DIY Suppressor Alignment Redux

Yup, another one of these :)

There's been a number of posts here in the past suggesting the use of precision drill rod as a makeshift suppressor alignment tool. This post is an attempt to gather that information into one place, as well as cover some fringe cases. Credit going to u/Cantonious for what I believe was the first post on the subject, as well as a few other users like u/alain4957 who have also posted on the topic.

For every option below, I will be including a McMaster-Carr part number for easy purchase. Keep in mind you'll see a minimum $7-8 for shipping, so you may want to grab all sizes you need or may eventually need in one go to dilute the shipping costs. So here we go!

• .2031" - P/N 8893K187 - Good general purpose rod for 22 caliber suppressor alignment - should work well for distinctly undersized match .22LR bores (think CZ452/455 at .210-.212" bore diameter), but otherwise may be a slightly loose fit;

• .212" - P/N 8893K191 - Better fit for many standard 22 caliber bores (.22LR at .217" bore diameter, .223/5.56 at .219" bore diameter, etc.)

• .250" - P/N 8893k204 - Good fit for 6.5mm Creedmoor/Grendel bores (.256" bore diameter);

• .295" - P/N 8893K217 - Good fit for 7.62x39, .308, 300BLK and most Western 30 caliber bores (.300" bore diameter)

• .339" - P/N 8893K229 - Good fit for 9mm (.346" bore diameter)

• .4219" - P/N 8893K252 - Slightly looser fit for .45 ACP (.442" bore diameter). Stepping up to a .4375" rod (P/N 8893K254) may generally work, but could be too tight for rare cases.

The sizes recommended here tend to be some fairly close fits - for some guns with tighter bores, going down one size may be necessary. My recommendations are based on SAAMI bore size specs, and are what I've used with success.

These drill rods ship from McMaster-Carr as roughly saw cut lengths, so they'll typically have sharp edges on the ends that you'll want to chamfer down to prevent damage to bores. The three foot lengths aren't exactly practical to use, but you can certainly cut each bar in half or maybe even thirds - consider the length of your suppressors and how much alignment rod would be in the gun's bore. The O1 tool steel these rods are made of is some pretty tough stuff, literally the kind of steel they make drill bits out of - be patient and careful when cutting down or chamfering the rods, as bending them will render them useless. They're not hardended and shouldn't tear up your tools, but tool steels can be pretty tough in almost any condition.

To check straightness of your alignment tools, you can roll them on a surface plate (or in a pinch, a glass-topped table) and look for any "eccentricity" in the rods sort of "flopping" or completely resisting rolling.

With a suppressor installed on the gun, you'll want to gently feed the appropriate rod through the suppressor and into the bore of the gun - don't force anything, as you could risk damage to the crown or bore of the barrel. Leaving just a tiny bit of the alignment rod sticking out the end of the suppressor, you'll want to look out how close the rod passes to the bore in the end cap or end of the suppressor. Ideally, the end of the rod should be centered in exit bore of the suppressor. If the rod contacts the end of the suppressor or completely refuses to be inserted, you may want to seek a professional evaluation of the suppressor-to-bore alignment.

If there are any additional recommendations for sizes, I'm happy to add them.

And now for a tangential personal diatribe!

Sometime around 2009, a group of engineers apparently had a bit too much to drink at a conference. As a result of their inebriation, they decided to redefine "concentricity" from its long-standing meaning as a position control, and turn it into an attempt to control the mass distribution of things that will spin very fast and might destroy themselves due to unintended harmonic vibration - if you're as bored a person as me, you should take a gander at ASME Y 14.5-2009. The standard makes it quite clear the part to be measured must be rotated about the datum axis and two dial indicators 180 degrees apart must be used, in order to attain a "concentricity" measurement.

Our area of concern with aligning a suppressor to a bore is position and runout - or really coaxiality as a composite control, not dynamical rotational load balancing as the American definition of "concentricity" has apparently been redefined to mean. In short, "concentricity" is apparently no longer the proper term for what we're talking about.

Semantics! Fine attention to jargon is necessary not for purposes of obfuscation but because there are important fine distinctions that must be clearly delineated.

/rant