Bullet ogive differences

[veezer]

I have been fighting with my 300 WSM loads that use 208 Amax's for an elk load. I have some loads that shoot fine, and then some that show pressure signs. I finally had enough yesterday and started pulling bullets. I checked my cartridge OAL using a sinclair comparator and noticed I was too close to my lands for one thing, so that is an easy fix with bullet depth. The next big issue I found was that when I measure my bullets from base to ogive, I have alot of variation. I pulled around 60 bullets and seperated them into 5 different piles. .720, .715, .710, .705 and those under .700. The biggest group was in the .705 group and had 25 bullets in it. The other groups had around 10 or so. I think these came out of two different boxes. The lowest measurement was in the .690 range and I know those came from a separate box because I still have the box with ".690" written on it.

I now have 3 100 count boxes with the same lot # on them. I opened one and measured a few that were .690. Hopefully, all 300 are the same.

I did notice a few boxes back that there was differences in the ogive length, but didnt notice the wide variation in them. I tried to load them to the same base- to- ogive length to keep the jump to the lands similar, but I think this wide variation is killing my accuracy and throwing high pressures.

My question is, what should I do with the bullets longer than .690? Should I just toss them and start over with load testing with the boxes with the same lot #? My worry is that the ones with longer bearing surfaces will cause wide pressure curves and therefore erratic speeds and high S.D.'s in velocity.

And then, after I get this figured out, the next time I need to buy more Amax's and they turn out to be an entirely different bullet ogive length am I going to be back at square one again? Should I ditch the Amax's and just go with something like a berger 210 hunting bullet to get better consistency across lot #'s?

 

[tbrice23]

If you have two comparators you can measure a representation of bearing surface length. Chances are that extreme lot differences are only .010" maximum.
I bet your pressure problem has a whole lot more to do with distance to your lands than bearing surface.

Now days when I order bullets I specify same lot# for all boxes, if possible. But yes, every lot you load you'll have to measure again to find your max CBTO. Whether it be Berger, Nosler, or Hornady.

 

[fishingstockwell]

Hi Veezer,

I measure a lot of my bullets and commonly find that some lot numbers are not as consistent. Typically the variance is in the front of the bullet, from the tip to the O-give. I recently posted a question about what consistencies were most important to accuracy, and overwhelmingly I was told not to worry about the tip to o-give measurement. The most important factors are the consistency of the base to o-give and the weight variance.

I don't believe that I have ever seen a variance of .030 in a bullet's base to ogive measurement. I just measured a random sample of some 215 Berger Hybrids and some 212 ELD-X bullets. The variance of the base to o-give on the bergers was .001 and the variance on the eld-x bullets was .0025.

Hopefully the 300 bullets with the same lot number will not have nearly the same variance. When you buy new bullets, it isn't not a big deal if they have different measurements than the 300 you have now, so long as they are consistent and your are seating your bullets to the same measurement from the base of the case to the o-give of the bullet.

 

[veezer]

I found two bullets that were the same length and measured the overall length, length from base to ogive and length from tip to ogive at the bottom and determined the bearing surfaces for each bullet. The .724 bullet was 0.47 and the .690 was 0.343, so there is a difference of 36 thousandths between the two. That has to be significant when it comes to pressures, wouldn't it?

 

[fishingstockwell]

Different bullets have different bearing surfaces. Significant differences in many cases. Some people believe that a shorter bearing surface creates less friction and allows you to push a similar weight bullet to faster speeds with equal pressure. A good example of this is that many people claim they can push the 215 berger hybrid faster than the 210 berger vld because the bearing surface is shorter. I have talked to the technical folks at Berger and they said it is not true, so I doubt .036" longer bearing surface is causing higher pressure problems.

It seem more likely that since the O-give is farther forward on some of your bullets, it is closer to, or even on the lands, where the shorter base to o-give bullets are off the lands. Going from near the lands to touching can cause a very big spike in pressure.

How far off the lands do you have the bullet set? If you set it at .010 off the lands with one of the short bullets, the longer bullets could be pushed into the lands .026, which would cause you to see a very noticeable change in pressure, particularly if you are near max load. I guess that is assuming that the difference in the bearing surface is on the front and not the at the bowtail.

Matt

 

[veezer]

I was trying to achieve .010 off the lands and I think those bullets with the shorter tip to ogive distance were doing exactly what you said. I was seating them to a depth measured from base of cartridge to ogive though, so it shouldn't have been a problem.

 

[dok7mm]

One of the great advantages of a micrometer seating die is how quickly you can seat bullets with varying BTO to the same CBTO length. You need to sort your bullets and label each tray. I seat & shoot the shortest first, then dial down for the others, to keep same jump to lands.

 

[Barrelnut]

One of the great advantages of a micrometer seating die is how quickly you can seat bullets with varying BTO to the same CBTO length. You need to sort your bullets and label each tray. I seat & shoot the shortest first, then dial down for the others, to keep same jump to lands.

+1 one I also check each round with the ogive comparator for correct jump after seating the bullet and adjust as necessary.

Also it is a good idea to keep your brass sorted by times fired. Don't mix 2 twice fired brass with 4 times fired, etc. Reason is the brass work hardens as it is fired and the necks with have different neck tensions and will take different amounts of seating force to reach the desired jump. In other words you can end up with bullets seated to varying depths pretty easily.

I sort 208 A-MAXs for my 300 WSM and have never seen base to ogive variances like the ones you are experiencing, but I don't think I have never sorted across lots. I sort Berger bullets also, and Bergers are always more consistent than Hornady bullets for me.

 

[fishingstockwell]

I believe that the seating die contacts the bullet below the tip and above the ogive If you set the die to seat the bullet .010 off with one of the short bearing surface bullets and then loaded a bullet with .036 longer bearing surface, the base of your case to your o-give would be .036 longer and would push your ogive .026 into the lands (assuming the .036 longer bearing surface was due to the ogive being farther forward on the bullet and not the bowtail being shorter).

If you measured every bullet with one of the base of the case to O-give with one of the comparators and they were the same, then that isn't the problem. If you set the die with a shorter bearing surface bullet and then loaded the longer bearing surface bullets without moving the die and measuring each one to with the comparator, it probably is the problem.

Just my best guess, not knowing your reloading practices. I had problems last year when I got a box of bullets with a lot of variance in the o-give to tip. I was loading to max magazine length and must have started with one of the shorter bullets. I checked the base to ogive measurement on every bullet, but not the COAL. When I was done, half the bullets fit in the magazine and half didn't. Pulled them all and found out that although they were very consistent from the base to o-give, they had a huge variance from the tip to o-give, making many too long to properly fit in the magazine. Made me mad. Threw away all the bullets, opened another box and the problem went away.

Matt

 

[veezer]

I usually measure each load using the CBTO method to avoid these issues. But, I think a few must have gotten through.

I sent an email to Hornady, so we will see what they say about how out of spec this box was.

I measured my 3 new boxes and another that I bought about a year ago and the first 300 were all .689 and the older box with a different lot # was around .686. i think the box of those over .700 must have just been a bad batch.

 

[Mikecr]

If you're setting a target CBTO, then nothing about the bullets matter to distance to land relationship(it's set in CBTO). Bearing, and BTO are meaningless -even where qualified to what you think they actually are. They play virtually zero role in pressure.

To clear some things, the 'ogive' is full length/curvature of a nose. Bearing end would be ogive begin, and your comparators do not actually take datum from this point on the nose.
A qualified measure here begins with matched ogive radius for each bullet, so that tool contact on ogives match from bullet to bullet(wherever that is).
Comparisons of BTO also begin with qualifying datums, and where they haven't been your measure is wrong. BTO is meaningless because it does not separate individual contributors(base length, base angle, bearing length, ogive datum). And BTO is meaningless to seated CBTO.

 

[veezer]

So you are saying the bullet comparator gauge is junk and a useless tool?

I don't see where my measurement is wrong.

U cant tell me that a bullet with a 1" bearing surface is going to have the same pressure and velocity as one with a 1/16" bearing surface.

 

[Mikecr]

So you are saying the bullet comparator gauge is junk and a useless tool?

Depends on the bullet comparator tool you're referring to. There are quite a few.

I don't see where my measurement is wrong.

If you're measuring 'base to ogive' only, then you have no idea what you're measuring specifically(not really). If measuring CBTO with a comparator keep in mind that is a local measure which follows no standard otherwise. It is important in that you define your best seating with it, and it's good as long as the condition is maintained with THAT specific tool, and THAT lot of bullets. Otherwise, start over.

U cant tell me that a bullet with a 1" bearing surface is going to have the same pressure and velocity as one with a 1/16" bearing surface.

That's hypothetical and not ever reality. So no, I'm not telling you that.
Normal variance in bearing means nothing to pressure beyond initial engraving force, for realistic ~10thou variance of soft copper. About what it takes to engrave a +/- fold of tin foil..
I've tested it to my satisfaction,, you're welcome to show where someone has tested and found other results. It would take a better chrono than mine(possibly LabRadar), and a fast powder underbore(like a 6PPC). However, most underbore shooters are not using long bearing bullets.
Good luck finding any more than blind assumptions with this.

If you've set your seated CBTO 10thou off the lands(OTL), and nothing about bearing in itself will change CBTO by 10thou, then bullet variance is NOT causing pressure issues.. Normal bullet variances are not enough to cause it.
Hell, it's likely fewer than 1% of reloaders think about this, and fewer than 1% of those worry about it, and fewer than 1% of those worry so much as to actually run a basic test.