Crowns???

T

Tony Shankle

Guest
I would appreciate some of you "Jedi Masters" giving your opinion on what crown to use. Long range rifle, larger 6mm (close to a 6AI), 105 grain VLD range of bullets.

Some say 90 degree, some 11 degree, what are your thoughts? Also, Harold Vaughn did quite a bit of testing on the "gas effect" for the first few inches and along that line what do you think of a recessed crown?

Thanks for your thoughts...I will sit back and listen.
 
Thought I saw somewhere that (within reason) it did not matter what the angle or recess depth was - so long as the crown was uniform. Obviously, something free of burrs at the muzzle would be a good thing. Not sure of the source, though. :confused:
 
Recessed flat crown perfectly 90 degrees to bore, and don't do the ball thing on the crown. The first few bullets will take care of any tiny burrs at the crown edge.
 
So just how far can you recess that crown to be ideal? How far until it starts to affect gases bouncing off and disturbing the bullet?

Your thoughts???
 
I seriously doubt you will see any difference in accuracy between a flat crown, a lightly recessed crown, a deeply recessed crown, an eleven degree crown or any of these finished with a piloted 60 chamfer if they are fairly square to the bore and the edge is burr free.
 
recessed crown

I recently chambered up a 8 twist 6br in a sporter. I recessed the crown an inch. My thoughts were to use it for the very windy, rainy days at 200 and 300yards. The recess was an effort to keep the rain out of my barrel.
So far, it kicks too hard for true accurracy and the groups look like owl under a tree.
 
crowns

i have a davis, calfee and a martini with a huge barrell the martini smithed 60 years ago by a smith by the name of sukhalle one of the foremost in his time. all 22 r/f. all of them have the barrells cut flat that s it.

there was a big discussion and heated words over this over on r/f central some folks say they can do their own-some say not. so i guess its a personal thing.

ive been told if there are no nicks in the crown to leave it alone.

bob
 
90 degree, slightly recessed. I add a tiny radius'ed transition from the bore to the 90 degree surface. I do the last polish the way Jackie said he does it. You have to run the lathe both directions while doing the crown this way. Inspect with a loupe and also look at the gas pattern after firing.

I think a sharp edge is wrong for the passage of the bullet and is too easily nicked up while cleaning.
 
crb

i dont get any designs on any of my barrells. i see a cloverleaf on the sukhalle but not a sharp pattern.

bob
 
Ok, so most will fall in the "it doesn't matter as long as it is square/true/deburred" crowd. We have one 1" recess but untested. So anyone care to take on the "Gas" & "How far to recess" issues? At what point is it a bloop tube? A better question is, has anyone tested recessed dept(s) for accuracy?
 
Well

About 6 years ago, I took a Rail Gun Barrel, and tried three different crowns, a flat 90 degree with no counterbore, a flat 90 degree with a 1/16 counterbore, and a 11 degree, (which was real popular back in the 90's).

I honestly could not tell the difference on the target. Since then, I just put a sharp 90 degreem reccessed about 1/16 of an ..........jackie
 
Tony
There was a poster here a while back that has a recessed crown and could explain the whole concept to you but he hasn't posted in a while.His name is Henry Childs and he mainly posted on the 1,000 yard forum.I have the dimensions of his barrels in my notes but somebody here probaly has them off the top of there head.Tim Sellars probaly has them as well.A search would likely get you alot of posts and unfortunately I don't remember which topic it was under.He posts as either Henry Childs or HBC.
Lynn aka Waterboy
 
Hi Tony, I have wondered the same thing and have been sitting back listening, also. My shooting bubby who doe's all of our barrel work uses a mill bit to cut a recess! Seems to work ok, we all have some fine shooting rifles that he has chambered. Lightman
 
Thank all of you for your responses. I did a seach and read all the past post on the subject I can find.

One thing I can't get past is the recessed/counterbore depth. Jackie (and proably a bunch more of us) has used a 1/16 counterbore. How about going much much deeper. Does anyone have any experience or theory about at what point it would effect accuracy? Is it possible that a deeper counterbore could actually help? Surely a 1/16 couterbore would produce a different result than a 1/2 inch counterbore?

Harold Vaughn found the issues but he didn't have time to test the solution. This really stuck in my head and it is hard to shake. Of all the things we "micro manage" I find it hard to believe that no one has tested the effects of "depth of counterbore". More of your thoughts would be appreciated.
 
I may have to by default Jim. My problem is that I am not capable of doing the Smith work so it will take a long time for the "back and forth".

Maybe I can talk Jackie into doing it if I buy the barrel...but then again I will have to talk him into to doing it with boat tails too and finding a tunnel to shoot into as well! :)

I suspect that there is a maximum depth you can recess a crown before you would experience some flow seperation and that depth may be fairly shallow. I also suspect that their may be an "ideal" shape/angle to those counterbore walls along with the small inside bore cut.

Much time is spent on perfecting bullets, elimanatiing cant in the bore, and now days even tuning for vibration at barrel end. But, I think there is a tendency to overlook the things/forces happening on and around our bullets for the first few inches after it leaves the muzzle. Anyone that has ever owned a "bad" muzzle brake vs. a "good" muzzle brake already knows that controlling these forces properly DOES make a difference (even though it is a stretch to compare brakes with crowns).

Maybe I am overthinking it.
 
Crown Depth

Quote: "Maybe I am overthinking it."

You wouldn't be the first.

Seriously, there is no reason to think that a very deep crown would affect accuracy as long as it is cut straight. High Power, F Class, and Service Rifle competitors add things to the muzzle end such as tuners, brakes, flash suppressors, front sight radius extensions (bloop tubes), etc. which would more or less duplicate the effect of a deep crown and do not degrade accuracy unless something is over torqued, out of alignment,or extremely close to the path of the bullet.

My philosophy is: "Simpler is better". The simple straight, slightly recessed crown that most benchrest gunsmiths use is easy to do correctly and works as well as anything more difficult would.

Scott Roeder
 
SGS said:
Quote: "Maybe I am overthinking it."

Seriously, there is no reason to think that a very deep crown would affect accuracy as long as it is cut straight. High Power, F Class, and Service Rifle competitors add things to the muzzle end such as tuners, brakes, flash suppressors, front sight radius extensions (bloop tubes), etc. which would more or less duplicate the effect of a deep crown and do not degrade accuracy unless something is over torqued, out of alignment,or extremely close to the path of the bullet.

Scott Roeder
Click to expand...

Scott,

I appreciate your input but we may have to agree to disagree. I have tested a lot of brakes and flash hiders that have had a negative effect on accuracy. I have seen this as recent as this spring with one of my long range guns from the bench.

I have had breaks that had no affect, brakes that help and brakes that have a negative impact, the difference...design?...powder/load?...??? That is my point about recessing a crown with proper angled walls from the bore to outside diameter. I think that we are all happy to accept several answers for a crown design because we are willing to do our tweaking through other areas like our powder/loads. What if we reversed that thought and found out that something like a reverse cone with a certain angle would allow better control over our gas flow and shock waves? We tune for vibration why not tune our gas and possibly our shock wave symmetry? How much thought and efford goes into reducing cant on the bullet down the bore compared to reducing cant from asymmetrical gas flow? We all avoid the transonic area of bullet speed like the plague so what about the trans-ballistic or transitional ballistic area that happens right outside our muzzle?

I started this thread to see how much thought has been put into the subject already and as a feeble attempt to get (what I consider) to be some of the best minds thinking on the subject. I don't pretend to have any of these answers but I do have faith that someone (or several) here at BRC can improve on our existing system and thought process.

Sincerely,

Mr. Overthinking It Again :)
 
Tony
Your not over thinking at all.Many of the things you are talking about have been published in Precision Shooting magazine.There is an article with the crown cut at all sorts of different angles but I don't remember which month/year it was.Somebody will probaly chime in with it for you.
Waterboy
 
tony sir

i have not disussed with henry about recessed crowns [sorry lynn] but there are some theories i had found a few years back from which i formed some of my own. a deep recessed crown or bloop tube can move the air out from the bullets tip while in flight,for this short moment of flight it allowes the bullet to find its center of gravity before it hits a wind that is not running parallel to the bullet , as soon as it hits open air the flowfield of air moves back towards the bullet almost touching the tip for the rest of the flight to the target which is more affecting on the bullets flight . such as if the flowfield were touching the tip resulting from too sharp of a point you would see more dispersion in your groups. but picture this for 4 inches the bullet is flying with a wind that is travling much faster then the bullet and is parallel with the bullet. so no flowfield is even around the tip to deflect the bullet in the tube.hope this helps sir tim in tx
 
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