Advanced Marksmanship Is there an optimal process to fit a chassis to the shooter?

[EchoDeltaSierra]

Hey all,

Didn’t know if this was the best place to post, so feel free to direct otherwise.

The Magpul Pro 700 chassis delivers Wednesday, and having limited experience with a chassis, I’m curious if anyone has discovered an “optimal process” for chassis/stock fitment. I’m seeking guidance on what to adjust first, second, etc. I have experienced a couple of road bike fittings and know the value of a properly sequenced fitting versus what I can do in the garage, and I suspect similar exists for setting up a precision rifle. I realize this is very subjective and there are no right or wrong ways; there are more/less optimal ways.

My initial ignorant guess looks something like; trigger and length of pull, then stock length, comb height, and finally buttpad height and cant. Then range trip, tune, repeat as needed.

Thanks in advance for any feedback. -ES

 

[OzzyO20]

I like to lay down prone, eyes closes and pull the rifle up. Then I decide what doesn’t feel ‘right’ and adjust. Repeat until it’s comfortable eyes closed. Then I mount the optic, lay down, close my eyes and open them. Ideally the optic is right in the eyebox. If not keep adjusting. You want a rifle you can be behind for a good amount of time and not fatigue, and glass in a natural and comfortable position.

Maybe not optimal, but if you do it systematically you’ll get there.

 

[EchoDeltaSierra]

I’ve done that with a few rifles, and with decent results. That said, tinkering that way generally means I fidget with things for several weeks. There has to be a more systematic approach. At least that’s me guess. ;-)

 

[308pirate]

My initial ignorant guess looks something like; trigger and length of pull, then stock length, comb height, and finally buttpad height and cant. Then range trip, tune, repeat as needed.

I've had more than a few rifles with fully adjustable stocks and IMO you've pretty much nailed it.

Terminology: what you call length of pull is really trigger reach. Length of pull is the distance from the center of the trigger blade to the rear face of the buttpad.

Whatever you do try to be systematic and write down measurements. If your stock's adjustments don't have index markings, use a small machinist rule, calipers, or measuring tape.

 

[SubOptimal]

I've had a lot of experience with stock fitting for shotguns mostly and with a gadget called a "try stock" which had adjustments for everything under the sun. Stock fit is everything on a shotgun, you don't use sights, you look at your target and pull the trigger when the sight picture is right. Some time getting all the adjustments right and some more time on a patterning board to confirm your adjustments are comparable with where the gun shoots. All this followed by some breaking of clays with an experienced shooter watching your shots and maybe a little touch up to follow..
My order of adjustments:

1. Set your stance. Pick the position that will best suit the majority of your shooting.
2. Mount the gun in that stance and adjust length of pull. Preliminary only, it may change a bit later.
3. Adjust butt plate height and angle to get comfy in your shoulder pocket.
4. All of the above without the scope mounted.
5. Mount scope and adjust comb height to center the eye in the scope for altitude. May require different rings.
6. Adjust comb laterally to center the scope for windage.
7. Check that all is comfy and feels natural to you back at #1.
8. Fiddle with shit until you can practically hit your target just by assuming your stance.
9. Continue to fiddle with adjustments until the gun no longer fits you and then back to #1 to repeat the process.

Seriously, find adjustments that work and then devise ways to repeat them. For example my comb height is perfect on my early AIAX chassis when a 45 ACP fired case is between it and the chassis, length of pull is 3 playing cards under the butt plate. One layer of mouse pad taped to the cheek piece.
I should add that for 10 or so months out of the year, it is tee shirt weather down here. Otherwise a very light jacket or a sweater will suffice. YRMV in colder climes.

 

[Crews]

Man, the post above is just classic. Thanks for taking the time to type that.

 

[damoncali]

This is assuming you're shooting from a bipod: Get behind the rifle, adjust the length of pull so that it is snug and comfortable. Then mount the scope so that the eye relief is correct. Next, raise the comb until your eye is aligned behind the scope. Finally, djustment of the butt plate can be used to balance out the height of the bipod and maybe reduce a little neck strain, depending on your position. The butt plate doesn't matter much in my experience (when shooting from a bipod).

Adjustable stocks are primarily useful for setting up a sling, and to do that well, you really need to be able to cant the butt plate more than 5 degrees. This is a useful guide to setting up a stock for a sling. It's for an Eliseo tube gun, but the same principles apply to any stock with enough adjustability. http://www.accurateshooter.com/stocks/configuring-the-eliseo-tubegun-stock/

 

[SubOptimal]

There are some good points in that Eliseo article.
They are really more specific to the adjustments available on that particular gun with a huge number of available adjustments.
The most critical ones, to my mind are the section on offset and sight alignment to the user's head/face.
I did not mention cast as it applies to stock adjustment as it is more a shotgun thing than a rifle thing.
Cast is the angle of the stock to the bore and is hand specific. It is defined as cast off or cast on. It is easy to see in a competition shotgun. Simply clear the gun (very important) and invert the gun so the stock is on the floor and look down the top of the barrel and see where the center line of the stock varies from the center line of the barrel. For a right hand shooter, the line of the comb will be offset to the left in this situation. This is called cast off. With the gun mounted, the stock will be slightly angled away from your cheek. It is subtle in most cases however it is critical for long term comfort behind the gun.
Shooting a gun with improper cast can be a painful experience. Most particularly when shooting a gun cast for a lefty for a right handed shooter. The comb will slap you in the cheek under recoil and lead quickly to a flinch. An adjustable cheek piece can easily be modified to allow a little cast off. It really is best to do this at the stock but shotguns are constructed differently than rifles for the most part and angling the stock to the receiver is difficult, at best. Of course, a folding stock makes it easy enough to to do.
This kind of esoterica is what makes a try stock, a very expensive device, such a wonderful thing to have.
The very top end of the shotgun world will fit a gun to you and your shooting needs. If you think an AI is expensive, you have only to price a Fabri shotgun. Besides the price of the gun, figure 2 trips to Italy for initial and final fitting a trials before the gun is final finished.

 

[EchoDeltaSierra]

Good stuff! Keep the ideas coming. I’ll document a process, test and tune it with the new chassis, and share. That means feedback prior to Thursday will be rolled into the initial test.

 

[Precision Underground]

I have found for me the most important thing is length of pull. If mine is too short I can’t relax my shoulder and my elbow is in the way when laying prone. This creates a position that is literally impossible to relax in. The elbow is bent too much and has to go somewhere so the shoulder has to tense and lift up and a chain of tension is created. For me most stocks, any stock I have ever tried, have too short of a LOP even when adjusted out to the longest length. I have a fully extended MBA 3 that I added about 3” to and an Aics that I added about the same or a little more to. I have long arms and am a slim guy, don’t have much to lay on when prone so guys with more padding prob don’t need the length that I do. More padding to lay on means higher off the ground means more room for a bent elbow.

So my advice is find the LOP that allows you to relax your strong side shoulder first. That was the key to my position after much trial and error. Most people said I just wasn’t getting positioned right behind the rifle. I wasted tons of time and ammo trying to do everything perfect. Finally I just did what I felt like I needed, added more LOP, and then adjusted everything to fit that LOP. Then everything felt right and started to work. Used the same method on my other gun and it worked the same.