Gun Fit/Gun Mount

Hi Bruce:

I just took up Sporting Clays this year and purchased a AL391 sporting clays model. I have been working on my mount as a first priority along with the vision. I do feel the gun is a bit long and may need other stock work and etc. At what point does one proceed? I have not addressed this issue prior to now because I wanted a decent, consistent mount first. Is this the chicken & the egg debate? What comes first perfect mount (if such a thing) or the stock work?

By the way you have saved me major bucks with your advice to others and myself over the last few months. My gun is untouched-no backbore, forcing cone work, or porting. It seems to pattern well as is. I have patterned it to the best of my ability following your response to my last written question.

Thanks for the savings.


Upstate New Yorker

Dear Bill,

Gun fit vs gun mount. Chicken and egg it is. There really isn’t much point in going for an exact fitting while the shooting style and gun mount is still under radical change. A good coach and fitter will be able to anticipate what you need when you learn to mount the gun correctly, but not everyone has that talent.

Your 391 has a number of possible adjustments that are fully reversible. You have the shim set for height and cast off, plus your gun came with two different length recoil pads for modest length adjustment. You could always temporarily substitute an uncut thin rifle pad for a recoil pad if you wanted to experiment with an even shorter stock. Just screw it on and let it hang over the edge.

I’m a bit hesitant to give you fitting advice over the internet as so much depends on seeing how you shoot now and how the current iteration of the gun fits. As a general rule, I like to set my guns up so that I have about 2″ of space between the rear of the base of my right thumb and my shooting glasses when the gun is fully mounted. Some people prefer more or less distance, but 2″ is a pretty good ballpark number.

Get the thumb to glasses distance set up right with a mounted gun and then learn to properly mount a gun of that length. Don’t keep shortening the gun until it is easy too mount. The goal is to have the gun fit once it is up, not to have it easy to get up. You can learn the latter. My general approach to lengthening a stock for myself is to ADD length until I have gone too far and then subtract a bit. I try to shoot the longest stock possible because it mounts more securely and reduces recoil due to gun movement. A long stock is more comfortable to shoot. You will find that you will probably be able to handle stock length within a 1/2″ variation. I always take the long side of the equation. With a proper gun mount, you can handle the length.

As to stock height, I like to set my guns up so that when I cheek down very hard into the bone, I am looking right flat down the rib. I don’t ever want to be able to drop my eye below the line if the rib. Naturally, you don’t shoot cheeked in that hard. With normal cheek pressure this setup has my rib showing a “figure 8″ of the mid bead underneath the front bead. To me that translates as about 3/32” of visible rib. More or less. Vaguely. That works for me and no, my guns don’t shoot high. I also don’t shoot guns with stepped ribs, so I never have to deal with that.

Cast is simply a matter of fooling with the Beretta shims (see instruction book) until you center your eye on the rib. Nothing easier. Beretta’s shim adjustments offer right hand cast and neutral. They may offer an extra set of shims for left cast, but the ones that come with the gun don’t do that in spite of what they say. It’s right hand or neutral.

Make sure to test you gun on a pattern plate once you make your adjustments. Do the test low gun, raising and firing as you normally would. I take four shots on the plate before repainting. All are from low gun position and using full choke for a well defined strike. My first shot is swinging the gun UP through the aiming mark. My second is mounting high and swinging DOWN through the aiming mark. My third is moving Right>Left and my fourth is Left>Right. All four shots are dynamic, not static.

This method of testing does require a proper gun mount, but it is also the most accurate assessment of point of impact as you are mimicking the way you actually shoot.

Don’t be afraid to experiment with gun fit. That’s the big advantage of the gas guns. You can tinker all you want to and yet always return it to the original condition. This is where O/Us are at an distinct disadvantage. You’ll find that your gun fit and gun mount sort of come together over time. You’ll end up with both the chicken and the egg, a well-deserved dinner!

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

This entry was posted in Shotgun related. Bookmark the permalink.

Leave a Comment

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.