Free bore measurement?

[stinkyduck13]

I was looking at it from the other end, ordering a new barrel not working with an existing one. If I'm ordering a barrel then how much freebore do I want for some particular bullet? Just accept SAAMI or ask for something custom?
But, I'm realizing that such a question threatens to derail this thread, so I'll ask this in it's own thread.

No. Not at all ask away! That's kinda where my question ic coming from. Reading what people have to say in regards to reamers ordering barrels and sticking long bullets into them. Derail away, they way we learn! Thanks guys, and Len what a nice gesture, I have those tools and cartridges I just drilled them in a drill press. Ha my creed drilled off center.

 

[stinkyduck13]

You pick your bullet and seat a dummy round so its not protruding into the case past the case shoulder. Take that sample to your gunsmith and have him ream your freebore to whatever distance to the lands you want. I suggest he sets it so your .020" off the lands.

So what's the reason behind not wanting the bullet to protrude down past the shoulder junction?

 

[QuietTexan]

So what's the reason behind not wanting the bullet to protrude down past the shoulder junction?

Maximize powder capacity mainly.

 

[Huntnful]

That's .202 freebore. Straight cut portion from where the case neck ends and the tapering of the lands begins.

That's how I understand it anyways

 

[FEENIX]

Freebore can be a confusing endeavor. As others noted above, the best way to establish the freebore is during the reamer design manufacturing. But even that is not a guarantee despite its precision manufacturing.



Most of the WBY chambering has a very long freebore, and touching the lands can be challenging. For instance, my .257 WBY has a SAAMI freebore of .378", and very few can get close to the lands with the traditional bullets as designed. However, using the Black Hole 145, mine can touch the lands without any issues.

 

[FEENIX]

So what's the reason behind not wanting the bullet to protrude down past the shoulder junction?

I think Greg explains it well.

 

[stinkyduck13]

Thanks Fenix I will have to watch that one again! I was wondering if I needed to make a small tape measure to stick in the bore and read it with my bore scope. Haha! I always thought weatherby got a bad rap years ago with their long leade or was it the freebore that nobody liked years ago? Now it seems that it is somewhat desirable for the longer bullets we have now.

 

[Koda_]

So what's the reason behind not wanting the bullet to protrude down past the shoulder junction?

Less case fill is less velocity or higher pressure. Ive heard it also causes "donuts" in the brass. IMO an optimal load has the explosion pushing only on the base of the bullet not around the sides at first so your getting the most efficient velocity out of your charge weight.

The Greytan video FEENIX posted was a great explanation of seating to the shoulder.

 

[JustMe2]

Free bore described in color.

Freebore - Google Search

 

[stinkyduck13]

Free bore in color.

 

[sloride]

Thank you Feenix i understand true freebore and leade really hard to explain to someone.

 

[Taylorbok]

IMO the only reason to concern your self with an actual freebore measurement is if you are ordering a custom reamer. If you are just having a barrel chambered your smith can cut the FB separately and basically just sneak up on it using a dummy road you load. It may be slightly beneficial to have it built into the reamer but with wait times for custom reamers being 6 months ish I'd opt to have it cut separate unless shooting F-class

 

[JAYgs8163]

Less case fill is less velocity or higher pressure. Ive heard it also causes "donuts" in the brass. IMO an optimal load has the explosion pushing only on the base of the bullet not around the sides at first so your getting the most efficient velocity out of your charge weight.

The Greytan video FEENIX posted was a great explanation of seating to the shoulder.

You also need to be careful with doing this. Seating the bullet too far out and you are beyond the ogive or widest section of the bullet as I understand this. Bullet will not seat properly and you can have terrible runout. I'm building a 270WSM now based on a couple of different projectiles that I want to run. Can't go too far out so I ended up with a total freebore of .200 on my 270WSM.

 

[JustMe2]

You also need to be careful with doing this. Seating the bullet too far out and you are beyond the ogive or widest section of the bullet as I understand this. Bullet will not seat properly and you can have terrible runout. I'm building a 270WSM now based on a couple of different projectiles that I want to run. Can't go too far out so I ended up with a total freebore of .200 on my 270WSM.

Most bullet designs have a flat area long enough to have some seating depth flexibility. The Berger VLDs had a problem with this and were therefore sensitive to seating depth as you mentioned. The Berger Hybrids are an attempt to remedy this.