760 musing

760 musing

Joined: March 1st, 2002, 12:22 am

November 13th, 2011, 5:10 am #1


so my contest entry is done, but I still need to write it up, edit the photos and sent it in. And I forgot the list of mods at the lab, so it will have to wait till tomorrow.

But this process has shown me some things, and I now believe if you have tools and the skill to use them, you can make a butt kicking gun.

Its my perception that flaws are small but fixable (affore mentioned tools and skill set), except for one thing: the magazine.

Shooting groups at the lab tonight, I finally correlated the pellets inconsistent seating in the mag with the bad groups/flyers. If the pellets all sat in the mag at the same depth, the group was pretty good. if the pellets all sat in the mag at random depths, the group would suffer with flyers.

PArt of that may be the bolt not seating the pellet consitantly and/or the bolt not locking. had many whiffed shots tonight cuz the folt had felt like it was rammed home, but was a bit short and didnt lock. After I made the effort to make sure it was rammed and locked, groups got better. Chrony numbers became more consistant too.

Never did break 500, well ok with SSPs  (660 ish) but the real pellets would top out around 485. I blame that on TP issues and the air leaking, or at least not flowing efficiently from the valve thru the TP and into the leade to drive the pel. I figured Id be around 525 to 550 with the valve mods, TP enlargement and piston stuffing. And maybe its there, but I aint making it and still make the deadline.

Most amusing part of the whole build was taking pics today for submission. ITs snowed here in bozeman, 3 or 5 inches down, just beautiful whne the sun was out, and the perfect back drop. I dropped the gun going out the door to photgraph. Snapped the butt stock right off at the clamshell. Turns out the buttstock plastic failed, not the joint so I consider my constrution efforts vindicated. Super glue to the rescue!

Making the trigger better screwed up my safety, so I had to mod that tonight too. I do think that some one could make a drop in 2 stage trigger that would not require much if any mods to the clamshells. Fit right over the exisitng trigger pins.....

 

 


dr_subsonic's pneumatic research lab
<img alt="[linked image]" src="http://img.photobucket.com/albums/v301/ ... od-1-1.jpg">
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
Last edited by dan_house on November 13th, 2011, 5:18 am, edited 1 time in total.
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Joined: April 28th, 2010, 12:23 am

November 13th, 2011, 6:42 am #2

even with my transfer mods and added orings and tricks with crazy glue, that transfer system sucks, plus i broke the dam breech block and had to repair that, i think a good amount of air is lost in this transfer, unlike the 2240s and such. Ultimately, with the 417 i decided i have to go bulk fill or hpa.I dont think that modding th gun otherwise will make it the lite hunter i want it to be.Im gonna use steel tube to elongate the compression tube, then thread a foster at the front , call it quits and bulk fill the 38ccs or so.as for the clip, i never got as far as testing accuracy on mine , and dont have a clip so i have no clue how that affects it, i also see this as an issue with the 417.Ill test accuracy for my own intrigue next week when the contest is all over,im kinda only gunning for the win on looks , becuse 90 percent my time was invested in that, making the stock and all.it was a worthwhile endeavor and proves that this 32 dollar gun can be a gem with lots of patience and hours invested.
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Joined: February 9th, 2006, 10:35 pm

November 13th, 2011, 10:17 pm #3

so my contest entry is done, but I still need to write it up, edit the photos and sent it in. And I forgot the list of mods at the lab, so it will have to wait till tomorrow.

But this process has shown me some things, and I now believe if you have tools and the skill to use them, you can make a butt kicking gun.

Its my perception that flaws are small but fixable (affore mentioned tools and skill set), except for one thing: the magazine.

Shooting groups at the lab tonight, I finally correlated the pellets inconsistent seating in the mag with the bad groups/flyers. If the pellets all sat in the mag at the same depth, the group was pretty good. if the pellets all sat in the mag at random depths, the group would suffer with flyers.

PArt of that may be the bolt not seating the pellet consitantly and/or the bolt not locking. had many whiffed shots tonight cuz the folt had felt like it was rammed home, but was a bit short and didnt lock. After I made the effort to make sure it was rammed and locked, groups got better. Chrony numbers became more consistant too.

Never did break 500, well ok with SSPs  (660 ish) but the real pellets would top out around 485. I blame that on TP issues and the air leaking, or at least not flowing efficiently from the valve thru the TP and into the leade to drive the pel. I figured Id be around 525 to 550 with the valve mods, TP enlargement and piston stuffing. And maybe its there, but I aint making it and still make the deadline.

Most amusing part of the whole build was taking pics today for submission. ITs snowed here in bozeman, 3 or 5 inches down, just beautiful whne the sun was out, and the perfect back drop. I dropped the gun going out the door to photgraph. Snapped the butt stock right off at the clamshell. Turns out the buttstock plastic failed, not the joint so I consider my constrution efforts vindicated. Super glue to the rescue!

Making the trigger better screwed up my safety, so I had to mod that tonight too. I do think that some one could make a drop in 2 stage trigger that would not require much if any mods to the clamshells. Fit right over the exisitng trigger pins.....

 

 


dr_subsonic's pneumatic research lab
<img alt="[linked image]" src="http://img.photobucket.com/albums/v301/ ... od-1-1.jpg">
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
What seemed like my biggest accuracy problem was not having a good rest to shoot from. That and not enough sleep and too much coffee lately.

I found that in one of the mags I was using that the pellets fit looser in the center hole than in the others. Most of the mags I have seem to hold all the pellets pretty well. Once you push the pellets in and they "click" into place, the gun shoots pretty well.

Dan, did you have all the bolt closing issues before you switched barrels? I've not experienced that kind of problem. I just shove the bolt home and it stays there. Maybe the breach end of new barrel needs a little more tweaking to allow everything to seat properly?

I still don't understand how Rob's breach block thingy broke....


I plink, therefore I am.
Last edited by airgunandy on November 13th, 2011, 10:18 pm, edited 1 time in total.
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Joined: April 28th, 2010, 12:23 am

November 13th, 2011, 11:25 pm #4

i got a 760 with stock rifled barrel , when i tried disconnecting the barrel from block, it snapped like the plastic it is. So i repaired as best i could lacking time to order another..Ill do most power mods after the fact, i know now i bit off more than i could chew in 7 weeks , still came up with a decent rifle.
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Joined: February 9th, 2006, 10:35 pm

November 13th, 2011, 11:34 pm #5

OK. Now it makes sense. I broke one too that way. I thought something happened while pumping or shooting the gun.

I plink, therefore I am.
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Joined: April 28th, 2010, 12:23 am

November 13th, 2011, 11:48 pm #6

or grime had the plastic almost welded to the plastic lol.Hopefully do alot more tinkering and modding this gun when the pressure is off
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Joined: February 9th, 2006, 10:35 pm

November 14th, 2011, 1:44 am #7

so my contest entry is done, but I still need to write it up, edit the photos and sent it in. And I forgot the list of mods at the lab, so it will have to wait till tomorrow.

But this process has shown me some things, and I now believe if you have tools and the skill to use them, you can make a butt kicking gun.

Its my perception that flaws are small but fixable (affore mentioned tools and skill set), except for one thing: the magazine.

Shooting groups at the lab tonight, I finally correlated the pellets inconsistent seating in the mag with the bad groups/flyers. If the pellets all sat in the mag at the same depth, the group was pretty good. if the pellets all sat in the mag at random depths, the group would suffer with flyers.

PArt of that may be the bolt not seating the pellet consitantly and/or the bolt not locking. had many whiffed shots tonight cuz the folt had felt like it was rammed home, but was a bit short and didnt lock. After I made the effort to make sure it was rammed and locked, groups got better. Chrony numbers became more consistant too.

Never did break 500, well ok with SSPs  (660 ish) but the real pellets would top out around 485. I blame that on TP issues and the air leaking, or at least not flowing efficiently from the valve thru the TP and into the leade to drive the pel. I figured Id be around 525 to 550 with the valve mods, TP enlargement and piston stuffing. And maybe its there, but I aint making it and still make the deadline.

Most amusing part of the whole build was taking pics today for submission. ITs snowed here in bozeman, 3 or 5 inches down, just beautiful whne the sun was out, and the perfect back drop. I dropped the gun going out the door to photgraph. Snapped the butt stock right off at the clamshell. Turns out the buttstock plastic failed, not the joint so I consider my constrution efforts vindicated. Super glue to the rescue!

Making the trigger better screwed up my safety, so I had to mod that tonight too. I do think that some one could make a drop in 2 stage trigger that would not require much if any mods to the clamshells. Fit right over the exisitng trigger pins.....

 

 


dr_subsonic's pneumatic research lab
<img alt="[linked image]" src="http://img.photobucket.com/albums/v301/ ... od-1-1.jpg">
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
After I had the internals done, and without anymore time to go back inside, I had an idea for a blow-thru bolt for the 760. I have a piece of thin wall brass tube just a bit larger in OD than the bolt. It passes through the magazine just fine. I'm thinking I could cut off the end of the bolt just behind the transfer port and then sand down the bolt so it fits in the tube. Drill a hole in the tube so it lines up with the TP and trim the tube to length so it pushes the pellet in just right. Using a tubing cutter would round in the end of the tube slightly making it fit into the pellet skirt better. When you fire the gun the air would be directed through the tube to the pellet and (hopefully) reduce the amount of air to go backwards out the breach.

I plink, therefore I am.
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Joined: April 28th, 2010, 12:23 am

November 14th, 2011, 2:55 am #8

my idea was to make a new breech block all together, wayyy simplified from a small block of metal(whatevers handy_ ) basically make the base cup the comp tube right over the TP, make it fit the bolt with slight interference friction, and afix to the barrel with set screw.. several hours of work with drills and dremels etc that I didnt have.All kids of mods to be done , you said on 5 pumps your gun is doing 500 fps, thats really impressive with the lost chamber volume , I didnt spend much time on the power mod area, was too busy getting the gun in its current configuration to function as it should.
Honestly, if I get the m417, im going straight to co2 bulk right off the batt. Im gonna have the tube and gauge already done before i even get the gun , and the foster too obviosly.
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Joined: February 9th, 2006, 10:35 pm

November 14th, 2011, 3:20 am #9

Lost chamber volume? I didn't do the valve volume reduction mods.

I plink, therefore I am.
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Joined: April 28th, 2010, 12:23 am

November 14th, 2011, 3:32 am #10

i never heard of 500 on 5 pumps ???? you must have stiffened the cup and reshaped?
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