Point Of Impact-How Close Is Good Enough?


Dear Technoid,

I have been shooting my over under for 0ne year and decided to take it to the shooting board to see what the POI is. I set up at about 20 yards with a shooting bench and shot a box of shells at the targets, white roller paint around a steel bolt. After shooting all combinations of chokes from top to bottom barrel, the top barrel was right on and the bottom barrel was one inch low. That seems to me to be as close as one could expect. I tried another O/U of mine and it was 2 inches high and 1 inch to the right and 2 inches low and 1 inch to the left. Based on this I retired the second gun. I could have chokes made to correct the bottom barrel of the first gun, but that just doesn’t seem necessary. How close do the barrels need to be? Thanks you

Peter

Peter,

First a definition of terms: Point of Impact (POI) as I use it is where a particular barrel shoots with a given load at a given distance when aimed like a rifle. Each barrel has its own POI. Just because they are soldered together doesn’t mean that they will both shoot to the same place- as you so properly noted.

How close does the point of impact of the two barrels have to be? That depends. I know of one manufacturer who felt that 8″ of separation at 40 yards was acceptable. Wouldn’t be for me, that’s for sure. Ideally, one barrel will shoot exactly to the same place as the other. Good luck on finding that.

Figure it this way. Your effective pattern at a given distance with the correct choke is roughly (more or less, sort of) 24″. How much of that do you want to give up? Your patterns were made at 20 yards, so double the POI errors for 40 yards. That said, as you so correctly mentioned, no gun is perfect. A little bit of separation is just a fact of life. Also, POI of the barrels will change slightly with the strength of the shells you are shooting.

Now here’s some good advice: If you have a gun that you own and shoot well, don’t test it for POI. It’s like going to the doctor when you are feeling good. All you can do is break even or lose. Many years ago I once had a Belgian Browning Superlight that I was absolutely deadly with on birds. The Devil, in the form of a shooting buddy, talked me into testing it for POI. I told him that I had tested it many times with both barrels on live game it is was perfect. But I tested it anyway. Of course the top barrel shot almost a pattern high at 40 yards. I never felt comfortable with that gun again and still wonder why it shot so well for me with both barrels. Another Superlight that I had had perfect POI convergence. Go figure.

My rule of thumb when getting a new (to me) gun is to immediately test its POI. I had a two barrel Parker Reproduction set with fixed chokes. One barrel set was perfect, but the other shot the left barrel far to the left, way off of the POI of the right barrel. The left barrel had plenty of choke, so I took it to a good gunsmith and he simply ground off some of the fixed choke on one side and brought the left barrel’s POI back in to match that of the right. You need a good gunsmith (my guy is now retired) and you do lose a bit of choke constriction, but it can be done with a fixed choke gun. Screw chokes are different. Briley will make you eccentric screw chokes if you wish, but that starts to get complicated.

Moral: check POI before you buy. If it is a used gun, you get a 3 day return privilege. Use it for testing. If the gun is new, you are on your own and have to deal with the manufacturer. Calling them to find out what their policy on POI convergence is before you buy might be wise. You may be surprised at what they tell you.

Best regards,
Bruce Buck
Shotgun Report’s Technoid

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