Gunsmithing What is the best type of crown with 5R rifling?

[glock24]

I was simply going to ask for another 11 degree target crown on my latest build, but I read an opinion recently that because the lands and grooves are different heights, an 11 degree crown won't cut them all evenly. This of course would allow for uneven gas escape.

The claim is that a 90 degree crown is superior to an 11 degree target crown.

Anyone have an educated opinion on this?

Thanks

11 DEGREE

90 DEGREE

 

[wnroscoe]

Re: What is the best type of crown with 5R rifling?

If a crown is cut straight and perpendicular to the bore, they're same/same. A crowns only purpose in life is to protect the lands at point of projectile exit. I've been using the recessed USMC type crown on all my field/hunting rifles and like the protection it affords. I also have an 11 degree and it works great. I've seen straight 90 degree crowns on BR rifles that work just as good but, offer zero protection for the actual protection of the exit point. Bottom line is this, once you get past the actual protection of the exit point, beauty is in the eye of the beholder, order what turns you on.

 

[Terry Cross]

Re: What is the best type of crown with 5R rifling?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body"> but I read an opinion recently that because the lands and grooves are different heights, an 11 degree crown won't cut them all evenly. This of course would allow for uneven gas escape.

The claim is that a 90 degree crown is superior to an 11 degree target crown.
</div></div>

The answer would be "a uniform one".
The number of lands in the bore profile will make zero difference in the performance of any one type of crown. Since the bore has all the lands/groove evenly spaced radially, the gas release will be balanced regardless of whether the barrel is a 3,4,5 . . . 72 groove rifling profile.

This can fairly easily be demonstrated with a good close up photo of a 3 or 5 groove barrel crown.

I generally cut a countersunk crown with 90* approach on barrels that will have no muzzle attachement. Similar to your bottom photo.

On barrels that will have brakes or suppressor adapters on them, I generally cut an 11" countersink with a very polished surface. My thinking is that the flat, smooth surface will help minimize the carbon crud build up on that surface.

Regardless of the relationship of truth versus my perceptions, the two types of crown have proven to have zero variation in the accuracy of the barrels as far as anybody can tell.

TC

 

[glock24]

Re: What is the best type of crown with 5R rifling?

Thanks gentlemen.

I'll stick with my 11 degree crown.

 

[texasaero]

Re: What is the best type of crown with 5R rifling?

Harold Vaughn in his book "Rifle Accuracy" took schlieren photos of the muzzle blast as the projectile exited the barrel for different crown types two of which are pictured above as well as recorded groupings. His results yielded no difference in consistency. But crown uniformity was crucial instead of geometry type.

 

[Deadshot2]

Re: What is the best type of crown with 5R rifling?

Supposedly, Remington puts an 11 Degree crown on their 5-R's. The crown on my 5-R looks like someone couldn't make up their mind between a flat 11 degree and one with a deep "dish" to it.

I re-cut the crown with a Brownell's piloted 79 degree (90-11=79) cutter and from the first touch of the cutter it was apparent that the factory job was sloppy.

Has anyone else re-crowned their factory 5-R and can relate any changes in accuracy?

 

[VonReich]

Re: What is the best type of crown with 5R rifling?

I'm considering on doing it to the 5R on my Remington, i agree it doesn't look at all uniform out of the box. I'm just not home to take the task on, going to have to wait until my tour in Afghan is over.