster seal wear.
Pull the spacer and chrony it again. Muzzle Velocity will most likely be the same.
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Thanks Sam, that's kinda what I thought. But I'm relatively new to this. Like I said, the way my new barrel seal looked, I put no spacers behind it and it protruded enough to make what I thought was a good seal. And 800fps doesn't seem like a bad sealing. But the Benji SS is rated at a much higher fps. Oh well, I'll pull the spacers till it starts losing power and THEN possibly add some.
Thanks again!!!!
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800 FPS is pretty good. Airguns are tested with the lightest pelllets available to get max velocity numbers. You seem to be in the ballpark for real world figures. 800 fps in .22 is very rrspectable!
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You should not have to use spacers with a new seal. That seal as Sam said, sits too high and could cause the barrel not to close properly.
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So, I'm guessing the spacers are to make up for any irregular machining of the seal slot depth? What's the rule of thumb for when to use and not use a spacer?????
Just trying to learn. It's the old radio chief engineer in me. LOL
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Normally you should use a spacer when you cannot feel the seal sitting just above the face of the barrel bore breech surface
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Sounds like a plan. (http://../jscripts/tiny_mce/plugins/emotions/images/smiley-laughing.gif)
Thanks Gene & Sam.
Dave
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That seal in the picture came from the used barrel I received. It looks like a couple of issues there. Looks to me there should not have been 2 spacers behind it, it protruded WAY too far and got crushed. And also looks like a victim of massive detonation. Whatcha think???
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Yes it got hot it looks like. Also remember it should crush down some when barrel closes. I have seen lots of breech seals that look like they are bad but not really. One sure way to check is to do the tissue test.
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Hmmm...just took another look at my picture and noticed something interesting. Seems someone installed THIS seal backwards. Not sure if it was done at the factory or by the former owner. That, along with 2 spacers, would explain the crushed seal.
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800 FPS?!?!?! Man that's haulin' the mail!!! Sam and Gene are right,...I wouldn't bother with the shims either. Most of the time they aren't necessary and inhibit correct barrel lock as well as add to barrel droop. To me, if you take a straight edge, and drag it over the breach,...and you feel the seal,...that's good enough. The tissue test is a good way to tell if you have 'blow outs' around the seal, but a visual inspection will tell you as well. I call it the 'dough nut' ring around the port in the end of the action (for rifles that seal from the breech). If there is a nice clean ring around it, chances are you're good to go. If you see where air/exhaust is blowing by the port and seal like a smear around the 'rings' outer edge then a shim might be necessary. I rarely clean the breech area of my guns, so a minute amount of dust helps with the visual inspection. I do wipe off the seal face periodically though. Hope this helps, tjk