30br throat erosion

[NC/Br Shooter]

In a 30br kreiger bbl, wirh a Robinett chamber shooting relatively hot loads, how many rounds would this barrel have on it if the lands have eroded 30 thousandth s?
About?

 

[Bill Norris]

In a 30br kreiger bbl, wirh a Robinett chamber shooting relatively hot loads, how many rounds would this barrel have on it if the lands have eroded 30 thousandth s?
About?

Kind of hard to tell about the 30BR as those barrels last much longer than the run of the mill calibers do. One of the frontier shooters of it said his had 7400 rds. on it when he stopped shooting it and was using the same brass as well. No mention of land movement.

 

[Kevin1990]

Can't help with your exact numbers, and probably not very scientific, but I used the wheeler method to measure mine after fire forming my brass. With my krieger barrel at 1300 rounds my touch point was .003 longer than when I started. I imagine it's starting to slow down now.

My accuracy dropped off some so I readjusted to .003 longer (that's why I measured in the first place.) and it's back to shooting small. I'm going to measure again at 2000 rounds just to see.

 

[DShortt]

Some 30BR chambers that are throated for 1' Bullet jackets or longer for cast bullets are cut for that length.
I'd like to see a Pic of the chamber.

Bullet Weights and Profiles by Al Nyhus
30BRs work best with bullets not exceeding 125 grains. Jacket lengths should be either .925" for the 110-112gr bullets or 1.00" for the 118-125s. Ogives can be either 7 or 10 tangent ogives, but be aware that the shorter .925" jackets require virtually no freebore length. The 'zero freebore' chambers can also be used with 1.00" bullets. I currently use a .030" freebore with the 1.00"-jacketed bullets and this works fine.
.....If it was cut at Zero Freebore than it has been shot 15,275 times.

I'm familiar with secant vs tangent gives, but I've never seen a 'number' used in the description before.

Could you point me in the right direction so that I can educate myself?

Thanks in advance.

 

[Kevin1990]

Some 30BR chambers that are throated for 1' Bullet jackets or longer for cast bullets are cut for that length.
I'd like to see a Pic of the chamber.

Bullet Weights and Profiles by Al Nyhus
30BRs work best with bullets not exceeding 125 grains. Jacket lengths should be either .925" for the 110-112gr bullets or 1.00" for the 118-125s. Ogives can be either 7 or 10 tangent ogives, but be aware that the shorter .925" jackets require virtually no freebore length. The 'zero freebore' chambers can also be used with 1.00" bullets. I currently use a .030" freebore with the 1.00"-jacketed bullets and this works fine.
.....If it was cut at Zero Freebore than it has been shot 15,275 times.

How did you come up with that number?

 

[gunsandgunsmithing]

 

[NC/Br Shooter]

Some 30BR chambers that are throated for 1' Bullet jackets or longer for cast bullets are cut for that length.
I'd like to see a Pic of the chamber.

Bullet Weights and Profiles by Al Nyhus
30BRs work best with bullets not exceeding 125 grains. Jacket lengths should be either .925" for the 110-112gr bullets or 1.00" for the 118-125s. Ogives can be either 7 or 10 tangent ogives, but be aware that the shorter .925" jackets require virtually no freebore length. The 'zero freebore' chambers can also be used with 1.00" bullets. I currently use a .030" freebore with the 1.00"-jacketed bullets and this works fine.
.....If it was cut at Zero Freebore than it has been shot 15,275 times.

Robenett chamber is 0 freebore. Least the two I got are.

 

[mgunderson]

How hard are you pushing your 30 br? Are you outside the norms?

 

[BoydAllen]

I'm familiar with secant vs tangent gives, but I've never seen a 'number' used in the description before.

Could you point me in the right direction so that I can educate myself?

Thanks in advance.

The numbers are the radius of the ogive curve expressed in bullet diameters. For example the ogive radius of an 8 ogive .30 caliber bullet would be 8 times .308. For a .22 caliber it would be 8 times .224, the same shape just scaled down in overall size.

 

[WSnyder]

Could you point me in the right direction so that I can educate myself?

To add to Boyd’s info. If you go to most custom bullet makers websites and look at the individual bullets they will usually have descriptors such as “10 ogive” or “7 ogive” or even something like “double radius 7/9 ogive” which as the description says, it has a double radius design. As Boyd stated those numbers are the radius in calibers. A 10 is going to be pointier than a 7 and may be pickier to get to shoot. A 10 in the same or similar weight and caliber will have less bearing surface than a 7.

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[AlNyhus]

To distill it down a bit...using the T.P. (Touch Point) of the bullet to rifling method....identical weight 7 and 10 ogive bullets (on the same length jackets) a 7 ogive will have more shank length in the case neck than a 10 ogive.

In the case of the .30's, a 7 ogive .925" and a 10 ogive 1.00" will end up with the base of the bullet within about .015"-.020" of each other...assuming the same seating depth.

Just a broad overview, fwiw.

Good shootin' -Al

 

[DShortt]

Thanks to all. I appreciate it!

 

[JEFFPPC]

I very smart shooter and gunsmith once told me accuracy comes from the front 10 inches of the barrel, not the rear. I have come to realize he is correct.