Trouble Understanding FreeBore

[ShootDots]

I "know" what FreeBore is>>>But I am having trouble understanding the dynamics of it... For instance: (Just for arguement's sake) Let's say you have a .284 Shehane and want to shoot 180 Hybrids. "Most" .284's will use a .188 freebore to shoot the vast majority of bullets in. So we have a .284 Shehane that is shooting a 180 Hybrid with 56.0grs of H4831. The person shooting has the bullet seated off the lands 15K and it shoots "good" but is getting some flyers and some pressure that appears to be unexplainable. Someone tells him he has too short of a freebore and needs to go to say a .230freebore. So he lengthens his freebore to .230 and once again sets his hybrid to 15K off the lands>>>but he noticed his accuracy is down somewhat and his velocity is also down, because of increased case capacity from the bullet being out further... So he increases the powder charge to get back to the same velocity as before. Now what exactly has changed? He is still 15K off the lands and upped his charge to get back to his velocity node... My mind is either missing something or simply incapable of understanding what is transpiring.. Can anyone explain this concept to me... Thanks in advance for your input...

 

[Immike]

The reason is to get the bearing surface in the neck ahead of the neck-shoulder junction and a little more to stay away from the donut.

 

[ShootDots]

So IF the shank of the bullet (ALL of the bearing surface of the projectile) is ahead of the neck / shoulder junction, you have plenty of freebore, correct?...

 

[Immike]

That area is a pinch point on the bullet with the brass thickness constantly changing and disrupting the release. I try to use no more than 3/4 of the neck for that reason. If you can get the jump you want then yes.

 

[ShootDots]

I see what you're saying Mike.... Thanks!! I appreciate it...

 

[LCazador]

+1 on what Mike says. You are now avoiding that extra bullet tension that was created by the thickness of the brass at the neck/shoulder junction. You have also created more case capacity, so you will have to look for a new node, maybe even a different powder!

 

[22BRGUY]

More "space inside the case" allows the same powder charge to dissapate over a larger area, thereby reducing its pressure on the bullet...so more powder is required in the larger space to get back up to the same pressure....my understanding if same powder is used.

 

[ShootDots]

I have finally grasped the concept... I knew my infantile mind would eventually get wrapped around the concept>>>especially when Y'ALL ( a bit of Texas lingo there) made it easy to understand... Thanks All!! I do appreciate it!!

 

[4xforfun]

Another reason is to keep the "pressure ring" that some bullets have ahead of the neck-sholder junction. If you push this ring inside the case you have..to a very small degree, streached the neck out and messed up your neck tension. Now, I know that the PSI ring is a very small dimention, but look what changing .001 in bushing size can do for..or against, accuracy.

The propper freebore for the bullet intended is a good idea.

 

[Mark Walker in TX]

Ben, if .188 FB in a Shehane is not working, it is due to a different issue…

 

[ShootDots]

Hey Mark... I do not have a Shehane>>>>that REALLY was just a "for instance / example"... However, I will have one in April / May next year... I have the barrel, 180 Hybrids and powder>>>>but my 6.5 x 284 is still going strong and I hope to make it to April>>>It will have 1600+ rounds thru it by then..

 

[ftrrookie]

That area is a pinch point on the bullet with the brass thickness constantly changing and disrupting the release. I try to use no more than 3/4 of the neck for that reason. If you can get the jump you want then yes.

How are you achieving this? Are you only sizing the first 3/4 of the neck or seating long? Also is it ok for the boat tail portion of the bullet to be in or past the donut area?

 

[Immike]

Hi Jay, we are talking about seating bullets long to get the best performance from our rifles. We are using the amount of jump to make minor adjustments to the cartridge in a attempt to find favorable results on the paper. We are only talking about the bearing surface that touches the case not the boat tail which will hang further into the case.

 

[ftrrookie]

Thanks Mike. I understood the conversation but I guess I asked the wrong question. When you stated that you only used 3/4 of the neck I was wondering if you were using a Redding "S" neck sizing die with the micrometer top. My Savage 223 has a short chamber causing me to have to seat 80gr Bergers fairly deep which brought up the "boat tail in the donut" question.

 

[Immike]

When you stated that you only used 3/4 of the neck I was wondering if you were using a Redding "S" neck sizing die with the micrometer top.

OK, I was referring to the seating depth in the neck of the bearing surface of the bullet. 3/4 of the neck or less. This is not a necessity but a detail of controlling the brass and bullet relationship.

 

[22BRGUY]

Another interesting thing about partial neck resizing is that even though a smaller inside diameter bushing is used to partially resize the neck, the actual neck tension on the bullet may be less than a larger inside diameter bushing because the neck is now only "gripping" on a smaller section of the bullet....if that makes sense. Also, since it is a smaller area of the neck that is resized, it is likely that the neck tension will be more consistent than with larger area resizing in my mind. Is there such a thing as too little neck resizing? I'm sure there is but where exactly that line is crossed, I'm not sure and it will probably vary somewhat in different cartridges. Additions, corrections, criticisms from the more knowledgable welcome.

Best wishes guys on a good post.

 

[Drop Port]

That area is a pinch point on the bullet with the brass thickness constantly changing and disrupting the release. I try to use no more than 3/4 of the neck for that reason. If you can get the jump you want then yes.

How are you achieving this? Are you only sizing the first 3/4 of the neck or seating long? Also is it ok for the boat tail portion of the bullet to be in or past the donut area?

I see what you are asking, often times the FB is long enough to put the boat tail junction above the neck shoulder junction. I have used bullets with not enough FB to get the boat tail junction above the neck shoulder junction. In that situation I only sized 3/4 of the neck as not to pinch at the bottom and it worked out.

 

[Immike]

Another interesting thing about partial neck resizing is that even though a smaller inside diameter bushing is used to partially resize the neck, the actual neck tension on the bullet may be less than a larger inside diameter bushing because the neck is now only "gripping" on a smaller section of the bullet....if that makes sense. Also, since it is a smaller area of the neck that is resized, it is likely that the neck tension will be more consistent than with larger area resizing in my mind. Is there such a thing as too little neck resizing? I'm sure there is but where exactly that line is crossed, I'm not sure and it will probably vary somewhat in different cartridges. Additions, corrections, criticisms from the more knowledgable welcome.

Best wishes guys on a good post.

This is getting more challenging with every post, lol. OK, this is not about reducing the neck sizing ,but about how deep you seat a bullet and the needed freebore in the chamber. I will try a new approach to this by asking you to put a bullet in a fired case that has several firings on it. You should feel the bullet hit the doughnut (if you have any) at bottom of the neck near the shoulder junction. With this you can measure the length of that and comparing it to your loaded rounds to see if you are in the doughnut with your bullets. If so then it is interfering with bullet release. This is a bigger problem in tight neck chambers.

 

[Drop Port]

Another interesting thing about partial neck resizing is that even though a smaller inside diameter bushing is used to partially resize the neck, the actual neck tension on the bullet may be less than a larger inside diameter bushing because the neck is now only "gripping" on a smaller section of the bullet....if that makes sense. Also, since it is a smaller area of the neck that is resized, it is likely that the neck tension will be more consistent than with larger area resizing in my mind. Is there such a thing as too little neck resizing? I'm sure there is but where exactly that line is crossed, I'm not sure and it will probably vary somewhat in different cartridges. Additions, corrections, criticisms from the more knowledgable welcome.

Best wishes guys on a good post.

This is getting more challenging with every post, lol. OK, this is not about reducing the neck sizing ,but about how deep you seat a bullet and the needed freebore in the chamber. I will try a new approach to this by asking you to put a bullet in a fired case that has several firings on it. You should feel the bullet hit the doughnut (if you have any) at bottom of the neck near the shoulder junction. With this you can measure the length of that and comparing it to your loaded rounds to see if you are in the doughnut with your bullets. If so then it is interfering with bullet release. This is a bigger problem in tight neck chambers.

This is what I was talking about, in my case / (circumstance) I didn't have enough FB but was able to fudge it by sizing the neck down short of the Doughnut. Not ideal but it worked.

 

[Immike]

I try to not seat past the sized area but that is interesting. In Mike Rattigan's book he has a diagram of this and called seating past the sized area a big no-no! I don't know if this applies to the boat tail bullets or not. I have removed the doughnut with inside reaming and decided it was easier to replace the brass. Since the doughnut is not perfect it tended to scratch up the inside of the neck on one side. You can push it out and turn it off the outside but I have my doubt about how perfect that is. It is not necessary to size the entire neck and 70-80% avoids the sizing of the doughnut area but still doesn't solve anything if it is smaller than the bullet in a fired case.