Bullet length, ogive, and COAL

S

Stats Shooter

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So here is a technical question:

Most of us already know that seating bullets by COAL is very imprecise since the bullet length on polymer tips, and small imperfections on BTHP tips, Soft points, and even fMJ's can be a bit erratic to say the least. Such that COAL is really only useful when you want the round to fit and feed smoothly from a magazine.

Therefore, most of use the "base to ogive" method of seating to get our optimal jump given the constraints set forth by the chamber/throat, magazine, bullet shape etc. However, even with supposed "match grade" bullets, base to ogive measurements can, in my experience, vary by up to 0.003 +/-. Now this variance is MUCH closer than any COAL I have incurred but it is a variable none the less.

I have read where people pains takingly change their seating die for every single round in an attempt eliminate this base-to-ogive variance believing that the variability inherently assuming the variability in jump is extremely important.

My question though is can't such a procedure be self defeating? - My thought is: If the beginning of the ogive begins later/earlier, holding all else equal, then you will seat some bullets deeper into the case by trying to hold the base to ogive measurement constant. In checking bullets i measured the distance from the base of the boattail to the ogive of the bullet and did in fact find them to vary. But this does not actually answer the question. Because if the bullets are porportionatly the same but just a tad longer or shorter from base of bullet to ogive, then changing the die on every load will keep the space occupied by the bullet within the cartridge the same. However, if it is simply that the ogive begins a bit further up/down on every bullet, then you are actually change the volume of air in the cartridege by adjusting the seating depth.

So to test the second premise, I seated a few bullets from different makers in different calibers making marks on the side of each to see how deep each bullet was seated into the case. Turns out that holding ogive perfectly constant does change the seating depth below the edge of the neck such that you are pushing some bullets deeper and some more shallow.

So then the question is, which has more impact on performance? Is it the jump, or the empty space within the case not occupied by powder or bullet? Unless you are willing to discard any seated round with a slightly different base to ogive as "range fodder", you are either going to have slight variability in jump or case "space".

For me, and I think most of us, a little variability in base-to-ogive is ok. But it seems those who are sticklers for perfect uniformity above the neck rim may be chasing their tails
 
I think what the "practical" perfectionist would do is weigh and measure each and every bullet and only use those that fell within a certain tolerance.

Now, I have not been in the long range match game long, but I feel load compression and jump pretty close to equally important, with maybe jump being slightly more detrimental. But again, I haven't been in the game long
 
Just shoot Berger bullets. And find a powder to fill the case more... and with all this free time to worry about something less then a hair size I would get out and make sure Hillary is not elected

My wife thinks I only have 3 guns
 
I think the "case head to ogive" would be the mot consistent for loading a COL for distance of ogive to lands measurements. But if the bullets vary from base to ogive, the seating depth would vary, amount of bullet in the case, and thus pressures vary. Jes thinkin'...
 
Mikld,

The pressure difference is what I was getting at. That by people chasing a perfectly consist seating depth they are too worried about what is sticking out of the case than what is going down into the case. So by monkeying around with their die, they are wasting time chasing something that is easy to measure at the expense of creating another variance issue.

And the poster below who said just try and get consistent bullets is right, it is truly the only way. But again, this is for folks shooting 600+ yards. I have not experimented with at my house on my range but my guess is that inside of the distance mentioned above, it wont mean much. In fact, my target software program estimates the point of impact difference holding velocity constant at 500 yards between a 75 grain Hornady BTHP and 74 Grain of the same bullet to be 0.22".
 
Some people think too much. I load mine to fit the magazine and with all the speed I can get and still keep 3 shots inside 1" at 100 yards. Sweating a bunch of details in order to find a way to keep 5 shots inside 1/2" just doesn't pay off in the real world.

Once you start shooting at ranges longer than 100 yards and doing it from field positions there is no practical difference between a rifle/load that'll shoot 1 MOA for 3 shots and a 1/2MOA 5 shot rifle.
 
I agree JMR,

I started this post to semi-emphasize that point. I do take my handloading seriously, but I'm more interested in the ACTUAL shooting. However, there are additional things the handloader can do that require very little additional time but increase performance. But the main two performance steps everyone should do is a ladder test, and jump test, these two things will usually let you find a safe sub moa load in my experience.

Beyond that there is a lot of extra effort for minimal gain.
 
There should be virtually no difference in pressure and velocity if one bullet is seated .004 deeper then another . The thing you want consistent is your jump . Your bullet base to ogive measurement is not as important then your case head to ogive measurement . Unless the bullet or seating stem is very inconsistent . Your head to ogive will likely be pretty consistent .
 
Agreed metal god.

And I have found that if you are using a good die and press like a Dillon or RCBS, there will be absolutely no variation. Where i think people find variation on base to ogive is where the may be a small burr on the case head causing it to stick up a bit when seating, or measurement error. Because 3 thousandths of an inch does not take a very noticeable burr or measurement mistake.

So, it appears this may jsut be a red herring.
 
I believe with things like this we reach a point of diminishing returns and a point where any improvement will only be noticeable in certain rifles. Sit down with a box of any match grade bullets and start measuring base to tip or using a fixture, base to ogive. Now if we sort several hundred to get let's say 50 as close to the same as possible how much will it matter?

We can only control so many variables when building match grade ammunition and what we can control we can only control to a point. Goes back to diminishing returns and if the rifle will even notice the difference.

Just My Take....
Ron
 
I've only had one rifle I was overly concerned about the particulars you talking about.

I was shooting custom bullets which I purchased in 1k batches. First I measured a batch of 500 from base to ogive and separated them in piles. I chose .002" as a max allowance. This gave me either +/-.001" to go by. Once I had my piles I bagged them. Later I took each bag and weighed each bullet on a nice digital scale, and again separated these by weight.

Once I had this completed I then measured these from base to tip and found that some of the heavier ones were actually longer and trimming the meplat changed the pile that some were initially put into.

Trust me this was a LOT of time consuming work. What I found at the end of it was that the biggest difference came from the weight differences than the length. These bullets were shot at ranges from 500-1175yds. When conditions were right I shot a 9.5" five shot group at the longest 1175yds. That said however most times it was fairly easy to keep them at or under 2" at 500 if I did my part.

These were all shot from a wildcat chambered .270 caliber magnum using heavyweight bullets which were either 169 or 195 grains. However using some standard factory 150gr bullets right out of the box produced equally accurate groups out to five and eight hundred yards.

So on one hand in my opinion it can make a difference IF you have a custom rifle built from the ground up for accuracy, top of the line optics, and shooter that can make it all work.

On the other hand, for the average day in and day out shooter with standard factory equipment I fully believe it is a waste of time. With most all of the other rifles I have if you dial in a load with a medium slow to slow powder, and find a good accurate grouping the powder or primer will change things more than the bullets.

Granted these are only my experiences and opinions, but I have found it to be fairly accurate for going on 35yrs of loading for multiple brand firearms and calibers.
 
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Some people think too much. I load mine to fit the magazine and with all the speed I can get and still keep 3 shots inside 1" at 100 yards. Sweating a bunch of details in order to find a way to keep 5 shots inside 1/2" just doesn't pay off in the real world.

Once you start shooting at ranges longer than 100 yards and doing it from field positions there is no practical difference between a rifle/load that'll shoot 1 MOA for 3 shots and a 1/2MOA 5 shot rifle.
Click to expand...

That may be true.

Some of do like to get groups as small as possible off a bench, so to each his own.

When I was hunting 1.5 inches was more than enough. Now, I love the 3/8 ones when I get them.
 
For match ammo I maintain the distance between
bullet and lands ( any variance in bullet length does
not affect performance )
( A competition seating die should have a micrometer
dial to adjust the seating depth for each bullet )

Chasing my tail, could be
But in competition every 10% improvement adds up
( 10% here, 10% there, it adds up )
giving me an edge over my competitors

My competition ammo uses the same hole at 100 and 200
at 300 yards all holes are touching, at 600 they are all in
the X ring providing I do my part
( with this ammo my part is the biggest variable )
 
In my copy of "Complete Guide to Handloading", all the data shows seating depth as just that; how deep the bullet is seated into the case. For example; 30-06 with 150 gr. Bronze point the seating depth is .275". I have no idea when "OAL" became the standard for bullet seating. No OAL measurements are given, so mebbe the handloader is expected too think about his reloads fitting in his gun (magazine, feeding, etc.)? :rolleyes:
 
Ogive measurements are irrelevant. OAL is measured from the base of the cartridge to the point of the bullet, not to the ogive.
Ogive measurements will be different with every rifle due to the differences in every chamber's dimensions. There is no standard ogive measurement.
Imperfect points of a bullet doesn't make the slightest difference to accuracy either. The only part that matters is the base.
Nobody except the Bench Rest guys would ever notice any difference between the jump or the empty space.
 
T. O'Heir,
I am confused by your comment: "Ogive measurements are irrelevant. OAL is measured from the base of the cartridge to the point of the bullet, not to the ogive. "

Base to Ogive measurements are very relevant. That is how one determines if they are seating their bullet to the proper depth. I aknowlege that it will vary from chamber - chamber, but base to ogive is possibly the most important measurement in hand loading as it determines the jump. And you don't have to be a bench rest shooter to know when your groups go from 2" to 1" because you moved closer to the lands.

The threads question is on weather using competition dies and adjusting the seating depth to get base to ogive EXACT is altering some other variable and thus pointless. But to say ogive is irrelevant is a bit strange.
 
I'll have to agree with Mississippi on this. Since the variations in bullet tips is common and can vary several thousandths even on "match bullets", measuring from the base to ogive would be more consistent. But I do agree that accuracy is not affected (much) by distorted bullet tips.
 
Some people think too much.
Click to expand...

This, this, this, this!

Sometimes it amazes me at how much effort is put into something that has an immeasurable impact. There is no such thing as "perfect", especially in anything mass manufactured like brass, projectiles, etc. The sooner you accept that fact and stop trying to attain the unattainable, the more you'll enjoy the loading and shooting process.
 
I can't help but point out that in the first half of the 1600's, Ottoman Sultan Murad IV banned the drinking of coffee and made it an offense punishable by beheading because it "made men think" too much. He feared the thinking would result in insight into his reign's inadequacies and lead to revolution. Of course, that could always happen to shooting technology, too, so let's not be too hard on thinking.

But in this case, it is correct that it doesn't amount to much. I've seen up to 0.008" in difference from bullet base to ogive, with 0.0029" standard deviation, so ±0.004" around the mean. This was a .308" 150 grain SMK. In QuickLOAD the effect is about like ±0.025 grains of powder charge error in a .308 Winchester cartridge and is about a foot per second for a full load of 4895 under that bullet. It's not zero, but it's not much, and certainly less than other shot-to-shot pressure and velocity variations.

Most seating dies, incidentally, push on the ogive of the bullet, so you won't get variation in case head-to-ogive position due to on bullet base-to-ogive intercept variation. However, if you want the bullet jump controlled, it isn't the case head-to-ogive length that matters, but the headspacing surface to ogive length that does.
 
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