POI and Tune

C

Cabrera

New member
Hello,

Been thinking and this is always bad.

Could POI be used as an indication of tune?
Example; if I get a good zero at a given yardage, 200y for instance, in a good cool day, with perfect wind, no mirage, perfect conditions, and the gun was in perfect tune that day, life is good.
Next time at the range -different day- the gun starts printing let's say 0.5" high from where it did last time. Is that an indication of a different tune, and maybe a way to correct it, is to change the load -up or down- to bring the POI back to where it was?
All this of course assumes there is no significant other factors influencing the event; like slow mirage, vertical wind components, etc.

Would like to hear your thoughts about it,

George
 
Poi and tune

You said it yourself mirage and wind. They have more to do with the poi.
{just my own opinion. I correct for the day" Usually a good load is a good load.
Other things also come into play. Like how comfortable you are on that given day and how you are reading the wind flags.
I try to read everythhing Grass trees feel on my neck etc.
Bench position is also another factor' set up.
There are many thing that can effect your POI
I hope this helps to answer your question>
 
Thank you Gerry for your reply.
If we could for the sake of a mental experiment, nullify those effects (wind and mirage), but still the impact is high -or low- from a good well known setting, what else is left to make this change in POI? Let's even make it happen not from one day to another, but instead from one relay to the next, same match day. In this next relay I now have to hold 0.5" low at 200Y, is that an indication the gun is getting out of tune?
My contention is such a change can not be explained by external ballistics alone (it will take a solid 100fps muzzle velocity change from one relay to the next to account for 0.5" at 200Y with 6PPC ballistics), so then it must belong or partially belong to internal ballistics affecting barrel time and tune. Following the same logic, if we could use the "good" POI as the goal to get back to, instead of cranking the elevation knob we should change the load to make it print in the same spot again.

But now out of the mental exercise, the first thing I see through the scope is a thick mirage engolfing the field and I'm sweating like a pig. I agree, now I don't know why I'm shooting high :-(
I need is a bottle of water.

George
 
Poi and tune

Mirrage is one thing you cant get away from. If the mirrage is flowing up in a boil as we say the shot usually is low. If you adjust for that particular mirrage , when the mirrage is not prevelent your shot will be high. Flowing mirage from the left , or right will also show wind speed.
It just takes practice to read.
Some of the shooters here can read it to the last 1/16 of an inch.
Warren page in the accurate rifle had a short discription of this calling it shooting thru the mirror Pool.
The second factor is the head and tail winds they also will change your elevation setting. stringing shots also can be from shoulder pressure. Pushing your shoulder into the rifle is one cause.
Here's another one a loose front bag or rest.
Any way i hope this helps some .
I have shot many groups and loosing one shot or two and usually it's just me and poor gun handling.
 
Cabrera, to answer your question, yes it is an indication of your tune changing. I would also say that this is more relevent as a day progresses and less from day to day. The proof shows when you do a ladder test when checking loads. Yes, the wind and mirage change but so does the load.
 
Thank you John, that makes sense.
I will try to do some more testing at 300Y to prove if I can keep the tune by locking on the point of impact. Will report back with what I find.

Thanks again,

George
 
Poi and tune

Yes i agree with the load changes also.
At the nationals some shooters used 3 different powders and played with seating depth etc to find the load for that particular range condition.
They were changing, measure setting 2 days before and keeping accurate records Tempeature , Pressure , humidity, and wind velocity
 
You must log in or register to reply here.
Back
Top