Bullet Brand/Pressure Differences?

[antelopedundee]

What would cause pressure differences if a 120 Sierra flat base bullet was used in place of a Hornady 120 grain flat base bullet? Why would one result in excessive pressures over the other? This is an observation of someone on another message board and not necessarily my experience. Do the .309 Lapua bullets cause higher pressures if used under the same conditions as .308 bullets?

The bullets were used interchangeably with the same primer, case, powder charge, etc.

[murray brook]

I assume you are refering to 25 cal bullets, 120 gr Sierra HPBT and the 120 gr Hornady flat base HP. Off the top of my head I would think both have different bearing surfaces. This would give different pressure readings as well as jackets of different hardness.

[jackie schmidt]

What would cause pressure differences if a 120 Sierra flat base bullet was used in place of a Hornady 120 grain flat base bullet? Why would one result in excessive pressures over the other? This is an observation of someone on another message board and not necessarily my experience. Do the .309 Lapua bullets cause higher pressures if used under the same conditions as .308 bullets?

The bullets were used interchangeably with the same primer, case, powder charge, etc.

Some years ago, Gene Bukys and I did a test with about 5 different 68 grn Benchrest Bullets. Some were rather straight shanked with a 7 ogives, such as Fowlers, others a much higher number ogive with not nearly as much full diameter bearing surface, such as a Barts Ultra or Bruno boat tail.

With the exact same load, within minutes of each other, over the same chronograph, the straight shank lower number ogive Bullet averaged about 75 to 100 fps more than the others.

I suppose a straighter, and fatter shank will build a pressure spike quicker, giving more velocity out of the same barrel.

[antelopedundee]

I assume you are refering to 25 cal bullets, 120 gr Sierra HPBT and the 120 gr Hornady flat base HP. Off the top of my head I would think both have different bearing surfaces. This would give different pressure readings as well as jackets of different hardness.

Yes, but could be 2 different 120 grain 6.5s too.

On another board I made the following comment.

"In my experience a 120 grain bullet should use the same charge weight regardless of brand."

So if I was using Sierra data for a 117 grain bullet, I would feel free to replace the bullet with another brand like Hornady with no other changes.

Looking at my copy of the Sierra manual open in front of me for the .25-06 they use the same data for the 117 gr flat base, the 117 gr BT and the 120 gr HPBT.

And another person commented thusly.

"And a 120gr bullet is not a 120 gr bullet.
Meaning if you use a Hornady, and find a load you like, chances are you'd be over pressure if you load up a Sierra.
For some reason Sierra always uses a lower powder charge in all my rifles."

So why would he see such a difference? IIRC from reading P O Ackley's Handbooks for Shooters and Reloaders he fired 8mm bullets down a .30 cal barrel with no ill effects saying that the 8mm bullet swaged down to .308 in the first few inches of travel. See page 31 of volume 2 of the soft cover issue. So I don't think bullet diameter is the reason. BTW, I think P O would have been a fun guy to hang out at his shop with and shoot the bull about shooting.

[Wilbur]

Different brand bullets have different velocities. They're different shapes! To overstate the issue, you would not expect a 120 grain 6mm bullet and a 120 grain 6.5 to have the same velocity when fired from the same rifle. While the difference in the bullets may be too small to measure...there's still a difference...and that difference causes a velocity difference to follow.

I don't know why the term "excessive pressure" was used unless the load was on the ragged edge of being too hot from the start.

[antelopedundee]

Different brand bullets have different velocities. They're different shapes! To overstate the issue, you would not expect a 120 grain 6mm bullet and a 120 grain 6.5 to have the same velocity when fired from the same rifle. While the difference in the bullets may be too small to measure...there's still a difference...and that difference causes a velocity difference to follow.

I don't know why the term "excessive pressure" was used unless the load was on the ragged edge of being too hot from the start.

The loads weren't necessarily at maximum. The poster stated that he worked up a load for 100gr Nosler Ballistic Tips [caliber not specified] and when he substituted a Sierra 100gr GameKing SPBT of the same caliber and with the same powder charge and primer that he experienced difficult bolt lift which he took to mean higher pressures. He said he saw the same thing with a 7mm-08 and actually blew a primer with a 7mm mag. So why would substituting a Sierra bullet of the same weight and caliber for a Hornady cause pressure? If I saw a load for a .25 cal 117 grain bullet for a .25-06 in the Hornady manual, I'd feel free to use any .25 cal 117 grain Sierra bullet with that same load data or tell me why I shouldn't.

[Joe S]

Different core hardness, different jacket thickness, bearing surface lengths, diameter variations, ogive differences causing one to have more or less jump to the lands. lots of ways to get pressure differences between two brands of bullets of similar weight.

[antelopedundee]

Different core hardness, different jacket thickness, bearing surface lengths, diameter variations, ogive differences causing one to have more or less jump to the lands. lots of ways to get pressure differences between two brands of bullets of similar weight.

But would any of those cause EXCESSIVE pressure differences?

[brickeyee]

But would any of those cause EXCESSIVE pressure differences?

It depends on how close to the edge the load NOT showing pressure signs is.

If it was barely shy of max it can some down to the many many things that cause pressures to rise.

Letting a round sit in a hot chamber while aligning the rifle for a longer time can all to easily heat them up.

[classcat]

What would cause pressure differences if a 120 Sierra flat base bullet was used in place of a Hornady 120 grain flat base bullet? Why would one result in excessive pressures over the other? This is an observation of someone on another message board and not necessarily my experience. Do the .309 Lapua bullets cause higher pressures if used under the same conditions as .308 bullets?

The bullets were used interchangeably with the same primer, case, powder charge, etc.

The Diameter of the bullet, on the body, pressure ring, and the OAL. Measure them with a snap gauge (indicating micrometer) and you will have your answer. A dial caliper won't do the job. One bullet may measure .308200, and the other .308600. The .309000 may measure .309500.

[antelopedundee]

It depends on how close to the edge the load NOT showing pressure signs is.

If it was barely shy of max it can some down to the many many things that cause pressures to rise.

Letting a round sit in a hot chamber while aligning the rifle for a longer time can all to easily heat them up.

He had the same issue with 3 different cartridges in 3 different rifles. Read my other posts. I copied his comments/concerns directly so you know as much as I know about it.

He is some more from him.

"My load development is done via ladder test, usua)y 80-90 degrees at 1, 600 ft elevation.
I don't go for max loads, i go for most accurate load. Chrono comes to the range after ladder then seating depth testing.

Load development is usually done with Hornady bullets, and transfers over well to Nosler and same weight Berger bullets.
Have learned that if i want to shoot Sierra's then fresh load development starts.

Not saying by any means that they are a bad bullet, i like them, and usually get some of my best groups with them. I have zero issues using them to hunt with."

So why are Sierras an outlier for him?

[Wilbur]

You asked a question and we've tried our best to answer. I'll ask this one in return....who do you think is giving you the straight skinny?

[antelopedundee]

You asked a question and we've tried our best to answer. I'll ask this one in return....who do you think is giving you the straight skinny?

I know nothing of the other person other than what I've posted here about him so whether he is being truthful or not I have no clue. I've read some ideas/suggestions here, but nobody has offered a clear cut definite cause. I suggested that he contact Sierra and see what they have to say. I have some .25 cal 117 grain Sierras and Hornadys. I will load few of each with identical components in my .25/.284 and see if I notice any differences. If there is a definitive answer, I figger someone here would have it.

[brickeyee]

I know nothing of the other person other than what I've posted here about him so whether he is being truthful or not I have no clue. I've read some ideas/suggestions here, but nobody has offered a clear cut definite cause. I suggested that he contact Sierra and see what they have to say. I have some .25 cal 117 grain Sierras and Hornadys. I will load few of each with identical components in my .25/.284 and see if I notice any differences. If there is a definitive answer, I figger someone here would have it.

They may not know or have any idea.

I am unaware of any bullet manufacturer that removes jackets from completed bullets and then checks jacket temper (hardness).

At least one precision bullet maker tried increasing forming speed and found the bullets did not match each other from the same set of dies as well as before.
Swagging at a lower speed into the forming die.

The core is being formed by using pressure so high the lead flows in a plastic manner.

It would make sense that trying to get it to flow faster using greater pressure to speed up the cycle might have undesirable effects.

The jacket metal is also being formed and its temper (hardness) will be altered from initial cupping.

[Doug Casner]

This is not a clear cut cause. There are a lot of operations in making a bullet or a case. A lot of annealing, draws.bullet assembly, etc. Operators, toolsetters. Some of them do their best others could give a rats a--. Ive seen stuff off the same machine vary terrible due to the previous operations running crap. Its hard to guage one after you shoot it then you would have to know the specs. Lake City loaded some Sierra bullets. Doug