Correct O.A.L. or free bore question

[acidone]

I just picked up a Hornady Lock n Load O.A.L. and am starting to go thru all of my chambers and figure out how far my lands are for all of my different loads.

I started with my Kimber Advanced Tactical in .308 Winchester and found that my chamber allows a 175gr Federal GMM to "jump" about .040" before making contact with the lands. This seems like quite a bit to me, although I've had really good luck with GMM factory ammo in this particular rifle.

My question is; is there a good "rule of thumb" as far as how far away from your lands to seat you bullet. I've heard people say anywhere from .005" to .050". That's a pretty big window to work with!!! I know every rifle/chamber is different, but I figured there is a good standard to work to.

Thanks in advance for your help

 

[MinorDamage]

Re: Correct O.A.L. or free bore question

.04 doesn't sound excessive for a factory chamber. Remember, the industry standard for 308 is a COAL of 2.8". The 175 SMK is a jump tolerant bullet IME, so you should not have issues. Now, if you are shooting VLDs you are going to have a harder time based on their finicky nature in relation to seating depth.

Sounds like you are figuring out the base to ogive measurement effectively. I always load my initial development rounds to .02 off the lands, find a velocity node, and then adjust seating depth from there. Just remember that the pressures will change as you seat them into or farther out of the case. Each rifle chamber is different.

Josh

 

[acidone]

Re: Correct O.A.L. or free bore question

Maybe excessive wasn't the right choice of words. I'm a tool and die maker by trade and most things i've ever come across usually work better closer in tolerance than further. What i meant to say was that if factory Federal GMM is .040" away from my lands, i think i can do much better with a hand load

Judging by what you're saying about starting around .020 away and moving around from there, i'm probably right.

Thanks for the response!!!

 

[acidone]

Re: Correct O.A.L. or free bore question

Now, if you are shooting VLDs you are going to have a harder time based on their finicky nature in relation to seating depth.

VLD???

 

[gcoulsey]

Re: Correct O.A.L. or free bore question

Very Low Drag..

VLD bullets are labelled, such as the Berger 210 VLD as opposed to the Berger 210 BTHP..

Easy to avoid VLD's if you don't want them

 

[MinorDamage]

Re: Correct O.A.L. or free bore question

VLD = Very low drag. Bullet makers like Berger, JLK, etc make VLDs. They have secant ogives which are generally more finicky about placement than the tangent ogives on many bullets like Sierras.

VLD Info (near bottom of page)

Josh

 

[Fuzzball]

Re: Correct O.A.L. or free bore question

"..a good "rule of thumb" as far as how far away from your lands to seat you bullet. I've heard people say anywhere from .005" to .050". That's a pretty big window to work with!!! I know every rifle/chamber is different, but I figured there is a good standard to work to."

You will hear a lot, most of those who make such statements have little experience; there is no reliable "rule of thumb". The seating window for sporting arms runs from maybe 5 thou into the lands to as much as 120 off, depending on the bullet and rifle itself. Most seem to do well in the range of 20 to 30 off but there are about as many exceptions, both ways, as not.

Start something like 10 off and develop your best charge. Then move in to the lands and out as far as needed to find what your rig needs. Use steps of 5 thou. Most rifles will have a seating window of 10 thou or more in which the jump makes no real difference. Load in the middle of that window and normal small seating variations won't matter.

 

[MinorDamage]

Re: Correct O.A.L. or free bore question

Fuzzball's experience has been the same as mine.

Josh

 

[acidone]

Re: Correct O.A.L. or free bore question

All of this sounds like very usable info )) Thanks!!!

As far as VDL's go, why would I or wouldn't I want to use them? They sound like something that would make sense for greater distances

I guess what it boils down to is if I were going to shoot a 1000 yard match would I stick with a great bullet like a Sierra BTHP or try a VLd style bullet instead???

Thanks for all the great responses

 

[MinorDamage]

Re: Correct O.A.L. or free bore question

Shoot what you can...

1. Afford
2. Shoots well in your rifle
3. You are comfortable with

Josh

 

[Immorteq]

Re: Correct O.A.L. or free bore question

The difference in load pressures between a round with freebore and a round with the bullet jammed into the lands can be dangerous. Be cautious.

 

[acidone]

Re: Correct O.A.L. or free bore question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Immorteq</div><div class="ubbcode-body">The difference in load pressures between a round with freebore and a round with the bullet jammed into the lands can be dangerous. Be cautious. </div></div>

I was aware of this but really appreciate the heads up!

 

[gcoulsey]

Re: Correct O.A.L. or free bore question

VLD's loaded near to/touching the lands, are very often too long to fit in magazines too..
Another deciding factor!!

 

[acidone]

Re: Correct O.A.L. or free bore question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gfunkUK</div><div class="ubbcode-body">VLD's loaded near to/touching the lands, are very often too long to fit in magazines too..
Another deciding factor!! </div></div>

That also makes a lot of sense!

Why is it so critical to have a VLD bullet seated at or in some cases past the lands of a bore? Midway's website makes it sound like the bullet won't work correctly if it's not touching the lands. What happens if i load a VDL back .020" from the lands???

Thanks

 

[MinorDamage]

Re: Correct O.A.L. or free bore question

Not exactly required to seat them into the lands. Straight from Berger...

VLD loading tips

Josh