Chamber question

[rcs9250]

I have a couple rifles chambered in 6.5CM. I recently purchased the Hornady chamber length gauge to see how much free ore they had so that I could experiment with OAL so as to minimize jump. Note: they are al factory built rifles with OEM chambers.
If I were to try and load rounds with minimal jump, the bullet would just barely be into the case mouth. Being I saw it on all my rifles it appears it’s done as a safety to make sure all factory loaded ammo chambers safely so as to prevent over pressure accidents. Sound about right ?
For a rifle to have a chamber that allows minimal jump,are they typically custom reamed chambers ?
With thes rifles, it pretty much appears that the chamber gauge was a waste of money.
Randy

 

[Someoldguy]

How do they shoot? Who cares if they are into the lands or jumping .120" if they shoot?

 

[rcs9250]

I’ll wait for an answer to the question.

 

[gunsandgunsmithing]

Not all factory rifles have very long freebores. Tikka for example and Savage another. They aren't as short as you can do custom but still. That may or may not answer your question.

 

[Drop Port]

What bullet and weight were you measuring with?

 

[strut64]

Can't answer your question(s). I will relate an experience I am dealing with. I have 2 savage 223 Rem barrels. When I measure the difference in Base to Ogive There is a difference of 0.140" between them. Both are 9 twist. The one that is a sporter weight is very long. While the other is a varmint weight and very short. When the bulet seating depth is set up to suit each barrel each shoots OK.

 

[Someoldguy]

Without a chamber cast or bore scope, it will be difficult at best to know precisely what the freebore length is.
If you are not satisfied with the accuracy you are seeing from your rifles, freebore length alone does not make a rifle shoot well or poorly. This is why I asked how they shoot. Freebore diameter, non-concentric freebore/leade and/or excessive chamber diameter and barrel condition are factors in accuracy and much more likely to cause trouble.

 

[Dusty Stevens]

Bullets can shoot real good jumped. Id put them halfway in the case then find a spot within .015 either way. Youll find one just as good as touch.

 

[243winxb]

it’s done as a safety to make sure all factory loaded ammo chambers

The longest heaviest factory ammo must have room to chamber, without contacting the rifling.

For a rifle to have a chamber that allows minimal jump,are they typically custom reamed chambers ?

Yes, for the most part. First pick the longest bullet that will be used. Then match the rifling twist to the bullet.

I did see a Savage in 6.5 creedmoor that would not chamber a factory round. It was returned to Savage for adjustment.

 

[Boisblancboy]

For a rifle to have a chamber that allows minimal jump,are they typically custom reamed chambers ?
With thes rifles, it pretty much appears that the chamber gauge was a waste of money.
Randy

Definitely not a waste of money for factory “sammi spec” or custom chambers. You want to be able to know exactly where your lands are to accurately set your seating depth. Whether that be a large just or a slight jam.

 

[338 Mollett]

You are experiencing the same thing I went through.I borrowed a friends reamer for a barrel only to find out the bad news.I had to order a reamer ground to my specs to get a minimal jump while staying at mag length.

 

[Bart B.]

When "freebore" is mentioned, what does it refer to?

* distance from chamber mouth to where the lands start tapering down to bore diameter.

or

* distance bullet moves from its place in the case neck to where its ogive first touches the lands.

 

[Someoldguy]

When "freebore" is mentioned, what does it refer to?

* distance from chamber mouth to where the lands start tapering down to bore diameter.

or

* distance bullet moves from its place in the case neck to where its ogive first touches the lands.

A picture is worth a thousand words.

 

[gunsandgunsmithing]

When "freebore" is mentioned, what does it refer to?

* distance from chamber mouth to where the lands start tapering down to bore diameter.

or

* distance bullet moves from its place in the case neck to where its ogive first touches the lands.

Yes, the pic above shows it pretty well but freebore is the untapered area between the end of the chamber neck and where the tapered leade area of the throat begins and is nominally of bullet diameter...give or take a few tenths.

 

[Bart B.]

A picture is worth a thousand words.

View attachment 1086537

SAAMI spec'd 308 Win throats are .1637" long starting .27" forward of the chamber mouth, the .310" diameter freebore length. Then tapers down to bore diameter.

.310" allows the spec'd bullet diameters .306" to .309" to fit the freebore without interference.