Question for you Benchrest score shooters

[lrgoodger]

When shooting a large target with multiple aim-points, I have noticed a tendency for the POI to change simply moving from one bulls eye to the next. I'm sure this is because of the minor shift of position in the bags as the front rest is cranked from bull to bull. The perfect example is this target I shot at a 200 yard match Sunday. I shoot clockwise from the top left, two shots at each bull. There is a two minute sighter period where I shoot 5 shots at the green sighter dot. Four of the five went in one hole at the top right of the dot, so I aimed at the bottom left of the bulls eye. (I never adjust the scope once the match starts) The first shot was nearly dead center and the second caught the bull with the two shots straddling my aim-point. Hardly the same POI I had on the sighter dot.

On frames 1,3,5,7,8 & 9 the two shots are right together, showing that the accuracy is there, but the POI changes as I move from bull to bull. My question for you experts is how to combat this. Is there any way of predicting which way the POI will go as one moves around the target?

As a side point, I have noticed after shooting many, many targets like this that the POI on the last three frames is almost ALWAYS to the left, like the ones on this target. I have in the past thought that barrel heating might be making the POI walk, but this was shot with a straight 1.25" barrel which handles the heat very well over a 20 minute string.

Ron

 

[gunsandgunsmithing]

I'd start with making sure the gun slides very freely in the bags. It is common to see dispersion from top to bottom and visa versa, but I usually see it as vertical, particularly on an IBS/NBRSA target, where the sighter is all the way at the bottom and the top left target is the worst. FWIW. Mike Ezell

 

[aj300mag]

"My question for you experts is how to combat this. Is there any way of predicting which way the POI will go as one moves around the target?"

Let me qualify this by stating I only shoot 100 yard score matches...

I've shot 5X targets which if you were to overlay each individual target the group size would be in the zeros by holding on the exact same place on the moth ball. I'm thinking your bag set up is the issue.

 

[GSPV]

In addition to what Mike said, try moving the gun back and forth at least once after you move to the new target.

Other people have told me that the put a strip of the soft side of Velcro on the bottom of their front bag.

 

[Greyfox]

Interesting target. Where would a person get some of these?

I could use a little more feedback for starters. If I understand what you are saying, you have used the same aim point for every shot (please correct me if I am wrong). I don't think I have evr shot s score target with the same aim point for every shot. I don't adjust the scope, but depending on what the wind flags tell me and what the previous shot shows, I adjust my aim point.

Certainly, as you move around the target the influence of the bag will have some effect on the POI, but if you are paying attention, you should be able to make the necessary adjustments to correct much of this. Of course, this is coming from a guy who pin wheels a sighter and the drops to the 9 ring on the first record shot frequently :

Tell us what size the dot is and what caliber bullet you are shooting. Seems to me that really isn't bad for a 200 yard target. But then, that depends on what the wind is doing. Please don't tell me you don't use wind flags because there isn't any wind :

Rick

 

[riverwolf1]

I have a different theory about this, and it has happened to me many times. I have not given it much thought until this thread started.
1. Parallax not quite adjusted correctly!
2while shifting from one target to the next you are also doing a reload, and when you go back to you shooting position, your head is in a different position.
If you couple these two issues together I think this is why shots drift out from where your sightseers are at.
I use a Farley rest and it is real easy to not pay attention to bench manners when you have a stable condition and you are trying to get your shots down range as quickly as possible.
When my relay is called I now check the parallax every single match and my shooting especially in group shooting is much better, I hav not shot score for a few months so I have yet to test this on score.

 

[lrgoodger]

Rick,

You might try Tom Kendig at tfkindig@dmcibb.net. He runs this shoot at the Hillsdale, MI rifle club. You might be able to order some from his supplier.

You are right, I do make minute adjustments to the aim point as I go along. After the first two shots I moved my aim to the center dot. I keep in mind my sighter group the whole match, but adjust as the shots tell me. The second and third frames (discounting the wild flyer - the worst I've ever had in any match) told me I needed to go back down to what the sighter group originally told me, which I did and elevation was good thereafter. I'm also cautious on the four center frames. As you can see, it is easy to miss the egg when shooting at those bulls. That hurts the score, so I tend to hold on the edge of the bull nearest the egg center with those four. That shows clearly on frames 3 & 7, but by frame 8 I was holding on the right edge of the bull. That is exactly opposite of what my sighter group told me. That left leaning persisted through frames 9 & 10 as you can see. If I did not adjust as I went, I would not have done as well as I did.

Wind is seldom an issue at this club, especially for this 284 Shehane shooting 180 hybrids. Flags are not allowed in their matches, but I do watch the grass and trees as well as pay attention to what I feel at the bench.

I do slide the rifle back a time or two after each shot to try and maintain consistent bag friction. I also set parallax before every match. I'm sure it's in the bag shifting and I don't know what to do about it. If the bags are lined up with the center of the target, moving to the left bulls would put the stock cattywampus in the front bag to that side and moving all the way to the right bulls would have the side tension shifted in the other direction. I've never tried minute rear bag adjustments to try and compensate, but that may be what is needed.

Just for grins I've attached one of the same targets from last summer shot with the same gun with my 30BR barrel screwed on. You can see that the three misses were by just a hair.

 

[LHSmith]

It's mostly conditions....wind/ mirage......mirage will move POI irregardless of bullet weight and speed.

 

[lrgoodger]

You may be right. There was not much wind, but mirage was bad that day. It was hard to see even the 284 holes when they were in the blue.

 

[LHSmith]

Sometime, set your rifle up in the bags and center your reticle to a bull....such as your egg target.....without touching the rifle or bags , observe where your POA is every 5 minutes.....do this for the 20 minute time allotment.......in IBS and NBRSA Score we have unlimited sighters throughout the entire 10 (sometimes 7) minute match and we can "chase" this phenomenon without penalty ...unfortunately your format you can't. For a real eye opener, do this POA test from AM to PM. If your 20 minutes happens to get a mix of sun and cloud cover, the POA shift is most noticeable.