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24 August 2003, 14:57

<G.Malmborg>

quote:
Originally posted by Randm'Man:
i'm thinking a (medium deep) recessed target crown with an 11 degree crown on that, and 1.5" of the bore turned out to .09 over bullet diameter so a muzzle brake is more effective. It would sort of act as a pre-muzzle brake
for the rifling,have a standard 45 degree angle cut-off.

What???

24 August 2003, 15:44

Randm'Man

i hate getting a lecture. i only need one person to tell me, thats it. [Mad]

[ 08-25-2003, 07:02: Message edited by: Randm'Man ]

24 August 2003, 16:25

Brent Moffitt

I'd read this section here, starting with the rebated boattail and then the ULD design etc, might find there's a little more going on with hot gas going 10,000 fps when it escapes.

Shock waves affect bullet flight in a big way. What you're refering to sounds like back boring the muzzle as if you were going to drill and use it as a muzzle brake, which is done all the time. The bore is over size so it DOESN'T touch the bullet and the brake is made with the barrel and isn't removable...

http://corbins.com/bullets.htm#uld

[ 08-24-2003, 07:32: Message edited by: Brent Moffitt ]

24 August 2003, 17:17

Customstox

Randm'man,
I echo Malm, What?????

The effective crown on this contraption you described is no longer at the muzzle, it is at the bottom of the 2" smooth section. The important area for a barrel crown is at the point where the bullet leaves the confines of the rifleing. It has to be uniform for the bullet to function properly. All the recessed crown and the 11 degree at the muzzle are a waste of effort because the bullet has already escaped the rifling. Your concept of how a muzzle brake works is a lot different to mine also. They work by redirecting the jet gasses that follow the bullet. Normally those gasses rush out of the muzzle and propel the rifle in the opposite direction. The brake creates ports so some of those gases escape to the side or rearward and thus reduce or even counteract the jet effect at the muzzle. Your description sounds good but from my experience it is more fiction than fact.

25 August 2003, 04:15

<Celt>

wouldnt work well.
There is not a good way to get a super smooth transition of the bore toi the "crown" at 2" into the barrel at just a little over bullet dia.
This will also allow gasses to escape around the bullet in the itght confined of that area possibly upsetting it.
It would not likely make a muzzle brake be more effecient either. A good brake will have an expansion chamber in it to allow the gases to expand well larger that the exit hole in the brake. When the expanded gasses slam against the front of the expansion chamber, they are rediercted 360 DEG and vented out the holes. The slamming of the gasses on the front of the chamber also helps to bring the rifle forward.

2" of bore cut out just over bullet dia. will do nothing to reduce the speed of the gas, at least not even enough to begin to turn it subsonic.

Celt

25 August 2003, 04:22

Bill Leeper

You don't really get out much do you?! I really think you should make the true crown angle (down in the counterbore) shallower. Perhaps 28.5 degrees give or take a bit. Also reduce the size of the counterbore to .050 over. A three angle cut at the muzzle might do something. Tie a ribbon on it and it will look real nice! Just kidding. There is no real evidence that any particular type of crown is more effective than any other providing the crown is well executed.
Winchester did a bunch of experimentation wherein they decided a counterbore which was 1 1/2 calibers in diameter and 2 calibers deep reduced bullet yaw but the methodology could have been flawed.
Muzzle brakes are an abomination so don't even enter into the picture! Regards, Bill.

25 August 2003, 09:55

Brent Moffitt

Celt,

You bring up a good point. On the expansion chamber, how much larger than bullet diameter are they usually, and at the end, are they square cut or longer at the OD than the ID of the exit dia?

How much larger is the brakes exit diameter usually than the bullet too, clearance?

25 August 2003, 16:03

Randm'Man

by the way, the exit diameter, according to brownells should be .04" over bullet diameter

25 August 2003, 18:28

<Celt>

Expansion chambers will vary in size because of barrel diameter / brake diameter because you just cannot put a 5/8-24 TPI thread on a .600" OD barrel.
That being said it usually depends on thread diameter of the brake, the chamber being the thread diameter. Bigger brakes with larger thread DIA will have a a bigger chamber.

Some expierenmenting was done when I was with Answer on brakes. We found that felt reduction in recoil was best when the chamber was about bullet length. Now that is impossibl;e to do since bullets vary so much by weight, but under controled testing that seemed to be the best.

When I do a brake that allows for me to decide on the exit hole size, I like to get then about .015" to .025" over bullet diameter. A 308 caliber rifle will get a .323 exit hole, or up to .328"
It helps greatly if the brake brake is well made and true and the muzzle is indicated in to .0002" just as if you where truing the action because I have found that even though a bullet does not contact the brake, if it is much closer to one side of the exit hole than the other accuracy will suffer.

FWIW
Celt

26 August 2003, 11:36

Brent Moffitt

Thanks Celt. [Smile]

Bbl dia on this 30 cal I'm getting ready to have the brake made for soon is 1.35" to the muzzle. Not sure at all what size thread I should go with for the brake and cap but I'll be shooting the 210 JLK and 200 Accubond in the 3 groove 11 twist Lilja. Got to round up a piece of bar stock for the brake still. Are all the holes/slots in the brake confined to and exiting the expansion chamber only or do they exit out from beyond the end of it too, or does it matter?