Thread: Muzzle brakes - Overbore Efficiency

What's the effeciency like with muzzle brakes overbored. Ie 308 bore on a 7mm barrel. Or in the more extreme case a 338 bore on a 7mm barrel.

Specifically talking a T2. I have a T2 on my 300 Win Mag although my gunsmith ignored my instructions not to taper it and it will no longer work with my new barrel. I'm thinking of buying another to go on a new rifle but this one's well overbored.

@Kiwi Greg is probably a good start

The closer the hole in the brake is to bore size, the greater the performance. Brakes are best at about 0.5 - 0.6mm (.020 - .025") over bore size but must be accurately fitted in true alignment. Having said that, you will find they still work reasonably well at 1.00mm over (0.40"). The number of impingement faces (chambers) is probably more important but there are diminishing returns as the number increases, 3 is about minimum and 5 about maximum.

Originally Posted by mimms2

Convert all your units to same.

.308 = 7.62mm

Does 0.3mm sound like something you need to worry about?

In certain things that's huge ie in barrel straightness.
I'd like to know real world experience because a barrel thats 0.3mm larger than the projectile sounds pretty big issue.

.338 - .284 =.052 or around 20% of .284

Originally Posted by gundoc

The closer the hole in the brake is to bore size, the greater the performance. Brakes are best at about 0.5 - 0.6mm (.020 - .025") over bore size but must be accurately fitted in true alignment. Having said that, you will find they still work reasonably well at 1.00mm over (0.40"). The number of impingement faces (chambers) is probably more important but there are diminishing returns as the number increases, 3 is about minimum and 5 about maximum.

Good to know the new ones bore is .344ish so would be 0.060" might be pushing things a bit

Im sure ive watched one of Gregs vids where he showed that a brake two sizes larger still worked totally fine.

Originally Posted by mimms2

Certain things. None of those things is what we're talking about though, huh.

Thats true but the point remains the same suggesting that the difference could (sound like it does listening to @gundoc its seems that this muzzle brake is infact significantly overbore to the point it will be less effective.) If I am going to go with a terminator its for its improved performance so I'm not that keen to lose even 10-15% performance.

Efficiency depends on brake design

90 degree ported brakes can easily close up with the peening induced by the powder striking the baffles so you have to be careful with clearance, to little & they can close up enough to cause bullet strikes, so some manufactures suggest cutting a bevel on the leading edge to reduce it

Here is a video I made over 5 years ago clearly showing the difference bigger through holes makes with my brakes



There is little to no loss of performance with my brakes putting a .284 through a .308 clearanced hole

Terminator breaks are friggen awesome, pity that KG seems to be very quiet on here ( & in general ) lately, be nice if he gave some of his bro's a call'n'heads up to see how things are going aye Brads

Originally Posted by Philipo

Terminator breaks are friggen awesome, pity that KG seems to be very quiet on here ( & in general ) lately, be nice if he gave some of his bro's a call'n'heads up to see how things are going aye Brads

Missing me Phil

Been busy playing with cars, not importing so much stuff now or building as many rifles