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Thread: Zero shift

  1. #1

    Zero shift

    Hi guys I have a cz550 in .243 with a t8 mod on I am using geco 105gr ammo and seem fine for about 20 rounds my zero goes is this because of fouling seems to be conflicting yes and no on how often h should clean all so how do clean the inside of a t8 mod?

  2. #2
    Probably - some would argue to just keep shooting and it will stabilise. Personally I clean my rifle regularly so I am shooting from a clean, or very nearly clean barrel. Some would also say that the 105 gn bullet is pretty heavy for most .243s to stabilise and it may be that after 20 or so rounds, there is enough fouling to prevent it stabilising properly. Every rifle is different, and yours is telling you that it wants to be cleaned regularly.

    The other big cause of zero shift, is barrels warming up - if you are rattling off 20 rounds, even leaving 30 seconds between, that will warm up any barrel, particularly a hunting weight barrel.

  3. #3
    Quote Originally Posted by Heym SR20 View Post
    Probably - some would argue to just keep shooting and it will stabilise. Personally I clean my rifle regularly so I am shooting from a clean, or very nearly clean barrel. Some would also say that the 105 gn bullet is pretty heavy for most .243s to stabilise and it may be that after 20 or so rounds, there is enough fouling to prevent it stabilising properly. Every rifle is different, and yours is telling you that it wants to be cleaned regularly.

    The other big cause of zero shift, is barrels warming up - if you are rattling off 20 rounds, even leaving 30 seconds between, that will warm up any barrel, particularly a hunting weight barrel.
    One question, how does fouling prevent stabilization?

  4. #4
    Quote Originally Posted by trxnav View Post
    is this because of fouling
    possibly

    Quote Originally Posted by trxnav View Post
    how often h should clean
    less than every 20 rounds it would seem

    Quote Originally Posted by trxnav View Post
    how do clean the inside of a t8 mod?
    you don't/can't
    quick squirt of WD40 and let it dry seems popular (I find WD40 gets stick when dry)

  5. #5
    Quote Originally Posted by j0e_bl0ggs View Post
    One question, how does fouling prevent stabilization?
    It may be that with 105 gn bullet its on the margin of being stable, but on the right side. A bit of fouling might but just be enough to tip it over the edge - it doesn't take much. Why - fouling will change the pressure behind the bullet which will have an affect on how it enters the rifling, accelarates down the rifling, barrel harmonics etc. With a high pressure, high velocity calibre like the 243 small changes can make a big difference in the end effect, and any fouling build up will be just a small change. In effect the rifle is shooting a slightly different barrel.

  6. #6
    Established Poster Muddy Springer's Avatar
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    Quote Originally Posted by trxnav View Post
    Hi guys I have a cz550 in .243 with a t8 mod on I am using geco 105gr ammo and seem fine for about 20 rounds my zero goes is this because of fouling seems to be conflicting yes and no on how often h should clean all so how do clean the inside of a t8 mod?
    more than half a dozen shots on the trot out of mine and the zero starts to shift, nice handwarmer on a frosty day tho. Needs a good few minutes to cool between sessions when doing a zero.

  7. #7
    I generally don't let the barrel get hot I will fire a couple leave the rifle with breach open then have a practice with the .22 or .17 then go back and have a couple more shots would I be better off goin down in bullet weight does any1 think that would help if I went down to a 90 or 95 grain?

  8. #8
    Quote Originally Posted by trxnav View Post
    Hi guys I have a cz550 in .243 with a t8 mod on I am using geco 105gr ammo and seem fine for about 20 rounds my zero goes is this because of fouling seems to be conflicting yes and no on how often h should clean all so how do clean the inside of a t8 mod?
    I suggest you need to explore a number of options and take notes on what works and what doesn't work. I would start by finding a pal with a screw on the end moderator that fits your rifle and try your zeroing routine with that. If you get the same loss of zero with a different mod, then explore ammo options. I quite like the 96gr RWS, but there's lots to choose from.

    I had a T8 mod and didn't like it one bit. I just put my moderators in the airing cupboard to dry off. I suspect the moderator is the source of your problems, but you need to explore all the options one by one and gradually eliminate them.

    Good luck. JCS

  9. #9
    Quote Originally Posted by Heym SR20 View Post
    It may be that with 105 gn bullet its on the margin of being stable, but on the right side. A bit of fouling might but just be enough to tip it over the edge - it doesn't take much. Why - fouling will change the pressure behind the bullet which will have an affect on how it enters the rifling, accelarates down the rifling, barrel harmonics etc. With a high pressure, high velocity calibre like the 243 small changes can make a big difference in the end effect, and any fouling build up will be just a small change. In effect the rifle is shooting a slightly different barrel.
    OK, so can you quantify this amount of change please? (pressure or velocity)

  10. #10
    Quote Originally Posted by j0e_bl0ggs View Post
    OK, so can you quantify this amount of change please? (pressure or velocity)
    No I cannot quantify as I do not have access to sensitive pressure measuring kit, nor chronographs. But I am sure that with appropriate measuring equipment and a staistically big enough sample you could demostrate this. I am merely speculating and may in fact be something to do with the alignment of cosmic forces and the stars. Please don't ask me for the appropriate statistical design of the experiment either!

    What I do know is that slight changes can cause big effects - just look at how the same rifle will shoot different ammo very differently, and why as home loaders we tune our ammo to find a sweet spot.

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