seating to the lands.

[TnTom]

When I hear reference to seating a bullet to the lands is the practice literal? If I drop a bullet into the chamber and hold it in place what is the bullet in contact with? The lands and grooves or could it be contacting the beginning of the free bore.

Next question. Is free bore the beginning of the bore minus any land/grooves with the diameter equal to the groove diameter? Would a bullet be able to enter the freebore and actually reach the lands/grooves without resistance?

Can a bullet be forced with minimal effort to actually contact the lands/grooves passing through the freebore and is that when a bullet has no jump or should a bullet become snug up against the freebore and would that be no jump?

I've read about seating bullets with negitive jump. Does that mean the bullet has been engraved by the lands?

The concern I have is if I'm moving back from the lands or the beginning of the freebore or am I on the wrong track.

Is there an illustration some where someone can point me to that illustrates a chamber and cartridge (.223 Rem ideally).

 

[6BRLongRange]

It is a literal term. The bullet is actually touching the rifles of the barrell. The freebore will be essentially the same diameter as the neck.

 

[TnTom]

I've approached my reloads with that being the case and adjust the jump to be a distance from the point of contact. For my current rifle its about .008" - .010".

If the freebore (freebore-throat are the same?) were longer then the bullet could be set out more, the rifling is further from the bolt face?

Can a bullet, without using excesssive force create a negative jump condition. Would the bullet show engraving of the rifling? Would this condition cause very hard bolt closing and why wouldn't the bullet be forced back deeper into the case creating a loaded to the rifling condition.

Ive heard of negative jump. How does this occur? Doesn't seem possible. Thanks for shedding light on this.

 

[6BRLongRange]

You are correct , shorter freebore means the OAL would be closer to the boltface. It isnt uncommon to load long and let the rifles uniformly seat the bullets back in to the case for consistent touching or 'kissing' the lands.

You need to use light neck tension to do this without having the hard bolt closing you were talking about. If you use high neck tension you could seat the rounds .030 or so long and this would result in heavy engraving of the bullets by the rifles.

Hope this helps. ;D

 

[TnTom]

You are correct , shorter freebore means the OAL would be closer to the boltface. It isnt uncommon to load long and let the rifles uniformly seat the bullets back in to the case for consistent touching or 'kissing' the lands.

You need to use light neck tension to do this without having the hard bolt closing you were talking about. If you use high neck tension you could seat the rounds .030 or so long and this would result in heavy engraving of the bullets by the rifles.

Hope this helps. ;D

That helps a lot and thanks.

 

[6BRLongRange]

Not a problem, glad to share.

 

[rg1]

Here's a chart with dimensions of .223 Rem showing different chamber reamers:
http://www.ar15barrels.com/data/223-556.pdf
http://www.zediker.com/articles/AR_chambers.pdf
These articles deal mostly with AR-15 rifles but some good info.

 

[Ackman]

The freebore will be essentially the same diameter as the neck.

No. Freebore is usually 1/2thou larger than bullet diameter.

 

[6BRLongRange]

Ie:essentially, Thanks

 

[BoydAllen]

When we are discussing an are where specifications are commonly given to four decimal places, saying that freebore is "essentially" the same diameter as the case neck is like saying that 10 inches is essentially a foot. For example, a factory .222 may have a neck diameter of .255 but the freebore diameter would be a few tenthousandths over .224. I usually find that my varmint rifles shoot their best groups with the bullets seated .006 to .010 longer than they would be if they were just touching the rifling. I find that the tool that Sinclair sells that uses an action adapter, rod , and two stop collars, in conjunction with a bullet and fired case, serves well to establish where "touch" is. I don't have difficulty closing bolts, and I work up loads with new powders at these seating depths, starting low, and watching for signs of pressure. In my experience, with a good rifle, there is more to gain by fooling with seating depth than small adjustments of powder charge. This is one area where the advanced rifle tuner sets himself apart from the crowd. Try it; you might have more accurate rifles than you realize.

 

[jsteiger]

BoydAllen, any experience in .308? If so what have been your most successful seating depths?