Canadian Airgun Forum

The stock bolt probe of the 760 is all plastic...with no o-ring to provide a good seal....just hard plastic pressing against the barrel. I sawed off the plastic bolt at the base where it joins the block and drilled a hole in the block to fit the new steel probe....which is actually a nail of the same diameter as the original bolt....The nose has been extended to push the pellet skirt to very edge of the port for a clear path of air....The bolt was fashioned so when the probe is fully closed and locked in...the seal is forced to expand slightly to form a very tight seal in the barrel. I did this be making the bolt with a very slightly wider circumference at the rear of the seal. Works very well as you can see by the numbers below, No valve work (except for plugging the hole) or porting has been done. It now shoots fast enough...reworked bolt probe added 40fps over just plugging the valve hole.

Stock numbers .............. 7.48 gr. wadcutter
3 pumps 262.8fps....witn new probe...422.6
5 pumps 327.4fps.................................519.2
10 pump 414.8fps.................................621.8

My gun now shoots with 3 pumps the same velocity of a stock 1377 with 10 pumps

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The cave you fear to enter....holds the treasure you seek

Excellent work!!

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Jonathan

Moderator

Thank You..it was harder than I thought to get the right angles on the bolt to mount the o-ring....And also how far up or down the bolt to place the o-ring......that was my 3rd attempt..3 hours of sizing..cutting..grinding and polishing to get the perfect fit.

This guy from the U.S. gets 577 fps with ten pumps AND he's using a 6.64 grain pellet so it looks like the new bolt on its own actually accounts for a lot more than 40fps increase...Lot of work but it was worth it..
https://youtu.be/64_OisMzrEY

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The cave you fear to enter....holds the treasure you seek

Nice work. A retail part like this would probably be equivienent in price to the entire cost of the 760.

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I have some airguns.

Nice custom work.
What did you use to cut the groove and profile?

For the short simple answer I used a power drill in a holder...I think they call it a poor mans lathe..a flat file....very small square file...a small triangle file and a small half moon file plus various grits of sandpaper and a micrometer to occasionally check that metal was actually being shaped/removed during the sandpaper phase.

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The cave you fear to enter....holds the treasure you seek

That there shows awesome ingenuity and skill! I have used my drill press occasionally as a poor man's lathe as well, but mainly for woodworking, although I have done a few jobs on brass and aluminum. Well done on this one,

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Iacio, ergo sum

Hey a drill press and a 4 way vise and you can do quite a bit of modding. Good on you for getting creative!!!

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Jonathan

Moderator

That's essentially what a mill is, with better axial bearings of course.

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I have some airguns.

That and the chuck wont drop out of a mill

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Jonathan

Moderator

Right on! I got by doing things with a drill press and files for years.
Got me started anyway.

I started with a table top drill press and a cross-sliding vise (over 30 years ago). Now I have two lathes, a milling attachment and a large floor stand drill press. It's worse than my airgun addiction.

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Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

Another good thing about the mods was that I only have to pump it twice for a 358fps ...7.48gr. wadcutter....great for indoor ranges to 30 feet..I think my 1377 is going to be gathering a bit of dust for awhile

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The cave you fear to enter....holds the treasure you seek

Pump twice? Ug... yeah I know. I'm so lazy.

Seriously though, great work.

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I have some airguns.

Well im sure this post will inspire our other members. Thats what it is all about.

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Jonathan

Moderator