Ever wondered how bullet clearance affects muzzle brake performance? Our findings may surprise you.
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Introduction
Zach Lester from Salmon River Solutions is joining us today. The last time SRS visited Ultimate Reloader, Ken Trapp and I tested recoil reduction across SRS’s muzzle brakes. While conducting these tests, we wondered what effect muzzle brake clearance has on recoil. Zach and I have been testing just that.
About Salmon River Solutions (SRS)
Above: Recent 7mm PRC build featuring SRS combo rail and SRS Ti Pro 3 ST brake
SRS has two main product categories: muzzle brakes and rails. All are geared towards lightweight hunting, though they can be and are used for a variety of purposes. Rails range from just ARCA to a combo ARCA/Picatinny.
I’ve used their products on both of my recent 7mm PRC builds: the full-custom Bergara and
Freedom Rifle build. I was especially happy with how OD green Cerakote looked on a Ti Pro 3 ST.
SRS products aren’t just for new builds. I’ve given new life to some old hunting rifles by adding the SRS Hunter’s Rail and other builds with brakes and ARCA rails!
The Test
In preparation for this particular test, SRS made a Chub 4-port stainless brake without a self-timer. I typically choose self-timing brakes, but we timed this one on the lathe so we could quickly come back up after a successive boring pass, hand-tighten the brake on the rifle and fire a few more shots.
We’re using one of Ultimate Reloader’s custom built rifles. It is chambered in 6.5 Creedmoor with a Foundation Genesis 2 stock, BAT TR action, Leupold Mark 5HD scope. If you’re looking for a custom-built rifle, head to rifles.ultimatereloader.com and get on the wait list! We also have a ⅝ x 24 threaded muzzle. This particular rifle is very solid and works well on the recoil rig because the buttpad gives a really nice recoil signature.
Typically when I put a brake on a rifle, I bore it to bullet diameter plus 0.030”. Zach and I discussed starting at 0.005”, but worried about things not lining up right or getting a bullet strike. We decided to start at 0.010” instead. We used Norma 130 grain 6.5 Creedmoor hunting ammunition and tested various clearance set-ups starting with the bare muzzle.
We recorded two shots for each and saw some really tight overlap in the first test at 0.010” between the first pass and second pass.
Above: Two different test runs with identical setups showing consistency of recoil data collected with this setup
This gave us really good validation that the quality of the data was good.
We tested bare muzzle, 0.010” over bullet diameter, 0.020”, 0.030”, 0.050”, 0.100” and 0.200”, using reamers on the Precision Matthews TL-1660 lathe for the tighter diameters. Once we had enough clearance, we transitioned to passes with the boring bar.
Results
Both Zach and I expected to get the best recoil reduction with the tightest fit. This wasn’t quite the case. We saw a significant reduction in recoil, almost half, from bare muzzle to using any of the brake set-ups. This brake is up there with the best brakes I have tested in terms of raw recoil reduction. What we didn’t expect was how close together the rest of the clearances would cluster. All of the clearances that we tested had good recoil reduction.
If we isolate just the brake tests, we can see some differences, but the patterns are the same. There’s the initial force peak and the secondary force peak. If you look at all the data, the secondary force peak lines up with the peak of the bare muzzle.
Zooming in on the data, everything was about the same until we went from 0.100” to 0.200”. That’s when we saw the reduction in forces start to diminish.
If we look at the numbers, clearance vs. forces, we broke down the first peak and the second peak. The first peak was lower in all cases. We had a convergence, then a divergence, then things remained parallel.
The peak force graph vs. clearance graph is oddly flat. It’s not nearly as distinct or sloping as we expected. This raises a lot of interesting questions.
Above: Total recoil impulse, far left is bare muzzle
The recoil impulse graph gives the total picture and net effect. 0.020” and 0.030” give by far the best effect, which is also an industry standard.
Conclusion
This test has been eye-opening and has challenged my assumptions. I’m also curious about point of impact shift and effect on precision. My theory is if you have more clearance, you have less POI shift because the pressures will be lower along the side of the bullet. I’m also wondering if you have one side of the brake closer to the bullet (ex. A bad muzzle threading job), will it lead to a POI shift consistent with precision, or will groups open up?
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Thanks,
Gavin Gear
