Effect of different bullets on ballistics/pressure

[NWcityguy2]

Some of us own a chronograph as well, and while those don't measure pressure either they can show when something is wrong with unexpectedly low or high velocities.

This is what I actually said, just a few posts up. If anyone doesn't understand that a chronograph measures results that are produced while following load data, reloading isn't for you.

 

[Charlie98]

This is what I actually said, just a few posts up. If anyone doesn't understand that a chronograph measures results that are produced while following load data, reloading isn't for you.

A chronograph also measures results that are produced while NOT following load data. It's a circular argument.

 

[NWcityguy2]

In this context, its a strawman argument. No one ever suggested it, and yet its being debated against like someone did.

 

[NMexJim]

Hornady eXtreme Terminal Performance - XTP. A self-defense bullet. I would imagine that Hornady has tested the expansion rates and velocities for this bullet to achieve max performance and that is why you see a lower fps which are matched to the bullet performance.

You can get hi-speed out of a lead bullet, but the base will melt away and cause extreme barrel leading. Buying lead bullets with a copper gas check will improve velocity w/o excessive leading.

But really, we're not talking apples to apples. The LSWC is more of a target bullet (although it has been used in SD) but it will not match the performance of the XTP. I wouldn't get too involved in trying to reason the two out.

 

[BBarn]

Chronographs measure velocity. They don't tell you if something is wrong or not. That would be a conclusion reached by an individual.

It would have been interesting to see what pressure (safety) conclusions might have been drawn if the OP bullets, powder charges, and velocities were provided; but the pressure data hidden.

 

[P Flados]

Extra careful, is not redundant. If your load matches up good with published data that seems to make sense, loading to the max listed is no big deal. If your stuff does not match real good, either get data that does match, or back off and do not go to the max listed. I added the qualifier about the load data, because I really like to compare all the data I can get (more on this below).

Using a chrono can work Ok as long as your gun matches up pretty close with the test gun. For revolvers, using a chrono is much less effective than most other gun types. Revolvers have lots of variables that can make a given gun shoot slower or faster than other guns.

The Quickload software is not perfect, but it is very predictable and completely repeatable. When one load from a published manual shoots a good deal below (velocity and/or pressure) Quickload and the next load down in the manual shoots above Quickload, I get suspicious of the published data. I have been around enough data gathering efforts to understand that any test data can potentially be off. I have seen plenty of variations in max charges for the same bullets in the same cartridges from different sources.

I recommend not using the hottest data you can find or pushing limits unless you know your gun has plenty of margin. I personally prefer getting a bigger and/or more powerful gun when I want more power instead of taking silly chances with a gun that will work just fine if not pushed too hard.

Again, the biggest risk is for specific combinations of cartridges and guns. A lot of rounds are not assured to show "pressure signs" at under SAAMI ratings. Combine this with guns that are not known to be high margin guns and you are in the risk area. This really is just common sense. I continually get amazed by the pushback from people that either do not like it or do not get it.

 

[P Flados]

You can get hi-speed out of a lead bullet, but the base will melt away and cause extreme barrel leading. Buying lead bullets with a copper gas check will improve velocity w/o excessive leading..

Wrong on the first point, maybe right on the second point.

I have pushed 35 cal coated cast bullets without gas checks to over 2000 fps in my carbines with good results. I been up around 1700 fps in TC Contender handguns. Base melting does not cause leading. The best explanation of typical leading is gas cutting from hot gasses leaking past the bullet. Undersized bullets are frequently the underlying cause. Gas checks are thought to do two things. They help seal better (reduce or prevent hot gas from leaking by) and they may help "scrape" off any residue from previous shots. For something like a 38 Sp (back on topic), gas checks are not needed and never have been.

 

[GeoDudeFlorida]

Wrong on the first point, maybe right on the second point.

I have pushed 35 cal coated cast bullets without gas checks to over 2000 fps in my carbines with good results. I been up around 1700 fps in TC Contender handguns. Base melting does not cause leading. The best explanation of typical leading is gas cutting from hot gasses leaking past the bullet. Undersized bullets are frequently the underlying cause. Gas checks are thought to do two things. They help seal better (reduce or prevent hot gas from leaking by) and they may help "scrape" off any residue from previous shots. For something like a 38 Sp (back on topic), gas checks are not needed and never have been.

Don’t forget to account for the alloy of the “lead.” Swaged lead, even when sized right, tends to be more prone to leading when pushed too fast -top-range .38Spl speeds, even - than Linotype or #2 Alloy, which are both much harder.

There are lots of factors to look at, even in the lowly .38Spl.

 

[Charlie98]

Undersized bullets are frequently the underlying cause.

As far as cast in rifle cartridges... I would opine that it's more than 'frequently.'

 

[lordpaxman]

Velocity readings are no indication of pressure, and cannot be interpreted as such.

I don’t mean to throw gas on the flames…. but there is a relationship between V and P. I suspect you mean for a given Vx, there’s no good way to determine Pmax or even know what the pressure curve looks like.
I’m still going to use my chrono to know what my Vs are and compare them to published Vs. I’m not suggesting I can exactly duplicate a published V setup but if my Vs are way out of line, that will give me pause. This has actually happened to me while testing one of the newer IMR powders in .243. Good luck!

 

[Charlie98]

I don’t mean to throw gas on the flames…. but there is a relationship between V and P.

There is, indeed! However, it is not a direct relationship when you consider all of the other factors. The one round that gives you X velocity in one firearm, might give you Y velocity in another... the round is the same, but there are other factors directly related to the differences in velocity.

I suspect you mean for a given Vx, there’s no good way to determine Pmax or even know what the pressure curve looks like.

Yes... and particularly the peak pressure. At least, that's my understanding of it.

 

[lordpaxman]

Indeed, there is a direct relationship between pressure and velocity. More pressure yields more velocity within the operating range of the system. However, since we don’t know the pressure curve, nor the formula for V for the system, we can’t measure V and calculate P or Pmax. QL or GRT approximate this but it’s a model and has those limitations.
Even so, I still pay attention to the chrono and have used it to measure loads at the higher end paying attention to velocity increases, or lack thereof. Good luck.