Back to Bullet base to ogive

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cdoc42

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FL members may recall I previously posted an accidental discovery of varying bullet base-to- ogive measurements in an old purchase of .270 Remington Cor-Lokt PSP 130gr bullets that I could never satisfactorily group in 4 different rifles.

I proceeded to measure 100 bullets from the base-to-ogive (BTO) and they ended up in 11 groups ranging from 0.588 to 0.574 inches. The difference suggested to me that if I seated the 0.588 bullet 0.02” from the rifling (leade), the longer 0.574 bullet would end up 0.014” further away, or 0.034” from the rifling if I seated it at the same die setting.

I then measured some Berger, Hornady and Sierra bullets of various calibers and found there were some variations, but not nearly as severe as those seen in the 130gr PSPs, which could very well be influenced by my measuring technique and precision of the Stoney Point comparator. But- there was even less variation when I measured match bullets.

I figured out how to compensate for the differences but other chores and duties interfered with my ability to load up some of those .270s and test the results.

But I ran into a situation last night which prompted me to share this with all of you.

I routinely load for my friend’s Sig 7mm Remington Magnum. He was shooting factory Federal 150gr Ballistic Tips and couldn’t get below a 1.5-inch group. I loaded Hornady 154gr SSTs, seated 0.02” from the rifling and the groups dropped to 0.716”. He has several 20-round boxes of the Nosler’s and decided he would just shoot them off. I suggested I would try to pull the bullets and reseat them to match the 0.02” seating of the SSTs to see if accuracy improved.
Here’s what I did:

BTO of 150gr Nosler BT = 0.724
BTO of 154gr Hornady SST= 0.717

The difference is the Nosler BTO is 0.007” longer.

The OAL, case base to ogive, of the Hornady 154gr at 0.02” = 2.750”

Subtracting 0.007” from that, the Nosler should be 0.02” from the rifling if seated at 2.743”.

Then, using the technique I learned from John Wooter’s “Practical Handloading,” I chambered the 2.750” SST (making certain the safety was on), inserted an aluminum cleaning rod into the muzzle and rested the tip on the bullet, then made a half-circle with a fine-tip black Magic Marker.

I chambered the 2.743” Nosler BT and made a full circle on the cleaning rod.

When I removed the rod, there was only one full circle, which indicates both bullets were seated 0.02” from the rifling.

Now my friend needs to fire the Noslers to see if accuracy improved.

This precipitated another thought. Suppose you shoot 130gr bullets in your .270 for deer and you want to load 150gr for elk. Your 130gr is accurate at 0.015” seating. Rather than using your usual process with a comparator to establish the cartridge base-to-ogive to the rifling for the 150gr, then seating from 0.01” and so forth, why not just measure the BTO of the 130gr and 150gr bullets and calculate as above to seat the 150gr at 0.015” and go from there?
I understand it’s not that simple, as bullets differ in shape, length, SD and BC, but I wonder if this process allows one to “jump the gun” to figure of what the bullet jump should be.
 
Those differences can be caused by.......

Different lots of jacket metal.

Changing the bullet forming dies settings during the production run.

Mixing production runs from different sets of forming dies.

Using an optical comparator, some lots of match bullets have revealed a few differences in shape proving more than one set of dies were used.
 
To me, there are no shortcuts. But, I could see that method as a way to quickly get to a place where you have gotten good results before. A "good enough" type deal. I'm generally not satisfied with "good enough" but do know that sometimes good enough is just that .. good enough

Sent from my SM-G996U using Tapatalk
 
My Hornady books and all the my other loading manuals all describe "ogive" the same way in their glossaries. It is the curved (or sloped) portion of the bullet from the "shoulder" (the point where the bullet begins to reduce diameter) to the tip /meplat. It is the entire length of that part of the bullet.

When you say you are measuring to the ogive, what you are actually doing is measuring to a point, on the ogive. Somewhere on the ogive.

A point you choose. From context, I assume the point you are talking about is the point on the ogive which contacts the rifling.

While this data may be useful to you, it is useless to me. Even if I had your bullet, I don't have your rifle. And as you have found using that point from your rifle, bullets vary, some more than others.

I proceeded to measure 100 bullets from the base-to-ogive (BTO) and they ended up in 11 groups ranging from 0.588 to 0.574 inches. The difference suggested to me that if I seated the 0.588 bullet 0.02” from the rifling (leade), the longer 0.574 bullet would end up 0.014” further away, or 0.034” from the rifling if I seated it at the same die setting.
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The logic here is sound, You are dealing with a single point (rifling contact) determined by one individual rifle barrel. You found that where on the bullet this point is vaires among the batch. And that variance would result in differing distances off the lands if the different bullets are all seated with the same die setting.

Assuming, of course, that your seating stem is contacting ALL the bullets at the same spot on their ogive. Just as the bullets don't all contact the barrel rifling at exactly the same spot ( measured from their base) the same can happen with the bullets contacting the seating stem.

I then measured some Berger, Hornady and Sierra bullets of various calibers and found there were some variations, but not nearly as severe as those seen in the 130gr PSPs, which could very well be influenced by my measuring technique and precision of the Stoney Point comparator. But- there was even less variation when I measured match bullets.
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Remington Core-Lokt PSP (pointed soft point) are hunting bullets. They were never made to be match bullets. The allowable range of variation (tolerance) is no where near as tight as it is with match bullets. You found a range where different bullets contacted your rifling at different points. Did you, by any chance weigh the bullets? I expect you'll find a range of difference in the bullet weights as well.

With match grade bullets, we expect a very small degree of difference, and we're PAYING to get that greater uniformity. Expecting a "deer bullet" to meet the uniformity standards of the more expensive match bullets is unrealistic.

Remington Core-Lokt bullets aren't even premium "deer bullets". They are the bread and butter ammo, plenty good for hunting and delivering acceptable accuracy as well as down range performance in the majority of
hunting rifles they are intended to be used from. So, no, they aren't going to be as uniform in the tiniest measurements, nor do they need to be, as the overwhelming majority of rifles and hunters won't be able to notice those small variations.

Suppose you shoot 130gr bullets in your .270 for deer and you want to load 150gr for elk....
Click to expand...

Here you are talking about a completely different bullet, And I think that while your 130gr bullet seating numbers gives you a place to start, I'd say that having the 150gr work the way you want at the 130gr's exact numbers would be serendipity.

Every rifle and ammo combination has the potential to be different. Most of the time they are very similar, but sometimes the difference is significant.
 
44AMP said: "Assuming, of course, that your seating stem is contacting ALL the bullets at the same spot on their ogive. Just as the bullets don't all contact the barrel rifling at exactly the same spot ( measured from their base) the same can happen with the bullets contacting the seating stem."

If I load 20 rounds or whatever, and I get the same final overall cartridge measurement of the seated bullets from the case base to the spot on the bullet that I believe is first contacting the rifling, doesn't that indicate there was no variation in seating stem to bullet contact point? How would one otherwise be assured the bullets are all seated from the anticipated jump distance?
 
If I load 20 rounds or whatever, and I get the same final overall cartridge measurement of the seated bullets from the case base to the spot on the bullet that I believe is first contacting the rifling, doesn't that indicate there was no variation in seating stem to bullet contact point?
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If your measurements come out the same, then obviously there was no difference in those 20 rounds.

But, consider this, you/ve already done the checking and have found that in that 100 bullet lot the distance from the bullet base to your measuring point on the ogive (where you believe the bullet first contacts the rifling) varies a measurable amount,

Now, the same process is going on when the bullet enters the seating stem as it does when it goes into the barrel. The front of the bullet enters a tube until to contacts the edge of the tube. This will also be a point on the ogive. But its not the same point where the rifling touches the bullet.

The seating stem cavity being smaller than the barrel, touches the bullet well ahead of where the rifling does. Often its something you can see, a mark on the bullet jacket a little bit behind the nose.

My point here is that if you are finding variations between bullets of the same batch measuring to one point on the ogive, you might also have variations measuring to another spot on the ogive for the same reasons.

Another thing you can check is cartridge overall length, case base to bullet tip. Check your rounds that are uniform case base to your spot on the ogive for uniformity of length from case base to bullet tip. I would expect some variation there, from Remington Core-Lokt PSP bullets. Not a lot, but some. Its not a vital area, just an example of how the bullet can vary in length in front of the rifle bore, or steating stem contact points.

And, if you don't mind, what were the 4 rifles you couldn't get satisfactory groups with those bullets, and what is your standard for satisfaction?
I'm curious, my experience with Core-Lokts isn't in .270 cal.
 
As 44AMP suggested, i'm pretty confident that you'll find different bullet weights from your different length bullets.

My thought is as such.

If the seating stem were consistantly touching the bullet at the same place on the ogive, then the difference in length from base to ogive wouldn't matter. You are not changing the distance to the lands. Your changing the depth of the base of the bullet into the case.
 
44AMP said: .

“The seating stem cavity being smaller than the barrel, touches the bullet well ahead of where the rifling does. Often its something you can see, a mark on the bullet jacket a little bit behind the nose.”
“My point here is that if you are finding variations between bullets of the same batch measuring to one point on the ogive, you might also have variations measuring to another spot on the ogive for the same reasons.”

I understand what you are saying. But no numerical measurement is being made because of the contact between the die seating stem and any specific point on the ogive. The stem is just pushing the bullet into the case to a specific depth. It doesn’t matter if there is a variation between the stem and the point on each bullet. The only measurement is the case base to that point on the bullet ogive where you have determined it engages the rifling, which is accomplished with the comparator collet.

The seating stem touches the meplat of a round nose and ogive of a spire point bullet of the same caliber at an obviously different point, but I can end up with both being the same distance from the rifling because the final OA measurement is to that point on the ogive of each that engages the rifling.

But this is directing attention completely away from my original point. We, or at least I, have always considered that each bullet in a given box is sufficiently the same so that when I determine what portion of the ogive touches the rifling, and I make a dummy cartridge with a final case-base to bullet ogive measurement, every bullet in the box seated to the same cartridge OAL length will be the same distance from the rifling. The “old” Remington bullet purchase revealed that was not true and was significant enough that if I seated one bullet 0.015” from the rifling, another bullet with the exact same case-base to bullet ogive OAL measurement would be longer and touching the rifling. That should explain any difference in the expanse of points of impact.

But I’m happy enough to leave it at that. I’m not interested in getting into a didactic exercise that transfers my presentation intent to the mechanics of the process.
 
The bullets listed are hunting bullets, not match bullets. The distance from the rifling to its contact point on the ogive will be much more critical than a few thousands of base variation.

For me seating depth has been the make or break in accuracy. Load up batches of 4 to 5. Start at the listed col in your manual. Seat each group 0.003 deeper than the last. 5 to 7 groups shoukd do. My rifle would not group under 1.25moa for anything until I tried this. Got it down to 0.69moa.
 
Shadow9mm, it was not strictly about getting smaller groups by finding the "sweet spot." It was about difficulty finding the sweet spot because of the variation in bullet base to ogive point of rifling contact. That might also explain flyers.

I do not participate in any rifle matches. I shoot 10% match bullets just for long-distance fun shooting. 90% of my rifle bullets are hunting bullets and my goal has been to get one-inch or less groups, which I most often accomplish. When I have difficulty or fail to duplicate a previously satisfactory group with a new lot number of the same bullet I now raise the question that the base-to-ogive may have changed. Just a theory. Time will confirm or deny it.
 
I brought this subject up with a friend/mentor today.
He has many years shooting different diciplines, including many years of different match shooting. And has helped custom bullet makers with his labor at times.
Our conclusion.
Measuring base to ogive will drive you unnecessarily nuts.
You'll end up with 20 different piles of bullets.
Since the secant, or tangent is the hardest to draw, and the part most worked, consistancy of the draw has a huge impact on this area.
And this area is where the seating stem presses. (Remember the ring on the bullet from the seater)
His recommendation is measure ogive to tip.
As this directly impacts the seating stem for your cartridge base to ogive measurement.
 
I don't participate in matches either. But I like to make the best loads that I can both for hunting and long range plinking that I can.

To be clear are you talking base of the bullet to the ogive, or base of the loaded cartridge to ogive. If the former, it should not matter for our uses. If the latter are you using compressed loads? that is the only time I have had problems getting bullets to seat consistently. It could also be a badly fitted seating stem that is pushing on the bullet point a point on the ogive.

What matters, as I understand it, is how far the bullet jumps from the casing until it contacts the rifling, which is effected by the loaded cartridge dimension, cartridge base to ogive.

In my experience total jump does not matter. What matters is tuning for the barrel harmonics so the bullets come out at the same point in the barrels movement. I do that with the seating depth test I listed above.

Here are 2 vids that should help explain the seating depth method

https://www.youtube.com/watch?v=oRXlCG9YZbQ
https://www.youtube.com/watch?v=9FKq8Jj8YEI

There are tools to measure both base to ogive from Hornady as well as where bullets engage the rifling in your rifle

Hornady bullet comparitor tool
https://www.midwayusa.com/product/101273351?pid=231904

and the seating depth tool, that you will need to buy a modified case for
https://www.midwayusa.com/product/1012747079

modified cases
https://www.midwayusa.com/product/1012753414?pid=290405


I have the tools. I rarely use the Overall Length Gauge. I start at the recommended COL and do seating depth testing on 0.003 increments. doing that has tightened up groups more than anything else I have done.
 
Shadow9mm, thanks for all the info. To answer your question I was referring to the BULLET base-to-ogive point of contact.

std7mag and his friend's conclusion was enough to convince me I'm entering an arena of operational futility, for even though I only have 11, not 20, piles of measured bullets, it is enough to drive me nuts and I'm getting too old to be wasting what neurologic circuits I still have that function.
 
I would check your seating stem, make sure it's hitting the ogive not the point. Seating off the point could be your problem. That's an easy problem hou don't have to go too far down the rabbit hole to fix.
 
Go to Sinclair and get one of their Stainless Steel comparator inserts. It is much closer to actual throat dimensions than the aluminum Hornady insert, so it gives you a more consistent representation of bullet jump to the throat. You can also look at the ring made by the contact of your seater stem with the bullet (paint with Magic Marker to help find it if necessary), then identify or drill out an insert to meet the same spot. You can the check the length of the two inserts to you bullet bases to sort bullet's by which ones will need the same sweater setting.

For obvious reasons, even with the safety on, there is risk in having a loaded round and a cleaning rod in the gun at the same time. There's also a precision issue. Since the cartridge is pushed forward by the firing pin during firing, to get the actual firing jump measured you want to take your pinky finger and push the cartridge as far forward in the chamber as it will go. Only when the case stops fully forward on the headspacing surface do you have the bullet in its actual firing jump position.
 
Correct me if I’m wrong, but the additional discussion relating to the seating stem seems to be unrelated to my original presentation.

In review, to establish the point on the bullet ogive that first engages the rifling, using the technique described by now deceased John Wooters, with the muzzle pointed at the floor, I insert a bullet into the rifling and gently tap it in with a cleaning rod, just enough to prevent it from easily falling out. I think this would be analogous to Unclenick’s advice about using finger pressure to properly engage a cartridge against the rifling.
I then insert the cleaning rod into the muzzle and slowly advance it until it stops at the bullet. I then draw a half-circle at the muzzle on the cleaning rod. There is no measurement involved. The cleaning rod does not need to be at the ogive. The half-circle drawn is only a reference point letting me know the bullet is engaged at the rifling.
Then I make a dummy round with that same bullet and seat it longer than anticipated. I chamber it and reinsert the cleaning rod. I then draw a full circle around the rod. If there is only one full circle my interpretation is that cartridge-seated bullet has its point on the ogive exactly where the bullet was when I first inserted it against rifling. If the full circle is behind the half-circle, the bullet is not seated deeply enough. In both instances, the cleaning rod touched the bullet at the same point, but not at the ogive where the bullet engaged the rifling, but at the same reference point. I then measure that dummy with the Stoney Point (or Hornady) comparator which gives me an overall case-base-to-ogive measurement of a cartridge that has the bullet engaged with the rifling. Let’s say it is 2.390.” I then subtract, let’s say, 0.015” from that figure so 2.375” on the next loaded round has the bullet 0.015” away from the rifling.

Now, when I seat a bullet into the final loaded cartridge, my die seating stem doesn’t engage the same point on the ogive either. But it doesn’t matter because the cartridge OAL is measured with the comparator. As long as the cartridge measures 2.375” from case-base to bullet ogive, the die stem contact is immaterial.

Or am I misunderstanding what you guys are saying?

Unclenick, I DO understand the suggestion about the Sinclair Stainless Steel inserts being more accurate than those supplied by S.P. or Hornady and I will look into that. I have both sets of SP and Hornady and I’ve found the same calibers are not interchangeable. Hornady will give a different result than S.P.
 
Yes, and the Sinclair inserts will get you the shortest number. Here are some measurements I made from bullet base to the insert contact point of some .308 150-grain SMKs.

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For the tool I made for myself, I drilled and reamed the contacting insert to 0.030", then ran a chamber reamer in so it makes contact exactly like the throat reamed with that same chamber. But the Sinclair comes very close.
 
Unclenick, let me ask you this. If I establish the contact point on the ogive with the procedure I explained, then used the Stoney Point comparator to assign a sequence of distances from the rifling, would my measurements be erroneous?

I can understand if I did exactly the same thing and used the Hornady or Sinclair tool my numbers would differ, but wouldn't every bullet still be the desired distance from the rifling? To be certain that 44AMP's position is understood as well, I recognize that whatever I'm doing is specific for MY rifle. The case-base to ogive measurement I develop and report should not be used by any neophyte unfamiliar with the procedure being discussed.
 
To my way of thinking, the whole "draw a circle on the cleaning rod" would be your most inconsistant means of measuring.
At what angle do you hold your marking device?
How thick is your line?
Where on the line are you measuring too?

Stick your finger in the action to hold the cartridge forward?
Why do that if the ejector is built into the bolt? (Sako, Savage & others)
The ejector spring would do that for you.

"Tap a bullet into the rifling"??!! What the heck is that going to measure??

Sounds like a lot of messed up, screwball ways to get you no meaningful information!
 
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Std7mag,

He is pushing the bullet by itself, not the cartridge. I suggested pressing on a cartridge base if using a loaded cartridge, thus avoiding the obvious safety hazard involved in having a bolt closed on a live round with an obstruction (the cleaning rod) in the bore. Tapping the bullet into the rifling to stick it in the throat mimics the same situation you would have soft-seating (Mid Tompkins's method) or jamming the throat. He's using that as the zero point for subsequently setting the jump. My concern would be the tapping can vary in exactly how far it puts the bullet into the throat if it isn't done by some calibrated method. Back when I used a cleaning rod instead of the Hornady style gauge, I used the rubber eraser end of a pencil to hold a bullet gently against the throat for that measurement to avoid involving any bullet jam.


cdic42 said:
...would my measurements be erroneous?
Click to expand...

I've used the cleaning rod method in the past. I would paint the rod with Magic Marker near the marking point, then lay a single-edge razor blade across the muzzle to produce a small scratch line in the ink as my mark. With magnification, you can measure the distance between scratch lines with surprising precision. In addition, laying the same side of the blade flat across the muzzle guarantees repeatability in the relative marking position.

Bullets have some variation in ogive shape. That lack of identicality is why Bryan Litz observed that even match bullets from the same box could have a three percent difference in their measured ballistic coefficients. That means the base-to-ogive diameter line lengths won't match exactly. They did pretty well in my example, but those bullets are all off the same tooling, and, even then, there was a tiny bit more variation for the Hornady insert.

For any of these kinds of measurements, the bullet variations are an enemy. If you are using this system, go through the bullets with a comparator first and find one whose length and bullet-base-to-ogive measurements are average. That will minimize the effect of any errors by making half of them closer and half further away.

This brings up a basic problem with these measurements. In firing, the rimless bottleneck rifle cartridge is driven forward by the firing pin and the push back of the firing primer. As a result, its case shoulder hits the chamber shoulder while the bullet is still in place, stopping any further forward movement by the neck and bullet. So it is really the difference in the shoulder and bullet ogive contact points that determine the distance the bullet jumps to the throat, and not the case head to bullet ogive distance. The only commercial tool that will measure this difference directly is the expensive Redding Instant Indicator. I made my own version a few years before theirs came out (the one I used the chamber reamer to make), also letting me read the relative difference in the shoulder to bullet ogive length directly on a dial indicator. There always seems to be at least a couple of thousandths or more variation.

Seating to the exact same location requires using a micrometer adjustable seating die, sorting the finished rounds by shoulder-to-ogive length, then using the seater adjustment to correct the long ones. I've done this, but not detected any performance change apparent on the target as I don't usually wind up seating close enough to the throat for 0.002" of variation to be a significant percentage of the jump. Guys trying to get 0.005" off the lands could see some added peak pressure fluctuation resulting from not keeping this dimension constant.

So whether you need to assess all that really depends on how far you have the bullet jump. I tend to think it's a good idea to try to keep this number constant during load development just to be sure I don't miss a good sweet spot close to the throat. But once development is done, I start dropping some of the tight controls to see if I can tell the difference on target paper. If I can't, I don't bother with them for that load.
 
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