ALG, sister (wife?) company to Geissele, puts out a great line of products. I’m especially fond of their EMR handguards. They’re super light, slim, streamlined, and ideal for the shooter who prefers to just carry the rails he needs.
They are a little more challenging than average to install, and you need a special wrench to do things by the book (instruction sheet here). The barrel nut timing is accomplished by means of a stack of shims, which starts off with a black “default” shim, and depending on where a reference line on that wrench falls, you may find yourself adding or substituting shims.
I’ve noticed for a couple years now that there’s something wrong about the table of values for EMR shims. They’re wrong. Or, at least, they don’t work with the instructions as given.
I’ve recommended these rails to lots of my friends, but nobody ever owned up to the fact that the shim list didn’t work, until I interrogated them directly. Replies from “yeah, I had to torque a lot more than I expected”, to “I kind of made it up as I went”. My local armorer’s reply: “well, that’s assuming I even needed them…” Well, OK.
So, after some measurement and calculation, I’ve come out with my improved EMR timing shim chart. Content first, for my ADD millennial crowd, then explanation and proof.
First, nomenclature I’m using:
| TurkeyShoot’s Improved EMR Timing Shim Table | ||
| Band # | ALG Suggests | I Suggest |
| -1 | “Two Blue” | Two Blue |
| 0 | Black (Pre-Torque Band) | Black |
| +1 | “Green and Purple” | One Blue and Purple |
| +2 | “Red and Purple” | Green and Red |
| +3 | “Blue and Black” | One Blue and Red |
| +4 | “Green and Black” | One Blue and Green |
OK, so let’s talk rationale and evidence.
I’ve listed ALG’s given information, and then just a few basic implied calculations, predicated on an 18 TPI barrel nut.
| ALG Info | Calculations on ALG Info | |||
| Band # | Shims | Thickness | Δ Thickness vs Black | Implied shift (°) |
| -1 | “Two Blue” | 0.016″ | +0.001″ | 6.5 |
| 0 | Black / Pre-Torque Band | 0.015″ | – | 0 |
| +1 | “Green and Purple” | 0.021″ | +0.006″ | 38.8 |
| +2 | “Red and Purple” | 0.022″ | +0.007″ | 45.3 |
| +3 | “Blue and Black” | 0.023″ | +0.008″ | 51.8 |
| +4 | “Green and Black” | 0.024″ | +0.009″ | 58.3 |
Let’s do a quick sanity check. The structure of the wrench and nut is such that it’s divided into eight evenly-spaced sectors. That’s 45 degrees per sector (360/8=45). That means that if you added a shim that produced exactly 45 degrees of offset, you’d be right back where you started. That shim, incidentally would be [(45/360)*(1″/18)]=0.0069″ or about 7 thousandths of an inch thick. Well, check out the +2 band. That particular shim produces an offset of 45 degrees from the black initial shim. Red+Purple times exactly the same as the black shim; it does nothing.
So here’s my improved version:
| My Measurements | Calculation | Result | |||
| Band # | Measured ° from Pre-torque “0” Band | Implied Actual Shim Thickness vs Black | Implied Actual Shim Thickness | Actual Shim Thickness, Adjusted to 0.015″ Minimum | My Suggested Shims |
| -1 | -8.5 | 0.001 | 0.016 | 0.016 | Two Blue |
| 0 | – | 0 | 0.015 | 0.015 | Keep Black |
| +1 | +11.5 | -0.002 | 0.013 | 0.020 | Blue and Purple |
| +2 | +16.5 | -0.003 | 0.012 | 0.019 | Green and Red |
| +3 | +24 | -0.004 | 0.011 | 0.018 | Blue and Red |
| +4 | +31.5 | -0.005 | 0.010 | 0.017 | Blue and Green |
My calculations agree with ALG’s on two bands: perfect pre-torque (the black), and the -1 indicator, with two blues. I am assuming here that because ALG specifies that the black shim must always be the start (and potentially end) shim, that the minimum shim stack is 0.0015″. Accordingly, I’ve adjusted some by +0.007″ to accommodate.
Note: I don’t have as much faith in my angular measures as I would like. Maybe someone with a better protractor or machinist’s drawings of the wrench would better be able to help; I’d be happy to rerun the math.
The Turkey Shoot 