GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: plinker99 on May 29, 2014, 03:03:36 AM
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after over a year of modding my 760, i figured that it's too light to shoot accurately. looking through the scope during the shot, i see the crosshairs jump around when i pull the trigger & it fires. i tried different holds & trigger finger positions with very limited success. it shot like a springer. one day i taped a weight to the barrel & there is was...better accuracy & less jumping around seen through the scope.
so the idea to make some weights inside the receiver. first i filled a plastic tube with some pellets. about 2oz. & wedged it inside the receiver below the barrel.
still too light. i filled one side of the bb resevoir with pellets & melted some wax to hold it in place. still too light.
that's where the old pellets come into play. i made a mold of the bb resevoir & made a weight that fits there with some silicone sealer holding it in. it came out about 4 oz. i made another mold for the area under the barrel in the receiver & made a weight there with silicone sealer holding it in. that one is about 8 oz.
so with the added 12 oz of weight, i find that i can stay on target much better when i pull the trigger. initial accuracy has improved. i still need to rezero the scope as everytime i take it off, rezeroing it takes a few days. i'll post some targets when i get to it.
so mods to this 760 so far.....
valve nose trimmed, piston stuffed & pump cup shimmed. solid pump pivot pin. stuffed the valve to reduce the volume to be close to a 2100 valve volume. tasco 3-7x-20mm scope. 2100 rifled barrel. flow thru bolt probe. honed the sear hammer surface. extended the sear on the trigger side. modified the trigger for a lighter 2 stage action. added weight below the barrel inside the receiver & weight inside the bb resevoir.
here's a picture of the weights inside the receiver.
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Drilling a hole in the stock and filling with calk helps also...
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Please pardon me for going a bit off topic but I have a question.... I have a 1966 760 and a significant amount of air comes out of the receiver past the bolt when I shoot it. Did you have this with your's? If so, how did you fix it? I would be more interested in buying an aftermarket replacement than modifying the original one.
Thanks in advance.
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avator,
i'm not sure what the 1966 760 looks like. the one i have i got in 2013. it has a plastic bolt. it leaked a lot when i first got it. since i changed the barrel i had to modify the bolt to fit it. that's when i decided to make a flow thur bolt. so far no leaks.
try this link might help .... http://www.gatewaytoairguns.org/GTA/index.php?topic=57504.msg549891#msg549891 (http://www.gatewaytoairguns.org/GTA/index.php?topic=57504.msg549891#msg549891)
the vintage gate has a lot of posts on the older 760's.
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Thanks Plinker;
I knew I had seen that post but I couldn't find it. Still up in the air about modifying the original bolt. This gun is 100% original except for the reseal kit and pump seal. I've also considered a rifled barrel for it. This one shoots pretty good for a smooth barrel but the leak really taxes the performance. I can actually feel the air hit me in the face.
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Two ways to get to there, I used a 66/664 to make a longer pump 13xx. had the rest of the 66 found a 760 at a yard sale used the pump tube and made a similar project...
http://www.gatewaytoairguns.org/GTA/index.php?topic=67286.msg643763#msg643763 (http://www.gatewaytoairguns.org/GTA/index.php?topic=67286.msg643763#msg643763)
I did not look at the picture before my first post.
how did you do the barrel I just used the 66 shroud had to move the hole for the barrel support/pump plug...
To me it looks? like a cut off, drilled out 760 barrel sleeving a 2100 straw barrel and were it exits the receiver rubber(bycyle tire?) on the pump tube also?
" i still need to rezero the scope as everytime i take it off, rezeroing it takes a few days. i'll post some targets when i get to it. "
there is a lot of movement on mine. maybe it would settle in and bed but I like open sights also
I can hit a quarter at 20-25 yards open sights so not in a hurry to put a scope on.
I am curious what the reduced volume got you... 630 fps at ten pumps?
I went more volume and thinner longer bolt probe.
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K.O.
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how did you do the barrel I just used the 66 shroud had to move the hole for the barrel support/pump plug...
To me it looks? like a cut off, drilled out 760 barrel sleeving a 2100 straw barrel and were it exits the receiver rubber(bycyle tire?) on the pump tube also?
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i did a post last year on the barrel mounting. i used the torrent barrel support, drilled out to fit the 2100 straw barrel with the transfer ports lined up. at first i just used the plastic spiral wrap for organizing computer wires but the barrel kept getting rust so i got a shrink tubing that fit the barrel & used that to cover it. in the area where the receiver clamps the barrel, i added a few wraps of electrical tape then added another larger shrink tubing over it. i did the same for the front barrel support. the inner tube rubber on the pump tube is to muffle the pump noise a bit.
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I am curious what the reduced volume got you... 630 fps at ten pumps?
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i made some shots today at 10 pumps & got low 690's with pointed 7.4gn & 650's with cphp 7.9 gn.
i usually shoot at 5 pumps for 550's with pointed 7.4 gn & 530's with cphp 7.9 gn.
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i noticed that with the cphp there is more air leaking from the bolt at 10 pumps. i'll need to work on that again.
more later.........
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I meant to say 630-650 ;)
I have to admit I like your bolt better.
how is the 2100 .22 conversion faring?
I used superglue to build up my 2100 bolt just a bit have not needed it on this one.
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how is the 2100 .22 conversion faring?
After shooting a little, to me it's a bit loud. It still needs some trigger work & a bolt that seats the pellets better. So for now it's on the back burner while I fuss with my 760 & 1377.
I also got a clone of a gamo delta in .22 Cal springer. I finally managed to find a way to hold it to be able shoot it decently. But it's still frustrating. It shoots cphp about 300fps.
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I have done the same thing by mixing spent pellets or BB's with epoxy. You just pour the slurry into the opening. Whatever the method, it seems like adding weight also stiffens those wimpy plastic clamshells.