Freebore ,throat and leade

[muleman69]

Can anyone explain to me what each of these do and where they are in relation to a chamber? If one extends his freebore does he need to lengthen leade? Bit confused with a lot of this and would like to no as I read a lot on this forum about the throat,leades etc.

 

[243winxb]

Freebore -right in front of the chamber. Same diameter as the barrel groove, plus a hair larger. Allows the bullet to chamber , with out hitting anything. When longer, it reduces pressure.

Throat is the funnel part. Guides bullet to the leade.

Leade- is the angle cut on the lands/grooves. Allows the bullet to engauge the lands with less damage. A swaging effect.


But i may be all wrong. Not a gun smith.

 

[tobnpr]

Throat in the diagram above is another term for leade.
"Throating" is a term used to lengthen freebore for heavier (longer) bullets by reaming the leade further up the barrel to get the desired additional length before the bullet engages the rifling.

 

[muleman69]

Throat in the diagram above is another term for leade.
"Throating" is a term used to lengthen freebore for heavier (longer) bullets by reaming the leade further up the barrel to get the desired additional length before the bullet engages the rifling.

So basically throat leade and freeborn are much the same?

 

[DaveTooley]

No
Picture a funnel with straight sides then a taper.
The straight sides are the freebore. Usually a fixed diameter.

Example 6.5 Creedmoor. Bullet diameter is .2640".
The freebore diameter is .2645"
In describing the throat area to a reamer maker the next number would be the length of the freebore section. For the CM it's .1992"
Then the leade angle which is 1'30"

So to summarize the throat would be
.2645" X .1992" X 1'30"

 

[muleman69]

No
Picture a funnel with straight sides then a taper.
The straight sides are the freebore. Usually a fixed diameter.

Example 6.5 Creedmoor. Bullet diameter is .2640".
The freebore diameter is .2645"
In describing the throat area to a reamer maker the next number would be the length of the freebore section. For the CM it's .1992"
Then the leade angle which is 1'30"

So to summarize the throat would be
.2645" X .1992" X 1'30"

Thanks ,Think I'm getting it figured out. So how much freebore diameter over bullet diameter should there be in a hunting rifle? Does leade angle change with different calibers?

 

[DaveTooley]

I hate to say this but it depends on caliber, use and the end user. I have some unusual customers so I engineer things so as not to violate rule #1. That rule is don't do anything to make the phone ring, get anyone injured or killed. 100% reliable function is paramount.
I like .0007"-.0012" clearance. The bigger the cartridge and the less sophisticated the customer the larger the diameter to allow for carbon build up. Also not all bullets are "on size". Some are a bit fat.
Leade angles, as spec'd in https://saami.org/ do change from cartridge to cartridge. Most smiths have settled on 1'30" for custom made reamers. Steeper angles can sometimes lead to accuracy issues.

There's a wealth of information on the SAAMI website

 

[dmoran]

 

[muleman69]

View attachment 1133129

Good info ,thanks

 

[rammac]

Freebore and throat are NOT the same thing, they are lumped together by some people because they aren't aware that some chambers actually a have tapered section forward of the freebore (and before the lead) and that tapered section is the throat. The throat's purpose is to help center the bullet to the bore and if your chamber has a throat then you'll find that it probably has a very small taper of 1.5 degrees or so. If your chamber hasn't got a throat it's probably because skipping that tiny taper saves money on cutting the reamer and the lead (the tapered entry to the lands) is thought to do the same job as the throat.

 

[Link]

View attachment 1133180

Is the angle of the lead in the print misleading? The taper of the red line looks backwards to me.

TY Don

 

[tobnpr]

Is the angle of the lead in the print misleading? The taper of the red line looks backwards to me.

How so? You're going from no rifling where the freebore ends, ramping to full rifling at the end of the leade.

 

[Will Henry]

I have always just considered throat length the be the length from the front of the neck to the top of the lands. In other words, freebore plus leade. This may be right or it may be wrong but it's my way; so there! WH

 

[gunsandgunsmithing]

For simplicity...
Lead=tapered section
Freebore=straight section behind lead
throat=both combined, i.e...a throating reamer cuts both at the same time. The lead is set but the freebore is dependent upon how far you run the throater in.

 

[M14AMU]

On my target barrels from Boots Obermeyer I had the leade cut to 1 1/2 degree. Worked quite well for me shooting NRA HP Long Range Matches like Palma!