Friday, December 27, 2013

Accuracy Issues

Today's project was to get to the bottom of some accuracy issues with a Marlin 795 .22 LR that I have had since early this year.

The Marlin 795 is one of the preferred firearms for Appleseed shoots.  It is a simple "blow back" design with a removable magazine.  It came from the factory with a polymer stock.  It is fitted with a Simmons 22 Magnum 4 power scope.

This firearm gave me fits when I tried to dial in the scope earlier this year.  I would make adjustments to the scope and they would either "not take" or would change the point-of-aim in some unexpected way. I put it aside and went on to more pressing issues.

The list:

Most accuracy issues can be traced to relatively few causes.  So rather than guess, it just makes sense to go down the list and address each potential issue.

Step One: Check to see if the barrel is free from contact with the forestock.

Nope.  This is as far as the feeler gage will go.
I removed the action from the stock.  I scraped and sanded where the forearm was contacting the barrel.  I checked frequently to reduce the risk of removing too much material.  I stopped when I could easily slide the dollar to within a couple of inches of the forward action screw.  This is particularly important if you intend to use your sling as an aid to accurate shooting and/or your gun has a flexible, polymer stock.

Step Two: Ensure action is properly seated in the stock and the screws are torqued (tightened) to the recommended torque.

Step Three: Ensure the scope mounts (rings) are fully seated into the dovetail and the screws/nuts are torqued in the recommended sequence to the recommended torque.

Step Four: Loosen all screws holding the tops of the rings and then re-tighten in the preferred sequence in the recommended manner to the recommended torque.

This was the root-cause of my accuracy issue.  Somehow, when installing the new scope, I failed to finish torqueing the screws that clamp the scope into place.  I went to loosen the screws and they spun easily with no "break-away" feel.

The Proof is on the Paper

The first group was about 2.5 inches to the left of my Point-of-aim

I fiddled around with a few more adjustments.  In actual practice, the second group would be good enough for 95% of my shooting.

The picture in my head is that the Marlin 795 will become Mrs ERJ's go-to gun.  She has the smallest stature of any in our family and the 795 is ideally suited for shorter people.  It is also light weight and is not fatiguing to shoot.

The expected trajectory is +0.2 inches at 25 yards, +0.2 inches at 50 yards, -1.7 inches at 75 yards and -6.0 inches at 100 yards.  So we are talking your basic minute-of-squirrel head accuracy from 15 yards out to 65 yards.

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