Measuring Your Barrel for an SBR
With the recent changes to NFA regulations, we have seen a surge in the popularity of shooters converting their rifles to SBRs. Unfortunately, while the tax stamps are now free, there is little information on how to set up a new SBR correctly the first time.
In fact, one of the most common questions we receive during the barrel ordering process is:
“How short can I go and still clear my forend with a suppressor?”
Many shooters want to run the shortest possible barrel while still clearing the forend with their muzzle device or suppressor attached. This keeps the rifle compact without running into clearance issues when mounting the suppressor.
Before ordering a new barrel, it’s important to determine how short you can go while still leaving enough barrel exposed in front of the stock or chassis.
In this post, we'll outline a simple method to determine the minimum barrel length that will still clear your forend.
Before taking any measurements:
- Ensure the rifle is completely unloaded.
- Remove the magazine if applicable.
- Visually and physically check the chamber.
- Close the bolt.
Taking measurements with the bolt closed ensures your measurement reflects the true distance from the bolt face to the muzzle, which is how barrel length is defined.
Method: Cleaning Rod or Dowel Method
This is the most accurate method because it measures the true barrel length from the bolt face to the muzzle.
Step 1
Insert a cleaning rod or wooden dowel down the barrel until it contacts the bolt face. Make sure the bolt is closed.
Step 2
Mark the rod at the muzzle. Stay as close the the crown as possible.
Step 3
Remove the rod and measure from the end of the rod to your mark.
This gives you the true barrel length.
Step 4
Now measure from the Forend back to the Muzzle.
Step 5
Subtract the forend measurement from your barrel length.
Example
This barrel measures right at 26”.
Our distance from forend to muzzle is 13 ⅞”
This means our minimum barrel length will be: 26” - 13 ⅞” = 12 ⅛”
NOTE: If we would like to thread the muzzle, we have to add .600” to our barrel, so that the shoulder of the threads is at our “Barrel Minimum”. In this case, that would give us a minimum threaded barrel length of 12.725” , which we would call 12.75" for ordering purposes.
It is generally a good idea to add some length to account for any muzzle device or suppressor that may hang over the shoulder of your barrel, so in this case, we would recommend a barrel that is around 13.0” long.
Just know that the closer you want the suppressor to your forend, the more accurate your measurements must be! It never hurts to measure a few times and compare your notes. We recommend you round up to the nearest .25" to ensure you have the clearance needed.
COMMON MISTAKES
#1. Not accounting for muzzle threads.
For this build, we calculated our minimum barrel length to be 8”. If we had made our barrel 8” long with a threaded muzzle, the threads would be inside the handguard. Instead, we added 0.600” to our length, bringing the overall length to 8.6”, for a perfect fit with the suppressor.
#2 - Measuring from an unlocked bolt.
Always make sure your firearm is unloaded, and the bolt is fully locked. If the bolt is in the unlocked position, your measurements may not be as accurate as possible, which can affect the fit of the finished barrel.
