pressure and velocity

[Bezoar]

alot of the internet just bases things on velocity as established through a chronograph, one that may or may not be set up correctly.

The attitude seems to be "i can increase my powder charge till i get the published velocity for this powder and bullet weight in my gun because if i get to much powder in i can see pressure signs in the brass"

But i have to ask because when pressure signs in a straight wall pistol cartridge arent always going to be visible, linebaughs writing on high powered ruger only loads talks alot of estimated 90,000psi 45 colt loads that never showed pressure signs other then the cylinder turning into shrapnel.

[Brian Pfleuger]

"Velocity chasing" is one of the most dangerous pursuits in which a handloader can engage.

"The internet" does a lot of things but people with understanding do a lot less of it.

Particularly in handguns, most cartridges would be way, WAY over proof pressures before any pressure signs were visible.

The quality of modern firearms probably saves more foolish reloaders than we'll ever know.

[Nick_C_S]

^^ Right there. +1 ^^

[Clark]

With strong rifles and pistols, I work up until the brass starts failing, and then back off a safety margin.

With weak rifles and handguns, the first pressure sign may be the gun being totaled.
I have bags full of gun parts that I overloaded just to see what would happen, but I have some guns I really don't want to damage. So for those I take it easy and follow published loads or wimpy loads as calculated by Quickload.

The trouble with inferring pressure from velocity, is that velocity might be pressure minus friction averaged over over 1.0 ms and the peak pressure might be in 0.2 ms. If the powder burns fast, the pressure is higher than the velocity would indicate.

That would be like asking a girl to marry you, after you only met her once.

[Bart B.]

Look at Hodgdon's web site for reloading data. Check out all the loads for the .30-06 noting the psi/cup numbers for different bullets and the velocities for each. You'll see quite a pressure range for a given bullet and velocity.

Having fired many of Lake City arsenal's 7.62 NATO proof loads having 67,500 cup pressure and noting the cases looked the same as M80 ball ammo with 50,000 cup pressure except for a very slightly more flattened primer with both fired in the same rifle, I'm convinced visual signs on fired cases for pressure is akin to measuring fish with a rubber ruler.

If one must use visible signs on cases, I suggest your get some SAAMI reference ammunition from ammo companies making it then shoot it in your rifle. Carefully examine the case for visual indicators. That'll show what their stuff loaded to exact SAAMI specs for velocity and pressure in a SAAMI spec test barrel does in your rifle. Go to page 112 in the following for info on reference ammo:

http://www.saami.org/specifications_...wnload/206.pdf

[steve4102]

Originally Posted by Bezoar

The attitude seems to be "i can increase my powder charge till i get the published velocity for this powder and bullet weight in my gun because if i get to much powder in i can see pressure signs in the brass"

There are those that believe a Chrony can help predict pressures in their firearms. Not so much by increasing the charge weight until the published velocity is reached, but by stopping with load development when either Max charge weight is reached OR published velocity is reached, whichever comes First. In other words, never load above max charge weight and never load above published velocity.

The second part of your sentence is the real issue IMO. We read it or hear it just about every day, " I loaded my XXX with YY grains of powder and didn't see any pressure signs so I know I'm good". Where did this mentality come from? Where is it written in any manual that "Pressure" signs will magically appear as soon as the load exceeds SAAMI pressure specs?

Take the 223 for example, it has a MAP of 55K psi while it's cousin the 5.56 has a MAP of 62K psi. How does the brass case or the primer know to show the handloader "pressure" signs just over 55K in the 223 yet be smart enough to wait till the load is above 62K in the 5.56?

The big question for me is at what PSI do these so called pressure signs rear their ugly head? If the handloader is on the lookout for them, he/she should have some idea as to when they will appear.

Sticky bolt lift is one we are all told to watch out for and to avoid. At what psi will this occur in a 270 Win (65K MAP) and at what psi will it occur in a 223 ( 55K MAP). If it is the same then the 223 loader is in for a big surprise if he is loading till he/she finds it.

[Bart B.]

Steve, I think your pressure numbers for the 5.56 NATO round are a bit high. And they're not measured using the same pressure transducer system as SAAMI specs for the .223 Rem uses. With the same pressure measuring system, both ammo types have little difference in peak pressure. For reference:

http://weaponsman.com/?p=604

[steve4102]

I use Quickload which I have total confidence in, you can use whatever reference you wish.

QL 5.56 NATO = 62,366 psi

QL 223 Rem SAAMI = 55, 000 psi.

The point is they are indeed different.

[Brian Pfleuger]

Steve,

What you're seeing there is a difference in measurement techniques and pressure sensor placement. The differences between them are irrelevant. They use the same brass, bullets and barrel dimensions. .223 does tend to have a slightly tighter chamber (typically) which could in theory cause higher pressures with ammo intended for looser chambers but there's positively no reason why one would be good at 55k while the other is 62k.

The pressure you see in QuickLoad for 5.56 is the CIP limit. They don't (to my knowledge) even list .223Rem as a separate cartridge.

[steve4102]

My point is that different cartridges have different SAAMI pressures limits. Take the 270 Win vs the 30-06. The 30-06 runs at 60K and the 270 runs 65K.

When looking for "pressure" signs, how does the brass case or the Primer know to give you a warning just over 60K in the 30-06 yet wait this the load is over 65K in the 270 win?

[MarkCO]

I'll ditto Brian's comments on the subject.

Let's also realize that revolvers, auto-pistols, bolt guns and gas guns all have different operating systems that can give false positives. For instance, an over-gassed AR-15 can have blown primers, bulged and scratched cases, FP retainers breaking and other "indicators" mis-read as high pressure when in fact it is just because the system is attempting to extract the case before the chamber pressure has dropped sufficiently.

Materials do behave predictably in most cases and for high-velocity rifle rounds, primer flow can be a good indicator of pressure in manually operated system, less so in an auto-loading system.

[Brian Pfleuger]

You don't and there's no reason, from a safety perspective, that you can't run a .270 at .30-06 pressures.

I've run my .204 (SAAMI 58k) up to about 65k. I run my .243AI (58k in theory but no SAAMI limit) up to 65k too.

The brass doesn't know there's an arbitrary limit. It only knows pressure.

Fact is though, that last few thousand PSI comes with very little benefit. Check the velocity differences in QL between 58k psi, which is approximately where barrel erosion goes exponential, versus 65k, which is roughly where brass life becomes an issue. You're usually gaining 1% or so velocity for a 10+% PSI increase.

[F. Guffey]

testing for pressure: On the internet, a format is used, questions start the same way and the rational for not being able to accomplish pressure testing proves 'it can not be done'.

Me? I have always thought if there was something in the chamber when the trigger was pulled it would be possible to determine the effect pressure had on the case.

AND THEN....? I realized there was something in the chamber when the trigger was pulled, 'THE CASE' the case is in the chamber when the trigger is pulled. I do not have the authority to give the case an exemption, when the trigger is pulled the case gets hammered.

I have tested receivers that I had been advised were suspect, one barrel, one bolt and 4 receivers. My methods were considered suspect. I used new cases. The receivers cost $25.00 each.

I measure before and again after, I have old shell holders that I use when testing the effect pressure has on case head upset. I can modify new shell holders, not a problem, it only works when I measure before and again after.

objective, I do not want to upset the case head, from the beginning there was a technique, the technique only worked if new cases were used.

F. Guffey

[Clark]

I do not care what my pressure is.
I just care about the effects of pressure.

In my strong rifles, usually loose primer pockets are the limit. In the solid case heads, it is primers piercing.

I use the pressure estimates of Quickload. Cartridges I load with the same case head will all get loose primer pockets at about the same Quickload pressure.
I load to 67kpsi in; 22-250, 243, 250 Savage, 257 Roberts AI, 260 Rem, 6.5x55 , 270, , 7x57mm, 308, 30-06, 8x57mm, and 35W.
I load to 72 kpsi in: 7mmRemMag, 300 Win Mag, and 338 Win mag.
I load to 78 kpsi in; .222 and .223.
I load to 85 kpsi in; 6mmBR, 260 from 308 Lapua palma brass, and 308 palma.
I load to 85 kpsi in; 25/35 and 30-30.

Now I don't care about velocity either.
I just care about the effects of velocity.

I used to care about velocity when I was using Quickload's Quicktarget to make drop charts.

Now I zero at 200 yards, and back up further away from the target while making marks on the elevation turret.

[steve4102]

Originally Posted by Brian Pfleuger

I've run my .204 (SAAMI 58k) up to about 65k. I run my .243AI (58k in theory but no SAAMI limit) up to 65k too.

How do you know this? Do you have a Strain Gauge or other pressure testing equipment?

[Brian Pfleuger]

Yes, I have RSI Pressure Trace and QuickLoad.

Frankly, I trust QuickLoad more.

[Bart B.]

I would trust Pressure Trace for the best numbers comparing load recipie A to B in a given barrel. That includes all the rifle's stuff to cause pressure albeit not what the same load would probably show for pressure in a SAAMI spec barrel and psi system. Quickload doesn't include inputs for all the rifle's stuff that impacts pressure numbers, most of them it does.

Not many folks know why the .270 Win's pressure's higher than the .30-06 using SAAMI's specs. Once folks realize what factory barreled actions there are out there for each and when each round was first used, they may observe that some of those for the .30-06 are a bit weaker and don't support the case head as well as those for Winchester's 27 caliber round.

[Brian Pfleuger]

Yeah, Pressure Trace is good for "is A more than B" but it's absolute numbers are heavily dependent on proper gauge mounting and extremely precise measurements that are not always easy to get.

Obviously, QuickLoad's number are dependent on measurements too but it doesn't depend on tricky gauge placement. There are still "voodoo" type variables too, like "Start Pressure" and "Weighting Factor" but they seem to be less critical.

Particularly with my .204, with very thick metal because of the small cartridge, it dramatically understates pressures. I pushed a 32gr V-Max over 4,200 with Benchmark, a load QuickLoad thinks will be 65,000-ish psi and PT shows under 55,000.

Neither is "absolute" but I trust QuickLoad to be closer to absolute and PT to be comparative.

I do think that Pressure Trace would/could be very accurate if every thing was done exactly right, it's just very hard to do.

[Bart B.]

Has anyone made velocity (or pressure) tests with firing pin springs at different load/force ratings below or above factory specs?

[Clark]

I designed electronics for a long time.
I have done math for a long time.
But there is no way for me to glue a CEA-O6-250UW-350 strain gauge on the outside of my rifle chamber, wire it up with a Wheatstone bridge, instrument amplifier, and storage scope.... and then think I have measured pressure in a way I can trace back to the NIST.
Way too many out of control variables and Roark's equations.

So there goes the first level of meaninglessness.

The second level of meaninglessness is "What would I do with the information if I knew the true pressure?"

Compare it to the number registered with SAAMI for that cartridge?
What good would that do me?

[steve4102]

Yes, I have RSI Pressure Trace and QuickLoad.

Frankly, I trust QuickLoad more.

Perfect!

With your ability to test actual pressures have you ever pressure tested loads to find out at what psi certain "pressure" signs actually appear in various cartridges?

For example, your 204 runs at 58K and you bring it up to 65K, Do you see any of the so called "pressure" signs at 65K? If not, have you brought it up over 65K looking for any of these so called signs, if so, at what PSI did they rear their ugly head.

[Slamfire]

The attitude seems to be "i can increase my powder charge till i get the published velocity for this powder and bullet weight in my gun because if i get to much powder in i can see pressure signs in the brass"

Basically I use my chronograph to establish maximum limits during load development. I believe that if my bullets are going faster than published values than I am exceeding safe pressures.

However, loads developed with a chronograph have given stiff extraction in different rifles on warmer days. So, I cut the loads because blown primers, difficult extraction are positive indications of over pressure.

Computer programs are good for modeling and predicting, but they are after all, just a formula and a data base, and what actually is actually going on in your rifle is something entirely different. Perhaps because of the sophistication, bells, whistles, and cost of the things, users believe that the programs are 'truth", but unless you have a pressure transducer mounted on your barrel feeding into that program, computer programs are a modern version of tea leaf readings. But a very sophisticated version of tea leaves.

[Brian Pfleuger]

Unfortunately, I haven't had any real time to play.

One thing I do get from PT that I can't get from QuickLoad is an indication of potentially hazardous secondary pressure spikes.

6mm Rem firing 55gr Nosler LF with Rl-17:



Notice the sudden pressure drop just after 1.0ms and the spike just following the drop. This indicates that the bullet is "out running" the powders ability to produce gases, resulting in the pressure drop and decreasing acceleration, which causes the pressure to catch up to the bullet and create a localized high-pressure zone, which increases burn rate and causes a chain reaction burn spike. (At least that's the theory)

[WESHOOT2]

I do not care what my pressure is.
I just care about the effects of pressure.

This.
I suggest it's the understanding of diminishing returns.......


Once again, Clark succinctly nails it: "Pressure doesn't matter; its results matter"

[Jerry45]

Not to get off topic, but Bart B brought up Hodgdon's site. I use it a lot but have always had a question about it. For the same bullet weight it gives CUP for some powders and PSI for others. Why?