Cobt vs. Sierra coal's

[Bc'z]

ok Bc, im ok now,,,,i did exactly what you said to do. i am good coal is 2.47 .01 off the lands. what was driving me nuts was the 3.34 in the manual. i still have to check the magazine. i see what you mean about the seating depth, plenty of room for that,,,,and THANK YOU.....

Glad I was able to help

 

[Dan wilson]

ok Bc, im ok now,,,,i did exactly what you said to do. i am good coal is 2.47 .01 off the lands. what was driving me nuts was the 3.34 in the manual. i still have to check the magazine.

No, it says you are paying attention and until you gain experience that will allow you to learn faster and keep your eyes and fingers where they still work too....

All three of the popular 30 cals have some potential for bullet seating depth tuning with the Sierra 165 GK. It is very similar to the 168 MK. It works well in 308, 30-06, and 300 mags. (And for the money, does a very good job on accuracy and terminal ballistics too. So it makes a good baseline hunting bullet choice.)

That particular bullet is very forgiving in most chambers and tolerates everything from hard jam to big jumps. That is not to say that there is nothing to be gained from learning to tune with seating depth, but that takes some experience as well.

A quick anecdote to explain what a good starting point would be if I knew nothing about the chamber... Suppose I was going to ask a gunsmith to make a custom hunting rig. He would attempt to chamber for a light touch to 0.005” jump for a dummy round that I would hand him. So, where would I then place that particular hunting bullet for a starting point?

I would observe the COAL when the junction of the bullet bearing diameter hits the boat tail, and line that up slightly (~0.010) above the neck to shoulder junction of the case to avoid seating into a potential donut later on. Of course, this just gets me a sturdy bullet seat. I also already know enough about that particular bullet at that kind of length to know it will feed from a magazine.

Could I have selected a longer length, yes. Could I seat deeper, yes but then I risk a donut issue and rob myself of case volume too. Going a little farther out allows me some room if I find the tuning like a little more jump so I can then seat a little deeper without hitting that donut again.

I’m guessing you get the picture by now. Here is some nightstand reading on depth tuning.
https://precisionrifleblog.com/2020/03/21/bullet-jump-and-seating-depth-reloading-best-practices/
That is one article that leads to several. Reading those is food for thought and comes for free, so I would soak it up while you practice cause eventually you will want to learn to run a sweep for powder charge and one for seating depth.

Hey rat, I took your advice and read the link you posted . Very good read...I managed to get it thru my thick head what Bc' was trying to explain. Thanks for your kind understanding. Here at the waning portions of my life I would like my shooting skills to be where they never have been. This new rifle is my Best and Last shooting project. So getting it right is a priority. Take care and be safe

 

[Bill Norris]

ok Bc, im ok now,,,,i did exactly what you said to do. i am good coal is 2.47 .01 off the lands. what was driving me nuts was the 3.34 in the manual. i still have to check the magazine. i see what you mean about the seating depth, plenty of room for that,,,,and THANK YOU.....

FWIW, the 3.34 listed in the load manual is just a number for that particular bullet. Once another bullet comes into play that number is out the window. I find it better to pay that part of the info no mind because most likely it would be no good to me.

 

[shoot4fun]

ok Bc, im ok now,,,,i did exactly what you said to do. i am good coal is 2.47 .01 off the lands. what was driving me nuts was the 3.34 in the manual. i still have to check the magazine. i see what you mean about the seating depth, plenty of room for that,,,,and THANK YOU.....

Now I feel confused. while the basis behind what @Bc'z is sound I still do not see where you are getting the 2.47 .01 off the lands. You do realize that the 300 Win Mag brass alone is longer than that number? SAAMI says a 300 WM case should be 2.620" in length WITHOUT a bullet seated.

 

[Bc'z]

Now I feel confused. while the basis behind what @Bc'z is sound I still do not see where you are getting the 2.47 .01 off the lands. You do realize that the 300 Win Mag brass alone is longer than that number? SAAMI says a 300 WM case should be 2.620" in length WITHOUT a bullet seated.

I'm thinking he did not zero calipers with comparator installed????
SWAG

 

[shoot4fun]

I'm thinking he did not zero calipers with comparator installed????
SWAG

‍Getting wrapped around the axle on COAL is not worth the trouble. Though Sierra does provide different COAL for different bullets in 300WM the Nosler data shows that 3.340" COAL for every bullet regardless of weight or shape.
Wouldn't not zeroing the calipers with the comparator installed give a longer than actual reading?
It is late here in the old Dixieland and maybe the OP's line of thinking is getting to me too?

 

[Dan wilson]

‍Getting wrapped around the axle on COAL is not worth the trouble. Though Sierra does provide different COAL for different bullets in 300WM the Nosler data shows that 3.340" COAL for every bullet regardless of weight or shape.
Wouldn't not zeroing the calipers with the comparator installed give a longer than actual reading?
It is late here in the old Dixieland and maybe the OP's line of thinking is getting to me too?

I'm so so not sorry for asking a question and upsetting your colon

 

[shoot4fun]

I'm so so not sorry for asking a question and upsetting your colon

You didn't.
Here is the thing. When you come to a forum, especially a reloading forum, and start a thread needing help it is most important that those who try to help are informed enough to make reasonable (more importantly SAFE) suggestions toward getting you to the correct place.
My actual versus printed COAL for 300 WM is much different. A difference of .125" is actually quite a lot but it works and works well.
Many of the other contributors to the thread gave excellent examples and explanations yet you just seemed more and more confused. Even when you "got it" your reply didn't contain information that actually showed you did have a grasp on it.
Sometimes, after 45 years of reloading, I learn new things. I did here, even if it was only that I should have just left you alone.

 

[Chubbs]

I'm thinking he did not zero calipers with comparator installed????
SWAG

The other way around I think. He measured CBTO with comparator fitted and then removed it without re zeroing. This 2.47" is his erroneous COAL not the CBTO. I.e his comparator is likely the missing inch. But then I could be confused too.

 

[Bc'z]

The other way around I think. He measured CBTO with comparator fitted and then removed it without re zeroing. This 2.47" is his erroneous COAL not the CBTO. I.e his comparator is likely the missing inch. But then I could be confused too.

I believe your correct, it came to me about 1 in the morning after rereading this post.

 

[RegionRat]

The 2.47” isn’t a value that rings any bells. The trim length of a 300 Win mag case is longer than that, so it can’t be a bullet measurement of any sort. The case alone is 67 mm or 2.620”.

 

[shoot4fun]

Be careful @RegionRat , @Bc'z and @Chubbs!
He may be happy he has "upset your colon" too.
Whatever he means by that.

 

[Chubbs]

The 2.47” isn’t a value that rings any bells. The trim length of a 300 Win mag case is longer than that, so it can’t be a bullet measurement of any sort. The case alone is 67 mm or 2.620”.

View attachment 1244474

It does if you add the 1" or so of the comparator.
I.E. He puts on comparator to calipers and zeros.
He measures his CBTO and the removes comparator.
He forgets to re zero and then measures COAL.
But is missing an inch off COAL due to not re zeroing.
He has his CBTO and COAL mixed up again.

 

[Bc'z]

Be careful @RegionRat , @Bc'z and @Chubbs!
He may be happy he has "upset your colon" too.
Whatever he means by that.

I'm getting read to release the preasure on my colon now and order some 6.5-284 brass.
Multi tasking!

 

[Ned Ludd]

Perhaps a picture is in order:

 

[Albany Mountain]

Dan, if you are shooting out of the magazine and the OVERALL length of the assembled cartridge (as suggested by Sierra) is too long to go into the magazine, shorten the rounds to give clearance for the magazine. You do not want to risk feeding failures by long shells in the field.

 

[divingin]

my question is how does one interpolate the reading from the guage along with the reading from the comparator to get the precision you have set forth.

I'm going to throw another wrench in the mix:

Think about the word "comparator". It's not called a gauge for a reason. It does not "measure" anything, rather is designed to allow you to compare a specific dimension between different samples without an absolute measurement. Sort of like a ruler vs a length of string: You put a ruler up to two things, and you can decisively say one is this length, the other is that length, while a piece of string will only tell you that one is longer.

To compare your different cartridges, you look at one dimension and how you measure it and bounce that against the other cartridge:

COAL (cartridge overall length) is easy; close your calipers, zero them, and then put the cartridge between the jaws and close them. That is a definitive measurement.

CBTO (case base to ogive, i.e. the measurement from the case head to a point very close to the diameter of bullet that will engage the rifling) is measured using a comparator: Open the caliper jaws, put the comparator on, close and zero the calipers, and insert the bullet nose into the comparator and take a reading. This is not a definitive measurement (primarily because the diameter of the hole in the comparator is a) an unknown, and b) generally has a chamfer to avoid marring the bullet.) You use this tool and measurement to compare between different cases assuming you used the same tool to take the measurements.

Note that with a different insert, the comparator can also be used to measure Case Base to Datum (with "datum" meaning an "agreed-upon point to reference where the shoulder is" - generally, but not necessarily, halfway down the slope of the shoulder.) The same cautions apply as it is a comparative measurement as well.

Bottom line: You shouldn't look at comparator measurements and actual physical measurements and try and correlate the two. Work with one or the other.