Discovery Velocity

[wlambert]

I have not been happy with the accuracy of my new Discovery.  It shoots about one inch at 25 yards.  These are ten shot groups.  It will shoot four shots into one ragged hole, then spread the rest around.  I could live with that, but my next group could be one to one and one half inches from the last.  I ordered the stuff from Brownells to redo the crown.  

Yesterday I shot sixty rounds over the chronograph.  Here are the results.

http://img.photobucket.com/albums/v632/wlambert/Velocity.jpg



I charged the rifle to 2000 psi.  The pump and rifle gauge match pretty close.  Notice, I get about 20 shots at maximum velocity, but they are at the end of the charge.  The gauge shows this too.  But what about the big steps in velocity???  They tend to occur in ten shot increments.  When I was shooting groups I was shooting 30 rounds and then recharging so I was working on the left side of the graph.  Looks like I should only charge to around 2500 psi.

Any thoughts?  Should the regulator work better than this?  Could this cause POI shift?

Thanks

[jeff124]

25  good shots is not unreasonable for the discovery.  On mine, the sear was rubbing on the hammer after release which robbed power and made for a lot of variation in velocity. A little polishing made a huge difference. I put in an HDD from Big ED, it smoothed out the variation some, and quieted the gun down.
 It looks like your sweet spot is at lower pressure. The good news is you don't have to pump as much.
I've heard that some of the barrels need to be re crowned, mine wasn't bad at all (luck of the draw?)
I found that my Disco .22 was not very accurate until I thoroughly cleaned the barrel and then put a hundred or so shots through it. Now I'm getting about 1/2 " at 20 yds. Have you tried different pellets? Mine likes Crosman Premiers and Beeman FTS. Other pellets are not that good in mine.
 Tuning the trigger also helped a lot, mine had a rough trigger which does not help accuracy at all. I polished all the contact surfaces and did the two screw trigger mod.
 I think the Disco is a great buy, and with a little tuning it really shines, it's now my favorite gun.
jeff

[DanoInTx]

Ditto what Jeff said, start with a lower fill pressure, you have a decent curve from shot 26-55 or so.  Shoot it across the chrony with a full fill, when it get's to 770 or so note the pressure...that looks to be a good starting point for that gun.  As far as the irregular shots, it looks like maybe your hammer is sticking a little somewhere, maybe try polishing it and also cleaning up the inside of the tube and sear surfaces (again, ditto what Jeff said).

You mention a regulator?  There's no regulator in that gun, air is metered by the valve, tube pressure, valve return spring and hammer spring, just a balance of pressures.....regulated guns can hold 5-10 fps spreads over many, many shots like my HPA TF79T, see string below:



That gun is actually regulated.  Those strings will look pretty much the same upto about 70-80 shots.

Crosman barrels are about $12 from Crosman if I remember correctly plus $4 shipping....if yours is bad still after a recrown, it's only $16 to try a new one:)

[longislandhunter]

Dan,,, I'm just curious,,,,, I've never done it before so I'm just wondering how you change a crosman barrel??? Does it just screw in???? Thanks......

Jeff

[kirby999]

Jeff, all the Crosman's with the steel breech are the same, even the 22XX pistols. To change a barrel involves removing the barrel band , the inside under the bolt breech screw and the rear breech screw. Once the breech is removed it's as simple as backing out on the grub screw in the top of the breech and pulling the barrel out. Care should be taken when removing the breech assembly as you have a transfer port that will come out as well as a small seal . Take note on how the transfer port is installed and replace it with the small end in the right direction. And on the New style breeches that are used on the Discovery , the bolt handle has to be removed to allow the bolt to be pushed back far enough to allow you to get to the small breech screw under the bolt. kirby

[longislandhunter]

Thanks David :)

Jeff

[DanoInTx]

longislandhunter - 4/20/2008  5:15 PM



Dan,,, I'm just curious,,,,, I've never done it before so I'm just wondering how you change a crosman barrel???  Does it just screw in???? Thanks......

Jeff

What Dave said:)