Confusing bullet length peoblem

[Lefty Trigger]

Here is my issue, loading 2 new bullets for my .243 and came across a weird length issue. The two bullets are Hornady 75gr Vmax (.506 ojive bullet length) and Nosler 80gr ballistic tip (.509 ojive bullet length). Measuring the bullet seating depth to lands with Hornady depth gauge I get 2.212 to lands for the 75gr Vmax and 2.272 for the Nosler 80gr, How does that work??? Shouldn't those two be within .003 of each other in seating depth? I can not even get the Hornady bullet to their COAL of 2.640 which is 2.220 measured with the comparator. The Nosler bullet COAL is 2.680 and at 2.272 (is 2.750 COAL) which leaves me a lot of room to play with seating depth. I don't understand how with only .003 difference they seat so far apart.

 

[Keith Glasscock]

Thinking about this one a little.

Looking at your photos gives me an idea. Since the measurement you are referring to is the bullet base to the ogive diameter (something just under full diameter), you aren't considering the shape of the ogive. Hornady V-maxes are quite sharp in their transition from the ogive to the full diameter (I believe they are a secant ogive). The last Noslers I had were a tangent ogive and the diameter near the bearing surface slowly increased in diameter over some distance.

Even with all of that, .060" is a huge difference. I mean, that could easily be the entire freebore length. Are you sure the Hornady bullet isn't catching in the freebore when you are measuring?

 

[Lefty Trigger]

Thinking about this one a little.

Looking at your photos gives me an idea. Since the measurement you are referring to is the bullet base to the ogive diameter (something just under full diameter), you aren't considering the shape of the ogive. Hornady V-maxes are quite sharp in their transition from the ogive to the full diameter (I believe they are a secant ogive). The last Noslers I had were a tangent ogive and the diameter near the bearing surface slowly increased in diameter over some distance.

Even with all of that, .060" is a huge difference. I mean, that could easily be the entire freebore length. Are you sure the Hornady bullet isn't catching in the freebore when you are measuring?

Man I wish it was because that would stop my head from hurting! I measured it many many times pushing the bullet so hard with the tool that it was actually getting stuck in the barrel making me use my cleaning rod to lightly tap it loose. Stuck "hard" I get 2.214 which I assume is a .002 jam? I have thought about making a dead round and seating long and seeing what I get after forcing the bolt closed.

 

[T-shooter]

The inner diameter of the Hornady tool isn't the same as the lands in your barrel. The profile of the bullet could be substantially different regardless of where you measured the ogive like the two .308 bullets pictures below. I only have a .223 and a .308 Hornady insert but both are .010" smaller than the bullet diameter. Also there is a small chamfer in the bore of the insert, and it will allow the bullet to sit deeper.

 

[dellet]

If you look at the taper from the lead Into the throat, you can see that a bullet with a smaller radius (more round, less taper) will not seat as deeply. The perpendicular hole of the gauge will make contact at .233” of either bullet. But a when they go into a taper like the throat, the more rounded bullet may make contact at say .238”.

i

 

[7887mm08]

This post is a perfect example of why I like this site so much. A member asks a question and other members are posting pictures and diagrams to offer their help. 99.99999% of the time these people do not know each other, I just find it amazing the good people we have on this forum THANKS!!!!!
Gary

 

[dkhunt14]

It looks like the bearing surface on the bottom bullet is way shorter, because the actual boattail is longer. I get about .080 difference in bearing length. It's like Keith said, one is a secant and one is a tangent. The bearing is way different. Matt

 

[Richard Coody]

perfect example of why you have to check overall length on each bullet you use. shape of ogive can have profound changes in seating depths.

 

[boltfluter]

The very best comparitors are made by using the same reamer the rifle was chambered with. Anything else, just gives you a reference number that may or may not help you. And many times just leads to confusion. Happy measuring!!

Paul

 

[mikecr]

I think your 'touching land' method/measure is inconsistent.
And keep in mind that a bullet's base to ogive (BTO) is base length + bearing length + datum length from bearing. They add up to nothing meaningful about land contact datum to cartridge base (CBTO), nor ogive datum point to actual land contact (land relationship).
Also, neither does bullet OAL, nor bullet bearing measure (just as useless here).

 

[K22]

perfect example of why you have to check overall length on each bullet you use. shape of ogive can have profound changes in seating depths.

Totally agree. The first thing I do after cleaning a new rifle is measure the MAX COL of the bullet I intend to use in that rifle. I generally seat .020" off the lands to more than compensate for variations in bullet ogive.

While an excellent bullet, which is my go to bullet for the 243, the Sierra 85 BTHP ogive requires me, in some of my rifles, to seat bullets considerable shorter than published values for maximum overall cartridge length of the 243, i.e 2.710 or published values for COL 'test at', e.g Sierra 2.650.

For example, the MAX COL in my Tikka 243 for this bullet is 2.630 whereas with the 80 grain Nosler BT it's 2.730. That quite a spread for the same rifle but it goes to show how much MAX COL can vary depending on bullet type. Also MAX COL can be considerably different for a different rifle. For example in my Remington 700, 243 the MAX COL for the 85 BTHP is 2.750.

Bottom line, measure the MAX COL of the bullet you intend to use in the specific rifle you are loading for.

 

[dkhunt14]

[QUOTE="mikecr, post: 37284264, member:
Also, neither does bullet OAL, nor bullet bearing measure (just as useless here).[/QUOTE]
Usually if bullet bearing is shorter, the ogive touch point is also. Matt

 

[Fotheringill]

If you put up a Berger and a Hornady and a Sierra and a Nosler in the exact same weight (just to name a few) there is going to be a wide disparity in the base to Ogive measurement as well as OAL.

For simplicity and sanity's sake, I would suggest you pick one bullet and stick with it for a while.

 

[mikecr]

Usually if bullet bearing is shorter, the ogive touch point is also. Matt

'Usually' means nothing real.
There are all kinds of bullet proportions, and no bullet attribute ahead of or behind actual contact datum matters to contact relationship anyway.

It's generalizations that lead to disparities like OP thinks he has.
I'm confident that what he's reporting is disconnected from reality.

 

[Webster]

Here is my issue, loading 2 new bullets for my .243 and came across a weird length issue. The two bullets are Hornady 75gr Vmax (.506 ojive bullet length) and Nosler 80gr ballistic tip (.509 ojive bullet length). Measuring the bullet seating depth to lands with Hornady depth gauge I get 2.212 to lands for the 75gr Vmax and 2.272 for the Nosler 80gr, How does that work??? Shouldn't those two be within .003 of each other in seating depth? I can not even get the Hornady bullet to their COAL of 2.640 which is 2.220 measured with the comparator. The Nosler bullet COAL is 2.680 and at 2.272 (is 2.750 COAL) which leaves me a lot of room to play with seating depth. I don't understand how with only .003 difference they seat so far apart.View attachment 1060311 View attachment 1060312

Not sure if you can learn anything from what i am going to describe but I think it may. I have a 1" long barrel stub cut off of one of my barrels when chambering and cutting to length. I need to try this on 2 Nosler 55 gr bullets with a different name. Take each bullet insert it in the stub and rotate it gently. The sharp rifling edge will scratch the bullet at land diameter. Put several scratched bullets of different types next to each other and see where the scratch is related to bearing length and ogive in front of the bearing length.

 

[gambleone]

The inner diameter of the Hornady tool isn't the same as the lands in your barrel. The profile of the bullet could be substantially different regardless of where you measured the ogive like the two .308 bullets pictures below. I only have a .223 and a .308 Hornady insert but both are .010" smaller than the bullet diameter. Also there is a small chamfer in the bore of the insert, and it will allow the bullet to sit deeper.
View attachment 1060317

Like T-shooter said, the inner diameter of your comparator is a different diameter than the diameter your barrel at the lands, which gives you two different measurements. If you had a comparator made from the reamer of your rifle, as boltfluter stated, you would get the same measurement with each given bullet. Hope this is understandable.

 

[Lefty Trigger]

Like T-shooter said, the inner diameter of your comparator is a different than the diameter of your barrel at the lands, which gives you two different measurements. If you had a comparator made from the reamer of your rifle, as boltfluter stated, you would get the same measurement with each given bullet. Hope this is understandable.

Makes since I guess, just thinking as close as these two are to each other seems like they should seat the same or at least closer than they do. It's all for nothing now anyway as I have sold the .243 and moved up to a .308. Just way too many issues trying to get the distance on the .243 and my twist rate and throat length was holding the gun back. Too much $$ to rebarrel it so I moved on.

 

[mtang45]

Man I wish it was because that would stop my head from hurting! I measured it many many times pushing the bullet so hard with the tool that it was actually getting stuck in the barrel making me use my cleaning rod to lightly tap it loose. Stuck "hard" I get 2.214 which I assume is a .002 jam? I have thought about making a dead round and seating long and seeing what I get after forcing the bolt closed.

If you are jamming the bullets hard enough to have to knock them out with a cleaning rod, then you are probably way deeper than .002

 

[T-shooter]

This is the method I use to find the lands:
This is the method I use.. I bought some drill depth stops and use them on a cleaning rod that is close to the bore diameter. I also got a kit several year ago that had some flat tip screw in plugs for the cleaning rod but they also had some flimsy plastic stops that I don't like to use. On a bolt gun, I sometimes use a rubber band just strong enough to keep the bolt against the case and the case in the chamber.

Close the bolt and run the rod in until it touches and make sure it's not on the ejector pin. Run the (#1) stop up against the muzzle and lock it. You need to make a dummy bullet that is seated too long to chamber. Lightly run it into the chamber until you feel it touch. Now add the second drill stop on the cleaning rod, then insert and lock it in place when it lightly touches the bullet tip. The headspace/COL is the distance is from outside to outside the drill stops minus the thickness of the last one (#2 here). By being careful, I can repeat measurements to .001". This will work on one exact bullet and sometimes only with one lot number. You can now seat the bullet to the same overall length you measured and take your measurements from there. Maybe use the Hornady bullet insert/comparator from your dummy test round to get a reading and then subtract what ever jump you want to have. Keep in mind, the overall length of the bullets can vary several thousandths even in the same lot. It takes a light touch not to jam the bullet into the rifling or to move the bolt backwards when the dummy round is in the chamber. Sometimes I use my finger instead of the bolt so I can feel when the rod makes contact. If you use another rod (aluminum would probably be best) instead of a cleaning rod, you won't need to plug the threaded end.

Sometimes the same part number but a different lot will measure differently. These were measured from both ends using the Hornady comparator and a dial caliper.

 

[mikecr]

I hope you don't mind a revision to your picture:


This is the basic cleaning rod method with which you can establish a consistent 'touching land' dummy round. You can do this with a new barrel & later to quantify erosion.

You pick a 'standard bullet' from lot for this measure, and dummy round build. You should want one well representing mean ogive radius from lot, and to determine this you need a tool similar to a Bob Green Comparator (BGC). Measuring bullets behind contact datum, with any other tool, would not help at all here.

Above, I'm using a light aluminum rod against the back of standard bullet, with no more than indicator force. I also use a cleaning bore guide for this rod. The indicator helps me see exact contact.
Once I have my zero head space COAL number, I make a dummy round, with that bullet, to match.
It's with this dummy round that I can then get touching baseline CBTO.
The log entry that matters to me is the CBTO that tested as best shooting (whatever that happens to be). But I guess it's somewhat useful, for description, to derive land relationship w/resp to touching.

Most other methods include a case & it's shoulder, but this only adds inconsistency to it. So folks average their readings to conclude a value. Here, you don't have to average anything. It is what it is.
And YOU control your head spacing, so if for some reason you desire to load at exactly touching lands (I never would), you simply seat deeper by your head space amount. That is, from 'zero head space touching'.
If you wanted to seat exactly 10thou OTL, and your HS is 2thou, you seat 12thou deeper to get it.