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#6434476 - 09/01/16 11:46 AM Dumb questions (maybe) - seating depth
Korean Redneck Offline


Registered: 06/24/09
Posts: 2274
Loc: Houston
Maybe obvious to some but I'm not too certain.

So I do the thing where I try to seat my bullets about 0.005" before the lands. I use the Hornady bullet comparator to measure the seating depth. Questions:

1. Is this measurement good for all bullets, meaning it can use this same value even if I go to a heavier or different type of bullet than than one I used to take the initial measurement?

2. I'm using an rcbs precison seating die. Do I have to reset the die if I change bullets? I'm mostly trying to go to a heavier one.


Edited by Korean Redneck (09/01/16 11:51 AM)

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#6434493 - 09/01/16 11:59 AM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Big Fitz Offline
Veteran Tracker

Registered: 12/06/09
Posts: 2001
Loc: McKinney, TX
My understanding is different bullet/rifle combinations can vary quite a bit in optimum seating depth. I'm playing around quite a but with my 6.5 Creed with Berger 130 hybrids and do see quite a difference. I think adjusting in .003 increments is the norm and mine showed a definite preference between .006 and .009. The .003 opened up a bit in 5 shot groups as did .012, .015 and .018.

You will most likely have to adjust your seating die for different bullets.

I'm sure the experts will chime in but think I'm directionaly correct.
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#6434583 - 09/01/16 01:33 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
DStroud Offline
Pro Tracker

Registered: 11/02/11
Posts: 1154
Loc: Waco
Yes changing bullet brand or weight will require checking each for relationship to lands.
And yes will require resetting of the seater die to adjust for differences.

In fact if you really want to get down to fine detail changing from one lot# of the same brand style and weight can be slightly different in the ojive area and can change distance from Lands

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#6437862 - 09/04/16 10:30 AM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Korean Redneck Offline


Registered: 06/24/09
Posts: 2274
Loc: Houston
But I thought the bullet comparator measures that the ogive location. The ogive is the the forward most point on the bullet where it's the full diameter, is that incorrect?
If so then how does that change from bullet to bullet versus the lands?

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#6437872 - 09/04/16 10:38 AM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
colt45 Offline
THF Trophy Hunter

Registered: 08/19/06
Posts: 5379
Loc: bastrop county
when I change bullets I use a marking pen to check..
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#6437952 - 09/04/16 12:18 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Big Fitz Offline
Veteran Tracker

Registered: 12/06/09
Posts: 2001
Loc: McKinney, TX
Originally Posted By: Korean Redneck
But I thought the bullet comparator measures that the ogive location. The ogive is the the forward most point on the bullet where it's the full diameter, is that incorrect?
If so then how does that change from bullet to bullet versus the lands?


I believe this is correct, however, the seating die likely does not index off the ogive and will need to be adjusted anytime you select a different bullet. I'm using Forrester with micrometer bullet seating die and I check with the bullet comparator each time I set up to ensure it is meeting my notes.
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Originally Posted By: syncerus
I prefer to think of myself as a control enthusiast. wink

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#6438005 - 09/04/16 01:25 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Williams8137 Offline
Green Horn

Registered: 09/02/16
Posts: 2
Generally when ballistic coefficient changes the angle from ogive to tip will change as well. Even when using the same bullet of different weights. This is a by product of the overall length of the bullet. (Google secant and tangent ogive for an example). As you know the ballistic coefficient can be found on the product box. For example the Barnes 7mm 168 grain TTSX has a BC of .550. The same bulletin 150 grain TTSX has a BC of .450. This creates difference is in the angle of the bullet and your seating die will make contact in a different location on each bullet changing your seating depth. It's best to use your comparator for each different bullet that you seat. Personally I measure every case after trimming and every C.O.L. as well. Just funny that way.

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#6438017 - 09/04/16 01:40 PM Re: Dumb questions (maybe) - seating depth [Re: Big Fitz]
DRD11 Offline
Green Horn

Registered: 09/05/13
Posts: 7
It's not a dumb question and be very careful seating bullets that close to the lands .005 jump as pressures will change. Start below max and work up. However, most do that - get at or close to the lands - to get better accuracy.

Yes the comparator measures off the ogive but I agree with the above and would also read the link below and be ready to change setups as bullets change. Also take multiple readings with the comparator as just a bit too much pressure can change the readings.

If you like the Hornady tools, you can send a couple of fired cartridges from your rifle and send them to Hornady and they will tap and drill that case so you have an exact match to the chamber of that rifle. Then when you change bullets you can use their other tool (can't remember the name but allows you to slide a bullet into the cartridge) to get a starting point for your dies as it will tell you where the lands are. Its the one that goes with the comparator. Sinclair makes some good tools as well. They are not perfect but
will speed up the process. You can also smoke the bullet or use a market to verify as mentioned to confirm. Hope that helps.

http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/

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#6438464 - 09/04/16 08:23 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
FiremanJG Offline
THF Celebrity

Registered: 12/16/08
Posts: 17893
Loc: Wolfe City, TX
Originally Posted By: Korean Redneck
But I thought the bullet comparator measures that the ogive location. The ogive is the the forward most point on the bullet where it's the full diameter, is that incorrect?

Negative. The ogive is the part that goes from bearing surface (full diameter of the bullet) to the meplate (forward most point of the bullet. Measuring on the ogive is measuring from case head to somewhere on the ogive. But the bearing surface is what is actually engaging the lands. All ogives are not the same.

If so then how does that change from bullet to bullet versus the lands?


Look at a Berger VLD with its' fairly straight line ogive, as compared to an A-Max with its' outward curved ogive. That's the difference in secant versus tangent ogive. When changing bullets recheck the relationship to the lands.
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#6438493 - 09/04/16 08:49 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Buzzsaw Offline
THF Trophy Hunter

Registered: 06/29/11
Posts: 5023
Loc: Frisco, Texas
I keep a log of each bullet brand, style and weight in each rifle measured to touch the lands.

Watch on U tube how to use a dowel rod inserted from the muzzle to contact bullet tip and work back n forth, this gives a really good feel for the bullet touching the lands.
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#6439558 - 09/05/16 08:05 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Korean Redneck Offline


Registered: 06/24/09
Posts: 2274
Loc: Houston
Ok good info. I lost some data and figured it was good time to change from the ubiquitous 168 bthp to the 178 a max for my 308. Thought I could short cut some.

Ugh this reloading thing is kind of a pain in the [censored]!

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#6439601 - 09/05/16 08:30 PM Re: Dumb questions (maybe) - seating depth [Re: Korean Redneck]
Buzzsaw Offline
THF Trophy Hunter

Registered: 06/29/11
Posts: 5023
Loc: Frisco, Texas
it seems that way sometimes but if you shoot allot you need too

KR, don't make it too difficult, get 1 great load, stock up on those components and run with it.

Most of our rifles aren't really accurate enough to tell the minute differences

Let Chad worry about all that mental stuff
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