Gunsmithing Rimfire barrel choke point ?

[maccrazy2]

So I am getting into precision rimfire shooting lately and have a couple questions regarding barrels. It seems according to the interwebs. Barrels shoot better if the crown is located where the barrel bore is tightest. This seems to be backed up by taper laping done by rimfire riflesmiths.
Anyone know what the theory behind this is. Trying to understand why a little extra squeezing of the bullet at the end of the bore would be better than a straight consistent diameter bore?

 

[1SMALLJOHNSON]

Here's the theory, as I understand it: The crown/muzzle area must be NO looser than the tightest part of the barrel's length. Therefore, the BEST way to ensure that fundamental principle is to "choke" the barrel at the muzzle. All that being said, "choke" is not necessary for a barrel to shoot well. However, if there IS some tighter point within the bore (other than the muzzle), the bullet SHOULD swage to that diameter. This swaging process would leave "wiggle" room for the bullet at the muzzle. Since you don't want that "wiggle", you avoid it entirely by "choking". The same is true for any other kind of barrel out there. They've all got to follow the same fundamental principles.

 

[maccrazy2]

That makes sense. I just never heard of it on centerfire barrels. Other than removing the ends to get to clean consistent rifling. I am curious if the larger bearing surface of larger caliber bullets negates the effect some. I would assume so or slugging and taper lapping would be more common on them as well.
On a side note I am really liking the tack driver 22s. Other than the whole finding ammo thing.

 

[eddieharren]

Bill Calfee, expert rimfire benchrest gunsmith did a series of articles, in the now defunct Precision Shooting magazine, that covered this extensively. You may be able to find the articles in the Archives of the IBS.

 

[Aeon1]

Calfee published a book with all of his old articles. Maybe it's still available. He posts frequently on world wide accuracy World Wide Accuracy - Home . More good information can be found at rimfireaccuracy.com

 

[maccrazy2]

Thanks for the info and the link