zero free bore whats the advantages

[English]

zero free bore whats the advatages or dis advatages of having a rifle chambered either way

 

[BoydAllen]

Basically, for me, freebore length or lack of it, is about being able to seat bullets so that they are engraved by the rifling, and still have enough of the cylinder part of the bullet in the case neck, for it to be secure, even after there has been some advancing of the throat, due to wear. The only reason that one would use zero freebore, is that he was planning on using bullets that were relatively short, and/or had high number ogives. The exception is when the intention is to jump bullets, so that a larger amount of powder may be loaded, giving higher velocity, without exceeding pressure limits. An example would be the stock Weatherby chambers.

IMO, the more bullet that is in the neck, the greater the influence that case to case variations in bullet pull have on the extreme spread of velocities within a group, and the alignment of the bullet to the CL of the bore as it enters the throat. On the other hand, some powder bullet combinations seem to like more neck tension, which can be made more difficult to obtain if necks are too thin, and the amount of bullet engagement too little, so getting freebore right it is a balancing act in which experience should play a large role.

 

[amlevin]

Boyd-

Doesn't reducing freebore to zero pretty much make the rifle a "One Bullet" rifle? Limit your selection to bullets of same profile?

 

[BoydAllen]

That would depend on the length of the case neck. Also, you could have a longer bullet with a very "pointy" shape work in the same situation as a shorter one with a more blunt shape. It is best to at least have a range of bullets in mind when you design a reamer, or pick a barrel twist.

 

[ReedG]

Most of the zero free bore barrels are for the 30 BR due to the use of relatively short, fat bullets with high ogive. My next 6 PPC barrel will have very little free bore. Using Benchmark, 8208XBR, etc., leaves plenty room to seat the bullet deeper and getter better control over neck tension. With my current barrel, a 65-gr. boat-tail will barely seat enough to hold it in.