[quote=.280Rem;205277]The simple answer is that velocity is the single greatest indicator of pressure that we have without using pressure testing equipment.
I don`t understand how. If you go from standard primer to mag. primers your presure curve will spike soon with that load and while velosity might be the same, or close presue could be alot higher. Stay with to what you know to look for, but keep in mind, that while you can safely get higher velosities than what the book state in some cases, especially if using a longer barrel, it will not be more than a couple 100 fps. The greatest advantage I find to useing a crono. is that you know what your actual velosity is and it makes it alot easier to work out drop charts.
The simple answer is that velocity is the single greatest indicator of pressure that we have without using pressure testing equipment.
Quote:
Originally Posted by Catfish
I don`t understand how. If you go from standard primer to mag. primers your presure curve will spike soon with that load and while velosity might be the same, or close presue could be alot higher. Stay with to what you know to look for, but keep in mind, that while you can safely get higher velosities than what the book state in some cases, especially if using a longer barrel, it will not be more than a couple 100 fps. The greatest advantage I find to useing a crono. is that you know what your actual velosity is and it makes it alot easier to work out drop charts.
Velocity tells you about pressure before the outward classic signs do. When you get to the classic signs, you're usually WAY over pressure. Most gun writers I have talked to say those classic signs don't show up until about 70K psi in the large centerfire rifle cartridges. Your statement about primers is true, as that would basically have the same effect of increasing the burn rate of the powder. Not exactly the same thing but close. Which in theory could mean an increase in pressure at the same velocity. But, if you were already running a safe load with a regular primer, and changed to a mag primer, and didn't see a significant increase in velocity, then you'd likely still be in safe territory.
.280REM, I do weigh each and every powder charge. I dump close to my desired weight and then trickle in the rest. Also had just gotten a new digital scale and was scared to use it so I actually weighed it first with the digital and then again on the old standby RCBS 505. When shooting, I only shoot three shot groups and let the barrel cool. This is usually done while looking closer at the targets.
Unfortunately, velocity can be a poor indicator of peak pressure and that's the kind that makes guns come from together, especially so if the powder is too fast for the load. Like, a very low velocity would come at a very dangerous pressure with a charge of Bullseye. Yeah, that's a pretty extreme example but I use it to illustrate the principle that we really can't be sure of the pressures by simply recording the velocity.
In my experience, increases in velocity (in rifles) tends to flatten as charges exceed normal levels; pressure quickly goes way up for little or no velocity gain. That's what makes attempts to gain more velocity by simply cramming in more powder so dangerous. BUT - if you have attained the published velocity BEFORE reaching the book max for a normal powder, that IS a good sign you have reached the full standard pressure, so stop there!
Best to stick with case observations and bolt lift to judge pressure, IMHO. But back off at least 5% if you see any of those signs, they are for sure indications of being far over max.
Well, I will have to go along with what boomtube is saying:
"Unfortunately, velocity can be a poor indicator of peak pressure and that's the kind that makes guns come from together, especially so if the powder is too fast for the load. Like, a very low velocity would come at a very dangerous pressure with a charge of Bullseye. Yeah, that's a pretty extreme example but I use it to illustrate the principle that we really can't be sure of the pressures by simply recording the velocity."
I have used a chonograph since the 80's and I have never relied on it to tell me anything about what the pressure was.
Some barrels are faster than others and some are slower. So you can't really rely on the velocity as to what the chamber will take for pressure.
Unfortunately, velocity can be a poor indicator of peak pressure and that's the kind that makes guns come from together, especially so if the powder is too fast for the load. Like, a very low velocity would come at a very dangerous pressure with a charge of Bullseye. Yeah, that's a pretty extreme example but I use it to illustrate the principle that we really can't be sure of the pressures by simply recording the velocity.
In my experience, increases in velocity (in rifles) tends to flatten as charges exceed normal levels; pressure quickly goes way up for little or no velocity gain. That's what makes attempts to gain more velocity by simply cramming in more powder so dangerous. BUT - if you have attained the published velocity BEFORE reaching the book max for a normal powder, that IS a good sign you have reached the full standard pressure, so stop there!
Best to stick with case observations and bolt lift to judge pressure, IMHO. But back off at least 5% if you see any of those signs, they are for sure indications of being far over max.
Again, velocity is the best indicator of pressure in the absense of any real pressure testing equipment. That is not to say that, for example, in a 30-06 shooting a 165 at 2850 that the pressure will be the same or safe regardless of the powder used. You must be able to interpret your pressure from the velocity based on the components you used. This information is obtained via published data. It's why the max load for each given powder is at a different velocity. Its why in cases such as the 30-06, that the slower the burn rate the higher the velocity at a given pressure the manufacturer has set as it's ceiling. But, still, when using a particular powder, your pressure is indicated by the velocity, relative to that particular powder and bullet weight. At a given velocity, pressure will increase as the burn rate of the powder gets faster, until at some point, that velocity is no longer being acheived at a safe pressure. Conversly, at a given pressure, slower burning powders will give increased velocity than faster ones. Still, the velocity is the primary indicator of pressure, in the absence of actual pressure testing equipment. If you're working up 30-06 loads with R-15 or R-22, your velocity is going to tell you when you've hit max, but that max safe velocity is going to be lower with R-15, but never the less, it will be the primary indicator, at least until you start going over safe pressures.
You are correct in stating pressure isn't linear. Also agree that if you hit max velocity prior to max powder charge, you've hit max. Conversly, if you haven't hit max velocity at a max listed powder charge then you haven't hit max. The max safe velocity will depend on the particular powder and bullet combination, but the velocity will tell the story.
As to your last paragraph...the consensus among many gun writers, and others in the industry, most of which have spent significant time in labs with pressure testing equipment and guns, is that the "classic signs" are not realiable. Many of them can "appear" and give false information. Cratered primers aren't always an indicator of pressure, but can indicate a large firing pin hole. Factory rifles often still have burrs in places and can leave shiny marks on brass. Different manufacturers of primers have differing hardness. Heck, many a factory round has flattened a primer. However, when the classic signs do actually appear, they are quite often significantly over safe pressures. Most say @ 70-72K psi in the rounds that have a SAAMI max of 60-65k psi like the .270 or 30-06. Meaning you can be shooting loads over safe pressures, but without them showing any classic signs, but any change, like a very hot day, or shooting the barrel hot, can result in catastrophic pressures. SAAMI max pressures are set with these deviations in mind so that you can load to SAAMI max, and the expected "normal deviations" will not put you in to thermonuclear pressure territory. Further, most data, is set a little below SAAMI, so there are 2 "cushions" built in to most data.
Well, I will have to go along with what boomtube is saying:
"Unfortunately, velocity can be a poor indicator of peak pressure and that's the kind that makes guns come from together, especially so if the powder is too fast for the load. Like, a very low velocity would come at a very dangerous pressure with a charge of Bullseye. Yeah, that's a pretty extreme example but I use it to illustrate the principle that we really can't be sure of the pressures by simply recording the velocity."
I have used a chonograph since the 80's and I have never relied on it to tell me anything about what the pressure was.
Some barrels are faster than others and some are slower. So you can't really rely on the velocity as to what the chamber will take for pressure.
You really should use your chronograph to indicate pressures, because it does if you read it and your data correctly.
The fast/slow barrel thing is true in a sense. But it's, in a way, been largely debunked as you seem to understand it. If you shoot the same load in 2 "identical" (ie two Remington M700s 30-06 with 24" bbls) and one gives higher velocity than the other with the same load, it's also giving higher pressure. There are no free lunches with velocity and pressure. A particular barrel may give higher velocities at the same powder charges you loaded for other rifles, but rest assured, the pressure is higher too. So, in reality, there is no fast/slow barrel, only different barrels. This is also the reason you hear many people proclaim that "X's data is optimistic, you can't get that velocity at that powder charge." In one sense they may be correct in that you can't get their velocity with their powder charge in your gun, but you can safely get near the same velocity at near the same pressure in the same legnth bbl, but you'll have to use more powder to do it. Most likely if they're producing data, they have test bbl's cut to very exacting SAAMI standards...tight tolerances. They're going to get higher velocity at lower powder charges...due to higher pressure at a given powder charge because of the tighter tolerances than your or my mass produced M70, M700, Sako, Browning or whatever.
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