On a recent visit to see our good friend Bobby Hart of Hart Custom Rifles we got talking about why customers sometime experience Point of Impact (POI) changes from one outing to the next.
"Sighted my gun in last weekend and went to shoot it again today and I noticed that my point of impact changed. How can that be?"
Atmospheric Changes Affect POI
Simply put, your bullet doesn’t travel as well through denser/thicker air and can affect your POI. A bullet will slow down faster in dense, thick air than it will in less-dense, thinner air. How does this affect my POI you ask? A slower bullet will take longer to reach a target — and therefore be susceptible to being moved off of its original path by gravity and wind.
The air’s pressure will change based on certain weather patterns and does make a difference in your POI if there has been a big change in weather.
In this video, Bobby & Jon discuss some of the causes of POI shift.
Blaming the Scope
Most of the time, if our POI changes, we immediately think it’s the scope. The scope is mechanical so it is logical to think someone in manufacturing had a bad day. However, in our experience, it’s not the scope. To be completely transparent, every person who has sent their scope back to us because it wouldn’t hold zero or would not track properly, has been shown (without a shadow of a doubt) that the scope performed perfectly.
Between The Barreled Action & the Stock
According to Bobby “It’s between the barreled action and the stock that’s the problem.” For instance, if you have a factory stock, they are typically 3 points of bedding where the stock makes contact with the barrel:
1) Contact at the rear screw
2) Contact at the front screw
3) And the little pressure points up near the top the stock to keep the barreled action centered to the barrel channel
If you have any contact point where the barrel is touching the stock, as soon as the barrel gets hot, it’s going to put pressure on it and cause POI change…Or as Bobby calls it, “walk up the target”
This can affect the barrel harmonics as well. As the bullet travels down the barrel, it vibrates. As the barrel vibrates, if it makes contact with the stock this can cause a change in POI.
A gun vibrates 58-68,000 PSI and when bedded properly will come back like a tuning fork to a natural given harmonic
How the Rifle is Rested When Shooting Could Be the Problem
The rifle should never be rested on a hard surface. When using any type of rest the position of the rifle must be the same for consistency. If you place the forearm of the rifle differently on your rest from shot to shot or between sessions this can also change the POI.
Cold Bore and Clean Bore
Many rifles may print a different POI on the first shot from a cold bore, and then settle in with subsequent shots. This is something you should experiment with. A clean bore may also have a completely different POI impact as there may be some residual oil or solvent left in the barrel. One school of thought is that a “fouled” barrel provides better accuracy and a more consistent POI.
Try a Log Book
Many experienced shoots and snipers use a log book to track their POI in various conditions. This is a great way to track and verify the changes and results of any of your POI changes and can help solve the mystery of POI changes you may experience.
Bobby believes that a custom rifle is not for everyone, that why he offers an "Accuracy Package" for your factory gun to help improve consistency at the range and in the field. See the Improving Accuracy of a Factory Gun Blog for all the details.
A little bit about Bobby Hart
He was born in to a family tradition of custom gun builders and gunsmiths. He now has taken over the lead role from his father, Wally Hart, at Robert W. Hart and Son Inc. as a 4th generation custom rifle builder. Located in Nescopeck, Pennsylvania, this small, family run business is known world-wide to the hunting, shooting, military and law enforcement industries. Some of Bob’s credits include:
5 Time Jr. Bench Rest Champion
1986 300YD Heavy Varmint Champ
2000 1000YD World Open Championship Light Gun
2001 IBS 1000YD International Championships High Score
A member of the Varmint Hunters 1500 Yard Club