Sep 1, 1999

Posted by in Shooting | 5 Comments

Adventures With Muzzle Brakes

AR15

A couple of years ago I got involved with brake development and
experimentation. This was purely for my own edification. I’m just a
hobbiest and needed something to do!

I bought a brand new Savage 112 in 308 with laminated stock and SS
fluted barrel to be used as a test bed. I threaded the barrel to 1/2-28.
This is the thread that most brakes are available in since it is the
standard AR-15 thread. I would be testing aftermarket available brakes
along with my own designs. I made a rifle rest that would allow the
rifle to recoil and the amount of recoil to be measured. I tried to set
up a scale to measure this recoil force, but it was inconclusive. I
made over a dozen brakes for this rifle. All different size port holes
from many, many small holes to just two huge holes on either side (sort
of like a military tank compensator). I would start out with the exit
hole a very few thousands over bullet diameter and ream it out in .005″
steps, testing between each enlargement. I tried different lengths. How
long is too long? Different materials. Different hole spacing and
location. Here is what I found….

Exit Hole- If the exit hole is too small, ie <.005″ over bullet
diameter, accuracy suffers. Accuracy really suffers if the exit hole is
more than .25″ deep. The depth of the exit hole creates a “tube” the
bullet must pass through on its way to the target. If the depth of the
exit hole is too shallow the metal around the hole will erode very
quickly. There is not much heat and pressure (5000psi) at the muzzle,
but over time a thin piece of any metal will fail.If the hole is too
small, I believe it is the air trying to get by the bullet that upsets
flight. Best accuracy and effectiveness of the brake was obtained with
.020″ over bullet diameter. There was no measurable reduction in recoil
between .005 and .020. Measurable change in recoil happened at .040″
over bullet diameter. Any exit hole over .040 and the brake began to
lose effectiveness rapidly.

Holes- Most effective braking was with a
brake 1″ in diameter with a 3/4″ exit hole on each side, just infront of
the muzzle. The bullet passes through a cone of 35 degrees before it
exits the brake. (Like the tank example), Incredible reduction of
recoil. But loud and ugly. Very easy to make since you don’t need a spin
fixture or a dividing head. As far as individual holes, it make no
difference the diameter or amount as long as they are large enough and
plenty enough to bleed off all the gas trapped in the brake. I’ve built
brakes with 48 – 1/8″ holes and 30 – 3/16″ holes and they both work
identical. I’ve drilled the holes completely random around the brake
(looks like hell!) and in straight patterns and helix patterns….no
difference on accuracy or reduction. I now use a left to right helix of
3/16″ holes .010″ apart at a 2 degree off set. A total of 5 holes in a
row, six rows for a total of 30 holes. The brake ends up at 2 3/4″ with
a 1/2″ thread depth for an overall extension of the barrel of 2 1/4″.
The helix keeps the brake tight and it doesn’t need to be indexed. If
the brake is indexed so the holes line up with the barrel, after
removing it a few times the holes will shift a few degrees and look less
than professional.

Material- I’ve made them of Stainless, CM, and
Aluminum…No difference at all. The Aluminum brakes harden somehow
after repeated firring and I have one on an AR-15 with over 12,500
rounds (Moly test gun) and the brake is perfect.

Holes on top only- In
my tests, not having holes all around the brake effects accuracy a bit.
I believe it does something to the bullet by the air pushed ahead of the
bullet creating unequal turbulence in the bullet path. I’ve tried a few
brakes where I drilled only holes on the top, test fired, and then
completed holes on the bottom and in every case, accuracy improved. Put
an old blanket down if you don;t want to kick up dust in the prone
position.

Expansion Chamber- A brake bored out to thread diameter
right up to the exit hole is much more effective than a brake where the
bore is exit hole for the full length, Having the bullet traverse this
large expansion area somehow improves accuracy and there is a marked
reduction of recoil.

Effectiveness- The higher the pressure of the
particular round, the more effective the brake. I have over 20 rifles
with brakes. The 220 Swift is the king of reduction. Followed very
closely by the 25-06, 6mmRemington, any Weatherby small bore. With a
proper brake and a hot handload under a 40 gr bullet, the Swift will
move 1/2″ to the rear and 0 muzzle rise! Big boomers with low pressure
like 45-70s and shot guns benefit the least. I have two identical
Remington 700s both with identical brakes. One in 308 and the other in
300 Win Mag. Both shooting 155 Sierra Palma bullets, the Win Mag about
300FPS faster, and the Win Mag has measurably less recoil! Must be the
pressure / amount of gas available.

Length- After 3″ there isn’t enough
gas left to do anything. The longer the brake, the harder it is to hold
concentricity of bore exit hole. If the exit hole isn’t +-.0005″ ,
accuracy will suffer.

Factory Brakes Available- I haven’t tried them
all but of the ones I’ve tried I will only recommend two. The Vias brake
is excellent! Very difficult to make in the home shop. Besides a series
of holes around the brake George Vias bores a series of holes to
intercept the radial holes, thereby bleeding some gas and noise out of
the front of the brake. You lose some braking effectiveness with this
method, not much, but you gain a measurable reduction in muzzle blast
and noise, Darrel Holland’s Ultra brake is IMO the most effective brake
on the market. It does everything right! Expansion chamber, exit hole,
number of holes, length. It is a quality product and it is inexpensive
($60 in CM. $75 in SS – Midway) And Darrel does about the best
installations I’ve seen. (and I’ve seen some horrible, nearly unsafe,
installations) The JP Enterprises recoil Eliminator (you may have seen
it, it looks like a tank brake) is the most effective reducer of recoil.
Period! But man, on anything but a 50BMG it is one ugly device. And
LOUD! Just too much muzzle blast for any hunting rifle. Hope this helps
those of you interested in building your own brakes.

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Thanks

RoyB

  1. I would love to do this, but have a few Q’s. First, what is the best way to get the end of my barrel threaded, I have a small lathe and mill that I could make the brake on, but I don’t think that I have the capabilities to put threads on the barrel. Also, would brass work, I just have alot of that around the shop, might look cool too on a SS barrel, all shined up?

  2. Gabrielallard28 says:

    I was thinking about machining one that would fit on the outside diameter of my rifle’s barrel.Did you ever try this method? I guess the o.d. of a bull barrel is machined straight with the bore?

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