.257 POI Shifts while shooting
Hi all, Asked on the GTA forum too. Have 2 .257 rifles. Randy built first in Feb with Ultima stock. I built with my gunsmith doing machining on one pictured here…..This one has TJ bbl 34″, carbon sleeved, HATSAN airstripper, 105 gram brass hammer, dyotat valve and one piece stem, also have his spring but used a tad heavier one on there now. Maddog BENCHREST STOCK, 4′ aluminum machined one piece barrel bushing. Can shoot 1/2 moa and then throw shots high, low and right left, Have to use another mil dot for awhile and then it goes back to same mil dot for same POI??? I didn’t chrono these but records shot with PW 0 and 3200 psi, shooting 72 gr fp at 1000-1010 fps..All screws blue locktite and are not loose. have tried 3 scopes and same thing….Try hard hold and free recoil and in between…………i have 4 molds. these were the 257420 . Have tried Porters bullets, and now mikes from Randy and all will shoot a good group or 2 then spread out 2-4 inches at 100 yds? Have hit rock size of mop bucket at lasered 460 yds…….If it shifts like that indicates to me something moving or loose but all seems tight to me? Bottom 2 groups were yesterday at 220 yds.. Help any IDEAS?
Thanks…………Carl
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I’d be happy with those groups. Mine will shoot hole n hole at 100 if I do my part. I just changed to a new valve from PCP tunes this valve has a huge stem and power went way up now my 74 grainers shoot crappy! I went to a 90 grain and it shoots tight groups but I’m still tuning it in I only get 10 shots from 3200 psi fill. With the first two hitting high and 6 running a bit lower and then two high again then a drastic drop off.
FROM : THE BIRDMAN
If you had READ the ORIGINAL POST, it says, ALL SCREWS are LOCKTITED and NOT LOOSE……………First thing done at the onset of the shifts…………..Thanks for looking………….Carl
Start with what might be the most simple and most unlikely noticed problem such as a loose screw .
FROM : THE BIRDMAN
I agree with how differing distance in stock forearm in the front rest cradle CAN help with the final tune….In my OTHER disciplines it CAN be noticeable at 100 yds in finely tuned rifle in maybe .1″ group differences…………Never seen variances from 1/2 moa to 2-3″ MOA with simple movement in the forearm……….But i haven’t messed with it until i get consistent MOA or better at differing distances, then the FINE tuning last……………..Carl
Never shot it less than 100 yds.. Shoot regulated from 3000 psi-3800 psi… I HAVE shot with 53 cu in tank to test for a curve and did easily with more volume tank.. Since I only shoot from a bench, only use regulator and always same pressure for a string….
My next moves will be shim rear of tank,,,,,,,Get screw loose from stripper cone to adjust, and then support end of frame the barrel with another bushing, possibly to end of barrel even? Thanks all for suggestions…..Carl
Air pressure . how does it shoot at 50ysd
I don ‘t think stripper Have taken off and groups worse ….And other .257 has same problem and plain barrel end?…..Carl
Rifle50, I’ve found that moving the rifle forward in the front rest gave me so more consistency, clamping the stock closer to the hammer shock area, I guess it absorbs some of the vibration, just a thought. Sweet rest, my bald eagle was junk till I disassembled it and cleaned and modded it, better now, but not like yours..
not sure if its the air stripper. it does good groups but shifting. id be interested to know what the strings like. should note for every shifted group too. do you have any kind of recording cam that can do slow mo? it could be at different fps the bullet/pellet spins differently at the beginning of exiting the barrel?
I’m willing to bet air stripper. I had a muzzlebreak on mine and it was doing the exact same thing until I removed it. You might just need to adjust the cone.
No offense taken and you don’t know my credentials and it COULD BE ME but i posted good groups to show it can shoot but can scatter them to be 3 inches at 100 yds and not wind. With 2 guns acting similarly, i doubt it having altered my pressure on the gun while firing..Gun is SOLID as if it was in a vise. ….Why i put in initial post, i have tried hard hold, free recoil and in between…….Tried bullets from 4 of my molds and purchased others, same thing….Below pic is my setup…….I shoot 1000 yard F-CLass and have rifles that at 100 yds groups are measured in the .1″ of even zero’s…..OR pretty much same hole………..The front rest is a joystick SEB NEO . The Rolls Royce of rests $1000 and 13 months wait to get one now. I waited a year……..Custom sized bag with heavy sand at rear……I also shot all through the 90’s at the World Championships for 50 bmg at Raton NM, 1000 yds…….1995 i won the World Championships……I compete in Rimfire Benchrest ARA at 50 yds….If your gun can’t at least group in the .150″ consistently you might as well be throwing rocks 😯 Thanks for the input and I DO HAVE A PROBLEM somewhere………I also don’t consider 220 yds a long way, even for a .257 airgun.My F-Class rifles i can hit 4″ clays at 1100 yds in back berm sighting in for 1000 yd play days …..Carl CLICK PIC TO ENLARGE
yesssss! i used rubber garden hose washers between my tank and stock, made a differance in shock vibration at lower psi, i forgot about that, Doug at MD sugguested it too me!
Not my design (It’s a 220swift creation, for a Rapid), but I’ll have one similar to it… Adjustable cone:
Nice looking stripper…..I would not be surprised it degrades or enhances accuracy through adjustment………I don’t believe if all is right with gun elsewhere, that moving the brass cone will make it go from 1/2″ moa to 2-3 inches? But only doing will i know……….I will screw it off and take to my gunsmith……..He has better tools and not as ham fisted as i am…….With heat gun on that tiny screw i was bending/flexing the allen wrench and close to rounding inside head….Gunsmith can remove it and re do if necessary…..Only about $28 for another…..I will try that and KNIFEMAKERS suggestion of shimming rear of the tank…………..Easy to do suggestions………….Again thanks for the suggestions……….SHot all my life and only had these airguns since FEB so ALL IS NEW to me but love the challenge, plus fun to shoot better groups at 200 yds than 2 of my friends and their AR15’s 😀 …….Carl
220 yards is a long way…. Don’t take this the wrong way, as your groups are better than I could shoot, but have you considered it could be you? The pattern doesn’t look like lose barrel bushings. It could be wind as someone else has said. Are you shooting from a bench or prone? Try changing your shooting technique and see if that changes things. Are you getting the same issue with different slugs or pellets?
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I am happy with GOOD groups and attached to show it CAN SHOOT……….Then it moves all over with 2 1/2 inch groups or worse….I have found the problem and with my Gunsmith/machinist, get it to where it will shoot 1/2 moa most of the time. Hope i can get the machining i need soon….By gunsmith hasn’t been feeling well……work stacking up…………I always shoot tethered as have a regulator and shoot from bench so i use it and have same FPS within 10-12 fps per shot…….