Pressure Indicators Are They Reliable?

[su35]

For 30 years now I have been reloading and used traditional pressure indicators to tell me if my loads were too hot for use.

Indicators being:
Heavy bolt lift,
Extractor marks,
Brass being used X numer of times,
Seating primers in pockets snugley,

I have read recently where a gun writer stated that standard indicators were unreliable.
qoute...

"I have explained before, here and in print, why traditional pressure signs don't work. Layne Simpson used them for workup on the 7mm STW. He got the same long use out of cases that you do, yet when pressure tested by Remington, most of his loads were 70,000 (psi) and some much more".

The writer now uses "Comparative Case Expansion" to tell him loads are safe.

Can Nosler expound on this? I think this very important for obvious reasons.

Thanks

 

[Rusty]

I've always counted on the indicators you have listed above.

As a matter of course, I don't try to see how fast I can push it or how close to Max I can get. I've always found the most accurate loads are well short of max.
Just my opine.

 

[su35]

Rusty, couldnt agree with you more. But more times than not, the most accurate load is a hot load. Ive a candle snuffer in a 260 that I had to back off a couple of grains. Accuracy backed off as well.

I

 

[NOSLER]

Please always use the tried and true pressure indicators. If they didn't work, our Ballistics Lab and all the others in the industry have been doing something wrong for 50 + years.

 

[5Redman8]

Isn't velocity a good measure of pressure???

Kyle

 

[squirrelsniper]

Isn't velocity a good measure of pressure???

All things being equal, yes. However, things are never equal and there are several other things that can affect velocity. So in a way velocity can be an indication of pressure, but yet some barrels are capable of producing extraordinary velocities at safe pressures, so you have to keep other things in mind.

As for the pressure signs being reliable, I feel they're reliable for the most part. Of course unless you have a gun problem, you're going to be a fair amount over SAAMI specs to get the pressure signs, but thankfully most modern rifles can handle it without any serious problems. Also, straight walled cases are often the exception and many times don't show pressure signs until you're realing pushing the limits, and then it usually first shows up as extraction that's more difficult than common.

 

[Dan in Va]

su35,

There are some renowned gunsmiths, bbl makers, and action makers who have written (e.g.: Hanson's book, Varmint Hunter's Odyssey) about this very same thing. It seems that when wildcat cartridges have less body taper their response to pressure can be different. It's very common to have none of the classic signs you mentioned until pressures become dangerously high. This is why it's strongly encouraged to use a chronograph during wildcat load development. The velocities can become irratic as pressure reach excess, and can be sensed with a chrony to tell you the max load, even though none of the traditional high pressure signs are manifesting. If one keeps adding more powder, it's easy to be over the edge and not know it. By the time one sees the classic pressure signs you can be so far over the edge that something dangerous can happen without any warning.

And since this cartridge is Layne's design, he was surely using a custom bbl that was lapped, smoother, faster, and offering less resistance than a rough factory bbl. More variables.

There may be more factors than I listed, but when considering that wildcats (especially with tighter chambers and/or necks) can behave differently than standard factory chamberings and need to be approached with more considerations.

dan

 

[longwinters]

I have been reloading 2 years now, and always stayed within the newer Reloading books guidelines. But I also always looked for the traditional pressure sign symptoms. Now I hear that velocity can be another "sign" of high pressure. How do you determine what velocities are safe in a specific caliber? If the reloading books are on the lite side then their velocities must also be on the slow side. So where do you get your guidelines?

For instance I have a Sako 280 that I shot yesterday with 57 gn H-4831 with 140 gn Nosler Partitions. This is 1 grain over what Nosler has as it's top load for the bullet. John Barsness says 58 gn of H-4831 is a great load. I hedged and went 1 grain less, even though the rifle is newer and just getting broken in. Traditional over pressure signs were not evident. But my 6 shot group was 1/2" @ 100. I have no idea what the velocity was.

Long

 

[Dan in Va]

Long,

A chronograph isn't necessary for handloading the standard cartridges. You ought to be just fine if you work up slowly and watch for the traditional high pressure signs along the way.

Because bbls and chambers vary so much they must be loaded for on an individual basis. You may have noticed how the old manuals list higher loads than current manuals. The newer conservative data is influenced by potential legal problems as well as some other factors like changes in brass thickness over the years.

You're right to work up loads cautiously, and as long as you're watching your business, you can work up factory calibers until you see some signs of pressure. Sometimes you can have a safe load that is way over max.

There are some other reasons that will allow you to use lots of powder. Some bbls are much smoother than others and diameters of grooves and lands can vary. Bullet luberication (moly or waxing) causes bullets to advance farther down the bore farther and faster than nonlubricated bullets. This gives you more space for gas to expand and requires more powder to achieve the same pressure. Another common thing is excess freebore, that lets bullets be seated out farther out to get near the lands, and increases the internal dimensions of the case. These situations together can allow the use of a great deal more powder. I have a .222 that is loaded like a .223.

Hope this helps.

dan

 

[longwinters]

Dan,

Thanks, your info is helpful and gives me more to consider. So has the thickness of brass actually changed in say the last 10 years?

Long

 

[Dan in Va]

Long,

Yes, .22 Hornet brass is one example of how brass has changed. It used to be quite a bit thicker than it is now. Any time you happen across some really old brass it's good to consider this. There are pluses and minuses to this. On one hand, thicker brass is stronger, but the flip side is that pressures can rise with less case capacity in the same load that works in newer brass.

With current Hornet brass production, Remington is significantly thinner and softer than Winchester. This can make some difference with my .22 K-Hornet and .17 Ackley Hornet pistol bbls.

It's even debatable how much difference it makes when cases of the same lot are sorted according to weight. My rifles have factory bbls, and I haven't found that sorting has done much for accuracy. But friends who shoot custom bbls can often see some group improvement.

I'm just a varminter and only shoot small rifle bullets lately... .17 Rem, .222, .220 Swift, and .243...so I don't know much about the big stuff. I'm grateful for the many shooters who have taken the time to share their experience with me. There are many others on this board who are also very helpful.

dan

 

[Jaywalker]

Nosler,

I believe you misunderstood the thrust of su35's question. The writer, John Barsness, was not advocating ignoring the traditional pressure signs. His point was that by the time you reach that far, you're already at 70,000 psi, so you should try hard never to get "tradtitional pressure signs." To avoid them, Barsness advocates using velocity readings from a chronograph. Can you comment on that?

Jaywalker

 

[vapodog]

There are many pressure indicators and today for as cheap as chronographs are folks oughtta have one as another pressure indicator.....also the use of a very precise micrometer to check the diameter of the case just ahead of the extractor groove is a fine pressure indicator.....even 1/2 thou growth is a strong sign of excessive pressures in my opinion.

 

[squirrelsniper]

The writer, John Barsness, was not advocating ignoring the traditional pressure signs. His point was that by the time you reach that far, you're already at 70,000 psi, so you should try hard never to get "tradtitional pressure signs."

I haven't read the article, but it sounds like Barsness was getting at the same thing I said above,

As for the pressure signs being reliable, I feel they're reliable for the most part. Of course unless you have a gun problem, you're going to be a fair amount over SAAMI specs to get the pressure signs, but thankfully most modern rifles can handle it without any serious problems.

.

Modern centerfire cartridges in modern rifles generally operate around 60k-65k PSI. Well, at 65k PSI, if everything with the rifle is okay, then you won't have the traditional pressure signs. Now, let's say you have a cartridge with a 65k PSI SAAMI pressure limit. Will the pressure signs magically appear as soon as you go over SAAMI max and reach 66k PSI? No. You're most likely going to be in excess of 70k PSI before you get any traditional pressure signs which indicate that the pressure is too high. Of course by that time you're way over pressure, but the pressure indicators did show up before you blew up your rifle and yourself. The pressure signs should show up before you get high enough to seriously damage a modern rifle, but just because they're not there doesn't mean that you're not a decent amount over SAAMI specs.

 

[Jaywalker]

sqirrelsniper,

Yes, I believe that was his point, too. He advocates use of a chronograph to determine velocity, which is a very reliable indicator of pressure.

Jaywalker

 

[NOSLER]

The writer, John Barsness, was not advocating ignoring the traditional pressure signs. His point was that by the time you reach that far, you're already at 70,000 psi, so you should try hard never to get "tradtitional pressure signs."

What issue was that article in?