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308 grouping fell apart
jb4lcm
Member Posts: 119 ✭✭
OK - so I had my Tikka zero'd in and working fine. Then I got the great idea to adjust the trigger to a lighter pull - - so OFF goes the stock, adjusted the trigger, stock goes back on and then I cleaned the gun - and ran a patch with OIL thru the bbl and put it in the safe.
I pulled the gun out today to see how the lighter trigger effects the grouping with less pull . . . I did NOT clean out the BBL of the OIL first. I just shot it. Groups went from near MOA at 100 yards to skatering around a little over 2 MOA.
Any chance the oil in the bbl hurt the situation? There WAS a 15mph headwind today . . but damn near directly at me. No cross wind.
Comments
Could be the oil, but usually the first few shots burn it away. Did you tighten the stock screws properly? Some rifles are extremely finicky about both the sequence the screws are tightened and the inch pounds they are tightened to. The turbulence of the head wind can also upset the bullets slightly. Not like a cross wind where you would get a horizontal dispersion but more of a vertical displacement. Lastly, how well did your barrel clean up? In your previous post you indicated that you shot quite a few rounds. Sometimes new barrels can be slightly rough until they are broken in. This can cause copper deposits that can hurt your accuracy. Get a good aggressive copper solvent, Sweets, Butch's, Blue wonder, etc..., and give it a good cleaning. Probably a simple fix, good luck and keep us posted. Bob
Play with the stock bolt torque.
Your Tikka manual tells you the stock screw torque.
This
It was likely the stock screws torque shifted.
I couldn't find any torque setting for that . . . my book is pretty basic and the Tika/Soka website doesn't have anywhere to ask questions.
I'll look again . . . Thanks!
Were the shots low? high? all over the place?
and this (page 12)
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲
I'd start at 25 inch pounds, and work up from there. Make sure you have a good inch/pound torque wrench.
https://support.beretta.com/how-tight-should-my-sako/tikka-screws-be
How many shots did you fire when seeing the 2 moa?
Check to see if the groups shift and how much as you slightly loosen by 1/2 turn the front action stock screw then back to snug tight? compare point of Impact shift of the group.
If the gun starts grouping 1 moa consistent again, do not do anything other than clean the barrel good again then check the group with a cold barrel. After the gun has rested for 24 hours.
Report?
Before I made any changes, I would give the barrel a good cleaning, without oiling, and try the grouping again. Also, check the muzzle to make sure there isn't a little ding that crept in, or something sticky near the bore.
Oily bore does all sorts of wonkie things to rifle POI and accuracy but usually goes away after 4-5 shots.
Taking stuff apart does wonkie things that may stick around longer.
There is no quicker way to screw up a good firearm than by 'fixing' it.
Hope you can get everything back to it's happy place and back to tiny groups!
Here's the 200 yard result from yesterday.
I'll clean the gun, dry the gun - no oil, and wait for a calm day and try again.
I am still looking for the manual with torque info.
From Beretta's web site
How tight should my Sako/Tikka screws be? (beretta.com)
Low. Could be the headwind.
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲
That is a 1.5 MOA group, not bad for a factory rifle. The 15 MPH wind could have been switching direction/speed down range at some point opening up the groups.
Just a couple of things to consider:
I would test the rifle on a calm day at 100 yards. (instead of 200 yards)
If you can loosen the front recoil screw 1/2 turn from snug leaving the tang screw tight and the group changes (point of impact changes) the action is not properly bedded into the stock. (aprox .001 shift at the muzzle will result in approx 1 inch shift at 100 yards)
I glass bed center fire bolt action rifles so as I can take the stock off and back on and the POI stay same at 100 yards.
I also pay attention to where the first shot from a cold barrel impacts as compared to the other shots as the barrel warms. Also I pay attention to the point of impact and size of groups right after a barrel has been thoroughly cleaned as compared to a barrel that has been shot more than 5 times without cleaning. I do not test fire oily rifle barrels. I dry swab with a white cleaner patch until the bore is dry.
A test that I do on a rifle that is going to be used for hunting and/or long range shooting is to fire one shot from the rifle on different days and when I see a rifle that will shoot a 1moa group or less doing such it's a trustworthy hunting rifle.
The guy pulling the trigger has to be capable of shooting less than 1 moa to proper test the accuracy of a rifle.
No question in my mind. Stock screws torque. -------------Ray