GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: nervoustrigger on April 09, 2013, 05:06:26 AM
-
Hey guys,
Firstly, this post on accurizing the Daisy 880 is a spinoff of the “Daisy Powerline 880 Pellet choice?” thread at
http://www.gatewaytoairguns.org/GTA/index.php?topic=44364.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=44364.0)
Having been disappointed by the poor accuracy we were seeing from the 880, I spent some time after work this past week out in the shop completely tearing down my son's rifle to rework it.
Literally took it apart down to every screw, pin, and O-ring. Deburred and polished up everything that looked like it could use it and turned my attention to the following areas:
Trigger work. I experimented with improving the horrible 6 pound trigger with a lighter spring. I had the trigger assembly cycling beautifully in my hand but after reassembling the gun, found that the cam-over action that throws open the valve was too weak. It would only release a light puff of air and throw the pellet weakly out of the barrel. I quickly noticed that I could recock it (without pumping) and fire again 3 or 4 times before all the air was expelled. Well, back in went the craptacular stock spring.
Barrel chop and recrown. The trigger was disappointing but the main thing I wanted to do though was chop and recrown the barrel. The factory crown looked pretty bleak. I removed the barrel from the breech block and cut off about 1". After doing that, I noticed that the rifling at the factory muzzle was very shallow compared to that of the freshly cut area. I thought that was a promising sign.
So I chucked up the barrel in my drill press and set up a fixture to act as a bushing to support the muzzle end where I would be doing the crowning work. I didn't take a picture of the actual setup but I took one when I touched up the crown on the Crosman 2289 a couple of weeks ago so that's what you'll see in the picture below.
I started up the drill press and used an emery wheel in the Dremel to square up the end and carefully grind a slight funnel taper toward the bore, then used 320->400-> 600 -> 2000 grit on the head of a #8 brass round-head slotted screw to give it a nice polish. The picture isn't the best but hopefully it illustrates the point.
Shroud and barrel adjustment screws. After reassembly, I noticed it was taking an inordinate amount of windage adjustment on the scope to sight it in. Apparently the little plastic dovetails on the receiver and the barrel are pointing in divergent directions. So I drilled and tapped 3 adjustment screws into the barrel shroud. That let me optically center the crosshairs in the scope and just adjust the screws until the POI matched the POA. This keeps the lateral POI from moving around at different ranges.
Reassembly and sighting in. After finishing up all my cutting and grinding, I wiped off all the debris and lubricants, then washed and dried the parts. Lubricated all moving parts during reassembly and got it all buttoned up, then headed out to run some pellets through it to sight it in. Interestingly, the Gamo Rockets that previously grouped the best were now spraying all over the place. It looked like the RWS Superdomes were grouping the best so that’s what I sighted it in with.
The results. So tonight after dinner my 7 year old son and I headed outside for some target practice. Turns out that for the sufficiently motivated, a flashlight supplies plenty of light. For myself, I hung some 1/2” diameter Mardi Gras beads from the target board at 25 yards to blast with the B51. For him, I set up some spinners at 15 yards and paper at 25. But he couldn’t resist the idea of the beads and proceeded to hit them 3 out of every 5 shots! I couldn’t believe it! I had shot some groups at the same distance one night previous and I couldn’t do that well. He’s only been shooting since September so maybe I’ve got a natural on my hands.
Overall, the best part was seeing him have fun.
-
That is the most accurate gun, with the most crisp trigger I have ever shot. You must have bought a lemon.
-
Cool write up!
I think it's fun to drive a slow car fast, and make a cheap air rifle perform like a champ.
-
That is the most accurate gun, with the most crisp trigger I have ever shot. You must have bought a lemon.
I'm glad you got a good one.
My wife usually does all the buying of sour fruits. I went to the store to buy an air rifle, haha ;). But that was the China lottery I was playing.
The trigger does have a clean break, it's just so stinkin' stiff until you get to that point. It's fine for an adult but not so well suited to a 7 year old, that's all.
-
Turns out that for the sufficiently motivated, a flashlight supplies plenty of light.
Not to say that the rest wasn't well-written or informative, but that just made my week.
I can't WAIT until my son is old enough to shoot...
-
Awesome post as I was looking to do the exact same thing to my 880 as well. How does it group now? Any data would be appreciated.
-
Jason that's the % of shots I was getting once I fixed the trigger. I never did any barrel work like you did though. Congrats.
That is the most accurate gun, with the most crisp trigger I have ever shot. You must have bought a lemon.
I must have bought 5 lemons. A lot of misses with them and issues as well.
That is the most accurate gun, with the most crisp trigger I have ever shot. You must have bought a lemon.
I'm glad you got a good one.
My wife usually does all the buying of sour fruits. I went to the store to buy an air rifle, haha ;). But that was the China lottery I was playing.
The trigger does have a clean break, it's just so stinkin' stiff until you get to that point. It's fine for an adult but not so well suited to a 7 year old, that's all.
They weren't fine for me at all. I had to grind it down for a smoother pull since I was pulling a lot of shots because of it.
-
Awesome post as I was looking to do the exact same thing to my 880 as well. How does it group now? Any data would be appreciated.
Hi jmcgall, welcome to GTA!
I saw your post in another thread and unfortunately I don't have as wide a pellet selection as you but here is what I'm getting at 25 yards with the pellets I have on hand. The RWS Super Domes seem capable of 1in groups at this distance but there are fliers.
The results for each pellet is given for 4 shots and for 5 shots. In some cases it becomes obvious that there are fliers responsible for swelling the group size by 50% or even 100%. I tend to think the 4 shot measurement is a good indication of a pellet's capabilities but others may view the 5 shot group as a better indication so I'll let you decide.
-
Yeah airgunwarehouse had a buy 4 get 2 so I went a little pellet crazy. After none of them worked well I setup shop and cut an inch off and recrowned the barrel too. I have only tried the Jsb and polymags, which were stacking pellets at 20yd, so I went out and got a squirrel :) will do a formal pellet test later
-
James, a detail I forgot to include in the spreadsheet is that all shots were made with 5 pumps. That yields about 530fps muzzle velocity for pellets around 8gr. I have not done any head-to-head tests to see if there is a meaningful difference in accuracy between 5 and 10 pumps. I think there shouldn't be, at least at the distances we're talking about, but if you've done any experiments along those lines I'd be interested in hearing about it.
-
Yeah I was planning on using the best two or three pellets and shooting them side by side while varying up the number of pumps. It's raining today and I have to work the next few days so unfortunately it will have to wait. If you have a chronograph that'd be an awesome thing to check, the velocity curve between pumps, that is.
-
The method i calculate velocity is by using the ballistic coefficient of the pellets at my alt. temp. pressure. humidity and the ballistic curve the pellets encounter as them move from 5-30 yards. Kinda time consuming and I'm curious to see just how accurate of a method it is.
-
I ran a few shots across the chronograph this evening and, with 10 pumps, the 880 is running between 7.5 and 9.0fpe depending on pellet weight.
I also wanted to see what it would do above 10 pumps and it seems to top out around 12 pumps. My heaviest pellet is the Crosman Premier Ultra Magnum at 10.5gr and it's emerging from the muzzle with a little more than 9.5fpe.
The numbers in the table are averages of relatively small shot counts. I took just enough shots with each pellet to establish confidence in the reading. If the first two readings were within 10fps of each other, I stopped there.
With regard to your calculated velocities, in your hunting thread you estimated 640fps with the 8.0gr Polymags and I think you also said all your shooting is with 10 pumps. Assuming our rifles are similar, I expect they are shooting at around 680fps (a 6% difference). That translates into the difference between 7.3fpe and 8.2fpe, or 12%.
-
I've taken some steps to try an improve the accuracy of my two Daisy 880's.
The biggest jump in accuracy occurred with pellet selection, number of compression strokes,
attention to pellet loading technique and careful pumping method.
And, I've had good results ... times two.
Daisy 880: How to Get Better Out-of-the-Box Accuracy (http://www.rimfirecentral.com/forums/showthread.php?t=501810)
Standing Position
Forearm Fully Supported on Rolled-Up Pad
5-Shots at 20 Yards
6-Strokes of Compression
Unpredictable Wind Gusts
(http://i84.photobucket.com/albums/k21/aom22/Daisy%20BB%20and%20Air%20Gun/880%20Long%20Range/JSB%20RS%20880/82f13183-6c7a-4019-ad31-28a0b207d2e5.jpg) (http://i84.photobucket.com/albums/k21/aom22/Daisy%20BB%20and%20Air%20Gun/880%20Long%20Range/JSB%20RS%20880/JSBRS20Yd6Comp880.jpg~original)
I dropped compression charge by one stroke.
Experimenting with different strokes of compression ... sometimes helps.
Standing Position
Forearm Fully Supported on Rolled-Up Pad
8-Shots at 20 Yards
5-Strokes of Compression
Unpredictable Wind Gusts
(http://i84.photobucket.com/albums/k21/aom22/Daisy%20BB%20and%20Air%20Gun/880%20Long%20Range/JSB%20RS%20880/7b53927e-7b90-42d3-b744-57fe1e3140ba.jpg) (http://i84.photobucket.com/albums/k21/aom22/Daisy%20BB%20and%20Air%20Gun/880%20Long%20Range/JSB%20RS%20880/JSBRS20Yd5Comp880.jpg~original)
-
Really enjoy the posts. I bought a peach rather than a lemon,,,fantastic accuracy out of the box. I was really dismayed with the trigger tho. JSBs were my best pellet with CPs being a close second. I plan on polishing my trigger as did Sqrl Klr. I like the idea of 3 screws in the shroud stabilizing the barrel, but also like the idea of a floating barrel with no shroud; I don't know which would be best
-
I like the idea of 3 screws in the shroud stabilizing the barrel, but also like the idea of a floating barrel with no shroud; I don't know which would be best
The barrel shroud is essential in my opinion. The straw barrel is way too fragile to leave exposed. Right about the time you get it sighted in, something would bump it and it would be back to the drawing board.
Also in my case there was a staggering amount of compensation needed to put the barrel in line with the dovetails on the receiver (so as to keep the scope near its optical center). I had to bend the shroud quite a bit as a coarse adjustment and then I used the three screws to fine tune it.
-
With regard to your calculated velocities, in your hunting thread you estimated 640fps with the 8.0gr Polymags and I think you also said all your shooting is with 10 pumps. Assuming our rifles are similar, I expect they are shooting at around 680fps (a 6% difference). That translates into the difference between 7.3fpe and 8.2fpe, or 12%.
[/quote]
I haven't had a chance yet to sit down at different distances and map out the pellet's flight path. Unfortunatly a relatively expensive experiment with polymags :) I simply used the muzzle FPE I calculated prior to chop with a different pellet and converted from FPE back to muzzle velocity. The spreadsheet was very useful it's cool to think how the gun actually transfers its energy more effectively to heavier pellets. I would almost expect the forces inside the barrel to be the same regardless of pellet weight, so the resultant muzzle velocity would simply be directly proportional to that force. The heavier pellets maybe spend more time in the barrel, and more pressure is applied over this interval and more force is transfered. force=mass*accel and KE=1/2mv^2 v^2 is the dominate factor yet the heavier mass is enough to overpower the loss of velocity. The change in mass from 7gr to 10gr increases by a factor 1.4 while the change from of 633 to 743 is an increase by a factor of only 1.12
There is so much to consider with these airguns. It really never ends.
-
Good afternoon guys,
I ordered some Predator Polymags and a JSB sampler from Pyramyd Air earlier this week and they were delivered yesterday. Given the success James has been having with the Polymags, I was hopeful my son's 880 would shoot them well also. So naturally I had to get outside today and try them out.
Setup
I started with a control run using the RWS Superdomes that so far have produced the best groups. It was a surprise when I measured the group at 0.97", the exact same size as the two previous runs I did a couple of weeks ago! So that suggests the biggest variable in the test (me) is giving pretty consistent results.
Very well, on with the testing then. The JSB sampler consists of 3 domed varieties in 7.3, 8.4, and 10.3gr weights, as well as a "Straton" pointed pellet weighing 8.3gr. The Predator Polymags are 8.0gr. As before, each pellet was fired 5 times from 25 yards bench rested, 5 pumps each except for the JSB Heavies (8 pumps).
Results
Suffice it to say, it looks like these 5 pellets were good choices:
Predator Polymags: With 5 pumps, the Polymags did not work as well at the RWS Superdomes. But with 10 pumps, they produced a 0.71" 4-shot group and a 0.92" 5-shot group.
JSB Sampler: All 3 of the lighter JSB's grouped similarly or better than the RWS Superdomes. And the JSB Heavies were significantly better, turning in a 0.63" group (ignoring an obvious flier). Based on that positive result, I shot another group except this time with 12 pumps. The resulting group was practically identical except the POI was a bit higher and there was no flier. All 5 shots were a 0.75" group. They were also going across the chrony at 650fps or 9.7fpe. Not bad for a $45 air rifle. Well, a $45 air rifle with about 20 hours of tinkering with it.
Summary
Have a look at the table for a summary. The new pellets are highlighted in yellow.
-
Awesome update! Mine holds the JSB's exact at around a one inch and seems to prefer the polymags, CPHP, and rws do well, too. I think the tightest group I have so far was .495 in ctc with the polymags. I haven't noticed a difference with different styles of loading the pellets, suh as shaking the gun and letting them fall into the breech. I did notice a slight poi change when shooting at different temperatures possibly due to the plastics expanding. It's still not as good as I'd like it to be, mainly because my standards are too high. It, however, has gone from the most frustrating gun, to putting 4 squirrels, 2 mourning doves, and one rabbit in the freezer all in under a week. It offers that extra challenge of needing to be extra stealthy in order to successfully deliver a powerful and accurate enough shot at close range. Thanks for the update! Glad to see yours is shooting well!
-
if your 880 shoots the crosman prems Ultra Mags well you are very lucky. for hunting they are devastating. mine does not group them well... But i can tell you that at 45 yards and 10 pumps they still bury themselves all the way in pass the skirt on a 2x4. great energy retention.
-
Hey man how did you remove the powerline barrel from the reciever?
-
The barrel is held in the receiver with a friction fit. I simply clamped the barrel carefully in my woodworking vise and just grabbed the receiver in my hand and separated them.
The vise jaws are lined with wood so they are somewhat forgiving on the barrel. Still, you don't want to use an excessive amount of clamping force since the barrel is thin.
If you feel like you're having to clamp too tightly to keep it from slipping, modify the approach slightly. Clamp two pieces of wood (e.g. some 2x4 scraps) together face-to-face and then drill a hole at the seam that is just slightly smaller than the barrel diameter. 1/64" or 1/32" smaller should be sufficient. That gives you a close-fitting clamping die that you can load into the vise...something that hugs the barrel fully around its circumference. That distributes the friction better so you don't have the clamping force concentrated on just two small spots like you get when using flat jaws.
I hope that makes sense but if not, let me know and I'll go out to the shop and mock it up and get you a photo.
-
nope that was perfect. I used a vice with wood i had drilled holes in to hold the barrel when i crowned it, simply leaving the receiver attached. I recently re-recrowned it, using a slightly better method of polishing.
I also tried floating the barrel (simply remove the shroud), not that i expected it to be better. and while it didn't perform horribly it didn't really improve either as the barrel is very flimsy. Currently mulling over ideas to make a full wood stock and replacing the plastic dovetails with a stronger material. I've noticed I get a lot of two shot groups, where i get a pellet in pellet hole before the POI changes slightly, and i believe this is due to torquing of the plastics, changing the plane of the scope slightly. So if i could make a new dovetail that is secured to the receiver maybe it will improve the accuracy just slightly more. I also would like to create a new shroud, one that is supported by the receiver, but i'm not sure if that is going to happen or help.
I think a floated barrel helps a PCP gun as there is a slight expansion and contraction of the air reservoir and freeing the barrel keeps it from being affected by this expansion. The powerline has the shroud connected to a steel support, which is floating in respect to the air compression chamber so the shroud might not affect accuracy at all. I also have yet to solve any trigger issues, I can deal with it and it is heavy, but it would be cool to make it lighter.
-
Yeah, I couldn't see any improvement from floating the barrel either.
Regarding the dovetail, I did not like how the whole thing is molded into one side of receiver housing. In other words, it sort of reaches out over the opposite side, and when you tighten down on the scope mount, you've basically got a wedge trying to peel the dovetail away on one side. So I installed a series of small countersunk screws through the top of the free-hanging side of the dovetail, down into the receiver housing, to firm it up.
-
That's smart i was thinking of trying that, too. What I just did was dismantle the entire thing, took a bunch of measurements, and started to notice some engineering flaws and strengths. The "spine" of the gun does keep the shroud from being affected by any part of the gun, so that shouldn't be affecting the accuracy negatively
THE STOCK, however, is attached to the inner housing of the receiver, which is all attached to the spine by the two screws, which happen to be perfectly parallel to each other. This means that when you apply pressure to the stock, it causes the whole receiver to move and pivot around the screws. I used some half inch self tapping metal screws, which i then cut after they threaded as they were a little long. Also drilled out the plastic receiver slightly so that it would fit flushly over the screw heads, the fix isn't visible once the plastic is put back on. Hopefully with testing tomorrow this will really dial this gun in. I know with the crown job it has potential for accuracy (stacking pellets) but something is floating around, and my groups often shift and move. I'm hoping this will have addressed all flaws except possibly the trigger and the dovetail security as you mentioned.
The picture shows the screws I added on one side of the receiver.
-
James, I hope you are getting some trigger time this weekend. Let me know how your latest mod works out once you've had a chance to shoot some groups.
-
Following closely here...
One thing I dislike about these is that they twist easily... feel cheap while being pumped. If you flex it, using the stock and the lever while watching this area, you will see where the weakness is. 3 tiny mig welds turn the channel into box... and make all the difference. A piece of thin sheet metal epoxied or soldered in would do the same. If welding, do not clamp or overweld. The shrinkage from those tiny spots pulled the sides square, and the cylinder fits without slop.
Gives it a whole new feel.
-
Good idea I hadn't looked too closely at the box construction. If I can get the welder working I'll probably try this and maybe weld more of the shroud, too. The welding ends where the barrel begins to overhang the gun. I really feel close to getting this gun where I want it to be. It seems very accurate but the groups float around. . A bit. Haven't really had a good day to test but I shot a few yesterday in the rain and at 21yd every two shots would be hole in hole, and then the next two would move slightly and do the same. Polymags bluffed me one day when I shot 2 sub half in 5 shot groups. But have since opened up to about .8in at 20yd. Not bad for $45 gun. I just know I can do better
-
Hey Jason,
If and when you get the time i would be very interested in seeing the countersunk screws in the dovetail, as i am having trouble visualizing exactly what you are talking about and i do agree that the plastic dovetail could be cause for concern regarding consistency and accuracy.
Have had no luck getting groups to shrink. I don't understand why the gun performs so well some days and not so well others with similar rests and conditions.
last test was June 8 -note, wasn't really planning to post this I was just shooting enough pellets to get a feel for how the gun was throwing them.
Sunny, no wind, humid.
22yd
AA Falcons 7.33gr 6 shots .981" ctc
Polymags 8gr 7 shots 1.415" ctc 6 shots 1.051"ctc
Re test 5 shots .690" 4 shots .480" ctc
JSB Diabolo 8.44gr 10 shot group yesterday in the rain. .700 in
7 shots .813" ctc 6 shots .580" ctc
CPHP These go from 10 shot groups of .712" CTC one day, to an amazing 7 shot group of 1.3 in ???
Crosman Pointed 6 shots .792
I was running low on some pellets which is why i only shot enough until i felt like i had a decent representation of that pellet. I shoot benchrested off a shoebox with a rolled dishtowel (very effective actually) and the cross-hairs remain on the center of the .5in bullseye until after the pellet has hit the paper. I shoot between heartbeats and am very confident that I am doing my part.
Some of the groups are reasonable they just float around a little. I'll adjust the scope and they almost never stay on the bullseye. A few will hit. Maybe one or two will go a little right. But in the next group i shoot it will shift, and one or two will go a little left or a little low. I'm fine with a .5in group. But i want it to take the bulls-eye out, and other than the two polymag groups a posted a few weeks back i haven't been able to duplicate those results consistently. Some days it shoots fine, some days things seem to shift around. Next step is to get the welder working and secure everything. The box "spine" of the gun, the shroud, even thinking of welding the shroud to the box and making some baffles to better secure the inner barrel to the shroud. Also would like to secure the barrel to the receiver better. Noting fancy just think if it is tension fitted it might allow air to escape so some hot glue to seal it off essentially. Then if that doesn't get the results I want, guess I'll just be waiting until i can afford a PCP, or even the new 125 with the vortek (vortex) piston
-
I've enjoyed reading this thread as the 880 was my first "rifle" years back. I wore it out, rebuilt it then wore it out again. It had the smoothbore steel barrel for BB's and pellets. The receiver was potmetal instead of plastic like current production. There were probably other differences as well. We never shot for groups back then, just shot for hits. That rifle got shot so much I could hit anything I could see within a hundred yards or so. We took all kinds of small game with them, including iguanas which can be tough customers.
The smooth barrel depends on the shape of the projectile to stabilize it rather than on spin (which is nonexistent). Still, we experimented to see how to improve them. A wrap or two of electric tape around the muzzle where it fits into the front sight centered the barrel in there and kept it from rattling around and shifting from shot to shot. It's been 30 + years so don't recall all the details, but it seems the early 880's had the barrel attached to the valve via a screw holding a clamp and there was a seal between the barrel and the valve. If they are friction fit now then the system has changed considerably.
A while back I picked up an old 880 in pieces. It's pretty much unrebuildable so the rifled brass barrel is getting eyed as a possible donor for a ???? project somewhere down the line.
Anyway, thanks for the memories. It's good to see folks playing with the old platform that gave me so many hours of enjoyment way back when.
-
I just thought I would mention that Gun Broker currently has two different 880's up for bid now. Both are listed as having the metal receiver and metal pump arm. NOTE you will need deep pockets.
DT
-
Hey Jason,
If and when you get the time i would be very interested in seeing the countersunk screws in the dovetail, as i am having trouble visualizing exactly what you are talking about and i do agree that the plastic dovetail could be cause for concern regarding consistency and accuracy.
Hi James, here you go. These little screws button down the freehanging side of the dovetail. I think I installed 6 screws total; 3 on either side of the loading port. The most important place is right beneath the scope rings.
A word of advice: if possible, use steel screws rather than brass. Just threading into plastic, I wrung the heads off of a couple of brass screws which means I'll have to drill them out if and when I ever decide to pull it apart again.
-
Very cool Jason, I appreciate you getting back to me on that, and I do believe the receiver is a big problem with the gun's accuracy. I think it's about strung out for all it will give. My last efforts will be towards machining a new receiver cover or fixing the one like you did and welding the box, the line going down the shroud, and the shroud to the box once I can get the welder working. Then it's off to a b-50 or some PCP once the funds are together!