GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: affegiraffe on March 29, 2015, 11:20:20 AM
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So i have been having problems with flyers and general accuracy with my trail np the last times.
Here is a target shot from 15m (16,5 yards). I shot Crosman Premier Hollowpoint and JSB Exact Jumbo RS.
shooting order: top right one, top left, bottom right, bottom left and last middle.
(http://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=3354)
As you can see the CPHP seem to have a very unstable flight while the JSB seem to have a much more stable flight, that is at least how it looks to me. But now to the question, i would love to get some advice on how i can make the groups tighter, and have less frequent flyers. From this target i will probably stop using CPHP pellets and make the switch to JSB.
Any advice on what I can do to the air rifle to improve accuracy is highly valued, also how much does the hold effect the group on a NP rifle?
Many thanks
Alfred
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Alfred, I don't know you so please forgive me if I start with the obvious. If you haven't already done so, clean the barrel. If your pivot has side to side play at all you'll need to address stabilizing it. I use bronze bearings.
My greatest problem with the Crosman break barrel was the trigger. Some people just replace the adjustment screw with a longer one. This can reduce the length of pull.
The pull is very difficult in the stock condition. That is due to a very heavy spring inside the trigger blade itself. This can be removed.
If you've only tried two pellets you may not have hit upon the one your gun likes yet. That liking can change over time.
Airgunning is not an exact science - lots of variables.
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Alfred, I don't know you so please forgive me if I start with the obvious. If you haven't already done so, clean the barrel. If your pivot has side to side play at all you'll need to address stabilizing it. I use bronze bearings.
My greatest problem with the Crosman break barrel was the trigger. Some people just replace the adjustment screw with a longer one. This can reduce the length of pull.
The pull is very difficult in the stock condition. That is due to a very heavy spring inside the trigger blade itself. This can be removed.
If you've only tried two pellets you may not have hit upon the one your gun likes yet. That liking can change over time.
Airgunning is not an exact science - lots of variables.
Thank you for the reply! No worries, I should have included a introduction to what is done and i have done so far in the original post!
So i have tried more pellets before, these are the ones that has been working best previously. About the pull and trigger i have the GRT III trigger from DaTuna which i have enjoyed as a very effective improvement.
The barrel was cleaned as late as yesterday for the days shooting and i shot around 150 pellets before this target. The pivot does not have side to side swinging, but i have been looking into changing the bearings anyways for a better lifespan. I have also changed the original piston seal to a seal from www.airrifleheadquarters.com (http://www.airrifleheadquarters.com).
So with this new information, any other ideas?
And where can i get the bronze bearings?
Many thanks
Alfred
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Alfred - the only reason I didn't suggest the GRT III is because they no longer ship it overseas - too much hassle. It appears you have done almost the same thing to your Trail as I've done to my Nitro Venom. The main difference being the pivot washers. That said, I have been known to get a half inch (1 1/4 cm) group at twenty yards (18m?) but not consistently. The shooter may be to blame. I use Crosman Premier Hollow Points in that gun because I've found nothing else to work better.
I believe I've posted about washers on GTA - try a search on pivot washers or pivot bearings. I don't get them, I make them. I prefer to start with a bronze thrust bearing, and living in America I work in inches. I don't know what (if anything) is available in metric. A standard 3/8" bronze bearing is 1/16" thick. A 5/16" brass washer is 0.062" thick. It's really about the same. Both are about 3/4" in outer diameter. That's too big. I put the proper size bolt through two of them, tighten the nut, put them in a drill, and hold a file against the edge until the outer diameter is correct (about 0.68").
Thickness is important. I measured the distance between the forks, subtracted the thickness of the barrel, and added back the recess on each side of the barrel. After combining the numbers and dividing by two I found my perfect thickness at 0.058" I sanded washers until arriving at that point, installed them, and the barrel had side play. A pair of unthinned washers fit tightly but I shot off to one side. I thinned a set to 0.060" and they seem to work fine. I drill small indentations on both sides of the washers and apply moly lube. I bevel the edges slightly while in the drill. I tighten the pivot until the barrel does not quite hold in position when left. I lube the alive jam (spring loaded wedge) so it works freely. That's about it. Enjoy.
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Thank you for the help! I have to start up my father's lathe and get to work then ;) I think I also will try recrowning but that is a later project.
Many thanks
Alfred
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Affe, try both artillery hold and a firm hold.
Lycka till!
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Affe, try both artillery hold and a firm hold.
Lycka till!
Will do!
Tackar ;)
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Also try some heavier pellets. JSB 18 gr. should shoot a lot better. My NP2 does fairly well with CPHP, but great with the heavier JSB.
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The JSB 18 gr. is your ticket to happiness !
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Is your rifle scoped?
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Is your rifle scoped?
My question, exactly.
If you are using open sights the barrel pivot should have little effect.
Too me, it looks like your problem is trigger control.
Remember, first digit only.
Not too tight on the hold.
Allow the rifle to move.
Have your dad shoot it.
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You might try H&N FTT's if you haven't already. I would try 5.53 & 5.54 head size, since the JSB's and Crosmans are 5.52 IIRC. The Q-Tip test on the crown might be in order. As to the question about the rifle being scoped, IIRC that rifle is not offered with open sights. Good luck and please keep us up to date on your progress.
Scotty
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use a wooden dowel rod to push pellets down the barrel..use a smooth even pressure and feel for tight spots
the last 13-15mm is meant to be tight....pay extra attention to the last 2-3mm before the muzzle exit..
My rifle had defective rifling for about 1mm at the muzzle end that caused many flyers and bad groups..
if you still have the factory plastic bushings (bearings/washers are other names for the same parts) the adjustment has to be much tighter than you would think to hold the barrel in the same place for following shots...search this forum from the main forum page, not from inside a thread for "pivot screw adjustment" for tips..
something else that helps is to use 2mm thick self adhesive foam between the stock and all contact points...search "stock bedding" for ideas
accuracy is also effected if the seal on the power piston and/or at the breech are not fully working....again search for "piston seal" or "breech seal" for information
loose screws for the stock or the sights/scope will cause trouble too....
incorrect power piston seal lubrication (too much, too little, wrong grease) can cause bad accuracy too....there is MUCH information on this forum about grease/lubrication
look at my Avatar pic to see one of my guns and read my signature to see a list of all that has been done to it....it now shoots as well as I can shot it, but it took a lot of effort to get it to do that
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Alfred, I didn't notice and motion at the pivot of my Titan GP either, but after installing bronze washers, my fliers were reduced drastically.
E. J.
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I have one of these with crosman pointed hunting pellets at about 7.9 grains it runs just a bit over 500fps and it stacks pellets. However I got it because it wouldn't push a pellet out of the barrel, so I went on line to Crossman to find a parts diagrahm and had to call them to get the factory model name for it. It is listed in the owners manual section as BBP77 I studied the diagrahm and noticed they have a shim listed and shown for the barrel seal so I cut a couple out of papper and tried them talk about a night and day difference this thing came alive, still I was getting the same results with accuracy you are flyers all over my targets looked like I was patterning a shot gun. One day I was checking screws I took the set screw out that holds the main barrel screw in and found that the main barrel bolt was loose I tightened it until I got just a little resistance on barrel movement(that was about 3/4 of a turn)and went out and tried it. I stacked 5 10.5 grain Gamo Silent Cat pellets under a quarter at 20 yards, with open sights and then turned around and did it again, and again, until I had a hole that measured 1"and had more then 25 pellets through it.
This is my favorite pellet gun I mounted a reflex sight on it and any small pest out about 20 yards is toast, but it has been love hate, this thing has a horrid trigger, it takes a solid hold and serious self discipline to get to group I think I am gonna either polish the heck out of it, or just try to find another trigger for it, I keep hoping someone on here will have some trick to improve it, I tried the longer screw the problem is the sear is shaped with a piece that actually blocks the cocking lever if you adjust it too far, I think maybe that piece can be cut back and then the longer screw will work I don't know yet but I will.
I also replaced the piston and barrel seals that was a huge improvement power wise, that and clean, clean the heck out of it. You can get every part you will ever need through Crossman for it at cheap prices just remember it is listed as model BBP77.
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Also check for movement up and down, my brother's XL could not hold a group. Found some up and down play, not much but it was there. sent it back on warranty, came back fixed.