Settle this for me! Friendly Debate

[Crowe284]

So a friend and I were having a conversation today about distance from base to ogive measurements. He proposed that the ogive is what contacts the lands first and that when you are using a 175 berger elite, or a 180 vld or even a 195 EOL that when you find the lands with any of these bullets that the measurement that you get (base to ogive) will be the same with any of the other bullets and that the only thing that will change that none of us probably never use is OAL from base to tip of bullet for the longer bullets as you go up in weight. What say you to this statement? Now, this is assuming that you are using your calipers with your comparator installed for that particular caliber, i.e., all measurements are using same measuring components.

SETTLE THIS FOR ME!

 

[Trnelson]

Depends on the reference method utilized to seat the bullet, among other things. If the seating die seats off the nose of the bullet you will end up with similar OAL, but different CBTO measurements due to the differences in the length of the bullet nose due to nose type. If you seat your bullets based on the ogive the CBTO measurement will be the same and the OAL will differ for the same reason.

 

[woods]

Well one thing you have to consider is that the Hornady comparator inserts are .011" below caliber; i.e. 338 comparator hole is .327", 264 comparator hole is .253", etc.

What that means is the comparator will hit the ogive (which is defined as the curve of the bullet, not a specific point on the curve) at a point forward of the point at which the bullet will actually hit the lands. Now land diameter as opposed to bore diameter comes into effect in that land diameter is typically .008" below bore groove diameter. That means there is still .003" difference between land diameter and comparator ID.

The bullet seater stem certainly hits well forward of where the bullet will first contact the lands but that can be compensated for by checking with comparator after seating and adjust as necessary.

You have to consider that the shape of the ogive will determine what numerical distance there is between where the comparator hits and the lands will hit. IOW that distance will be longer in a bullet that has a long gradual ogive as opposed to a bullet that has a nose shape like a round nose bullet. That is the reason you get different CBTO measurements with different bullets because your friend is right, the CBTO as actually physically occurs in the chamber is the same for all bullets.

Clear as mud?

 

[Crowe284]

Depends on the reference method utilized to seat the bullet, among other things. If the seating die seats off the nose of the bullet you will end up with similar OAL, but different CBTO measurements due to the differences in the length of the bullet nose due to nose type. If you seat your bullets based on the ogive the CBTO measurement will be the same and the OAL will differ for the same reason.

Bingo. So what I hear you say, is that if you are measuring from ogive to base (I never measure OAL as mag length is not a issue) when you switch bullets, you ought to be able to use that same measurement (CBTO) to put ogive at lands. Correct?

On a side note...I discovered tonight while messing around that neck tension has a major impact on seating depth....Kind of one of those the sky is blue facts but had never experimented with it. Check this out. So, I took a piece of brass that I sized with expander in die and bumped shoulder .001. I then cut a slit from neck to shoulder junction with dremmel tool so that I could basically have just enough tension to seat bullet by inserting cartridge in chamber with no primer and push in firmly with cleaning rod and blunt jag. I took measurement at ogive after repeating 10 times (would gently push out from muzzle end with carbon fiber rod and same blunt jag). All of the measurements came in within +/- .001 of each other so felt good about that measurement. I pulled bullet out of slit case and then ran seater stem down to touch ogive. Seated bullet in this loose neck tension case and came out spot on with my measurements obtained from method above. Then...I took three pieces of brass, sized them with expander in die and bumped shoulder .001, so brass was exactly the same dimensions as the slit case except for neck tension. I then seated three bullets in the three prepped cases and came out with a CBTO measurement that was .007 longer. I sat there for like 30 minutes pondering everything. The only difference in any of the brass was neck tension. So, I inched my stem down to get to what I measured to be CBTO with slit case and left it and called that my dummy round at lands with prepped neck tension. Just want to verify that this is common. Have read that inconsistent neck tension can cause variance in seating depth but never experimented the in depth.

 

[ShtrRdy]

Bingo. So what I hear you say, is that if you are measuring from ogive to base (I never measure OAL as mag length is not a issue) when you switch bullets, you ought to be able to use that same measurement (CBTO) to put ogive at lands. Correct?

On a side note...I discovered tonight while messing around that neck tension has a major impact on seating depth....Kind of one of those the sky is blue facts but had never experimented with it. Check this out. So, I took a piece of brass that I sized with expander in die and bumped shoulder .001. I then cut a slit from neck to shoulder junction with dremmel tool so that I could basically have just enough tension to seat bullet by inserting cartridge in chamber with no primer and push in firmly with cleaning rod and blunt jag. I took measurement at ogive after repeating 10 times (would gently push out from muzzle end with carbon fiber rod and same blunt jag). All of the measurements came in within +/- .001 of each other so felt good about that measurement. I pulled bullet out of slit case and then ran seater stem down to touch ogive. Seated bullet in this loose neck tension case and came out spot on with my measurements obtained from method above. Then...I took three pieces of brass, sized them with expander in die and bumped shoulder .001, so brass was exactly the same dimensions as the slit case except for neck tension. I then seated three bullets in the three prepped cases and came out with a CBTO measurement that was .007 longer. I sat there for like 30 minutes pondering everything. The only difference in any of the brass was neck tension. So, I inched my stem down to get to what I measured to be CBTO with slit case and left it and called that my dummy round at lands with prepped neck tension. Just want to verify that this is common. Have read that inconsistent neck tension can cause variance in seating depth but never experimented the in depth.

I have experienced what you described.

 

[Crowe284]

Well one thing you have to consider is that the Hornady comparator inserts are .011" below caliber; i.e. 338 comparator hole is .327", 264 comparator hole is .253", etc.

What that means is the comparator will hit the ogive (which is defined as the curve of the bullet, not a specific point on the curve) at a point forward of the point at which the bullet will actually hit the lands. Now land diameter as opposed to bore diameter comes into effect in that land diameter is typically .008" below bore groove diameter. That means there is still .003" difference between land diameter and comparator ID.

The bullet seater stem certainly hits well forward of where the bullet will first contact the lands but that can be compensated for by checking with comparator after seating and adjust as necessary.

You have to consider that the shape of the ogive will determine what numerical distance there is between where the comparator hits and the lands will hit. IOW that distance will be longer in a bullet that has a long gradual ogive as opposed to a bullet that has a nose shape like a round nose bullet. That is the reason you get different CBTO measurements with different bullets because your friend is right, the CBTO as actually physically occurs in the chamber is the same for all bullets.

Clear as mud?

Clear as mud! Ha! So....Lets say you are using nothing but berger VLD type bullets and just switching weights, you ought to be **** close?

As for the comparator issue....I have a GAP built 6.5 4S that I bought from a forum member. Also bought all of his loaded rounds that shoot bug holes. His CBTO measurement differed from mine as I wanted to document his exact jump (which was .001) when I started loading. Although we got two different CBTO measurements, as long as I used MY equipment on loaded rounds and duplicated using MY measurements I should end up with same jump, correct? Have worried about this ever since I found the load he developed was unbelievable and wanted to duplicate. I measured everything on the loaded rounds (headspace etc. etc.) and on fired brass so that I would have all of this to duplicate. Even though he did the loading, if I use my measuring tools and use those measurements, I think I should be close....hopefully?

 

[Crowe284]

I have also saved 5 loaded rounds for future reference. The wont get shot! Its an unreal load. 4.5" 5 shot groups at 1K with 2-2.5" vertical ES and SD are single digits over magnetospeed V3. Sure does make life easier when you have base line like that....watch me go screw it up now! HA! I have 10 PP in Colorado this year for Deer and Elk, plan on carrying this rifle as I bought it for a backcountry rig being as light as it is with bartlein #3 fluted at 24" with vias microbrake and elite fill manners MCS-T. Sweetest gun I've ever owned. Building a 7saum on a stiller predator long action now with proof sendero finished at 26" and elite fill MCS-T manners. Wont have it for Colorado...if we get drawn due to lead time on Manners....5-6 months and then 2 month lead from smith....Oh well, that GAP ought to do the job. Killed a ton of deer here in Texas with it this past year out to 880 and all of them looked like they got hit in the head with lightning with high shoulder shots...all DRT.

 

[Crowe284]

Sorry for ADD...I know I'm going all over the place. Will STOP with sidebars now!

 

[Trnelson]

Clear as mud! Ha! So....Lets say you are using nothing but berger VLD type bullets and just switching weights, you ought to be **** close?

As for the comparator issue....I have a GAP built 6.5 4S that I bought from a forum member. Also bought all of his loaded rounds that shoot bug holes. His CBTO measurement differed from mine as I wanted to document his exact jump (which was .001) when I started loading. Although we got two different CBTO measurements, as long as I used MY equipment on loaded rounds and duplicated using MY measurements I should end up with same jump, correct? Have worried about this ever since I found the load he developed was unbelievable and wanted to duplicate. I measured everything on the loaded rounds (headspace etc. etc.) and on fired brass so that I would have all of this to duplicate. Even though he did the loading, if I use my measuring tools and use those measurements, I think I should be close....hopefully?

Measuring one of those bullets will tell you exactly what your equipment gauges it at. If you use the same measuring equipment to build new rounds based on those dimensions you recorded with your equipment should be good to go. Of course within the tolerance of your tools and the degree of accuracy that you are able to replicate them at.

 

[Crowe284]

That's what I wanted to hear! Thanks men!

 

[Crowe284]

Actually bought his redding bushing dies put together by Copper Creek, so will have exactly what he used to load original rounds I purchased with rifle.

 

[FEENIX]

You have to consider that the shape of the ogive will determine what numerical distance there is between where the comparator hits and the lands will hit. IOW that distance will be longer in a bullet that has a long gradual ogive as opposed to a bullet that has a nose shape like a round nose bullet.

Ditto!

Clear as mud! Ha! So....Lets say you are using nothing but berger VLD type bullets and just switching weights, you ought to be **** close?

For what it is worth; this is with my .300 WSM using Hornady LNL OAL gauge comparator (CBTO touching the land) ...

190 Berger VLD = 2.253"
208 Hornady A-Max = 2.258"
210 Berger VLD = 2.246"
215 Berger Hybrid = 2.277"

 

[Crowe284]

Ditto!



For what it is worth; this is with my .300 WSM using Hornady LNL OAL gauge comparator (CBTO touching the land) ...

190 Berger VLD = 2.253"
208 Hornady A-Max = 2.258"
210 Berger VLD = 2.246"
215 Berger Hybrid = 2.277"

Wow, so there is significant variation when changing bullets. Well, not that big of a deal to determine when switching bullets just to be accurate. Thanks for the info!

 

[dok7mm]

FEENIX finally nailed it. I read this over and over, and thought WTH. I test all the bullets, I am considering using in a chamber, for CBTO to lands and record it in that rifle's log. It sure makes it easy to change bullets, when working up new loads.

Sometimes there is a slight difference in length to lands within a box of one lot, I have found significant variances, in seating depths to lands, in different bullet brands, ogive styles and weights. Like FEENIX, I thought this was common knowledge.