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Thread: Strange results zeroing - Your thoughts?

  1. #1

    Strange results zeroing - Your thoughts?

    Here's a little bit of a puzzler for you.
    I went out the other day to set up a new set of scopes and mounts and to try changing over from 130g ammunition to 150g ammunition in my 270 rifle. The rifle is a Parker Hale Safari and the ammunition used was PPU (SP). The scopes (An unbranded set but guaranteed Fog Proof, Shock Proof and Recoil Proof) and the Scope Mounts (A brand new set of Nikko Stirling Platinum Mounts) were fitted to the rifle and were checked for tightness both before and again after the zeroing session. I am positive that they hadn't moved.
    I checked the zeroing with the 130g ammunition while sat at a bench at (Aproximately) 100 yards and found the rifle's zeroing to be pretty much spot on. I then set out a new target (Exactly the same range and shooting position) and "double checked the zeroing" with 1 round of PPU 130g (SP) ammunition. The resulting shot showed that the rifle and scope was spot on for this ammunition. I then loaded the rifle with 4 rounds of PPU 150g (SP) ammunition and carefully shot them at the same target. The first round went 4cm low, which is something that I expected it to with a slightly heavier bullet head. However the next shot went marginally lower and left again from the previous shot. When the third and fourth shots were fired they did exactly the same, each shot going exactly the same amount further both low and left than the previous rounds, giving a very regular diagonal "laddering" effect.
    I have my own thoughts as to what has happened but before I say what they are I would welcome your thoughts and opinions on this "unusual situation".
    A photo of the resulting target is attached for you to form your opinions from. To put things into perspective the red "bull" is exactly 40mm dia.
    Click image for larger version. 

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    Last edited by FrenchieBoy; 08-11-2014 at 10:48.

  2. #2
    Hi frenchieboy. We couldn't do that if we tried! I am guessing it's the scope or mounts moving with each shot. However I do own the same gun as you but in .243 and it always gives me a headache zeroing it due to barrel expansion with the heat from each round. I have had similar results as you all be it not as accurate as your laddering effect and that was a mod come loose on a 22lr.

  3. #3
    Try it again Frenchie with a cold barrel and only fire three rounds carefully aimed, this time with plenty of time between shots. Do not look at the target between shots and call any shots where you may have made an error. Then post the results for comparison.
    Be very conscious of finger placement and trigger control. Try for a smooth slow controlled pull.
    Last edited by 8x57; 08-11-2014 at 11:01.
    It's the calibre of the shooter that counts not the calibre of the rifle.

  4. #4
    SD Regular
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    With Mike on this - s l o w l y ......!!
    Nooooooooooooobody expects the Spanish Inquisition!! Our main weapon is.........

  5. #5
    Thanks for the replies guys. Maybe I should have added that I took my time while shooting the 4 shots, about 6 or 7 minutes so that the barrel did not heat up too much. Jonylandrover is however thinking on very similar lines to me so now I will tell you what my thoughts are and what action I have taken to rectify the "problem"!
    The scopes were a "Cheap as chips" set of 6-24X50 off "The Bay"! at 23.98 -
    What I believe that happened is that (being a "dirt cheap" set of scopes - False economy I know but worth a try) while they could just about handle the recoil (Initially) from the 130g shots the recoil from the 150g was just a little bit too much for them and this has caused a fractional of shift of the cross hairs with each shot fired.
    I have now taken the scopes off and fitted them to my .22LR and tested them and found that after almost 100 shots there is no shift on the POI so that uis where they will stay - Unless they play up at all in the future in which case they will go in the bin.
    The .270 is currently re-fitted with my (Very) old and well used set of 8X56 (Unbranded) scopes and they are fine, so much so that I was out on Thursday and was shooting a (Tightish) 3 inch group with them (In pretty strong wind) at 250 yards - The only think that I ca fault with these scopes is the fact that the reticules are a bit on the thick side fo my liking. These however are going to be replaced with a brand new set of Hawke 3-9X50 HD (Mil Dot) Scopes which I have just ordered and paid for this morning.

    Thanks for your thoughts guys!

  6. #6
    The scope is certainly one possibility. While I am not exactly equipment obsessed I have to admit that my thoughts are you normally only get exactly what you pay for with scopes and that cheap ones are exactly that.
    You have done right to eliminate the questionable scope from the equation but I would be inclined rather than to fit another new untested scope to test using one of known proven reliability.
    It's the calibre of the shooter that counts not the calibre of the rifle.

  7. #7
    it would have been interesting to put another 130gr down the tube to see if the POI had shifted down and left

    FYI - heavier bullets don't always hit lower than lighter bullets
    depends entirely on where in the barrel whip cycle that they exit the muzzle

    i have a 52gr AMax and 60gr SP load for my .222
    60gr hit exactly 2" higher at 100yds

    If the scope change doesn't solve it I would be surprised if the stringing group pattern is down to barrel temperature alone otherwise you would have already seen this with the 130gr..if not even more so with more powder and more velocity

    what is the rifle sitting on/in?
    what position are you firing from?
    stringing like this is often "muscling" of a shot. i.e. the shooter is applying pressure to get the reticule on target
    when the shot goes off the recoil allows the natural lie of the rifle to resume slightly pushing the shot in the direction the rifle wants to naturally go

    get it set up for the shot so that without you holding the rifle at all the cross hairs are on target.

    report back when homework has been completed!

  8. #8
    More often than not it always comes down to one of two things, mounts or scope.
    Been down this road before.

  9. #9
    My guess is that it's you. You're not following through with the slower, heavier bullet. ~Muir

  10. #10
    In reply to the most recent replies:

    8x57 - I have tried it with a "proven scope" and this has solved the problem so I am fairly confident that the fault is with the cheap scope - Typical false economy!

    Bewsher500 - The rilfe was sitting on it's bipod on the top of a fairly steady table. This change of POI was not noticable when using the 130g bullet heads, even after puttung 10 rounds through it in a matter of 5 minutes which fairly warmed up the barrel so I would be inclined to eliminate barrel temperature as the problem. I haven't tried it again with 130g heads since changing to the "proven scope" and zeroing with 150g PPU Ammunition, but that is something that might be worth trying to check to see the difference in POI between the 130g and the 150g heads. I will (When we get some better weather - It's pretty wet and windy here at the moment! I will also try doing a string of "more relaxed" shots (Maybe prone position which I prefer whenever Practical/possible) and see what results I get but with the "proven scope" fitted the problem has been solved so I am fairly certain that it was down to the cheap scope, however time will tell, especially when the new Hawke Sport HD scope arrives and is fitted.

    Devon Deer Stalker - I am pretty sure that you have hit the nail fair and square on the head with your reply. I suspected scopes straight away and the other "tried and tested" scopes seem to have confirmed my suspicions. Once again the new Hawke Scopes will kopefully help things along!

    Muir - I can see what you are saying but all seems well with the 150g ammunition now that I have re-fitted the "tried and tested" scopes.

    Many thanks to all of you for your thoughts, opinions and helpfull advice!

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