Help Reading Pressure Signs (Rifle)

[RDub]

Hmm..
Ok lets yak about this..

I have a chronograph, an Oehler Mod 33. I've had it since 1980.

When I worked up this load, 180 Nos Par ahead of 72.0grs IMR4831, I shot 3-shot strings in 0.5grn increments. The velocity, ES(spread) and Sd Standard Deviation remained pretty uniform all the way up to 72.0grs where I stopped.
That velocity averaged 2970fps.
Sometimes,.. when you working up the strings and you get into high pressure, and this is known by the pressure signs we are familiar with and what the books say.. you will see velocities stop increasing, or going the other way, getting slower. Of coarse this means you are way past where you should be!
In this instance I didn't see any of these signs.

Now, if this load, 72.0grs, is generating pressures in the 70,000psi range, why is the velocity only 2970fps?? And the velocities of the strings working up to that were fairly uniform as they increased.
I should be seeing much higher velocities with that much pressure.
What do you think?

 

[MEHavey]

You have hit upon the real issue: Without the chronograph there is no way to determine where you are on the curve. With the chonograph, and with the manuals (which almost to a page say 2,900fps is the DNE loadout irrespective of differences in powder) you have a pegpoint on which to hang your max load.

The IMR site says you can go 100(+)fps beyond that 2,900 before you hit the wall.
Who do you believe?
ALL the manuals...?
...or a website?

Watching the brass is only going to tell you when you've finally exceeded the elastic limits. Up to that point you don't know how close you are to the knee in the curve, just that you haven't dropped over the edge... for the conditions at the range that day. So we load up and take off for Africa -- 50 degrees hotter in the noonday sun where mad dogs & Englishmen hang out.

Now we wouldn't be having this conversation if the cartridge had moderately consistant recommended loads across the database. But those Max loads range from 66.0gr to 73grains -- an incredibly wide swing -- even if the manufacturer is on of those sourcs. And normally we don't want to snuggle up onto max'd-out loads anyway, even with dependable data.

So we're back where we started. Joe SixPack is looking at inconsistant data for which he doesn't have the background or tools to interpret. As you recommended, he should take a middle-of-the-road approach which while likely safe, doesn't take full advantage of his equipment. It's the price he pays to ensure the bolt doesn't freeze on him when he needs that follow-up shot.

 

[918v]

When the brass exceeds its elastic limit, the bolt begins to stick. This isn't rocket science.

 

[lilquiz]

Good ole' QL . I just recently wasted two weeks and money on two types of powder which were supposed to give me better results at safer pressures due to someones QL predictions. It is a wildcat round with no book data. My current load was obtained by starting low and reading primers for pressure signs. There is one type of factory ammo available . The primers for my loads were no where near as flat as the factory's. In my dilemma I tested the loads pressure signs via another method as well. The reloads show no signs of overpressure with that test either.QL is a good concept but it is based on data and math predictions ,if either is off by a decimal point it is way off.

 

[MEHavey]

QL's default database is a starting point -- easily "as good" as many/if not most manuals for bottleneck cases. It comes into its own where you just worked with it -- minimal information loading of strange cartridges.

QL's burn rates are also calibratable using the straightforward methods discussed elsewhere in this and the FiringLine forum. Start low, get a second or third point in a sequence of loads, then "best fit" the burn rate for that powder lot. I just had to do that for an H380 powder lot in an M1A.

Now "someone else's" predictions is not where QL shines. It's a tool. And just like any tool, if you aren't the one wielding it, you are at the mercy of that "someone else."

Out of curiosity, what was the cartridge, and what were the powders?

 

[918v]

QL is not to be used to develop max loads. The goal of reloading is not to develop max loads. People who load to the max would be better served by having a bigger gun.

QL is a tool for comparing variables/components and how they change the pressure, velocity, etc.

For max pressure data, bullet manufacturer data is always best.

As far as your wildcat goes, QL was 200 FPS faster than my 22-250 wildcat actually shot, but I can't really trust a Crony to be all that accurate either. That thing deserves to be shot.

 

[USSR]

QL is but one tool in a load developer's tool box. It is best used in conjunction with a chronograph, empirical load data, and experience. Just MHO.

Don

 

[MEHavey]

."...QL was 200 FPS faster than my 22-250 wildcat actually shot...."

Were you able to adjust burn rate to match velocities at two or more points? (i.e, calibrate the powder lot?)

post script: If you really don't trust the Chrony, I'd recommend getting rid of it/getting an updated system. `Nothing worse than not believing what being fed to you.)

 

[kingmt]

People who load to the max would be better served by having a bigger gun.

I don't think I can agree with that. If you had a neighbor that drove his car past your house as fast as his car would run would you think he needed a faster car. People that are always pushing the limit would still push the limit when the boundary moves.

This is some great info here but I have to make do without QL or a chrono for now. I'm not trying to make a max load I just don't want to fall over the edge. It would be nice to know where the edge is though so I can decide how far is a safe distance.

 

[USSR]

kingmt,

I have seen nothing in this thread about the details of the load you are working with. It would be helpful if you could state: brass mfg, powder & charge, primer, and bullet. Oh, yeah, cartridge would be helpful to.

Don

 

[RDub]

MEHavey I agree..

I was just playing devil's advocate with you, hope you didn't mind.
Only because this particular rifle, and/or cartridge, don't know which, has been a tough nut to crack with respect to understanding where the 'wall' is.. especially with some of the newer powders out now.

I've worked with a lot of cartridges for myself or others and have always been able to find 'something' that works within the published data. Never had the desire or need to exceed this. But this one, has been a bit puzzling at times, because the data available varies widely.

I was wondering if QL has been updated to show data for Alliants new 4000MR?

 

[kingmt]

I'm working with both a 30-06 & a .223 Rem but the .223 is the one that I'm mainly talking about.

Powders are WC 844 & WC 846. Bullets are "M193 - 55 gr. - FMJBT - Air pulled, no marks" & "M856 Tracer - 62gr. - Orange Tip - Hand Pulled - #1 grade" both from hi-techammo.com . Primers were CCI but I have switched to Tula. Cases are steel wolf. I have been using load data from Hodgdon for H335 & BL-C(2).

The only problem I have had was the 62gr tracers with the WC 846 was piercing primer & stuck cases after firing at minimum load. I think I have switched powder scales since then though. I was using a RCBS that wasn't that great & switched to a electronic. I have not tried the 62gr tracers with WC 846 since then. I have had no problems with the WC 846 since then.

I have been saving what little brass I have for this gut until I figure out what I'm doing. When I think I have got this grouping the best I can & think I have a better understanding I will switch to brass & better bullets.

All of the steel cases that have been fired through my gun hold 31gr of water if this is meaningful.

 

[918v]

If you had a neighbor that drove his car past your house as fast as his car would run would you think he needed a faster car.

We are not talking about velocity. We are talking about pressure. If your neighbor had to redline his engine sust to get to speed, he would be better served by a car with a more powerful engine.

 

[kingmt]

I agree just saying there is a difference between doing it & needing to do it. I don't think most people that load as hot as they can need to they just like to push what they have to the limit & a little over that limit is still OK to them. They will still do the same with a faster car or a bigger chamber.

Your also right about it having little to do with my question on reading pressure signs.

 

[amlevin]

Went to the range last wednesday and tested some rounds that were exactly the same with the exception of the primers.

Winchester cases, .308 Nosler 175gr Custom Comp bullets, 43.5 gr Varget. Only difference was one group was loaded with Winchester Large Rifle Primers and the other batch was loaded with CCI BR-2's.

The winchester primers were flattened as much as they could be in the primer pocket. The CCi's looked as if the load was somewhere in the middle of the load range for that cartridge. Chrono speeds were almost the same with the CCI's having a lower Extreme Spread and Standard Deviation.

Primers are, for me, the worst method of determining pressure signs. My Remington will show a slight extractor mark when I'm reaching what I consider max loads.

I have also found that my loading software gives great predictions when I measure case volume with water rather than just using standard case dimensions.

 

[Clark]

918v

When the brass exceeds its elastic limit, the bolt begins to stick. This isn't rocket science.

I read that over and over.

Now I am typing over and over:

All work and no play makes Jack a dull boy.
All work and no play makes Jack a dull boy.

 

[kingmt]

918v

When the brass exceeds its elastic limit, the bolt begins to stick. This isn't rocket science.

I read that over and over.

Now I am typing over and over:

All work and no play makes Jack a dull boy.
All work and no play makes Jack a dull boy.

I don't understand.