GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Ribbonstone on October 11, 2017, 08:56:22 PM
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One week of testing every day, but I may have found a cure of a potential problem. (I don't have a bunch of Beeman Chiefs....have just one...so not telling of the problem is universal or just unitque to my example).
HERE ARE THE # TEST MOST SERIOUS PCP SHOOTERS DO:
1. ACCURACY (with a variaiety of pellets).
2. VELOCITY
3. SHOT COUNT (inside of velcotiy varaion...whatever that is, is pretty much up to you).
But most of use don't tend to test is the 4th test:
#4. STABILITY of point of aim/point of impact over time.
Do not get me wrong here...a whole lot of PCP's just can't take rough use/abuse. But I'm not a delicate/subtle kind of guy, I use my "inexpensive" (Cheap) PCP's kind of hard....in the rain...with some rough transport between here and there (Jeeps...Jeeps and small boats at worst).
So they get a little bumped around, occasionally (lightly) banged into things, and kind of (escuse me, no disrespect to you men of the land that allow us to eat daily): " FARMERED".
I don't want to present a potential problem without a potential solution.
From the safe to the home range, nothing really showed up....shot great, shot as expected, and kept it's POI/POA.
As the rifle was (stable POA/POI so long as I taook care as if it were made of glass):
(http://i157.photobucket.com/albums/t50/ribbonstone/chief/9144bc29-a1ba-4ae5-9026-93deb138fff9.jpg) (http://s157.photobucket.com/user/ribbonstone/media/chief/9144bc29-a1ba-4ae5-9026-93deb138fff9.jpg.html)
Then I tried the 4th test, which I think is a must do for a potential hunting rifle. For a home shooting/hanger queen rifle, likely not needed as we kind of treat them as royalty and convay them to an frow as if they were the Vestal Virgins.
Well...my first attmept FAILED BIG TIME.
Carefully sighted in on day 1, after a trip in the soft case on the floor boards of my Jeep, to and from work, it was off to the left/low by 4MOA.
This is CERTAINLY NOT THE ONLY PCP WITH THIS PROBLEM (at least a problem for us ham-handed-sons-of toil that can't baby a tool like it was made of spun sugar.)
Can "Figure 8" barrel band, hanging out in the open air, with one tiny little set screw on the air tube at 6 o'clock and one little tiny set screw on the barrel at 12 o'clock just cannot resist a rotational force.
You can see the evidence of this by the scrape markes on the barrel (with equal scrape markes on the air tube). The "rub" marks are where the littls set screws just cound;t hold thier place (and there are NOT detents in ther barrel or air tube...well for the air tube, there are good reasons for not drilling dents).
(http://i157.photobucket.com/albums/t50/ribbonstone/chief/0eaf9e86-aa8a-4a58-ba22-f3a30e4a1cf9.jpg) (http://s157.photobucket.com/user/ribbonstone/media/chief/0eaf9e86-aa8a-4a58-ba22-f3a30e4a1cf9.jpg.html)
So the cures could be to add more screws to the bottom part of the barrel band so that it can't rotate (dragging the barrel to one side of the other) when given side ways pressure,
Or giving the two existing screws little detents to reat in to resist rotation...but drilling part way into an air tube is a "NO NO", and you'd need both screws set in detnets to be a help.
Or moving the barrel band back, then bedding the barrel band into the stock firmly, soit just can't roated unless you break the bedding/stock
I went with option 2, moved the barrel band BACK 6 1/2" and bedded the band to the new band inletting in the stock. I'd have to beat it pretty ding-dang hard to get the band to move.
(YEah...I filed a few hidden "flats" on the band to "bite" into the epoxy bedding and not rotate).
(http://i157.photobucket.com/albums/t50/ribbonstone/chief/7feec969-73cc-4dd2-a565-c2d9c199f583.jpg) (http://s157.photobucket.com/user/ribbonstone/media/chief/7feec969-73cc-4dd2-a565-c2d9c199f583.jpg.html)
Just as a note, the band is now tight and firmly fixed to the air tube, but the top screw is just barely loose form "fixed". Just enough "slcak" on the top part that if "stuff" wants to expand, the barrel will slip in or out of the top half and not be bound up/hog tied.
(http://i157.photobucket.com/albums/t50/ribbonstone/chief/316008d8-3607-4718-a98b-123d3c66bc40.jpg) (http://s157.photobucket.com/user/ribbonstone/media/chief/316008d8-3607-4718-a98b-123d3c66bc40.jpg.html)
Sighted it in with ONE FILL on day one. Packed it in a soft case and drove it to and from work in my Jeep for a 26 mile round trip (and one thing the New Orleans area does not have is smooth streets).
Shot the 2nd group at the same range, not touching nothing....as was the 3rd group...and on to the 6th 5-shot group.
(http://i157.photobucket.com/albums/t50/ribbonstone/chief/d5f7a066-5b17-4e8f-86ac-807fd783644c.jpg) (http://s157.photobucket.com/user/ribbonstone/media/chief/d5f7a066-5b17-4e8f-86ac-807fd783644c.jpg.html)
Well...the POA/POI stayed pretty much put, the velocity/energy didn't change, and the accuracy is the same on average (although it will shoot 21gr. H&N's measureraly better...I just have a whole bunch of 16gr. pellets, and they shoot well enough fr this comparsion).
So....lets consider the hardest of the variables to control: POA/POI.
You haul-butt to the boondocks, rifle in a hard case, but still boncing around in the truck or back flooboards....wander the woods and occasionally samck a branche or a tgree trunk as you find your way though the brambles....and then wonder why your first shots are "off".
It's because of stability....all that happy-wahppy-stuff that bolts together has to stay in the same alignment even when you accidently stress it to one side or the other.
AND this is not the first time I put a hard-hunter though this kind of happy-horse-ship....did the same tests on a Benjmain Disco . In it's case, added an inletted rear band that was tight to the barrel and air tube, and a 6-screw front band that was adjusted to be tight to the air tube, but just enough "slack" to allow any expansion/contraction without dragging the barrel along with it.
Which isn't match-grade accuracy either...but pretty stable as to POA/POI and extramly useful for hunting.
(http://i157.photobucket.com/albums/t50/ribbonstone/Disco/57722e48-5e7d-4523-b367-eb3d97e15789.jpg) (http://s157.photobucket.com/user/ribbonstone/media/Disco/57722e48-5e7d-4523-b367-eb3d97e15789.jpg.html)
But only over a 3 day test (but more shots per test):
(http://i157.photobucket.com/albums/t50/ribbonstone/Disco/DSCF1122.jpg) (http://s157.photobucket.com/user/ribbonstone/media/Disco/DSCF1122.jpg.html)
So...did I REDUCE the potential accuracy?...or did adjusting for stable POI/POA make for a better hnting rifle?
Question for hunters:
If you have a real-life 1/2MOA rifle that will move around by 1MOA with just a little knock/twist/stress/looked at crooked...how is that better than a 1 1/2MOA rifle that stays right on target even if you knock it around a little bit?
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Question for you,
I am a hunter and also use my equipment in ALL environments, and are taken care of when I finish hunting.
What about glass bedding the action/psi tube etc?
I do this with my PB and have outstanding success, and they are hauled around by everything from ATV's, trucks, knocked around in the woods,
and the worst hauling mode is horseback, a word to the wise, don't EVER leave a rifle on a horse, you won't like what you find,
when you get back, as they are about as destructive as a Marine.
No offense meant, Marine guys. LOL.
See that the inletting and 1 action screw on most of the AR I have handled,
and they don't seem to be bedded that well, going by the QB 79 "Leaking Lena", I have,
could lead to the results you are posting about.
Just food for thought....... ;)
Tia,
Don
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Been thinking about a second barrel band, but with the Maximus and its very thin, hollow stock------I don't Know!
Knife
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"If you have a real-life 1/2MOA rifle that will move around by 1MOA with just a little knock/twist/stress/looked at crooked...how is that better than a 1 1/2MOA rifle that stays right on target even if you knock it around a little bit?"
Totally agree. My cothran has 3 bands, both my aces have the barrels in the upper tube so no movement there. They are definitely more accurate than I am. Great post and food for thought!!
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From what I can see/test....if the barrel band is a barely "slide fit" to the barrel but a hard fit to the air tube, then it doesn't seem to matter to accuracy...barrel part acts more like a bumper guard. Important point being that it can withstand side-hits without rotation issues....which is something that one cross screw.nut betweet the barrel and air tube or two set screws at 6 oucking and 12 o-clock don't seem able to give.
Because of the Disco/Maxi's kind of weak fixation of the breech to the air tube, would much prefer an inletted barrel band as far back/close to the receiver as can get. That one simply pulls down (or is shimmed down as the band screws aren't all that strong)) for a tight "clamp" to the air tube. Front band on the pictured disco is set up with 6 screws. Three on the bottom are adjusted tight to the tube and the top 3 are kind of tripods that just barely DO NOT touch the barrel. Just a little "slack", but enough that if there is any expansion/contraction the barrel slides rather than is fixed.
Other folks found other ways....but then again, I don't know if they laid them on a Jeep's floorboards and took a 26 mile trip between test days or not.
Will say this: If the rifle was INACCURATE before, doing all this won't seem to help at all. IT doers seem to keep it stable, but doesn't seem to help make it any more (or less) accurate over all. Does make the groups stay put...but doesn't seem to cure a grouping problem.
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Nice job.
I really like how this guy made this breech and barrel band. I saw it on another forum and can't remember his name. I wish somebody would bring one like this to market.
(https://i.imgur.com/WFt1ETR.jpg)
(https://i.imgur.com/K76L4Dm.jpg)
(https://i.imgur.com/VYBNuj6.jpg)
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Nice job.
I really like how this guy made this breech and barrel band. I saw it on another forum and can't remember his name. I wish somebody would bring one like this to market.
(https://i.imgur.com/WFt1ETR.jpg)
(https://i.imgur.com/K76L4Dm.jpg)
(https://i.imgur.com/VYBNuj6.jpg)
that was made by anthony, goes by 5star here. he's a great guy and maybe hook you up if you ask him nice enough. he also posted it on this forum.
peace
kj
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Question for you,
I am a hunter and also use my equipment in ALL environments, and are taken care of when I finish hunting.
What about glass bedding the action/psi tube etc?
I do this with my PB and have outstanding success, and they are hauled around by everything from ATV's, trucks, knocked around in the woods,
and the worst hauling mode is horseback, a word to the wise, don't EVER leave a rifle on a horse, you won't like what you find,
when you get back, as they are about as destructive as a Marine.
No offense meant, Marine guys. LOL.
See that the inletting and 1 action screw on most of the AR I have handled,
and they don't seem to be bedded that well, going by the QB 79 "Leaking Lena", I have,
could lead to the results you are posting about.
Just food for thought....... ;)
Tia,
Don
it seems most guys avoid bedding the tube cuz as it changes pressures it can change poi. most tubes swell a certain amount. i believe it best to bed the action and let the tube free float..my opinion such as it is.
peace
kj
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Lol found the FARMERED comment funny! No offense taken as it's a very real thing for my guns as well. It drives me absolutely up the wall if I have to resight my guns in all the time. That's why I'm going to a full floating tensioned barrel system with a rock solid scope for my needs. Great idea and have been doing similar tests on my guns for awhile. Guess what I've owned and sold alot cause many didn't pass the tests. Some have passed but not my style exactly.
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KJ
Thanks for that info, I did not know that the psi tubes expand etc.
IMHO, a second action screw added and with glass bedding the action, and then free floating the pressure tubes would be a great start,
lock the action down in place, then free float the rest.
Just look at the balance point of the action in relationship to the length of the psi tubes,
you have 1 action screw in a questionable inletted piece of wood, with very little to hold the action in place etc,
see sawing on 1 screw point? :o
I know, I have been looking at my 79 for future mods, in the stock area,
this stock is horrible, it is not fit-able for a 6' tall, long necked/armed person, then add high mounts to clear the magazines,
it's a wonder that I can hit the target, I wish I could find a good solid plastic stock for the 78/79 series of AR,
I might find a base stock to work with at least.
Do you know of any AR that have 2 action screws?
Tia,
Don
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Nice job.
I really like how this guy made this breech and barrel band. I saw it on another forum and can't remember his name. I wish somebody would bring one like this to market.
(https://i.imgur.com/WFt1ETR.jpg)
(https://i.imgur.com/K76L4Dm.jpg)
(https://i.imgur.com/VYBNuj6.jpg)
that was made by anthony, goes by 5star here. he's a great guy and maybe hook you up if you ask him nice enough. he also posted it on this forum.
peace
kj
Thanks, kj
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Nice job.
I really like how this guy made this breech and barrel band. I saw it on another forum and can't remember his name. I wish somebody would bring one like this to market.
(https://i.imgur.com/WFt1ETR.jpg)
(https://i.imgur.com/K76L4Dm.jpg)
(https://i.imgur.com/VYBNuj6.jpg)
that was made by anthony, goes by 5star here. he's a great guy and maybe hook you up if you ask him nice enough. he also posted it on this forum.
peace
kj
Thanks, kj
I did that build about a little over a year ago. It would nice if someone with the ability to crank out several breech's with a similar layout for folks to buy.
This is the full post.
http://www.gatewaytoairguns.org/GTA/index.php?topic=110808.msg1058469#msg1058469 (http://www.gatewaytoairguns.org/GTA/index.php?topic=110808.msg1058469#msg1058469)
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Great post, Ribbon, as always.... You are one of the few guys that actually pay attention to the stability of POI/POA over time.... I have it on my "Hunters", and it is usually accomplished by a barrel band (typically about 40% of barrel length from the receiver) located solidly to the reservoir (2-3 screws) with the barrel (or shroud) located in an O-ring that is inside the upper hole in the barrel band in a single sided groove, so that it can be easily inserted or removed.... I call this approach "semi-floated", with the same idea as your "set-screws almost not touching" the barrel, but the O-ring IS in contact with the barrel, but of course being resilient can allow the barrel to expand/contract with temperature and pressure changes.... It acts, as you say, as a bumper/protector, preventing the barrel from moving far enough that it won't come back to zero on its own....
Works for me, anyways.... I'd sooner have an MOA rifle that always shoots where it is aimed, rather than a 1/2 MOA rifle that might be anywhere within 2 MOA of where it was the last time I picked it up.... for hunting, anyways....
Bob
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I don't "cuss" barrel bands...find them useful for stability of POA/POI. The least stable rifles have been the pure free-loading barrels...great if they never take a "ding", but haven't been "better" than a well set up barrel band (one that acts as a "bumper guard"...how can it hurt if a front band doesn't actually touch the barrel or shroud?).
NOT if they are hog-tied tight to both the barrel and the air tube. May be that expansion of one changes the others if you tightly join them. May be some kind of stiffness issues (After all, if tension makea a barrel stiffer,,,then air pressure makes an air tube stiffer....so variable air pressure in a tube equals variable tension and variable stiffness?
Anyway, if changes in the air tube are isolated from direct efects on the barrel, I rahter like barrel bands.
But I'd prefer NOT to have the barrel band tight to the barrel (for that isolation)...doesn't have to be "rattle loose", but I'd prefer the band's fit to the barrel to have a nearly undetectible "slack" (just enough to allow "slide" if needed).
As for the very rear mounted bands...the ones as close on on the reciever as possible...it's a mater of keeping the arse end stable, which always does some good...esp. for the poorly affixed actions.
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A thin piece of paper applied between the joints of the barrel band and the barrel-tube will do wonders to prevent slipping. The use of paper is SOP when fixturing a part or tooling for a precarious machining set up. Although I usually use a page from a phone book, abrasive paper or a dusting of powdered rosin will also work.
For the folks that insist on scoping there springers, a piece of tissue paper will stop the scope from slipping in the rings. It sure beats a dented and marred scope tube.
Have fun with it, Mike
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Important thread ,
OR
Inside CF tensing barrel shroud can reduce barrel harmonics of thin free floating barrel and the next outside barrel shroud with more bands can act also as a bumper/protector.
Ten years stability of air pressure is another issue
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Not sure what direction that points....there is a lot of room, and could likely mount a dozen barrel bands on some rifles, but I suspect some point before that you reach the "ain't moving" stage.
And I'm wondering...looking over the PCP's still made, is there really one LESS free floating than a Sumatra?
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I canīt disagree.
I have just checked only tree PCPs through this summer ( Noblesse, S510 and yesterday also Puncher ) but can confirm that after removing bands on them I was able to shoot subMOA at 77 yd but only if the gun stay in bench rest longer time and after shooting 2-3 magazines. Next day POI obviously start different cca 1-2 ".
Material fluxion ???
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I've often though about buying those rubber tipped set screws for applications where too much pressure on the barrel is not good, I've just never got around to it myself.
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Been thinking about a second barrel band, but with the Maximus and its very thin, hollow stock------I don't Know!
Knife
I have 3 on mine. It's not a problem inletting the stock. I used a dremel and a model knife to clean things up.
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One other thing I have noted on factory barrel bands. Often, at the factory the band is slightly "torqued" (pulled to the side, twisted, shifted) from its natural relaxed position when they tightened down the barrel band. Before the First zeroing, I loosen the band and let the barrel "relax" to its normal/neutral position. Then, I carefully re-tighten the set screws (grub screws) in the barrel band so the natural position of the barrel does not shift. I have seen point of impact shift as much as 3 Minutes of Angle from letting the barrel move to a relaxed position from the factory tightening (A Maximus in this case).
When a barrel is shifted in position due to torqueing, it is more likely to drift with each firing or being bumped. A barrel which is already in a relaxed position is less likely to shift due to being bumped or fired. All barrels want to shift to a position where the metal is most relaxed. If you start in that position, you get less drift... Now it is time to make sure your scope mounts don't shift, but that is an entirely different thread ;)
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Had the same problem with POI shift on my .177 and fiends .22 Chief. And did pretty much the same thing about a 2 weeks after having them. We did not inlet the stock but just simply moved the band as close as we could get to the fore end of the stock. This helped tremendously. But I believe moving them even further back and inlet-ed into the stock will be even better.
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I've not cured all the toys from wandering, some still just resist anything I've tried. Even the holdouts have gotten better.
It's not all barrel bands. A barrel loose in the receiver or a breech not well fitted to the air tube? O-ringed barrel breeches give a false sense about this. O-rings are compressible, so check that fit with the barrel shank o-rings off.
Receivers aren't always a great fit to air tubes even without the transfer port. More of a PIA to check, but if you ever get it to the point of a buck-naked air tube and a buck-naked reciver/breech, might be sureprised at how little of the breech actually contacts the air tube. Little burrs, irregularities, and just not quite matching contours can make the actual contact between the two much less that they could be (and the more contact, the stronger/less variable the fit).
Sometimes we make the problem. A little too long transfer port (usually one we modded, but sometimes a factory port) can certainly seal as still be "wrong". Screws tighten down, feels solidm, transfer port seals, but if it keeps the breech from fullly contacting the air tube. We've created a "see-saw" that's balanced on the too long transfer port.
Beding can screw you too....but it's subtle and easier to find errors with wood stocks that plastic ('cause you can see any inletting compression marks more easily). Be good if you could remove the stock screws and not find any rotation of front to back "shucking". Would also be good to take a hard look at the inletting and be sure that one side isn't taking more of the load than the other side.
LESSONS FROM FIREARMS:
While these aren't heat engines (like firearms), don't have the same problems with internal barrel stresses changing as the barrel heats up. Do belive there are internally "tweaked" barrels, and in firarms will find them "walking" shots as the barrel heats up and acutally warps a little (OK...heat brings it back towards the bent state it was in before it got tweaked into straightness when cold).
So I'm not really sure that airgun barrels have a reason to change from their straightened state..they just aren't subjected to those forces/heat.
There is no real recoil in a PCP (In Newtonian sense, there is always trecoil when a projectile is tossed out) so no real need for the heavy-duty buttressing used in big bore firearms stocks/actions. HAve had stocks split from springer recoil, but never on PCP's (although I'd dropped them from height and shattered them...or rolled a Jeep over them).
Both airgun and firearms barrels vibrate when fired. With PCP's, we're basically wacking one end of a long hollow pipe with 3K pressure (with firarms, are whacking one end with 55K pressure), so the tube is going to kind of occilate as the pellet travels and the pressure wave moves on down. What we don't have is any significant "whip"; with airguns, there is no great recoil force also adding to the barrel motion).
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Anyone ever buy a DAQ?.... You are supposed to do the initial sighting in by twisting the barrel band so that your shots align with your (supposedly optically centered) scope in windage.... I swear, that is what the instructions say.... ::)
Bob
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Been thinking about a second barrel band, but with the Maximus and its very thin, hollow stock------I don't Know!
Knife
Thanks LongHunter!
Guess I'll take a longer look see at it. ;)
Knife
I have 3 on mine. It's not a problem inletting the stock. I used a dremel and a model knife to clean things up.