A proper crown . . . Is there only one type?

[barrabruce]

Thanks!
I’m sorted then.
I will cut mine at an angle so it will be 8 Moas high at 100 yards.
That’s inchez for non NZ people
Then my 22lr will self compensate out to 100 yards or pretty much shoot flat.

[303Guy]

Not if you're shooting at giant Moas.

[GregLaROCHE]

There are a number different ways to cut crowns. One reason for not cutting them square is so that the bore is protected. A target rifle will often have a different crown than a hunting rifle that risks having impacts to the muzzle.

[JSnover]

What target shooters do is use target bullets with perfectly symmetrical and consistent bullet bases and trailing edges. Tests have been done on bullet noses, damaging them in different ways. Nose damage had little to no effect. But damage to bullet bases was found to have a large effect. That only means the trailing edge effects bullet flight.

Correct! Even that hacksawed muzzle was consistent (more or less) from shot to shot, that's why the group size was so surprising.
The reason we buy premium bullets or try to cast 'perfect' boolits is partly because the base is the last part to pass through the crown.

[GregLaROCHE]

A rifle is a precision piece of equipment and should be taken care of accordingly.

[akajun]

When you get to the high end of the accuracy game crowns do matter. It is well know that a damaged or inconsistent crown will affect accuracy and in some case a simple re-crowning will restore accuracy. What is much less understood what is the best type of crown if there is a best?. Lots of arguments generated and many articles have been written over the subject but very little agreement on what is best. Also looking at the winners circle equipment there doesn't appear to be a clear this is the best. The stepped 90 degree and the 11 degree tend to be the most popular.

Does the crown affect accuracy? yes
IDK if you remember when the Marines figured out that they needed to re crown the NM m14's every so often to keep the 600 yd scores up since they were wearing out the crown b/c you cant clean them but from the muzzle and even a bore guide didnt do crap.
Supposedly they could tell when it was going by the 600yd scores, and they would touch up all the guys on the big team before Perry so they could have good zeros and finish the nationals since pulling the muzzlebreak would change them.

[Conditor22]

That is a bizarre article you posted 303Guy...he cut that barrel over and over again and did an intentional awful job on the cut(s)...didn't do anything at all to the crown and yet all the various cuts and barrel lengths produced groups at 100 yards that hovered around one MOA.

He got a wild hair and did this to the crown...



It shifted his POI 16 MOA at 100 yards but after re-sighting the scope...this dang cut of the barrel still produced MOA groups...I am astounded at this.
The average group size was 1.106″ (1.056 MOA)!

Here's his bottom line regarding the crown...


Does a rifle’s crown affect accuracy? Yes, it can. Bear in mind what accuracy means, how close we are to the target. We can have a precision rifle that isn’t accurate and an accurate rifle that isn’t precise. If you have a zero on your rifle and damage the crown you’ll most likely have a POI change which in turn affects accuracy.
Does a rifle’s crown affect precision? Not necessarily. I think the takeaway message from this post is that you can do some pretty awful things to your muzzle and still have a rifle that groups fairly well. Am I shooting 1 and 2″ groups? No, but I’m not about to do any load development on this gun. Would I want to take a rifle with these crowns to a match? No way. But it sure is interesting to see how well a tube-like this can shoot!

I am still going to get Bill Calfee's opinion about the crown. I read earlier in his book that he distinguishes between a lead shooting barrel crown and say a centerfire that deals with jacketed.
When I find the right paper in that collection I'll be sure to post it here.

I also read somewhere you could adjust the POI by beveling the crown/end of the barrel, where ever the gas exits the bore first will slightly deflect the flight of the boolit

I believe they recess the bore ie crown to protect the end of the bore from damage. IF whatever crown you choose is not perfectly perpendicular to the bore and evenly cut the boolit will deviate off-center.

[rbuck351]

I traded for a chineese sks, bolted a scope on it and went to the gravel pit.I set up a piece of cardboard about 16" x 20" at 50yds and started shooting with some cheap ammo and some reloads. I got about 50% hits on target many of which went through sideways. After checking the crown it appeared to have been hand cut with a fork. I cut off 1/4" and crowned with a brass round head screw and valve grinding compound. It now shoots about 3" at 100yds which I consider fair for an sks. Bench rest rifles aren't the only ones to gain from a crown job.

[JSnover]

I also read somewhere you could adjust the POI by beveling the crown/end of the barrel, where ever the gas exits the bore first will slightly deflect the flight of the boolit

You can. Double rifles were regulated that way. I believe they started with wedges and silver solder, finished with a file or stone.

[MostlyLeverGuns]

One of the 'WORN OUT' crown theories is that the mix of gases and air cause additional erosion just as the bullet exits the muzzle. Some of the 1000 yard bench rest folks in PA would shorten and rechamber due to throat erosion and the shorten the muzzle by 1/4" and recrown to remove possible erosion at the muzzle. The barrel maker , Obermeyer, quite often used 60* as his muzzle crown as that is used when on the lathe center when turning and fitting barrels. The is little said in the previous posts that is untrue, flat and 11* degrees are most popular, but where did 11* come from. I have heard speculation that it is due to some theory about some boattail bullets and exiting gas but little definitive experimentation has been done. I have found 60* works well, but I have a piloted 60* cutter that I use to carefully cut new crowns. There are other pilot cutters made for crowning that are at 45* but have not heard about results that are special, good or bad. I think exiting the bullet without damage is the key, as long as the bullet is not damaged and is held tightly, all other conditions should hold shot after shot.

[M-Tecs]

One of the 'WORN OUT' crown theories is that the mix of gases and air cause additional erosion just as the bullet exits the muzzle. Some of the 1000 yard bench rest folks in PA would shorten and rechamber due to throat erosion and the shorten the muzzle by 1/4" and recrown to remove possible erosion at the muzzle. The barrel maker , Obermeyer, quite often used 60* as his muzzle crown as that is used when on the lathe center when turning and fitting barrels. The is little said in the previous posts that is untrue, flat and 11* degrees are most popular, but where did 11* come from. I have heard speculation that it is due to some theory about some boattail bullets and exiting gas but little definitive experimentation has been done. I have found 60* works well, but I have a piloted 60* cutter that I use to carefully cut new crowns. There are other pilot cutters made for crowning that are at 45* but have not heard about results that are special, good or bad. I think exiting the bullet without damage is the key, as long as the bullet is not damaged and is held tightly, all other conditions should hold shot after shot.

Boots is/was a friend of mine. I shot with him and had dinner with him many times. Through the years I purchased 40 to 50 barrels from him and yes he was fond of a 60 degree chamfer for the edge break. Most consider the edge break chamfer different than crown. I don't remember what type of crown he preferred. Most people that use 90 degree or 11 degree crowns still use some type of edge break chamfer.

https://forum.accurateshooter.com/th...amfer%2C%20etc.

[DougGuy]

I use a 20 degree crown. I watched a video of a 1911 firing in slow motion, paused the playback at the moment the gas cloud exited the muzzle, then I used a welding rod to match the angle of the gas cloud, divided this angle in half and measured it, 20 degrees. I figure there is less turbulence and less backflow if the crown is parallel to this gas cloud. Seems to work quite well for the 1911 style barrels.

This also works out that I can clean up pretty much 100% of the 45ish degree crowns that many factory barrels come with. I would estimate that over 80% of these are eccentric.

Attachment 281546

[M-Tecs]

Doug do you use additional edge break?

[B R Shooter]

I have used a 60* break, pulling from the inside out, for many years. I use a bronze brush every time I clean, and it just doesn't make sense to drag a brush back over a sharp crown. As long as the groove is indicated properly, flat, recessed, beveled, makes no difference on paper. Burr free is important.

[M-Tecs]

I have used a 60* break, pulling from the inside out, for many years. I use a bronze brush every time I clean, and it just doesn't make sense to drag a brush back over a sharp crown. As long as the groove is indicated properly, flat, recessed, beveled, makes no difference on paper. Burr free is important.

That what I do also but I don't use bronze brushes anymore. Nylon only. Normally I do 60 degrees for myself and 45 degrees for others. I also have piloted bushing 60 tooling that uses the same bushings as my chamber reamers. I have bushing in .0002" increment for all the sizes I do chambers for. I single point for the initial chamfer and use piloted tooling if a touchup is ever needed.

[DougGuy]

Doug do you use additional edge break?

No more than is required to blend the new crown into the muzzle.

[M-Tecs]

I've had people request them to be left sharp. In those cases I just use a CRATEX rubber abrasive 45 degree point hand spun for a couple of very light hand turns. I am not sure how else others deal with this but I am always looking for better methods.

[samari46]

Thanks for the tip regarding getting a copy of Jim Calfee's book. Much appreciated. Going to expand my library and this one should be a good addition. Frank

[uscra112]

Dr. Mann showed that an asymmetrical crown will cause the bullet to spiral. Absent any other factors, the spiral will be consistent, so at any given range the groups will be good. BUT at any other range the mean POI of the group will be different. (i.e. the zero will shift). He proved this by shooting through paper screens set at various distances, with the rifle barrel mounted in his "shooting Gibraltar" rest system. He and Harry Pope also shot a lot of bullets with out-of-square bases. Same thing - they spiral. Dr. Mann got so he could predict the point of impact on any one of his screens by knowing how the bullet's base was oriented before it was fired.

Somewhere there is a high-speed video of a tank cannon shell in flight. It is seen to wobble a good 20 degrees off the line of departure from the barrel. Amazing.

[David2011]

My preference is for a square crown, either flat or recessed. I’ve crowned on a lathe but the Brownell’s piloted tool is easy to use and does a beautiful job. On 1911s I like the 11 degree crown, cut flush with the slide or bushing depending on if it’s a standard or bull barrel.