Cold shooting

[Abe51]

Hello Air gunners.  I have a question I'm at my wits end. Bought a new Benjamin Discovery and pump last year. Been target shooting at targets all winter. I have been trying to site it in every time I try, it keeps moving when it's shot a few times. Thought it might be the cold weather but it is still doing it today. (85 degs today) . I have replaced the scope twice and even removed the barrel and check if it was straight.  Is this normal for it to move after the first few shots. Yesterday I shot at a paper target and the first shot was 3" low at 25' and slowed moved up until after the 5th shot it was dead on and stayed their. I wont be able to hit a rabbit like this, unless he lets me shoot at him 5 times. Not likely.   Any help would be helpfull.                           Thank You,  Abe

[Gipper]

First check your breech screws to ensure the barrel is tight in the breech and the breech is tight to the air tube. Second there is alot of discussion on the topic of barrel bands and the discovery.  Some guns seem to do fine with 1 while others work better with 2 (seems to be the norm) so take a look at that as well. One close to the breech and one in the stock location may be a good place to start, though it will require carving the stock a bit.  Personally I always felt that moving the small breech screw under the bolt on the disco created/magnified this problem as I never had this issue with 2240 pistols converted to carbines.  I have a tactical stocked short barrel disco that has the same issue as yours though not to the same extent,  seems to take a shot or 2 before she hits dead on.  I designed a new barrel band for it as it has a 1/4" breech riser on it.  I will be 3d printing it tonight when I get home and am hopping it helps.

Brian

[toddbrat]

It sounds like you're "shooting the curve." Not sure if you're new to PCP's or not, but most will have a shot curve based on the fill pressure. For example, if you fill your Disco to 2k psi, it sounds like the first 5 shots are coming in low due to lower velocity. After that, the valve is more in-tuned to the pressure and you get a relative flat shot string, could be 5-10 shots that are pretty consistent on power and FPS so they're on the money. After that, as the pressure drops, the velocity will drop as well.

You may have to vary the fill pressure to get the consistency you want. I fill my Maximus to about 1850psi, that's the point it starts to level off, and can shoot it down to about 900-1000psi. I know after 'x' number of shots if I shoot past 50 yards I'll have to add some hold over.

[dan_house]

^^ what Todd said. Sounds like slight valve lock, try a fill at 1800 and see if it happens then too.....

[Abe51]

You might be right. I'll lower the pressure tomorrow and see how that works.  A second band sounds like a good idea also.                                      Thanks for the reply

[Xraycer]

Is this normal for it to move after the first few shots. Yesterday I shot at a paper target and the first shot was 3" low at 25' and slowed moved up until after the 5th shot it was dead on and stayed their.

Not normal. I'm up in NH, and I shoot my AG throughout the winter, and there's really little changes, if any, with cold temp.

Now, when you stated that it the POI moved up, are you saying it moved up on its own, or were you adjusting the scope to move up the POI?

[bmoney]

I bet if you fill to 1800psi it is going to solve your problem.  My .177 Marauder will do that if I fill it to 2900 or 3,000psi.  Shoots ok but at 2,750 it starts shooting ragged holes. 

[AmBraCol]

If you've not shot it over a chronograph, you're just guessing.  Since you seem to have vertical stringing it would indicate a change in velocity.  As mentioned above, try filling it to less air.  You could try to fill it to where the gauge is after those first five shots and see what happens.  There are things you can do to adjust the pressure to which you fill it and still be on for the first shot.  Changing springs, hammer weight, pretension on the spring are just a few of them.  Do some reading on this forum from a few years ago when the Discovery first hit the market and you'll see some of the things folks have learned over the years about these versatile rifles.

[Abe51]

OK I went out and shot it again at around 1800 psi.    Three shots at 25 yards, 3 shots in the the same hole. I'll try again in the morning  but as of now I'm happy. Just need to do something about the nose.  I need to check BNM's Breach and quite barrel shroud.

[pecor]

And if the problem still exists  I would check and Clean, The hammer and the bore that it slides in, Don't Use Any wet lubes, secret sauce or grease on these parts.  Dry Lubes Only!!!  I believe your {Hammer is Dragging}, And not repeating when hitting the valve with the same force each time it is cocked and fired,  Wet Lube or No Lube will do that!  You want your hammer to glide like it's on ice. Clean it all up! The hammer and tube with some 90% rubbing alcohol and paper towel's, If theirs any rust film in there Clean it out.  Then use a dry lube like Molybdenum Disulfide      Or this   These go on wet then dry leaving a non oily slippery dry lube, You can get these at an auto parts store, That should fix your problem If Not check you valve poppet for sticking issue's, Don't use any silicone grease in the valve ether. Use silicone grease only on static O-Rings.

[tracker1955]

Discoveries have to much spring most of the time, had to cut two coils off mine to get a normal shot curve and reasonable extreme spread. I'm wondering about his gauges being accurate and being over pressurized causing partial valve lock and then verticle stringing. Most stock discoveries shoot with a declining string and no curve unless the spring is shortened to allow for a curve. Only a chrony will tell the true story.

[Killfire]

OK I went out and shot it again at around 1800 psi.    Three shots at 25 yards, 3 shots in the the same hole. I'll try again in the morning  but as of now I'm happy. Just need to do something about the nose.  I need to check BNM's Breach and quite barrel shroud.

I have a TKO on my maximus. It quieted it down a lot. Just another option you may want to look into. Unless your looking for the multishot of the BNM.

[pecor]

Read this thread first before you get a BNM breech, https://www.gatewaytoairguns.org/GTA/index.php?topic=142819.0

[Abe51]

Tried again this morning,pumped to 1800 psi. Shot dead center. I will not get as many shots like this but the ones I get will be on target. Thank you for your help. Shot two flea Squirrels in my yard this morning. That's the main reason I have a pellet gun in the first place. To keep Flea squirrels and rats out of my yard,as I live in the country.

[Bentong]

Beauty of low pressure PCP is low on effort topping it off. Check this link out...simple mod for 40+ shots >>  https://www.gatewaytoairguns.org/GTA/index.php?topic=110145.0

[Tater]

Glad you got it set right Rick. My Disco and my wife's Maximus both like a 1800-1850 psi fill. With a TSS or similar in them we both get 25-30+ shots per fill.