GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: YEMX on September 02, 2014, 02:00:26 AM
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I'm interested in building a QB78 PCP, but don't want to do the bottle route (I know, it's cheaper, and has more air capacity), I just don't like the look of it. I'm also going to have a custom tube made, as I need it to be longer, I also don't like the accuracy of my personal QB tube, some of the holes are a little off. I digress, the question:
If I'm having a custom tube made, can I use a Discovery's fill adapter/dust cap? I don't plan on going any higher than 2k psi (in fact, I want to keep it lower). Thoughts? Thanks for the help!
A side question:
What are your thoughts on the QB78 deluxe's barrels in .177? I have one I've never put pellets through, and I've read both good and bad, what's y'alls experience? I'm thinking of using it for a .177 pistol build, only because I already have one, all I have to do is have it machined.
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Have you tried here > http://www.wolfairguns.com/index.php?cPath=22&osCsid=947ebb6fb805b40eb8ddd2c17983a6ff (http://www.wolfairguns.com/index.php?cPath=22&osCsid=947ebb6fb805b40eb8ddd2c17983a6ff)
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For your side question about the QB78 Deluxe barrels in .177 cal, one I tuned for GTA member toine in January liked JSB 10.3gr at 14-15fpe. Example groups at 25 yards:
(http://i779.photobucket.com/albums/yy80/jmneal1/projects/airguns/toine%20QB78%20177/JSB_103_25yds_011414_zps9dc4dbda.jpg)
But it also shot several pellets decently:
(http://i779.photobucket.com/albums/yy80/jmneal1/projects/airguns/toine%20QB78%20177/pellet_test_25yds_011214_zps027d47ef.jpg)
Note the QB79 has the same slightly larger barrel. It's referred to as a 15mm OD but it measures more like 14.5mm. Anyway, my son's QB79 is a good shooter as well. Not very pellet fussy. Here are some 25 yard groups with 10 different pellets, 5 of which turned in groups under 1/2":
(http://i779.photobucket.com/albums/yy80/jmneal1/QB79/pellettest1071013_zps76effb5b.jpg)
(http://i779.photobucket.com/albums/yy80/jmneal1/QB79/pellettest2071013_zps4d9f7e7b.jpg)
(http://i779.photobucket.com/albums/yy80/jmneal1/QB79/pellettest3071013_zps3c00c679.jpg)
And lastly, a couple of cherry-picked groups at 42 yards:
(http://i779.photobucket.com/albums/yy80/jmneal1/QB79/QB79_42yds_CPUM_071313_zps928bcc62.jpg)
(http://i779.photobucket.com/albums/yy80/jmneal1/QB79/QB79_42yds_CPUM_071113_zpsf7d0046a.jpg)
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I'm crossing my fingers I'll get groups as good as those!! That's really surprising from a china barrel! I've heard too many bad things about the wolf tube/customer service... I think the qb's tube is the same O.D. as the 22xx/disco, but is the wall the same?
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I hope you do as well. I should have pointed out that I did some light cleanup work to those two barrels to remove sharp edges that might damage the pellet (barrel port and the leade's transition to the rifling) and touched up the crown with a brass screw coated with polishing compound. But to be honest, I don't know if any of it was really necessary. These two barrels shot pretty well right off the bat but doing those things has never hurt so it has just become standard operating procedure.
Other times, barrels can be persnickety little devils, seemingly incapable of ever putting a pellet in the same place twice. Such was the case with GTA member Vigilandy's QB79. When I first got it, it struggled to do better than 1.5" groups at 25 yards. After trying a combination of the usual things (including a complete recrown) plus several things suggested by others, it was doing between 1.0" and 0.75". Then as a last ditch effort, I chopped an inch and a half off the end of the barrel and carefully dressed the crown. Then it started doing one-hole groups and cloverleafs. The whole shebang is documented in this long thread (http://www.gatewaytoairguns.org/GTA/index.php?topic=71442) if you have 30 minutes to kill. ;)
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;D ;D ;D ;D
Basically if your gun shoots like mine did, you had better have plenty of patience and skill.... Jason saved my QBs life. It was about to become an organ donor! I was ready to use the tank block for a FDPCP conversion and part out the rest.
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the theads on the qb tube are on the outside, and the disco has them on the inside, so no you cant use the disco cap unless you cut and re thread. I have a qb78 HPA that uses the original tube. have been running it at 1600 psi and get 15 shots at low 8s, high 7s, in .22 i did the barlow calculation in my tube to figure out the fracture point on my tube and it cam to about 2200psi worst case scenario. I am running mine at 75% for the past 4 years and it has not given me any problem. As per accuracy mine will do .466 inches at 35 yards, and will do 1/2 at 50. the barrels are a &^^& shoot, but more likely you'll get a good one. I have also a carbine sized .177 and a rifle .177 with the bolt to convert... both will do 1/2 at 35 all day long, some better depending of the pellet. the .177 are more pellet fussy...
PS i also have a qb77. with the LW barrel that gun is amazing...
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Nervoustrigger: Thank you for that link!!!
Well, as long as I can use a "Disco" sized tube, (From what I'm reading I can) I can use a disco fill adapter because I'm having a custom tube made, that way I can have the threads cut on the inside- I'm also making the tube longer so that the AR2078 barrel's muzzle will be juuuust past the dustcap. I'll also have to have a really short breech spacer so that the AR2078 barrel will clear the main tube by a hair. UGH, then I'll have to have a custom barrel band made.... jeeze. Oh well, it's all in good fun!
I am interested in how to improve the accuracy of a china barrel because I have a spare Deluxe .177 barrel floating around and I want to try it on a Crosman 17xxP/T pistol build I have slowly going. I know, I know- there's a LW barrel already made for them. However, I like the extra heft of the 15mm barrel, and I can have the breech area machined to fit the breech tighter... I'm a glutton for punishment, I know!!
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No, I totally get it. It's rewarding to get a cheap rifle shooting excellently.
I am glad to share with you some recommendations. How familiar are you with accurizing in general? Or with the terms like crown, leade, barrel port, etc.? Just trying to frame my response appropriately.
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Oh, don't worry. I have an understanding of all the terms that are likely to come up! I get a little fuzzy on math, like with the pump pneumatic stuff (yeah, building one of those too!) but tuning stuff I'm good to go. *(&^, I've lapped some of my barrels, and have also touched up the crowns with some success. I really appreciate you guys taking the time out to answer my questions! I sometimes have some off the wall ideas.
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Good, that will save us some time then. ;D Though it was said better by Brick Top in Snatch.
I'll write up a list and get back with you.
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Well, as I look back over what I've drafted up here, I guess I got a little carried away but here's a list of the things I typically do when accurizing a barrel.
[edit]
Snipped long draft...please see the barrel troubleshooting and accurizing guide at this link
https://www.gatewaytoairguns.org/GTA/index.php?topic=130555 (https://www.gatewaytoairguns.org/GTA/index.php?topic=130555)
[/edit]
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If you are having a custom tube made, from the same dimension tube as a Disco (7/8" OD x 0.065" wall), then you can have the inside threaded for a Disco fill plug.... The QB valve may have to be skimmed down to fit inside the tube, it's a few thou (~0.003") smaller.... Depending on the pressure you want to run, you may want to look at the valve and backing block screws for strength, and either way it is important that the valve sit tightly against the backer block as most of the strength in locating the valve is supplied by that....
Bob
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AMAZING info!!!!!!!!!! I can't wait to get some free time!!!! Thanks again Nervoustrigger!!!
Thanks again for the help rsterne!! I'll be sure to look at that area when I go to assemble- I'm only going to run it 1500-1600 psi MAX. It doesn't need to shoot too hard. A bit under 12 fpe is just fine.
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you can get that on Co2... and a more consistent velocity spread as well as more shots... just get a qb and the bulk fill cap... still do all the tuning possible. My qb will run 688 fps with 14.3 for a good 35 shots... that is about 15 fpe... on Co2. it works well when i go away with the rifle camping as i bring 6 powerlets with me on a butt stock sleeve bandolier... or i hook up a 20 oz paintball tank to it and just shoot shoot shoot... that 20 oz tank was filled on 2013... still filling it up now...
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I'm trying to stay away from CO2, I'm already set up for HPA, plus I live in Md, and I like shooting whenever I'm able- even in the winter... After doing some more reading, I won't be going over 1200 psi MAX. I'll likely keep it at 1100 psi and call it a day.
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Well, as I look back over what I've drafted up here, I guess I got a little carried away but here's a list of the things I typically do when accurizing a barrel. First off, a short pre-flight inspection:
Before you start removing metal
I like to start by giving the barrel an inspection to get an idea of what I'm working with:
slug the barrel and feel for issues - Push a pellet through the barrel, from breech to muzzle. We're looking for possible issues in 4 areas:
- barrel port - pneumatic rifles only (not springers)
- leade->bore transition
- bore
- crown
Firstly, note whether the pellet felt as though it snagged as it went over the barrel port. Most inexpensive factory barrels have not been deburred. Next up is the transition from the leade to the bore. Often there is a sharp edge where the leade necks down to the bore. Here, the sharp edge at the beginning of the rifling will tend to smear the head and skirt. Continuing on, note any loose or tight spots along the barrel's length. What I'm wanting is a pretty consistent, light resistance all the way through...that is, unless the muzzle is choked. Lastly, pay close attention to resistance just as the head and skirt pass over the crown and emerge into the outside world. Hanging up here is an indication of a burr left after crowning that will need to be dealt with. BTW, distinguishing between a choked barrel and a burr at the crown normally is fairly easy. In a choked barrel you'll encounter resistance for the last inch or two. If the crown is defective, you'll hit a snag just as the pellet comes out the end.
inspect the pellet - Now inspect the pellet(s) with the help of some magnification. Damage in a confined spot around the perimeter of the skirt usually indicates a burr at the barrel port. Smearing of the skirt where it met the rifling usually indicates a sharp edge at the leade->bore transition. Slight rifling marks around the head are a good indication that the pellet is a good fit for the barrel...enough to prevent yawing as it hurtles down the bore but not so much that it damages the head. By contrast, rifling engagement of the skirt should be deeper because the skirt is a larger diameter by a few thousandths.
Now with some expectation of what you have to deal with, on with the barrel treatments...
Down to business
deburr the barrel port - Use a small diamond ball grinder to radius the edges of the barrel port. What I do is load a 3/32" (for .177 cal) or 1/8" (for .22 cal or larger) diameter ball into the Dremel running at its lowest speed, and work it from inside the hole and up over the sharp edge all the way around the perimeter of the hole. Don't go crazy with it; the radius need only be ten or fifteen thousandths (0.010" - 0.015"). Just trying to get rid of the wire edge left from the drilling operation. Then take a small dowel or skewer wrapped in 320 then 400 grit to polish the newly-formed radius. Apply some light oil (mineral oil, WD40, etc.) to help shed the swarf. Since this work is done at a shallow angle, round over the end of the dowel so it can dip into the hole as you pass it back and forth. Expect to chew up the paper a couple of times; just keep refreshing the abrasive and work it until it is smooth. It will become apparent when you've done enough because the paper will no longer be as apt to shred.
treat the leade->bore transition - A picture is in order: (thanks to Kirby)
(http://i779.photobucket.com/albums/yy80/jmneal1/projects/airguns/barrel%20accurizing/leadetoboretransition_zpse4ede88e.jpg)
Knock down the sharp transition between the leade and the bore. A regimen of 320, 400, and 600 grit is good for this operation. Wrap the paper around a small dowel and sweep it in and out, applying pressure all around the perimeter.
polish the bore - The pros swear by this. I've only done it a handful of times and I haven't formed a strong opinion about it yet. It does seem to improve precision a bit and will extend cleaning intervals (lead will not abrade and stick to the walls as readily). Some claim it also makes a barrel less pellet fussy; I don't doubt it but I haven't noticed it in my limited experience. Things you will need:
- cleaning rod - Critical that it be a good double ball bearing cleaning rod to ensure the cleaning pellet/wad/patch follows the riflings
- rod adapter - Brownell's VFG stuff (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/weapons-care-system-pellets-prod13839.aspx) is recommended for .22 cal and above. Specifically, the 084-000-002WB adapter (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/22-cal-vfg-adapter-sku084000002-25903-4136.aspx). For .177, use a good jag and cotton patches.
- cleaning pellets - firm felt pellets for Brownell's VFG system (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/weapons-care-system-pellets-prod13839.aspx) such as part number 610 for .22 cal.
- abrasive - A fine friable abrasive like J-B Bore Paste seems to be the most recommended but folks have successfully used stuff like Flitz metal polish or rottenstone.
- lubricant - Kano Kroil seems to be preferred but another light oil can be substituted. Its role is to help float away the swarf.
See these two excellent threads for more information, in particular the guidance offered by Motorhead and SeanMP:
J-B bore paste (http://www.gatewaytoairguns.org/GTA/index.php?topic=64525)
Deburring riflings - JB Bore Paste (http://www.gatewaytoairguns.org/GTA/index.php?topic=47627)
touch up the crown - Firstly, there are many different geometries that can be applied to a crown but most air rifle barrels will have a simple chamfer so that's what I will focus on. Give the crown a closeup visual inspection. If the chamfer is a uniform width all the way around the perimeter, a little touchup with a brass screw will do. What you will need is a round head (not pan head) brass screw. #6 is good for .177 cal and a #8 is good for .22 and .25 cal. Whereas most everything that has been discussed thus far should be done with the barrel removed, you can do this procedure with the barrel installed. Secure the barrel in an upright position so you can have both hands free. Stuff a small piece of cotton into the muzzle to keep debris from falling down into the barrel. Chuck up the screw into a handheld drill. Coat the head of the screw in polishing compound and press it against the muzzle and operate the drill at low speed, moving it in an irregular circular pattern. I use the term "pattern" loosely; you expressly want to randomize the movements. If you try to hold the drill in one position, invariably more pressure will be applied to one side which will abrade an irregular bevel into the crown. Afterwards, very gently drag a cotton swab across the crown and see if it snags. If it does, you still have a burr that needs to be worked down. A good crown will also have a distinct cog-like appearance when viewed under magnification, owing this to sharp, burr-free lands and grooves.
If the chamfer is irregular, the end of the barrel will need to be reworked. If you can have someone with a lathe do it for you, that is probably best for most weekend warriors but if you are confident in your abilities, you can chop and recrown on your own. Here is a link to my DIY crowning guide (http://www.gatewaytoairguns.org/GTA/index.php?topic=55681) using a drill press to achieve a perfectly square crown without a lathe. There are many different ways to go about it and some good videos can be found by searching youtube.
Checking your work
After all the work has been completed, I like to use compressed air to blow away any loose and/or heavy debris, then run a few cleaning patches through the barrel. Then I slug the barrel again, looking for any remaining trouble spots. If all looks good, back on the gun it goes and then off to shoot groups with various pellets to see what the gun likes.
This is very interesting. You are a kid genius!
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;D Nice revival maybe needs to be saved to my puter for future refrence
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Way to bring back up an old thread Troy!
Now I gotta read through it and get lots of really good information by one of GTA's finest (Jason). Ugh, the humanity!
:D
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"Coat the head of the screw in polishing compound and press it against the muzzle"
i've been seriously thinking of trying to clean up a crown on a barrel so what do you guys suggest to use for "polishing compound"?
what would you use for a cut off and complete re-crown? 8)
thanks, bob
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Bob, I suggest getting both some medium and some fine polishing compound. The medium for removing material to form the bevel, and fine to polish it. You can find it at most auto stores.
Valve grinding compound will do as a medium. Usually in a paste form sold in a tube.
Something like rottenstone works for fine polishing, or a fine metal polish like Fitz or J-B Bore paste. Some have said certain kinds of toothpaste can be used but I have not tried that.
You can also use the abrasives sold in stick form at tool centers...the stuff used with bench polishing wheels. Just have to scrape a little off with a blade and put in on your workpiece.
As far as doing a complete cut and recrown, there are lots of ways to do it. It usually comes down to what tools you have access to. A lathe is preferable of course. Next would be a special crowning tool...pricey unless you're doing a lot of barrels to justify the expense. A link to my DIY method with a drill press is toward the bottom of my previous post. Or you can do it by hand with a great deal of patience but don't expect a perfectly perpendicular result.
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Thanks Jason,
you're always so good at helping us. it's appreciated. 8)
bob
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Way to bring back up an old thread Troy!
Now I gotta read through it and get lots of really good information by one of GTA's finest (Jason). Ugh, the humanity!
:D
Doing my part to keep the addiction alive!
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The only real problem in building a QB PCP is getting or making a 3K air tube. There is enough striker weight, internal striker spring length, air flow, and over all strength to make a 3,000psi PCP.
Way back in the day were two choices, Jack Haley occasionally made tubes, was an on-off availability as he preferred to use the tubes in his custom rifles. When I wanted one, he had none. Cross that source out as Jack passed away awhile back.
Comasseco (a defunct retailer) did have some made and were marketing a QB PCP. Was only marketed for a very shot time as (1) the price as Disco-ish and (2) they had no clue what it took to make a decent PCP.
Ordered the Compasseco .177 PCPs. Testing found it pretty much of a “$)((#” but the air tube seemed healthy. So I put a barrled breech (.25 LW barrel) on the tube and fixed the short cuts.
(Was a complete standard valve including piercing pin. Fiber filter shredded and destroyed the stock valve stem. Striker spring was 1 1/2 QB springs (they literally cut a 1/s a spring and added it to the spring guide along with a full length spring). Same mushy/soft, restrictive transfer port seal as in the co2 models. Way-way too fast in .177. Basically, it was ‘carp’.)
Reworked valve, new Delrin valve stem poppet, new one-piece spring,, and a bit of tuning got it working right as a .25.
Hobbiest have made tubes from scratch. Some have made tubes from Discovery tubes, although if going that route I’d not stress it to 3K (maybe 2.2-2.5K). Probably with starting with a Disco tube is that once you cut off the superfluous holes/cuts you can’t use and machine in cuts/holes you can use, the tube ends up short (small volume).
Are others that just make the sign of the cross, ask the Saints to look over them, maybe sacrifice a rooster at the crossroads under a full moon, and use the issue tube. I’d really-really-really rather not.
Haven’t read many reviews of the Polish company (Wolf?) offering PCP tubes and PCP conversion kits for QB’s. The ones I’ve read haven’t been “glowing endorsements”. What I suspect is that they can be MADE to work, but a direct drop in fit is not what they are (but I’ve not tried one).
Haven’t had much problem in getting it to go fast. Are some limits, and the air volume isn’t large, so shot count hasn’t been great but the foot pounds can certainly get up there.
(http://i157.photobucket.com/albums/t50/ribbonstone/QB%20mods/f0727cd5-da07-4c1d-a9c6-c277d2560b60.jpg)
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If you are going to limit your pressure to under 1800 psi, which can be achieved by CO2 on a really hot day, in theory at least you can use a stock QB tube.... The problem is that it doesn't hold much air, about 55cc, less than a 2260, and only about 40% of what a Disco holds.... Ribbonstone outlined the availability problems, and the best solution would be to use a tube of good quality with the same dimensions as a Disco tube, 7/8" OD x 0.065" wall.... 1021 Steel is good to 3000 psi with a 3:1 safety margin, and 4130 CrMoly will be 3.7:1, and those figures are to yield, not burst, providing the valve is located properly, of course.... If you are looking to get one made, I would suggest you contact stalwart.... He does a lot of work on the XS-60c, which is somewhat similar, and has the necessary tubing and the equipment to make HPA tubes, including thread the end for a Disco fill fitting....
Bob
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Perhaps a strange question- but why is a disco rated to only 2k psi, and the Prod to 3k? Is the main tube different material? I do see that the fill plug is different between the two, is this the reason? Theoretically, you can have a tube made, with all the QB holes and slots, but the front will be threaded for either a disco or Prod fill plug, right? I wonder how the valve would be pinned? Is there enough material to pin it?
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The tube in the Disco isn't the problem, it's the valve mounting screws.... The Disco was designed to be pumped by hand, hence the lower fill pressure.... The QB valve is almost identical to the one in the XS-60c, and they both use a steel backing block that the valve sits against (or should).... That backing block can be fastened to the tube with three 10-32 screws arranged identically to a Disco, and that will look after the 3000 psi fill, providing the tube is strong enough.... I suggest you look at the "Grizzly" HPA conversion I did on the XS-60c to see how I fastened the valve.... The Disco fill fitting is not a problem at 3000 psi, provided the O-ring sealing it to the tube is on the full 0.065" tube wall the way it is designed to be used....
The QB valve and hammer may be a few thou too large to fit inside a Disco sized tube.... It is 0.003" smaller ID nominally.... It just depends on where the tolerances fall if they will work or not.... but skimming down the valve isn't an issue anyway....
Bob
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Cool beans- I forgot about that steel block the QB valve rests against... I was thinking like the Disco valve, where the retention screws thread into the valve body. Thanks for clearing that up for me Bob!!
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Bob... what is the capacity of the disco tube? also i built a 2240 with a hpa bottle and wanted to run at about 600 fps. I achieve that but i adjusted the regulator to run at about only 750 fps. with the hammer spring i have it seems to "fart" on each shot and im getting only about 62 shots (very consistent) from 2500 to the reg limit... how would i go about making it more efficient yet retaining the power level i desire?
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A Disco tube holds 135 cc of air....
You likely have too much hammer strike for the pressure you are running, and getting hammer bounce.... Try backing off the preload on the hammer spring, or a lighter spring, until the velocity starts to drop.... My guess is that won't be immediately.... Once your gun is tuned to just below the maximum velocity for the pressure, your hammer bounce, and the brraaappppp sound that goes with it, should go away, and your shot count will increase.... If by the time you tune it that way your velocity is a bit too low, increase the pressure 100 psi and retune it....
Bob
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I increased the regulator pressure to 900 psi and replaced the hammer spring with a stiffer spring. velocity has reached 700 fps but the burping has stopped. I will refill to 2500 psi and will sit in front of the chrony till the velocity drops. lets see if my shot count increased. (by the way, if i took the string from say 2500 to 2000, and multiplied by 3, would that give me a somewhat accurate shot count as i stopped right above the regulator limit?) just trying to see if its necessary to do an entire string or i can use this aproximation...
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I increased the regulator pressure to 900 psi and replaced the hammer spring with a stiffer spring. velocity has reached 700 fps but the burping has stopped. I will refill to 2500 psi and will sit in front of the chrony till the velocity drops. lets see if my shot count increased. (by the way, if i took the string from say 2500 to 2000, and multiplied by 3, would that give me a somewhat accurate shot count as i stopped right above the regulator limit?) just trying to see if its necessary to do an entire string or i can use this aproximation...
The string of a regulated gun should be linear down to the setpoint.
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just wondering about shot count... if i get 30 shots between 2500 and 2000 psi, would i get 90 from 2500 down to 1000?
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You should, and 120 from 3000 down to 1000, assuming the setpoint is 1000 or less.... You REALLY need to experiment with the hammer spring preload and see how it affects the velocity.... You should get something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg) (http://s378.photobucket.com/user/rsterne/media/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg.html)
More preload than you need to reach the velocity plateau just wastes air.... and can waste a LOT of air.... plus the gun is prone to hammer bounce as well.... You want to operate on the "knee" of the curve, which on that graph is 4-5 turns out from coil bind.... The tune I chose was 4.5 turns out....
Bob