What does "throated for 210 Bergers" mean exactly?

[Centuriator]

If a 300WM rifle is "throated for 210 Bergers" does this mean it can not use "regular" 300 WM ammo?

Thanks for letting me put this stupid question here in the stupid question section of the forum.

 

[Supersubes]

Forward of a rifles chamber(where the case ends) is a cylindrical section that is cut very slightly greater than the bullet diameter. This area is called freebore. Since bullets vary greatly in the lengths of their bearing surfaces, the freebore length can be adjusted to accomodate certain bullets. Freebore is usually ground into the chamber reamer and is fixed. Some gunsmiths adjust freebore in a seperate operation using a throating reamer. There is a lot of overlap, but imagine that you have a long freebore cut in your 300 winmag to accomodate the 240 gr sierra bullet. Then you try and shoot a 180. It will probably work, but you'll be forced to load way off the lands(short bullet, short neck of the 300wm). Conversely, if your rifle has a short throat, for 180's, and you want to run the 240, you'll have to seat it deep in the case. The winmag in particular has a rather short neck, making freebore specs a little more important. Sometimes there are magazine length requirements, where freebore would be adjusted so your range of usable seating depths with your chosen bullets produce a cartridge that will actually fit in your magazine. There are some other dimensions that come into play, but freebore is the meat an potatoes of it.

 

[Sheldon N]

Throat or "freebore" is the section of the chamber starting after the end of the brass case and ending where the rifling starts. It's basically a hollow tube with no rifling that the bullet can slide through.

A bullet can only protrude out of the case up until it jams into the rifling.

A longer throat/freebore allows a bullet to be seated farther out of the case, freeing up room inside the case for more powder and allowing the bullet to sit in the proper spot in the neck (bullet bearing surface above the neck/shoulder junction).

A short throat/freebore combined with long bullet requires that the bullet be seated deep into the case.

A long throat/freebore combined with a short bullet means that the bullet can't reach out and touch the lands... it will fall out of the neck before it reaches them. That means it needs to "jump" to the lands when being fired.

Some bullets shoot best when close to the lands, so people have their chamber cut so that the throat matches their desired bullet. However, there's nothing wrong with a large jump to the lands in many situations. I've had bullets shoot excellent with big jumps.

So a 300WM "throated for 210 Bergers" will have a longish freebore, Longer bullets like the 230 Berger might be pushed farther into the case than ideal, and shorter bullets will have to jump to reach the lands.

Hopes this helps!

 

[Edds]

Someone has cut the throat length to what they think is the perfect length to use a specific bullet. In this case a 210 gr Berger. But, there is more than one 210 gr Berger and the bearing surface length varies by about .100". Plus, someone else might think a different length throat is the perfect length. So, It means "exactly" nothing unless you have a number to go with it.

 

[Threadcutter308]

Agreed with all of the above. The statement "throated for 210 Bergers" only tells half the story. The other information that is very relevant is;

What depth is the bullet seated to ? (how much of the base of the bullet is in the case neck, calipers helpful)
Loaded cartridge OAL ? (Bullet tip to case head, requires calipers)
Cartridge OAL, Ogive to case head ? (requires an OAL gauge and calipers)

I go by OAL, Ogive to case head, because I load my rounds to be consistently some distance "off the lands", which is typical for bolt guns.

 

[Centuriator]

Some guy is selling his 300 WM rifle and one of the features he lists is "throated for 210 Bergers" ... that's why I asked.

 

[SubOptimal]

The statement is more or less meaningless unless the rifle is unfired. Each shot fired is going to erode the throat slightly and thus change the distance. Throated for 210 Bergers on a barrel with 3000 rounds through it would be a joke.