GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: astroman on February 06, 2011, 06:55:21 PM
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Have lately experienced a worsening accuracy problem with my .22 M-rod. Out of the box it was incredibly accurate -- characteristic of the gun we've come to love. Now my best 35-yd groups are 3-4 inches (were dime size before). But more puzzling is the fact that on a fresh 3000 psi fill, the POI is 2-3 inches below POA, but as pressure drops to 2500 psi, the POI rises back to my orginal scope elevation settings. This seems counter-intuitive -- shouldn't the POI drop as pressure does? I've read here about M-rod owners changing barrels/baffles, etc, and I'm wondering if I need to do the same. I've exonerated the scope as contributing cause and I've not changed pellets (CPHPs). Chrony figures are consistent with when the rifle was spot-on accurate. Any ideas what could be causing these strange symptoms?
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Could still be baffles... at varying pressures the pellet may be more likely to strike the ID of one. I agree it's baffling but too soon to rule that one out, I think. Do you have a chrony? Any departures from previous velocities?
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Did you take the shroud off before the accuracy problems?
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WRT the chrony figures -- the velocities have not changed -- still shooting in the 920 fps range with 14.3 CPHPs just like she did when new. I haven't cleaned the bore for about 1000 rounds -- I didn't think this would be a factor, but I'll give it a good cleaning just to see if any improvement in accuracy results. What is the issue with baffles, and the potential of a pellet striking one or more of them on the way out the barrel? Can the segments move out of alignment? I've never had the shroud apart or baffles exposed, but the rifle did fall over once when it was leaned against a tree. How do I check for alignment?
Thanks for the feedback so far.
-jim
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Ah, it fell once.
Try switching scopes to see if it is a scope problem. I would think the scope would be damaged before the gun was from a fall like you said.
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Yep -- tried swapping/re-mounting scopes....no joy.... :(
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Astroman, you can look at the barrel band and how the shroud is aligned inside of said band.
The shroud should be centered in the barrel band and the shroud should not be touching any part of the barrel band.
The holes in the baffles of early models were a tad too small, so Crosman ended up drilling the holes at about .281" to allow for more clearance for the pellet skirt as it passes thru each baffle hole.
If the Mrod fell over, the shroud could be misaligned with the barrel band and touching it.
If the shroud is misaligned, its easy enough to center it back up by loosening the two set screws on the barrelband, and re-align, then tighten set screws in place.
Also, easy enough to drill out the holes in baffles if they arent .281".
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just adjusted the barrel band. Turns out it was touching against one side, so I fixed it so I could see an equal amount of daylight around the gap between the barrel and the band. Will shoot a few groups tomorrow and see if there's any improvement. As to drilling the baffle segments, how does one access the donuts in the shroud to drill them?
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Astroman, you just loosen the shroud slightly(like about one half a turn), take off the endcap and dont lose the oring underneath, take out the 4 baffles, drill out the holes if necessary, put the baffles back in....put the oring on top of the baffles...thread on the endcap, and finally...tighten the shroud at least the half turn and if needed a little more.
The shroud should be snug, with minimal hand force, just enough to seat it and feel a little resistance. No need to crank on it or you'll damage the soft aluminum threads.
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Thanks for the advice -- will give it a shot (pun intended) and report back the results in a couple days
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Try this. Clean the barrel well (probably lead fouled), Loosen stock bolt (Marauder is sensitive to bolt tension), try pellet lube with your Kodiaks.
Read This:
" I ask a popular Field Target shooter what he does to make his Marauder rifle shoot consistant small groups. He shoots a .177 caliber, but the same should apply to the .22 cal. Here is what he said:
"Clean the barrel then Clean the barrel ,Clean the barrel ,Clean the barrel ,Clean the barrel ,Clean the barrel ,Clean the barrel
and when you think it is spotless then Clean the barrel.
Then lube your pellets. Slick 50 one lube. Try them sloppy wet. Try them just damp and even almost dry. CPL's on mine liked to be pretty wet. JSB and Air arms 8.44 shot best dry and then I pull a bore snake every morning before I start sighting in for a match. At the Nationals I shot a 5 shot clover leaf group on the 50 yard paper shot at a diagonal in the wind. I held the same place and they just all stacked. Not where I aimed but they stacked.
You have to find the right combination of pellet and lube that your gun likes and also chrono it to make sure you are shooting within a tight spread. there will be one pellet that your gun likes above all others. You may not have found it yet.
A few other tricks.
My stock screw is loose. the inletting is relieved so that I can run a paper around the reservior and slide it all the way to the guage port and to the front without it binding. That way any pressure on the stock will not transfer to the action and change POI. With the stock screw loose the action can shift if pressure is applied to it by the stock. that way there are no stresses on the action and in turn the barrel etc. Consistently no pressure. Everything free to move as it will. That way the scope will always stay in line with the barrel and nothing ever has stress on it.
Does that help?"
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good info here hope you figure out what is causing your innacuracy..