Home Forums Reloading Big Game Rifles Chronograph - the great truth serum

Well, I just got a Competition Electronics Digital Pro Chrono with a tripod for Christmas. Naturally, I had to go to the range and see how it works. Well, i absolutely love it. Easy and quick to set up, which is important when you have to travel to your favorite range. Does all the statistics I need - Individual velocity, Average Velocity, Hi, Lo, Extreme Spread, and Standard Deviation. It will do this for 9 different strings, and store the data in non-volitile memory for future reference. Dispaly is pleny big enough to read from the bench. It was an overcast day, and I had not a single failure to read the shot.

Anyway, I chronographed the load my son 10 year old son used to kill his first deer last weekend. It was, by the manual, a max load of R19 with a 100gr Sierra Flat Base. Supposed to chronograph 2925. Any guesses on the actual velocity? I could hardly believe it - 2617fps! More than 300fps less than Alliant's reloading guide said it should. No pressure signs at all, so will probably go up a little and see how it does. This also gives a new perspective on just what is needed to effectively kill a whitetail. The deer didn't seem to notice that the bullet didn't leave the muzzle at 2900 fps.

I also chronographed a few loads from my .250 AI. They were much more as expected, with the load I used on my first head of game killed with my .250 Ackley averaging 3102fps.

Here's some of the velocities my .250 AI is giving. No traditional pressures signs showing on any of these.

Bullet Brand Bullet Type Bullet Weight Powder Charge Primer Velocity Standard Deviation
Hornady Interlock 100 H-414 43.00 Win WLR 3023 12
Hornady Interlock 100 H-414 43.50 Win WLR 3081 15
Hornady Interlock 100 H-4350 44.00 Win WLR 3102 14
Hornady Interlock 100 H-4350 44.50 Win WLR 3148 12
Hornady Interlock 100 R19 45.00 Win WLR 3021 15

These were the average of 6 shots across the chronograph for each load.

John

Nothing like a chrono to tell you what's really going on.

Don't know how I ever got along without one...

I agree with you about the value of a chronograph. I wish I had one. Borrowed one to test some loads for my 06 a lot of years ago, and found out why they shoot such tight little groups. I was using 58.5 grains of IMR 4350 and 165 gr BTSP Sierras. 10 shot string across the screens averaged 2892 fps with an extreme spread of 23 fps. 10 shots into 5/8" at 100 yards. Good hunting load.

Consistent loading techniques produce consistent loaded rounds which produce uniform velocities and small groups --- all other things being equal.

Hondo, Now you've gone and done it! As my hunting bud says, "More "great loads" have been ruined with a chronograph than anything else."
Enjoy your new toy and keep us up to date on your load testing. RS

That's quite a jump in velocity for only 1/2gr of powder. Would be curious to what another 1/2 would do.

OK, here's a dumb question. Given that the load was 300fps below a published safe value, would it be wise to keep adding powder until the velocity is up to the published level? Assuming of course that no pressure signs are shown in the work up.

Which 1/2 grain jump? The H414 load jumped 58 fps with 1/2 grain increase. Is that too much? Primers looked ok. Bolt lift seemed ok. The H4350 load jumped 46fps, and it seemed ok too. Guess I need Charlie to put the strain guage to it. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

John

Hondo.....guess it seemed like quite a bit to me but most of the bullets I load are a lot heavier...mostly 300gr for my 9.53.

Not obtaining the published vels has been the norm for me. I have kept increasing the powder charges until the primers are plesantly flat. I keep a wary eye for ejector marks, cratered primers and difficult bolt openings. I have noticed rapid increases in vels as you near the max loads. 50-100 fps jump per gr. This is on small bores. One thing that can make a vel dofferance is case brand, I find that the fed cases hold the most, next is win and then remmy. A strain gage would just scare ya. I have noticed over the years that there seems to be different operating pressures for some ctgs. There was no mention as to action type. Why can one ctg run a higher press than another, if they are shot in the same style gun>
dingus

I think a chrono is the most reliable pressure measuring tool most of us handloaders have. It takes a certain pressure to accelerate a given bullet in a given length barrel from a given case with a given powder. If we are getting more velocity that what the manual says, we are exeeding loading manual pressures. Conversly, if velocity is slow, we are likely under the pressure.

Bill, you got me thinking, and that's not necessarily an easy thing. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> I looked through a couple of my manuals and plugged some numbers into excel. Learned some interesting things.

First, I think you are right. Both the H414 load and the H4350 load are definitely getting on the warm side, and I'll not increase them any more. I was content, because I was not seeing any of the traditional pressure signs. But, in and Ackley chamber, supposedly you don't, because of the case gripping the chamber wall better as opposed to pushing back against the bolt face.

At first, I started thinking in terms of fps gain per grain of powder, but then thought that wouldn�t work, because of different powder capacities of different cartridges. So, I plugged a bunch of data into excel (yes, I am on leave and currently have no life, and am loving it), and derived some numbers which compared the percentage of increase in powder charge to percentage gain in velocity. First thing I noted was that the smallest cartridges showed the greatest gain. No real surprise. Next thing I noticed was that the cartridges working at higher pressures, also showed greater gains per percentage of powder added.

In comparing book data to my own, the .250 Savage showed an average of 1.10% increase in velocity per percentage increase in powder charge. The .243 showed a .82% increase, the 7mm-08 a .91%, and the .270 a .90% increase. My .250 Ackley averaged a 1.10% increase, which at first would make it seem that I was right in line with my data. But�.. What I think happens is the pressure (velocity) increase is not linear (which my calculations are), but instead follows an increasingly steep curve. This can be demonstrated by comparing the % increase in velocity for each increase in powder to the previous velocity. While I still need more data from the chronograph on my own loads to develop a useful curve, if I compare the � grain increase (1.14%) to the previous velocity, I get a 1.30% increase in velocity, which is a little high. I don�t think I would be able to increase much more and not run into problems.

All that being said, the H4350 load does not exceed the maximum according to Sierra data. Sierra is the only published data by a major manufacturer for the .250 AI that I am aware of. Not sure about the H414 load, Sierra doesn�t show it, but it does how the max with 760 being 44 grains, and Supposedly, 760 and 414 are extremely similar.

Anyway, thanks for the heads up, and if you would like to see the excel data, drop an email or pm and I will be glad to send it to you.

Have a Happy New Year!

John

While a chronograph is a handy tool it is in no way a reliable way to measure pressure.As an example I have two 7mmstw's both with 26" barrels.Using the exact same components and load one produces 75fps more than the other.If I try to increase the powder charge in the slower rifle pressure signs such as sticky bolt lift and extractor marks appear indicating high pressure.Yet the other rifle is producing 75fps more without showing any pressure signs even though both chambers were cut with the same reamer and the same lots of powder,brass and bullets were used in both rifles.A friend has a factory sendero(26" barrel) in 7mmstw that produces 100fps less velocity than my slowest 7mmstw.He also tried increasing the powder charge and also ran into pressure signs.He was also using the same lot of brass and components.All three guns were chronographed with the same chronographs(we used both of our chronographs for each gun) on the same trip to the range.Even with the same pressure some guns will produce more velocity than others even with the same barrel lengths and identical components. Trying to increase powder charges in order to attain the velocities that another gun produces or a loading manual lists is an open invitation to trouble.A chronograph is meant to measure velocity which it does well.It is not meant to measure pressure because it has no reliable means to do so.

SJ:

Not meaning to put words in AFP's keyboard here, but I think his point is well taken. As you say, a chrony does not tell what the pressures are, but it is a tool in your arsenal of "pressure guessing" factors. As you point out, there are great variations in rifles. These can lead to wildly different velocities with the same components.

Barnsess wrote a great article about this subject recently. He makes the point the some rifles simply don't show traditional pressure signs despite pressures that are too high. If you don't use your chrony to double check your progress, you could be in trouble.

For example, you have a rifle, maybe a nice trued up custom chambered for a cartridge that should max out at say 62K PSI. You load her up one grain at a time until you see traditional pressure signs, then back off a grain or so and call it good. In some rifles, this could be 65K-68K or even more PSI. Just because your rifle does not show the normal signs, does not mean you are in safe territory. If you chrony the load and see that you are 150 fps. over the listed max vel. in the book, that's a sign that you are in dangerous territory.

The inexperienced shooter or velocity freak may stuff powder into the case until the bolt locks up and the primers pop out, or the cases are toast in a few loadings. He then reduces (maybe) by a grain and feels that he's in tall cotton because his rifle shoots 200 fps faster than the book, "with no pressure signs" The reality is that there's no free lunch and that extra velocity comes with excess pressure as a corrolary. Shooters that regularly report velocities of ~~ 200 fps over the book max velocities are simply kidding themselves (and us) that they are in safe territory.

I'm getting a little long winded, but a perfect example of this is my custom Ti in 284. The rifle was barreled and trued by Kreiger and does not show pressure signs when expected. I reached a velocity w/139 gr. bullets that just did not feel right despite no visible pressure signs. In this case, the Chrony was the tool that told me to back off, not the more "normal" indicators.

JimF

JimF-The key words in your post are exactly as you said them"pressure guessing".If you look at several loading manuals you often see velocities for guns with the same barrel length and with the same components vary by up to 200fps and yet both manuals quote nearly identical pressures.The pressure testing gear that these large companies use are far more accurate than any guesses that we may make so whose velocity are you going to accept as the one that you should be able to attain?

Jim is right,

Well before Barsness published his article, Stan Watson performed pressure testing with an Oehler 43 PBL and found much the same thing. Bottom line, the conventional methods we use to check for pressure are inconsistent and unreliable. One lot of Rem brass he checked went 80,000 PSI without showing any pressure signs. Typically, no pressure signs of any kind will show up until pressures are past 65,000 psi.

As such, I load up to published velocites, using the bullet manufacturer's data. (Often, I don't have any data.) If I get other pressure signs first, I back off. If I happen to exceed listed a powder load without seeing any of the notoriously unreliable conventional pressure signs, I'll keep going until I reach published velocity, with one exception. In cases of 30-06 size and above, it takes at least 1 grain of powder to achieve any statistically significant change in group size or velocity unless you are at the "pressue peak" so to speak. If I ever see a grain or 1/2 grain of powder produce a disproportionate increase in velovity, I immediatley back down. If the manual says to expect 3075 fps with a 300 Win, but 1 grain of powder causes a jump from 3000 to 3050, the pressure is likely too high with that powder.

When you know how to interpret the data, a chrono is a far better pressure tool than any of the conventional ways handloaders typically check for pressure.

stubblejumper,



I must thank you again for turning me to the 7STW. I thought about it last night when I posted something to someone. Anyway to my point...



From what I read in your post, there is 175 feet per second difference in the fastest to the slowest; with all using the same caliber and length of barrel and components. Fasinating.



I don't understand why something is "unsafe" if there are no preasure signs. What is unsafe about it? Is the bolt going to break its lugs? I don't understand.

SJ:

I think we are agreeing here. I look up everything I can find when starting out with a new rifle. Especially with a cartridge I have not loaded before like my 284. When I look at the various sources, I never assume that I will equal the highest velocity listed in any one manual, let alone the highest overall of the five books I usually reference.

I do believe that pressure signs (or) a Chrony reading that is touching on the maximum velocity available are both big red stop signs. Problem being, if you don't have the chrony, that takes away one of your diagnostic tools.

It's very possible to reach max velocity in some rifles at 2-3 gr. under the listed max powder charge. If you are getting the max velocity available, then you are certainly getting max pressures as well, despite the fact that you are under the max listed charge. If you have one of those rifles that do not show traditional pressure signs, the opportunity is there to make a big mistake by continuing to add powder. The chrony could provide that extra level of warning that stops you from entering dangerous territory.

JimF

AFP and JimF-Using my previous example where two manuals list max velocities that are 200fps apart but are both listed at the same pressure.Assuming that there are no visible signs of pressure do you stop when the lower velocity is reached or do you continue on until the higher velocity is attained?Maximum published velocities for some cartridges such as the 7mmstw and the ultramags and weatherby mags vary tremendously between different manuals and 200fps difference is quite common.

Ringman_ My fastest 7mmstw attains 3550 fps with a 26" Schneider barrel and 80gr of imr 7828 behind a 140gr ballistic tip.My other 7mmstw attains 3475fps with a 26" kreiger barrel and 78gr of imr 7828 behind a 140gr ballistic tip.My friends stock sendero with a 26" barrel attains 3375fps with 81gr of imr7828 and a 140gr ballistic tip.Maximum loads in the various manuals and reloading sites vary from a low of 77.5gr of imr7828 to a maximum of 83gr of imr7828.Published velocities range from 3375fps to just under 3600fps.With all three of the guns mentioned pressure signs first show when two grains are added to the loads specified.I like to back off two grains from the first signs of pressure to be on the safe side and to provide good case life.

I go with the manual published by the company who manufactured the bullet. Different brands and styles of bullets--even of the same weight--generate different pressures and velocities. For example, I usually find uncoated Barnes X bullets to be slower than say a Nosler Parition of the same weight and caliber. Swift Sciroccos seem a bit slow as well. I stop at best acucracy anyway, and that is usually a bit under the max listed. Usually, I reach the manual velocity before I start seeing other pressure signs.

For me, the chrono has caused me to throttle back a tad bit. I no longer seek that last 50-100 fps. The chrono also helps when I am loading for a bullet/powder combo for which there is no data. Usually, I'll get a velocity spike before any other kind of pressure sign, and I do not exceed that point. Using the chrono as I do, I rarely even see a flattened primer anymore, and the velocities I obtain are usually with 100 fps of the max listed.