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farrlarr · Member

My Crosman Sierra Pro has recently developed a problem. Every 5th or 6th shot is a major flyer, 1.5-2 inches away from the preceding shots, usually low but occasionally high. I think I have narrowed it down to a scope problem. The rifle carries a Crosman 3-9X40 AO scope on the one piece mount that came on the gun. There is nothing obviously wonky about the scope, and all screws are tight but I can shoot reasonable groups with open sights, without the flyers. Anyone have any ideas/suggestions for me?

donec · Senior Member

I don't see how the scope would mess up just 1 shot in 5. Sounds more like maybe a slightly messed up crown or maybe a loose bolt altering how your hold effects the gun.

packrat · Senior Member

It could also be B A D pellets..I've had that same thing happen to me, more than once!! In every case, it was a tin of pellets that were of such different sizes thta there was no way to tell from shot to shot what was gonna happen....threw i'em in the trsh, started buying a better grade of pellets....problem has not re-occurred Mr. Green

walter · Veteran Member

i have a pretty big container of daisy and gamo pellets that are junk. i purchased then before i realized how important the ammo was to accuracy. now its rws, jsb and the like. money well spent. no need to struggle with bad ammo and get frustrated about not hitting what you aim at. lesson learned! Rolling Eyes

Bozo · Veteran Member

If the gun shoots well with iron sights, but throws the flyers when the scope is mounted, then there is something wrong with either the scope, the mounts, or possibly the weight of the scope is throwing something out of wack with the rifle. The reviews I read almost all thought the stock was very soft wood. So something cheap and easy would be to to make sure the screws holding the action to the stock are tight and even; perhaps the soft wood has compressed some under the screw heads. Tighten them very firmly; don't try to strips the threads, just nice and snug. And use blue Loctite on them so they stay tight.

If that doesn't do it, replace the scope with a known good one. If that fixes it, then it was the scope. If not then that leaves the mounting system. Take the mounts off, clean them and the dovetails, if the scope stop is a separate piece make sure it's on properly with the screw(s) tightened firmly with blue Loctite. Carefully reattach the mounts(s), tightening screws firmly and using blue Loctite. Clean the rings and re-mount the scope, again tightening all the cap screws firmly and evenly, and using blue Loctite. Use a pencil to make some jury marks so you can see if the scope or mount is moving at all.

The previous comments about pellets are well taken; it pays to use a good quality pellet that your gun likes. They don't have to be expensive pellets, but the pellets have to be consistent in diameter and weight, and come out of the tin fairly undamaged. I haven't shot nearly the variety of pellets that some here have, but I have found Gamo pellets to be wanting on all counts, and impossible to shoot with any accuracy at all. They may make a grade of pellet better than I've tried, but I don't know of them. In my rifle the undersized ones in particular caused flyers.

Hope something here is helpful. If the problem gets fixed, come back and tell us what it was that fixed it, so others can benefit. If it doesn't get fixed came back and tell us that, too, and we'll keep working on it. Good luck!

farrlarr · Member

I have been pretty much limited to pellets available locally, not having submitted an order to Pyramyd yet. So far, I have heavily used Crosman Competition Wadcutters, with which I have previously shot 0.154, 0.173, 0.177 and 0.182 inch 5-shot groups with this gun/scope, among lots of slightly larger groups. I recently tried some Stoeger X-Sport Wadcutters and had the same problem. Gamo Target wadcutters, Hunter, Masterpoint and Magnum do the same. Again, I can group reasonably without flyers with open sights, it is only when using the scope that the flyers occur, which is the reason I suggested this might be a scope problem.

I have removed/remounted the scope a couple of times, using blue Loc-Tite each time. This has involved removing the complete scope/mount complex and removal of the scope from the mount. Everything seems to be setting normally and all screws are tight. I have Loc-Tited and tightened the stock screws but should probably go over everything again.

The barrel seems to lock up tightly when cocking the rifle. I can't see anything there that seems to be wrong.

Thanks for all the input. I will keep working on this and let you know if/when it gets corrected.

Slavia · Moderator

All of the above is correct. Also...

I had similar problems with my Crosman G1 (same action). If I bumped it down a little too hard on a rest the barrel would open slightly because the alive jam wasn't latching very well. (The alive jam is that chisel-shaped thing that latches the barrel.) Polish and lube helped that. I have read elsewhere of people adding little spacers to the alive jam spring so it has more preload and latches tighter. Try reaching under the barrel before each shot to make sure it's all the way closed.

The barrel pivot is a little different than some guns. Instead of clamping both sides of the compression tube yoke to the barrel's breech block, the screw head simply rides in a hole on the left side. That means that cocking can exert torque on the screw head, loosening it. For me blue Loctite slowed it down, and adding a setscrew to keep the pivot screw head from turning stopped it completely. Check your barrel for side play and tighten the screw if necessary. Blue Loctite is your friend.

rsterne · Moderator

Your description of the barrel lockup sounds just like the one on a Crosman Phantom/Quest.... I had one where the bushing on the pivot bolt that was not concentric.... When you opened and closed the action, the bushing would rotate and change the POI... with a scope only, of course as the open sights are mounted on the barrel....

I made a new bushing in the lathe so that it was concentric and replaced one of the plastic washers with a steel one (on the right).... I customized the length of the bushing so that when the pivot bolt was tightened, it went up hard against that steel washer, and put a slight amount of compression on the plastic washer on the left side.... That cured the problem....

I have also seen people drill and tap the end of the left fork for a set-screw which they tighten against the pivot bolt to prevent it from rotating.... but I understand the metal is pretty hard and it's really easy to break the tap....

Bob

Slavia · Moderator

farrlarr · Member

I don't know whether this is coincidental or not but I realized tonight that I had not recently added chamber oil to the compression chamber of my Crosman Sierra Pro as the manual indicated should be done every few hundred shots. Tonight I did so and then shot eight 5-shot groups of 0.133, 0.174, 0.198, 0.235, 0.258, 0.339, 0.355 and 0.471 (not in order as they were shot although the largest group was the last one shot and there was one flyer which was my fault; keep in mind that these were shot off a rest at only 7 yards because that is all the space available in my house for shooting). It seems odd that a drop of oil in the compression chamber would have that much effect, but I didn't change anything else. What do you think?