Getting the Disco stable

Getting the Disco stable

Joined: November 17th, 2006, 3:51 am

July 31st, 2011, 5:01 pm #1

Damn...as if things weren't complicated enough... yet another variable.

Wife out, so had a chance to set up on the kitchen table and shoot 25 yards rather than my more normal 20.
[/IMG]

Think I got the Discovery sorted out (after goofing with it for a couple of years..so doubt this is the last word). Barrel showed promise, but the point of impact would wander around.

Had done most of the mods discussed on line. Trigger mod, barrel polishing, recrowning, deburring the barrel breech, etc. Although it shot well, still had a stability issue.

Took a lesson from the Challenger and added a barrel band just ahead of the action. Have to inlet the stock, split the sight rail (or toss it), but set up to pull the action down tight, it really does seem to stabilize the rear end of the barrel.
[/IMG]
[/IMG]
[/IMG]

Which leaves a whole lot of thin whippy barrel hanging out in space. Can shoot pretty small groups this way, but they tend to shift point of impact from day to day and shoot different pellets to widely different spots.

Decided to make a 6-screw barrel band. Three set screws anchored to the bottom tube, and three to the barrel (think tripod). Set up solid to the bottom tube, its best if the barrel is set just barely able to move slightly in and out, but not side to side. Better to not hog-tie the barrel and let it have a chance to slide in and out a bit when the bottom tube expands/contracts.

This leaves a whole lot of barrel to play with. Think of it as moving the slide in a trombone, getting different tones (vibrations) depending on that slider's movement. Can try the front band anywhere from the very end of the air tube to right up against the forearm, and will find that there seem to be certain spots that shoot better than other spots.
[/IMG]

It usually isn't a whole lot of difference, but the little bit of difference that is there seems to be centered on certain areas. Adding things to the end of the barrel (like brakes/LDC's, etc) also seems to change that vibration (and if whatever you added is even slightly loose, really plays hell with getting the gun to shoot).

So I played this morning with setting the front band in various locations. When I found one that seemed to be working a little better each time that spot was tried, settled in for a bit of 25 yard target shooting.

Targets shot alternatively (one AA target/ one H&N), refilling to the best of the sweet spot after 20shots:
[/IMG]

Yes...is sighted a bit high. Was not going to break my good luck by mucking about with the scope.

Shot very early this AM before the wind became so much of a factor (as well as the heat...but still sweat drenched).

A word about crappy printer paper targets. Really have to look hard at them for the lead smears made by round nosed pellets that cut into existing holes to get a better measure of the real group. Would be better to use real target paper...but once you get critical and take a hard look at the marks on paper, can use printer paper for common use.

Nope...not a MOA Crosman barrel; good enough that I'll not be spending the $ to replace it.

Will have to test it for stability. My test is kind of random. Will put the gun in a soft case, put that case on the floor of my jeep, and drive to and from work each day letting it bounce/rattle/slide. IF it won't stay on target, will go back to the 2nd band near the muzzle...which didn't shoot as well, but might be more POI stable.
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Joined: June 29th, 2009, 6:38 pm

July 31st, 2011, 5:24 pm #2

I love your in-depth posts. They are very much appreciated!
You seem to be as anal as I when it comes to solving a problem. My problem being that no matter what it is, not just airguns, I have to get to the bottom of everything! In my mind, it can always be better than it is. We can always "rewire it", in the words of Tim Allen.
Keep up the good work!

Tom



"What, me worry?"

"If I were two faced would I be wearing this one?" - Abe Lincoln
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Joined: November 17th, 2006, 3:51 am

August 2nd, 2011, 1:23 am #3

Damn...as if things weren't complicated enough... yet another variable.

Wife out, so had a chance to set up on the kitchen table and shoot 25 yards rather than my more normal 20.
[/IMG]

Think I got the Discovery sorted out (after goofing with it for a couple of years..so doubt this is the last word). Barrel showed promise, but the point of impact would wander around.

Had done most of the mods discussed on line. Trigger mod, barrel polishing, recrowning, deburring the barrel breech, etc. Although it shot well, still had a stability issue.

Took a lesson from the Challenger and added a barrel band just ahead of the action. Have to inlet the stock, split the sight rail (or toss it), but set up to pull the action down tight, it really does seem to stabilize the rear end of the barrel.
[/IMG]
[/IMG]
[/IMG]

Which leaves a whole lot of thin whippy barrel hanging out in space. Can shoot pretty small groups this way, but they tend to shift point of impact from day to day and shoot different pellets to widely different spots.

Decided to make a 6-screw barrel band. Three set screws anchored to the bottom tube, and three to the barrel (think tripod). Set up solid to the bottom tube, its best if the barrel is set just barely able to move slightly in and out, but not side to side. Better to not hog-tie the barrel and let it have a chance to slide in and out a bit when the bottom tube expands/contracts.

This leaves a whole lot of barrel to play with. Think of it as moving the slide in a trombone, getting different tones (vibrations) depending on that slider's movement. Can try the front band anywhere from the very end of the air tube to right up against the forearm, and will find that there seem to be certain spots that shoot better than other spots.
[/IMG]

It usually isn't a whole lot of difference, but the little bit of difference that is there seems to be centered on certain areas. Adding things to the end of the barrel (like brakes/LDC's, etc) also seems to change that vibration (and if whatever you added is even slightly loose, really plays hell with getting the gun to shoot).

So I played this morning with setting the front band in various locations. When I found one that seemed to be working a little better each time that spot was tried, settled in for a bit of 25 yard target shooting.

Targets shot alternatively (one AA target/ one H&N), refilling to the best of the sweet spot after 20shots:
[/IMG]

Yes...is sighted a bit high. Was not going to break my good luck by mucking about with the scope.

Shot very early this AM before the wind became so much of a factor (as well as the heat...but still sweat drenched).

A word about crappy printer paper targets. Really have to look hard at them for the lead smears made by round nosed pellets that cut into existing holes to get a better measure of the real group. Would be better to use real target paper...but once you get critical and take a hard look at the marks on paper, can use printer paper for common use.

Nope...not a MOA Crosman barrel; good enough that I'll not be spending the $ to replace it.

Will have to test it for stability. My test is kind of random. Will put the gun in a soft case, put that case on the floor of my jeep, and drive to and from work each day letting it bounce/rattle/slide. IF it won't stay on target, will go back to the 2nd band near the muzzle...which didn't shoot as well, but might be more POI stable.
2nd day:
Failed the Jeep-stress-test.

After riding around in my Jeep to and from work (a 17.8 mile trip) on the floor boards (in a soft case) the point of impact shifted quite a bit.

So went back to the old barrel band setting of near the muzzle (the rear band still just ahead of the breech).
[/IMG]

Almost as accurate (statically the same for the small tests) but has proved to be more stable at this point. Have done the Jeep Test for a couple of weeks at this setting and found the POA/POI to have stayed stable, so that's where this Disco is going to live.

Teat targets at the new (old) setting: 5 shots/2oyards/ 13.5gr. AA pellets:
[/IMG]

Rifle will get another trip to and from work, then tested...and if it passes that test, will get trips and tests every day for the rest of the week.

What I want is decent accuracy and a stable point of impact...may be ways to eek out more accuracy, but if the pellets aren't consistently to the point of aim, it's not a useful gain for hunting.


Last edited by gubb33ps on August 2nd, 2011, 1:23 am, edited 1 time in total.
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Joined: November 21st, 2009, 6:21 am

August 2nd, 2011, 5:33 am #4

On mine the transfer port was too long and caused the breech to rock some I guess.Took it down some and it fixed by poi wandering issue.Just what worked for me,you probably checked that but thought I would mention it.


Don
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Joined: October 29th, 2008, 2:38 pm

August 3rd, 2011, 7:14 pm #5

2nd day:
Failed the Jeep-stress-test.

After riding around in my Jeep to and from work (a 17.8 mile trip) on the floor boards (in a soft case) the point of impact shifted quite a bit.

So went back to the old barrel band setting of near the muzzle (the rear band still just ahead of the breech).
[/IMG]

Almost as accurate (statically the same for the small tests) but has proved to be more stable at this point. Have done the Jeep Test for a couple of weeks at this setting and found the POA/POI to have stayed stable, so that's where this Disco is going to live.

Teat targets at the new (old) setting: 5 shots/2oyards/ 13.5gr. AA pellets:
[/IMG]

Rifle will get another trip to and from work, then tested...and if it passes that test, will get trips and tests every day for the rest of the week.

What I want is decent accuracy and a stable point of impact...may be ways to eek out more accuracy, but if the pellets aren't consistently to the point of aim, it's not a useful gain for hunting.

If you find your POI still wandering from day to day. Try what worked for me.

Drill out the barrel band to 1/2" and do not use any set screws on the barrel. Do use the three grub screws on the air tube but none on the barrel. Let the barrel free float and place the band way out at the end.

Works the same as the Marauder barrel band idea.
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Joined: November 17th, 2006, 3:51 am

August 4th, 2011, 12:15 am #6

<p>...even after a 20 mile trip on the floor boards of a jeep?  Have gotten wonderul accuracy with a free floated barrel, but free floating has failed the jeep test (wich is easier than the bottom-of-the-boat test) by wandring off by 1MOA or more (which is only 1/4" t 25 yards...but still unacceptable in a serious hunting rifle).</p><p>Not confrontational...if itreally works, will take the guna aprt and try free floating again from jump.  Would much rather have a 1.5MOA consistent rifle than a 1/4MOA inconsistnet one.</p><p>What I needi s a dead solid POI even under tansportation stresses, even if the groups are 2X as large, if they are in the exact same spot day to day the gun is a more useful hunting tool.</p><p>The good news is that with the rear band and the front band near the muzzle, even though groups are about 15% larger on average, they haven't changed POI even with after two jeep tests. A 1.5MOA rifle that stays on POA is much more deadly than a 1/2MOA rifle taht wonders its POI around.</p>
Last edited by gubb33ps on August 4th, 2011, 12:44 am, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

August 4th, 2011, 9:46 pm #7

Damn...as if things weren't complicated enough... yet another variable.

Wife out, so had a chance to set up on the kitchen table and shoot 25 yards rather than my more normal 20.
[/IMG]

Think I got the Discovery sorted out (after goofing with it for a couple of years..so doubt this is the last word). Barrel showed promise, but the point of impact would wander around.

Had done most of the mods discussed on line. Trigger mod, barrel polishing, recrowning, deburring the barrel breech, etc. Although it shot well, still had a stability issue.

Took a lesson from the Challenger and added a barrel band just ahead of the action. Have to inlet the stock, split the sight rail (or toss it), but set up to pull the action down tight, it really does seem to stabilize the rear end of the barrel.
[/IMG]
[/IMG]
[/IMG]

Which leaves a whole lot of thin whippy barrel hanging out in space. Can shoot pretty small groups this way, but they tend to shift point of impact from day to day and shoot different pellets to widely different spots.

Decided to make a 6-screw barrel band. Three set screws anchored to the bottom tube, and three to the barrel (think tripod). Set up solid to the bottom tube, its best if the barrel is set just barely able to move slightly in and out, but not side to side. Better to not hog-tie the barrel and let it have a chance to slide in and out a bit when the bottom tube expands/contracts.

This leaves a whole lot of barrel to play with. Think of it as moving the slide in a trombone, getting different tones (vibrations) depending on that slider's movement. Can try the front band anywhere from the very end of the air tube to right up against the forearm, and will find that there seem to be certain spots that shoot better than other spots.
[/IMG]

It usually isn't a whole lot of difference, but the little bit of difference that is there seems to be centered on certain areas. Adding things to the end of the barrel (like brakes/LDC's, etc) also seems to change that vibration (and if whatever you added is even slightly loose, really plays hell with getting the gun to shoot).

So I played this morning with setting the front band in various locations. When I found one that seemed to be working a little better each time that spot was tried, settled in for a bit of 25 yard target shooting.

Targets shot alternatively (one AA target/ one H&N), refilling to the best of the sweet spot after 20shots:
[/IMG]

Yes...is sighted a bit high. Was not going to break my good luck by mucking about with the scope.

Shot very early this AM before the wind became so much of a factor (as well as the heat...but still sweat drenched).

A word about crappy printer paper targets. Really have to look hard at them for the lead smears made by round nosed pellets that cut into existing holes to get a better measure of the real group. Would be better to use real target paper...but once you get critical and take a hard look at the marks on paper, can use printer paper for common use.

Nope...not a MOA Crosman barrel; good enough that I'll not be spending the $ to replace it.

Will have to test it for stability. My test is kind of random. Will put the gun in a soft case, put that case on the floor of my jeep, and drive to and from work each day letting it bounce/rattle/slide. IF it won't stay on target, will go back to the 2nd band near the muzzle...which didn't shoot as well, but might be more POI stable.
3 day test:

After the last band setting, changed NOTHING about the gun or scope at all. Filled it to 2K, put it i9n a soft case, and let it ride to and from work each day. Did take a different route to and from work each day, so the distance traveled laying on the floor of my Jeep (Wrangler) varied from 15 to 20 miles between tests.
Day 1:
Shots #1 to #15 shot on 8/2/11. Not my best groups, but at least they are are where I left them.
Day 2:
Have to wonder about the first groups shift to the left...but as the other two groups seemed about where I left them, can consider that pilot error (but it still counts).
Day 3:
SAME FILL..gun is tuned to about 40 good consistent 14.3foot pound shots, so shots #41-45 are outside of the sweet spot by a little bit. Still on target.
[/IMG]

So after 3 days, about 50 miles of travel in a soft case laying on the floor of a Jeep Wrangler, the POI is staying usefully" consistent. Group size at 25 yards is good enough for honest 50yard work, which is as far as I'd push a 14 foot pound squirrel rifle.

Idea here is that keeping a HUNTING gun stable to point of aim/point of impact is worth more than a few 1/10ths of accuracy.

I haven't been able to keep the point of impact stable with a free floated barrel quite this well...the groups are often smaller, but also often formed outside of that ½ white inner circle.

Last edited by gubb33ps on August 4th, 2011, 9:51 pm, edited 1 time in total.
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Joined: October 29th, 2008, 2:38 pm

August 10th, 2011, 3:06 pm #8

If you find your POI still wandering from day to day. Try what worked for me.

Drill out the barrel band to 1/2" and do not use any set screws on the barrel. Do use the three grub screws on the air tube but none on the barrel. Let the barrel free float and place the band way out at the end.

Works the same as the Marauder barrel band idea.
Day to day POI is the same. The trick is to use three screws on the air tube to keep the barrel band held firmly in place and yet still allowing the barrel to free float.

It did not completely fix the POI shift from high to low pressure though. I have to start at 1750 psi and end around 1500 psi. Meaning I only get a dozen or so dead on shots at 21fpe. But those dozen shots are dead on every single time.

Of course I have not attempted to bounce mine in the floor of a Jeep. Just normal use.

You may have to build a rack of some kind to hold the gun and protect it during transport.
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Joined: November 17th, 2006, 3:51 am

August 10th, 2011, 8:20 pm #9

..sometimes there is an hour long flat bottom boat ride after that. Do take care, but test for the worst case rather than hope for the best case.
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