Muzzle brake pull off , what is it and is it real ?

[Metal God]

Hey guys and gals . I was debating on where to start this thread because this is both internal and external ballistics and decided here instead of the reloading sub forum .

Several years ago I read and or watched a video about something called "muzzle brake pull off" and although the theory seemed possible I never really gave it much thought .

So what the heck am I talking about you ask ? Muzzle brake pull off as I understand it is the effect/movement of your muzzle caused buy the air/gasses being pushed/forced out of the barrel and engaging the muzzle brake BEFORE the bullet exits the bore . The theory is that there is at minimum air in the bore in front of the bullet . When the bullet engraves into the lands that seals that end of the bore forcing everything out the other end ahead of the bullet . Well air compresses and the bullets movement forward actually compresses the air in the bore as it's pushed/forced forward . The forward compressed air exiting the bore and hitting a muzzle break and really any muzzle device can and does move your muzzle and creates POA to POI shifts or worse inconsistent groups .

I hope I explained that well enough for it to seem like a reasonable theory to all of you . I had never gave all that much thought until last night when I saw this video of the shock waves of a bullet in flight .

https://www.youtube.com/watch?v=BPwdlEgLn5Q

On the whole the video is pretty cool at first but when the video reaches the 6:51 mark when they looked at the muzzle blast . OMG I can't believe how much air and gasses come out of the bore BEFORE the bullet exits ! Not only air but am I seeing actual blast coming out before the bullet ???

If so , then this would seem to confirm something Unclenick has talked about many times over at TFL forum . That is gasses passing by the bullet BEFORE it engages the lands .

Anyways I just wanted to get your guys thoughts on this and If I'm seeing what I believe I am seeing . Which is in fact enough air and or gasses exiting the bore in front of the bullet to cause your muzzle device to pull you off target ? You can see it much better on the revolver being fired but I suspect the rifle has quite a bit too.

[ar15barrels]

I don't think it's feasible.
The weight of the air in the bore is so much lower than the rifle, bullet and powder.

A MORE feasible explanation of movement of the gun before the bullet leaves the muzzle is recoil.
Recoil begins the moment the bullet starts moving and absolutely pulls the gun off target.
This is why consistent position behind the rifle is so important.
With a consistent position, the amount of movement of the gun is BUILT INTO the rifle's zero.

[Metal God]

Randall , I don't disagree . It does how ever show the phenomenon of the air and or blast leaving the bore before the bullet , which I never thought I'd actually see . I found that to be very cool to see , especially at the 8:35 mark when they tested the revolver . It really appears to show gases from the powder burning/expanding to exit the barrel well before the bullet . That makes one ask , how did some of the expanding gases that are behind the bullet at the start leave the muzzle ahead of the bullet ?

[Fjold]

The bullet does not form a perfect seal with the bore.

[CSACANNONEER]

The bullet does not form a perfect seal with the bore.

Good to see you back. You are an asset to the community.

[scotty99]

[ar15barrels]

how did some of the expanding gases that are behind the bullet at the start leave the muzzle ahead of the bullet ?

That's called leakage.
Some gas slips by sometimes.
The shorter the bullet or the looser fit of the bullet to grove diameter, the more that will slip by.

[ar15barrels]

Do the 120's shoot lower than the 140's with the same scope zero?

[scotty99]

Do the 120's shoot lower than the 140's with the same scope zero?

[ar15barrels]

Yes

That makes sense.
140's take longer to get out of the barrel so there is more TIME where the rifle is recoiling before the bullet leaves the barrel.
The rifle is also recoiling more with the 140's so the barrel is pointed higher by the time the bullet leaves the barrel.

[newbutold]

I shoot much tighter groups with my braked rifles than those without. Not scientific, just fact.

[ar15barrels]

I shoot much tighter groups with my braked rifles than those without. Not scientific, just fact.

It's usually because they are easier to concentrate with.
The unbraked ones give more cumulative punishment than the braked ones.

In teaching precision rifle classes, I see shooters of unbraked rifles lasting between 10 and 30 rounds before they can't concentrate on making good shots anymore.
I see the braked rifle shooters lasting 40 to 60 rounds before they can't concentrate on making good shots anymore.

[scotty99]

I shoot much tighter groups with my braked rifles than those without. Not scientific, just fact.

[scotty99]

That makes sense.

140's take longer to get out of the barrel so there is more TIME where the rifle is recoiling before the bullet leaves the barrel.

The rifle is also recoiling more with the 140's so the barrel is pointed higher by the time the bullet leaves the barrel.

Seems reasonable. And a 5.5lb rifle with a #1 contour barrel simply magnifies the effect, hence the dramatic POI shift. I bet another 3 lbs on the gun and/or a heavier barrel would change the offset dramatically.

[broadside]

Randall , I don't disagree . It does how ever show the phenomenon of the air and or blast leaving the bore before the bullet , which I never thought I'd actually see . I found that to be very cool to see , especially at the 8:35 mark when they tested the revolver . It really appears to show gases from the powder burning/expanding to exit the barrel well before the bullet . That makes one ask , how did some of the expanding gases that are behind the bullet at the start leave the muzzle ahead of the bullet ?

The barrel is not in a vacuum so there is air in the barrel ahead of the bullet that is being forced out by the bullet pushing on it