How To Mount a Scope on Bushmaster M17S

Bushmaster Firearms International produced the Bushmaster M17S, a semi-automatic bullpup rifle. The Bushmaster M17S is presently the sole commercially produced bullpup rifle in the United States. The weaver scope attachment on the rifle fits a wide range of red dot and low-power compact rifle scopes. 

While basic emergency iron sights are provided, they are not suited for field usage. For quick target acquisition, most users add a red dot electronic sight. The Bushmaster M17S is a semi-automatic rifle with a revolving, gas-operated bolt. The design utilizes the Armalite AR-18 operating system and puts the pistol grip forward.

How To Mount a Scope on Bushmaster M17S
  1. Optic Mounting Equipment

To install an optic, you will need five tools. You can do it without any of these items, but they will make your life a lot easier:

Torque driver in inch-pounds with suitable bits; small bubble level; thread locker; paint marker or nail polish.

You might be able to make an improvised rifle rest. Some pretty cheap ones operate quite well. This is a beautiful gun vise with certain features that make it simple to work with, but you don’t need something like this. A handmade or cheap rest is ideal as long as it maintains the rifle upright and level while you’re working on it.

There is no replacement for a torque driver. Many folks get away with without using one, but I won’t install a scope without one any longer. It’s a smart purchase if you plan on mounting more than a handful of scopes throughout your lifetime.

The other items — the levels, thread locker, and paint marker — are all cheap and generally accessible, so there’s no reason not to have them on hand when installing a scope.

  1. Installing a Rifle Optic

Let’s get started attaching the optic. The first and most important step is to clear the weapon and ensure it is not loaded. I’m going over the chamber and mag well again. Even though I know the rifle is empty, I will keep the muzzle pointing in a safe direction.

  1. Do You Require a Scope Base?

If you’re using an AR-style rifle, you can skip this step. You will need to mount your scope base to the receiver of certain other guns. The base is where your scope mount or scope rings will be attached.

Picatinny rails are machined into the top of the receiver of Bushmasters and many other contemporary semi-automatic rifles. These rails work with a broad range of attachments, including optic mounts.

If your rifle lacks a Picatinny rail or other type of built-in scope base, you’ll need to install one before you can mount anything. There are just too many different types of scope bases to teach you how to mount them all. If you follow the manufacturer’s directions, it’s usually quite simple. However, certain rifles, especially older ones, may not have a receiver that has been drilled and tapped to take scope bases. If you want to attach an optic to the gun, you will need to speak with a gunsmith.

  1. Positioning the Optic and Mount Initially

Okay, let’s just put the mount on top of the rifle, presuming you already have a rail or a scope base. You may start by moving the mount as far back as it will go because I’m not exactly sure how far forward I’m going to want this scope to be. The mounting screws will then only need to be very slightly tightened. Just don’t mount to wiggle around; you won’t torque them down at all at this point.

The upper part of the rings must then be removed. Each ring in this instance contains four screws. Yours could just have two rings, or it might have six. Set the rings aside for the time being and remove all of those and store them safely.

When you’re setting up the scope on the mount, there are two main considerations. Eye relief is the first. That is the separation between the eyepiece and your eye. The scope’s cant is the second. We must ensure that it is level before tightening the rings.

To obtain a general notion of where the scope will be, simply lay it on the lowest part of the rings. Every person and every scope requires a different amount of eye relief. However, with scopes like these, you usually want the eyepiece to line up such that it is just slightly beyond the castle nut here on the buffer tube.

It appears that the scope is now getting closer to where you may like it to be. If you need to, you’ll have plenty of room to slide it back and forth. This particular one-piece cantilever mount has the benefit of allowing you to move the mount further forward if necessary.

On the majority of SAs, the rail above the receiver is not attached to the rail above the handguard. These two parts are independent ones. They are not precisely aligned with one another. Your aiming point may move when you are shooting if you have one half of your mount or any of your rings on the receiver and the other on the handguard. Unless you have a receiver and handguard that are both one piece, be sure everything is installed on the receiver.

  1. Thread Locker use

For the time being, you must tighten these screws just enough to prevent the scope from moving about as you move the rifle, but leave them loose enough to allow for easy adjustment. Because you need the distance between the top and bottom to be about identical on both sides, you can only tighten each screw a tiny amount at a time. It is improper for the top and bottom to contact. If they are, you are either overtightening both sides or you have one side that is tighter than the other.

It’s a little bit simpler to get them even if you tighten these in an X-shaped pattern. On one side are the top and bottom screws. The top screw is on the opposite side of the bottom screw, which is on the first side. Additionally, you alternate between the rings to avoid having one of them tightened while the other has no tension. Although it may be a bit excessively cautious, it doesn’t hurt.

Some shooters prefer that the adjustment dials be exactly in the middle of the two rings. But that’s simply a matter of taste. The location of the dials doesn’t important in terms of functionality.

  1. Adjusting Eye Relief

I can now adjust the eye relief. The eye relief is particularly sensitive at higher magnification settings using a variable magnification scope. Therefore, you must adjust my eye relief while using the scope’s greatest magnification. Therefore, you must turn it up to 10. You must remove the weapon from the rest for the time being and mount it exactly as I was going to shoot. It’s not necessary to direct it to something specific. The ideal wall should be bare.

Bring the eyepiece closer to my eye if the image is unclear on the sides or if you see a dark shadow on one side of the scope. You’ll see a lot of black outside the circle if it’s too near. A second black circle will eventually appear inside your range of vision.

To ensure that the eye relief is appropriate for my natural head position, you can drop the rifle and remount it several times. All of this should be performed while standing since it is simpler to illustrate. But from the shooting posture, you’ll utilize the most, you should assess your eye relief. Between shooting positions, the position of your head will somewhat alter, which will cause your eye relief also changes.

  1. Getting the Mount Screws Tight

Now it’s time to tighten down the mount now that the scope is where you want it. Just place it in the gun vise once again. The mounting screws should be slightly loosened. Typically, a bolt used with Picatinny mounts extends through the rail’s slots. So that those bolts are in contact with the front of the slots, move the mount forward as far as it will go.

Use thread locker sparingly on the mount screws. We will torque them down tightly since they are considerably larger. If you’ve never used a torque driver before, they generally operate similarly. You’ll hear and feel a distinct click after you’ve reached the desired torque level. That indicates your presence. You don’t have to keep driving it after that click, at least with this tool.

  1. Adjusting the Scope

We must level the scope before tightening the ring screws. However, you cannot just place your little bubble level on the scope. You must first check that the firearm is level. This may be a little challenging. You must locate a level area where your level will fit. Once more, the handguard is not exactly on the same plane as the receiver, therefore you shouldn’t use it.

You may now tighten the ring screws. Always considerably less torque is required for the rings than for the base. With these screws, you need to be quite careful. You risk crushing the scope body if you crank down on them too firmly.

  1. Marking Witnesses

Now that the scope is attached. Making some witness markings will be your last action. Simply draw a tiny line or dot next to each screw so that it contacts the screw. In this manner, you will be able to detect any screws that begin to back out. Any mounting system’s weakest link is always its screws. Those screws will be the first item you inspect.

Bushmaster M17S Scope Mount

What location should a scope ring be used?

At the greatest magnification, insert the optic into the rings; however, do not tighten the ring screws all the way yet. We advise placing the rings centered, or slightly in front of the center on the tube in the front, and no closer than 3/8″ from the magnification adjustment ring in the back.

How near to the barrel can a scope be?

The distance between the top of the barrel and the bottom of the objective must be at least 1/8 of an inch. You will have an adequate room with your second choice (0.160) for the scope base height.

When should a scope be placed back?

The eye box on most scopes is 3 to 4 inches beyond the eyepiece. That often implies that the majority of users will find this to be most comfortable when the eyepiece is either slightly in front of or just about lined up with the charging handle’s rear.


I hope that this post has been useful to you in learning how to mount a scope on a Bushmaster M17S so far. We’re heading to the range the next time to sight this thing in. In a week or two, keep a look out for that. Soon I’ll see you.

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