BORE ALIGNMENT
Frequently Asked Questions — Muzzle Devices & Suppressor Mounts
Every device we install gets checked with a rod.
// Why This Page Exists
Your suppressor doesn’t line up on the barrel. It lines up on the muzzle device.
A brake or mount that looks perfectly straight can still be canted enough to send a bullet into a baffle. You cannot see the amount of error that causes a strike, and neither can we — which is why we measure it instead of looking at it. A bore alignment rod is a precision-ground rod run down the barrel and past the installed device. It takes a cant far too small to see at the muzzle and turns it into a gap you can measure a foot downrange. We run that check on every muzzle device and every suppressor mount we install, after final torque, and we write the number on your build record. The answers below explain what that check catches, what it doesn’t, and what it means for your can.
// The Numbers Behind It
The whole tolerance is about a fifth of a degree.
Inside a suppressor, a bullet passes through a series of baffles with only a few hundredths of an inch of clearance at the end cap. Divide that clearance by the distance from the mount to the end cap and you get the angle at which the bullet’s path and the suppressor’s bore intersect — the point where a strike becomes possible.
For most rifle-caliber cans, that angle lands somewhere between roughly 0.19° and 0.43°. An unevenly crushed crush washer can introduce that much on its own. So can a metal chip the thickness of a sheet of paper trapped on the shoulder. Neither is visible. Both are routine.
The rod uses the same geometry in your favor: the further from the muzzle you measure, the larger a small angle becomes. The rod doesn’t create the error. It makes the error big enough to catch.
| Clearance at end cap | Mount to end cap | Angle at contact | Measured at 10″ | Our reject limit |
|---|---|---|---|---|
| 0.030″ | 7.0″ | 0.245° | 0.043″ | 0.021″ |
| 0.030″ | 9.0″ | 0.191° | 0.033″ | 0.017″ |
| 0.045″ | 7.0″ | 0.368° | 0.064″ | 0.032″ |
| 0.045″ | 9.0″ | 0.286° | 0.050″ | 0.025″ |
| 0.060″ | 8.0″ | 0.430° | 0.075″ | 0.037″ |
// Questions We Get Asked
My barrel was threaded at the factory and the brake is on tight. Isn’t that enough?
Often it is. Sometimes it isn’t, and there’s no way to know which without measuring. Alignment is the total of several separate errors, each small on its own, that can stack in the same direction:
- Threads cut off the bore. If threads were cut with the barrel gripped by its outside profile rather than indicated on the actual hole, they’re square to the outside of the barrel — which isn’t quite the same thing.
- A shoulder that isn’t square. Torque against an out-of-square shoulder doesn’t seat the device; it tips it, and tips it harder the tighter you go.
- The washer or shim stack. More on this in Q 03.
- The device itself. A brake is a machined part with its own tolerances. Its mounting taper may not be perfectly concentric with its threads.
- Debris. A single chip or a raised burr on the shoulder will tip a device past the entire tolerance budget. You will not see it and you will not feel it through a torque wrench.
Can’t you just eyeball it?
No, and neither can anyone else. The tolerance in question is a fraction of a degree. At the muzzle, that’s a few thousandths of an inch of offset — roughly the thickness of a human hair, distributed evenly around a circle. There is no lighting, no angle, and no amount of experience that makes that visible. Anyone who tells you they can see it is telling you they don’t measure it.
Do you use crush washers on suppressor mounts?
No. A crush washer works by deforming unevenly — that asymmetry is how it lets you time a device. On a standalone brake that’s fine. On something a suppressor mounts to, it is a reliable way to introduce exactly the cant we’re trying to eliminate. We use peel washers, shim stacks, or the device’s own timing nut on any build that will host a can.
When in the process do you check?
Twice. Once on the bare barrel before anything is installed — that tells us whether a problem belongs to the barrel or to the installation. Then again after final torque, with the shims compressed and the timing set, because a device moves as it seats. A hand-tight check proves nothing. If we re-time the device for any reason, it gets checked again.
What happens if my barrel fails?
We call you before we do anything else. Depending on where the error is, the fix may be re-cutting the shoulder and threads true to the bore, re-indexing or replacing the device, or replacing the barrel. What we will not do is install it anyway and let you find out downrange. A failed check is a conversation, not a surprise on the invoice.
Does the check cost extra?
No. It’s part of every muzzle device and suppressor mount installation we perform, and it isn’t an option you can decline. Corrective work beyond the check — re-threading, a new device, a new barrel — is quoted separately and only with your approval.
Do you check the device bore, or the mounting surface?
Both, and the second one is the one that matters. Your suppressor doesn’t ride on the brake’s through-bore — it locks onto a taper, a shoulder, or a HUB thread. A device can pass a bore check and still carry a mounting surface that isn’t concentric with it. Skipping that step is the most common way a build passes inspection and still strikes a baffle.
Can I check this myself?
You can screen for gross problems with a caliber-correct rod, and it’s worth doing. Three cautions: use a rod ground for your bore so it rides the lands and not the grooves, support it so its own weight isn’t read as runout, and rotate it — a reading that changes as you turn the rod is telling you the rod is bent, not the barrel. Treat a home check as a screen, not a clearance.
Which firearms does this apply to?
Two cases: firearms purchased from Second of Ten, and firearms sent to us for muzzle device or suppressor mount installation. In both, the check is part of the work and the number goes on the record. We do not offer alignment verification as a standalone inspection on firearms we didn’t build or mount — the check is only meaningful as part of an installation we control from bare barrel to final torque.
Why does this matter more with a suppressor than a bare brake?
A bare brake gives the bullet an inch of steel to clear. A suppressor gives it seven to nine inches of baffle stack with a few hundredths of clearance at the far end. The same cant that a brake shrugs off is what a can catches — and the consequences run from a ruined can to gas and fragments vented back toward the shooter.
// What a Passing Check Does Not Mean
We’d rather tell you the limits than let you assume there aren’t any.
- It’s a cold, static check. How the barrel behaves under firing and as it heats up is not something a rod on a bench can measure.
- It doesn’t measure how repeatably your can mounts. A mount can be dead concentric and still index the suppressor slightly differently each time you install it. That’s a separate property of the mount system.
- It can’t see inside your suppressor. Baffle alignment, tube straightness, and end-cap centering belong to whoever built the can. A verified mount on a defective suppressor can still produce a strike.
- It doesn’t replace a first-round witness check. We recommend inspecting the end cap for even carbon distribution after your first string with a newly mounted can, every time.
// What You Get
Your build record carries the measured number. Not a checkbox, not “inspected” — the actual displacement figure, the distance it was measured at, the rod used, the date, and the initials of the person who took the reading. Our alignment rods are verified on a surface plate on a set schedule and pulled from service if they’re dropped, because a gauge nobody checks is just an opinion. If you ever have a question about your rifle, the number is there.
Measured, recorded, and signed.