Stock Lengthening and Point of Impact


Brother Bruce,

Using a typical field style stock (no monticarlo, parallel comb, etc) is their any general rule as to what direction the point of impact will move, if the stock is lengthened sans any other stock dimensions changed? Provided that the stock still fits the shooter but is somewhat longer; is there an expected shift in POI up or down? It seems to me that the POI should generally move the POI downward due to a slightly longer (1/2 inch) LOP, but don’t know. I know the only sure way to know is to try the added length, but I have been pursuing the more advanced course work needed in order to complete requirements toward my Junior Technoid accreditation. Thanks.

Bill

Bill,

Your question is a good one and required me to put down my Jolt Cola and Twinkie and get one of my guns to fool with. And I agree with you. I think that if the stock is lengthened, the point of impact should go slightly lower.

Here’s my reasoning (or lack thereof): The typical field stock lowers in height as you progress from the nose of the comb to the heel. Typical field dimensions might be something like 1-1/4″ at nose, 2-1/4″ at heel, for a drop of 1″. So, as you lengthen the stock, in theory you will move your face and cheeking position further to the rear of the stock. Further to the rear means that the eye is now lower in relation to the rib.

Of course, the gun’s POI doesn’t change. If you sight flat along the rib and shoot it like a rifle, it will still shoot to the same POI. But, as your head moves to the rear and thus downward, the POI you generate when you sight the gun will lower.

Let’s say that when you cheek your gun normally, you look down on the rib to see about 1/4″ of rib. With this sight picture, the gun shoots to a certain POI. If you cheek further back due to a longer stock, your eye will lower in relation to the rib and you may now see only 1/8″ of rib. If that is what you see, then your POI will be lower. The gun hasn’t changed, but the way you sight it has.

But… (always one of those).. if you currently look flat down the rib, lengthening the stock to lower the eye will either make you entirely lose the rib and thus any point of reference, or it will force you to slightly raise your head to obtain a sight picture that looks flat down the rib. Raising the head is not good.

In the real world (a foreign land, as far as I am concerned), lengthening the stock 1/2″ will move the face and thus eye back 1/2″. With a typical stock, the amount of height lost in 1/2″ is hard to measure. It is minuscule. A 14-1/2″ stock lengthened to 15″ that has 1″ of drop nose to heel, will lower at face only 1/29th of an inch. That’s a touch more than 1/32″. As sensitive a man as I am sure you are, that will be tough to notice.

Bottom line: lengthen that stock 1/2″ and forget about it.

Best regards,
Bruce Buck
Shotgun Report’s Technoid

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2 Responses to Stock Lengthening and Point of Impact

  1. Thomas says:

    I recently lengthened the stock of a new gun by over an inch, and I found that I had to reduce the cast also. I find a lot of value in A.C. Jones’s Shotgun Insight programs since they allow me to quantify point of impact, etc.

  2. Jay says:

    In my considerable experience with me it is normal for the cheek position to move back less than the LOP is lengthened. Too short a LOP usually causes the shooter, me, to scrunch back from his thumb a bit. The shooter, me, will usualy extend his heck comfortably with a new, longer LOP. I would plan on 1/40 inch rather than 1/29 inch eye depression.

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