Bullet Jump Versus Expansion Ratio

[scatterbrain]

Bart's answer/question to the Bullet Jump question gives raise to another question along the same lines: the curve of a box of bullets will not be the same, I've measured a lot of them. That means that the bullet seating die will not touch the curve in the same spot, bullet to bullet, making the distance from base to ogive different, some I've measured will be .008". I've experimented with seating the bullet bases to the same measurement, takes some work, but can be done. But, I don't see any improvement in results. Question is how much does it take to make a difference and which would be more important, constant expansion ratio, or constant bullet jump?

 

[akinswi]

Scatter,

My redding competition seater die will seat a 168 SMK too within half of 1thousandths. I can usually get a consistent Base to ogive Measurement with in half to 1 thousandths if I sort the bullets by overall length. Some will say sort to base to ogive, But after sorting by both methods and the end results were the same.

But again calipers and bullet compartaors will have some errors in machine tolerances etc.

 

[hounddawg]

that begs the question, do you chase the lands? If so how how many rounds do you go before adjusting your seating depth and how much throat erosion do you see.

 

[Unclenick]

The trick is that bullet contact with the throat occurs at close to full bullet diameter before different ogive radii have diverged to a very great difference in diameter. The Hornady bullet comparator inserts touch the bullet ogive at a narrower diameter than the actual throat, so it sees a bigger difference. I switched to the Sinclair Stainless Steel inserts because they mimic a real throat shape more closely. In measuring samples, this is confirmed. The base-to-ogive measurements are shorter and more consistent.

That said, the narrower hole in the Hornady insert is better for helping you sort matching bullet's. The idea is the differences in bullet ogives comes from them being the products of different tooling sets that are subsequently combined in the same box. So if you can sort them into clear base-to-ogive length groups, you have probably sorted them by tool set, and if you find one of those groups shoots tighter than the others, you can save them for important matches. You may find you can sort even better by using an insert intended for the next smaller caliber bullet.

 

[akinswi]

Nick,

The Test I did with a lot of 500 Sierra matchkings I measured one group base to ogive with calibers was beyond tedious, then I measure bullets by Overall length. The results that I found that across the whole lot the ogives were pretty much with in .001 . But it was by far easier sorting by Overall Length than Base to ogive.

Then I measured the Base to Ogive of the finished rounds and they were almost identical.

 

[Unclenick]

Mine were 150-grain SMKs, and the base-to-ogive varied 0.008" (ES) with either the Hornady or the Sinclair insert, but SD for the Hornady was 0.00297" while the Sinclair was 0.00245". These bullets were about 30 years old, so I should repeat with some newer production. My assumption has been that it accounts for the 3% variation in BC that List measured for match bullets from the same box.

 

[akinswi]

you should measure those 169s I sent you see how consistent they are

 

[hounddawg]

differing base to ogive measurements will only affect the amount of bullet inside the case itself causing differences in case volume when loaded. BR shooters and long range shooters may see a difference.

If you want higher consistency than major brand name bullets buy custom bullets such as Bart's. They are not that more expensive than Bergers etc and the BTO consistency is a lot better

 

[Unclenick]

Then I measured the Base to Ogive of the finished rounds and they were almost identical.

I may have caused confusion. The base-to-ogive I was measuring on the 150s was the bullet-base-to-bullet-ogive, not the loaded cartridge base-to-ogive. For the loaded cartridge, your result is expected because the Hornady insert touches the ogive very close to where the seating die touches it. As a result, if one bullet has its bullet-base-to-ogive measurement a few thousandths longer than another, the seating die just pushes it that much deeper into the case neck, so the loaded cartridge base-to-ogive measurements match.

 

[MarkCO]

that begs the question, do you chase the lands? If so how how many rounds do you go before adjusting your seating depth and how much throat erosion do you see.

Chasing the lands is a fools errand, even though most of us have done it at one point or the other.

I use larger jumps now than I have had in the past. Less throat erosion, lower SDs, better groups. Moving to Redding competition shell holders and shortening my OAL have made my ammo so much more consistent. I am typically sub 5 for an SD.

Granted, I am not shooting benchrest, just steel and game. So getting under 1/2MOA is golden for me if that load will last as long as the barrel. I can also use the same load in other rifles and they will also shoot well.

 

[scatterbrain]

Sorting by weight has been the most productive in improvement. Take the box of 168 grain matchkings and weight them. You would think they would be the same, but they are not. Next measure the length of each bullet, you will find that you have already sorted them by length when you weight them.

 

[Bart B.]

I don't expect all match bullets of a given make, model and weight to be exact in all measurements. None are. They don't have to be exact.

What accuracy specs do Sierra's 30 caliber HPMK's have to meet before they're sold at retail in green boxes?

 

[Bart B.]

Some top ranked competitive shooters soft seat bullets long such that they go a few thousandths deeper in the case neck when the round is loaded. I've shot a few thousand that way. Keeps jump to the throat equal across all shots.

 

[scatterbrain]

Bart, from your response bullet jump would be better than constant expansion ratio, which should give uniform pressure. I can get one or the other, only wanted to know which was the better of the two.

 

[reynolds357]

Bart's answer/question to the Bullet Jump question gives raise to another question along the same lines: the curve of a box of bullets will not be the same, I've measured a lot of them. That means that the bullet seating die will not touch the curve in the same spot, bullet to bullet, making the distance from base to ogive different, some I've measured will be .008". I've experimented with seating the bullet bases to the same measurement, takes some work, but can be done. But, I don't see any improvement in results. Question is how much does it take to make a difference and which would be more important, constant expansion ratio, or constant bullet jump?

It would depend on the rifle. Some rifles like some things and others like others. The last barrel my 6PPC had on it shot it's best with almost no neck tension. Use body die only, Leave neck unsized, Long seat the bullets, let bolt closing do final seating. New barrel does not like being in the rifling, but does like almost no neck tension with a slight bit of jump.

 

[44 AMP]

Question is how much does it take to make a difference and which would be more important, constant expansion ratio, or constant bullet jump?

The answers are going to be as varied as the rifles and ammo used.
The specific micro variances in your rifle and ammo WILL BE different from mine. Does this matter? Yes and no. Yes because you have your rifle and it likes what it likes, and no, because I have mine and it like something different from yours.

Any time anyone tells you, "load it this way, and you will get better performance", they're giving you a blanket statement, which does not, and can not apply equally to every rifle in creation. IF they include the qualifier "probably will get better...." that's a different statement.

Show me a rifle where it matters, and I'll show you one where it doesn't. That is just the nature of things....