OzFclass

No doubt been done to death already but .....?
Just about to lengthen the throat on a barrel from using 200.20X currently to 200 Hybrids
What is the general consensus of minimum bearing surface engagement within case neck?
And optimum?
Thanks in advance

Start just above the neck shoulder and just keep chasing it

With respect , that is not answering the question I asked?

I must admit I do it the other way round. I use a ptag FTR reamer that gives 308 freebore. Neck engagement is the result of whatever jump/jam i end up with.

I take it you want to know the ideal neck engagement in order to determine freebore?

Tbh Shane i don't think anyone has looked closely enough at the heavies to make that call, but it would be interesting to find out.

Tim L wrote:I must admit I do it the other way round. I use a ptag FTR reamer that gives 308 freebore. Neck engagement is the result of whatever jump/jam i end up with.

I take it you want to know the ideal neck engagement in order to determine freebore?

Tbh Shane i don't think anyone has looked closely enough at the heavies to make that call, but it would be interesting to find out.

The ideal minimum is 1 caliber.
Keith H.

KHGS wrote:

Tim L wrote:I must admit I do it the other way round. I use a ptag FTR reamer that gives 308 freebore. Neck engagement is the result of whatever jump/jam i end up with.

I take it you want to know the ideal neck engagement in order to determine freebore?

Tbh Shane i don't think anyone has looked closely enough at the heavies to make that call, but it would be interesting to find out.

The ideal minimum is 1 caliber.
Keith H.

Hmmmm, I'd be lucky to have 5mm

They shoot ok though

Just for interest sake, where does the 1 calibre come from.

1 Calibre is the old rule rule of thumb. The neck length on a 308 is barely more than one caliber long and even some of the heavier bullets only just have 1 cal bearing surface.

Something worth a read if you want to look at the extreme end. It can't be bad if its shooting in the .1s. http://bulletin.accurateshooter.com/201 ... benchrest/

I get close to that extreme shooting 155s from an FTR chamber. I'd have less than 2mm of bearing surface in the neck. Just enough to hold it. The shoot pretty damned good though.

Tim L wrote:

KHGS wrote:

Tim L wrote:I must admit I do it the other way round. I use a ptag FTR reamer that gives 308 freebore. Neck engagement is the result of whatever jump/jam i end up with.

I take it you want to know the ideal neck engagement in order to determine freebore?

Tbh Shane i don't think anyone has looked closely enough at the heavies to make that call, but it would be interesting to find out.

The ideal minimum is 1 caliber.
Keith H.

Hmmmm, I'd be lucky to have 5mm

They shoot ok though

Just for interest sake, where does the 1 calibre come from.

It just happens to be a long time industry standard, that said it is NOT an ideal world and at no time did I say that anything different would not work. A question was asked an answer was offered do with it as you will, I know many match rifle shooters that use less than your 5mm with success. In effect whatever works is fine, but that is not an answer!
Keith H.

KHGS wrote:

Tim L wrote:

KHGS wrote:
The ideal minimum is 1 caliber.
Keith H.

Hmmmm, I'd be lucky to have 5mm

They shoot ok though

Just for interest sake, where does the 1 calibre come from.

It just happens to be a long time industry standard, that said it is NOT an ideal world and at no time did I say that anything different would not work. A question was asked an answer was offered do with it as you will, I know many match rifle shooters that use less than your 5mm with success. In effect whatever works is fine, but that is not an answer!
Keith H.

I wasn't criticising you answer Keith, you have way more experience than I.
Neck engagement is not something I've ever considered, for me neck engagement is is simply what I end up with, not my starting point. I was wondering if it should be.
Maybe the actual answer for Shane is that there is no "science" suggesting a "correct" amount of engagement, just a rule of thumb which has no basis. Whatever works, is then the answer.

Tim L wrote:I get close to that extreme shooting 155s from an FTR chamber. I'd have less than 2mm of bearing surface in the neck. Just enough to hold it. The shoot pretty damned good though.

I’ve got a Archer barrel Keith did for me with a Bisley 150 chamber that has done a few rounds and with 155.5 touching the lands I’m about 3mm hold in the neck still shoots lights out

you actually don't need any neck engagement at all.
with a tool, you can seat a bullet into a specially prepared freebore, and then a case of powder behind that such that there is a gap between the bullet and the case neck.
adjusting this gap is another tool to tune for accuracy.
however this method is most inconvenient for target shooting, and impossible for hunting and military use.
that is, the function aspect of ammunition requires bullet to neck contact sufficient to keep a round of ammunition as a unit.
a benchgun might only need 1/10", while a military or dangerous game rifle a whole lot more.
the more the bullet contacts the interior of the barrel, and the less the case, the more effect the barrel will have on bullet alignment and vice versa.
bruce.

I think the 1 calibre 'industry standard' as a minimum is more related to military ammo which may have a rough life. Reloaded stuff, individually and lovingly packed, is a different situation. Military Ammo used in a machine gun has to stay together after severe slamming.

When attempts were made to increase the rate of fire of quick firing naval and very large AA guns, one limitation to using fixed ammunition was holding the projectile in the case. Crimping was eventually insufficient and some were even threaded in for trials.

In our game, I think it is more determined by a potential donut than anything else.

Can't answer what the MINIMUM required is but with 210SMKs and 215hybrids I've found 3mm to be ENOUGH. That provides enough case capacity to keep them supersonic out to 1200 so I don't see any need to seat them further out.