Why does the ZERO on a rifle change so much in a year?

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On the subject of ammo. It is amazing that different loads can be so different when the bullet weights are the same. I had a 742 Rem in 30-06 that would shoot 180 gr Rem and Win 8" apart at 100 yards. Plus the little CZ 455 that I have might print groups 4" from another brand at 50 yards. Pick one brand or load and stick with it.
 
Here is the Rem 7600 pump which will hold ZERO so far, with any scope on it.
Cheap set up, but from a new rifle we stripped it down to camo if homemade back about 1990 I guess.
It has a Nikon BDC in the pic I think.
Love that old rifle.View attachment 871261
The reason that the Remington 7600 pump holds its zero is that it's all steel and the barrel is not attached to the pump mechanism, but is free-floating. It's a great hunting rifle due to that and that it's quick to fire multiple shots when a deer is moving, provided the operator has practiced pumping well.
 
On the subject of ammo. It is amazing that different loads can be so different when the bullet weights are the same. I had a 742 Rem in 30-06 that would shoot 180 gr Rem and Win 8" apart at 100 yards. Plus the little CZ 455 that I have might print groups 4" from another brand at 50 yards. Pick one brand or load and stick with it.
Unlike the 760 and 7600, the 742 is attached to the forend, due to the gas piston. That causes different points of impact as the barrel heats up. Still, I've fired some that shot very well for two or three shots in a row, then barrel heating usually caused shots to hit lower due to barrel expansion and rigid forend attachment.
 
On the subject of ammo. It is amazing that different loads can be so different when the bullet weights are the same. I had a 742 Rem in 30-06 that would shoot 180 gr Rem and Win 8" apart at 100 yards. Plus the little CZ 455 that I have might print groups 4" from another brand at 50 yards. Pick one brand or load and stick with it.

It's barrel timing. It matters not only how heavy the bullet is and the velocity, but also how long it takes to get down the barrel. The barrel moves quite a bit during firing in several different ways and exit time in particular matters.

CZ 455s are particularly vulnerable, because the majority of their barrels get lead buildup in the throat due to tool marks. This swages down the bullet (especially when fired cold when the lead is hard) and as a result they're more prone to gas blow-by at the muzzle than many .22s. They are particularly susceptible to the "breathing" mode of barrel oscillation.
 
If you’ve got two hours and really want to understand the process more thoroughly I’d recommend the following. Even if you never decide to attempt it you’ll know what to look for and, if you choose someone to do it for you, have them show you their work.
I saved the VIDS to watch later, Love rifle work videos=thanks Skylerbone.
 
Sure, mirage can become an issue when looking through a high magnification scope in certain conditions, but that doesn't do anything to change your zero

I believe what he was referring to was, if the rifle is set to zero on a hot day, hot enough for heat waves to show EASILY, then you wait until cold
weather to shoot it again it will be off for clear line of sight & air density changes.
Not speaking for him any more than the original statement I posted.
 
i'm not following where the zero change came from. you're right mirage doesn't change your zero.

I am going to have to call him about this just to get his input but I have to get you to understand about of him -And What He Has Gone Thru- he is
sometimes very defensive when he feels challenged or on the other hand he may even shrug if off with a few choice words.
I never press him for tech info, seems like a Tiring subject to him but no one has ever done better here on my little range.
 
It's barrel timing. It matters not only how heavy the bullet is and the velocity, but also how long it takes to get down the barrel. The barrel moves quite a bit during firing in several different ways and exit time in particular matters.

True, Very Very true.
In my opinion consistent grip & rest are [ sometimes ] important, according on the weapon, like revolvers & pistols BA rifles seem more
forgiving.
I watch so many guys on TV hunting have a rest for a shot at a deer or whatever & they reach out & press down on the scope area what
looks like very hard sometimes. Wouldn't that mess with the timing?
Or a fence post while pressing down hard on the scope, that has to make a difference.
Just wondering more than making a positive statement.
 
Many years ago, I bought a used Rem 700 Sendero stock, found in a barrel at Kittery Trading Post, for about $50. Even though the stock has an aluminum bedding block in it, I skim-coated the block with epoxy bedding, for a perfect fit to my .270 Win, Stainless Rem 700 BDL. The barrel channel is for a bull-barreled Sendero, but I haven't bothered to add epoxy to reduce the gap feeling that it allows the barrel to cool faster when shooting at the range.

Anyway, the rifle groups first shot from a clean barrel within 3/8" of center of a group and subsequent shots group handloads under 1/2 min...and that's with 130 grain Nosler Ballistic Tips. The rifle's zero changed recently because the rifle fell and the changed zero with the new load, so I'm glad that I took it to the range. The new ZERO required change of 1" left and 1 1/2" lower. That's not much, considering the new load and a bumped rifle.
 
Something I haven't seen posted here is the need to tighten stock screws to recommended torque settings and record them for each rifle. Sometimes when we hunt in inclement weather, it's necessary to remove the action from a stock to dry things out. Having a torque wrench with you on a hunt can prevent change in zero, should it become necessary to dry the action. Reassembly/torquing may not save a perfect zero, but should be very close, especially with a bedded action and free-floated barrel.
 
that's been discussed a few times, particularly whether you use a torque wrench each time, or use the torque wrench the first time and make a witness mark. maybe it was in gunsmithing forum
 
Something I haven't seen posted here is the need to tighten stock screws to recommended torque settings and record them for each rifle. Sometimes when we hunt in inclement weather, it's necessary to remove the action from a stock to dry things out. Having a torque wrench with you on a hunt can prevent change in zero, should it become necessary to dry the action. Reassembly/torquing may not save a perfect zero, but should be very close, especially with a bedded action and free-floated barrel.

Right her a few years ago we sighted in a 700 rem 30-06 with wood stock.
I had heard about torque & screws but never kept up with it,
The rifle was sighted in at -about- one & one half inch group at 100 yards, probably a flyer in there as well.
I happened to try the OLD dollar bill around the barrel to test for a floating barrel, it passed the test at
first then hung up on the way back. The fore stock screw was loose.
I tightened it with a screwdriver of course & the bill slipped perfectly then we shot again.
Had to sight it back in but this time after zero, I put 5 rounds inside an inch = reloads of course.
I still don't use a torque on mine but perhaps the CZ could use it, will try at noon tomorrow
if weather allows.
 
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