Chronograph Challlenge

[Bradley Walker]

I would like to see if anyone would be interested in doing a test.

I would like to see the difference in SD and ES for velocities of a cartridge (say a 6BR) between weighed charges and thrown charges. Using some kind of small kernel powder.

I mean there is lot of talk about the need to weight powder to the smallest tolerances, I would be curious to see the REAL data.

 

[Heavies]

This would be a fun experiment. I'll be watching, but I don't have my BR anymore for me to try the experiment.

My smith throws his charges exclusively, for his mid range F-class loads, and does very well. My OCD makes me cringe at this though. LOL

I am thinking that the small cartridge like a 6mmbr would be more suseptable to charge weight variation, however, a larger case like .308 or 30-06 would be more forgiving of charge variation.

I believe it to be true that thrown charges can be very accurate, however, velocity variations probably doesnt have much of an effect at short range. Longer range, the variation would be greatly maginifed.

 

[Larryh128]

You will varying results depending upon the brand of measure being used. If you are using a top flite measure AND a powder that has small kernal or a ball powder, you can throw very accurate, repeatable charges. Your technique has to be consistant on how the measure is operated. I have seen & had a couple measures that couldn't throw consistant charges & never would. They had short lives in my loading room. The measure that I use now will stay within a 1/10 of a grain consistantly+ or -. OR 2/10ths. If I trickle my charges, I will cut group sizes by .100 @100 yds from being thrown. There would be less variation from a better measure.

 

[Keith Glasscock]

I think an experiment of that kind would only be valuable to the person conducting the experiment. There are just too many variables in the causes of velocity variation to be able to say that powder variations would or would not make a difference.

Let me explain. If I were shooting a load with an ES of 25, and I varied the powder +.1 grain in my 308, the velocity variance would be ~5 fps from powder alone. Now, if I happened to put that charge in a case that was on the slow end of my 25, then the ES wouldn't change (might get better if it was the slowest one), but the SD would improve. On the other hand, if that one hot charge went into the highest velocity round, the ES and SD would increase.

This is an example of the noise making it very difficult to asertain the actual effect of a variable. If a variable can be turned into a constant, that is actually better regardless of the results of a small sample fired over a chronograph.

Here is how a proper test would have to be designed:

Take 20 or 40 of your best match cases and fire 10 or 20 with weighed charges and another 10 or 20 with thrown charges at 1000 yards (even 600 would mask some of the velocity variation) and determine group sizes. Then repeat the experiment at least 5, and perferrably 10 times to get some good average data.

IMO, at least 100 shots are absolutely necessary to get anything of value out of the testing.

 

[Bradley Walker]

I don't think it would be tough to set up a reasonable experiment.

I would suggest using a short grained powder like XBR 8208 or H322.

 

[LHSmith]

I am a short range guy......LR ---I don't know....but I think they all weigh charges.
As was mentioned, it would only be of value to the person doing the test. I cannot throw charges on my Harrell as accurately as a seasoned (nice way of calling someone old) competitor. This is why I use a CM. You could say I have embraced the technology. It is uncanny to watch these BR veterans throw charges, if it don't feel "just right", they dump it back.....it's a learned "feel" that only comes to most of us through repetition and more repetition. When I was throwing 133 on the Harrells.....nothing felt "right".....as I would be cutting kernels 7 times out of 10.
Secondly, give these guys an identical Harrells, and they will most likely will notice a difference and probably not throw as well.
Choose a method that works best for YOU...the one that gives you the most confidence...... and master it.

 

[amlevin]

I'm all done thowing charges. I use too much Varget and my blood pressure goes too high when trying to get an accurate load by just throwing.

A Chargemaster does all the Varget handling now.

I'm thinking of a similar test but involving the cases. Give each case in a set an ID number, load them all with the same prep steps and anneal after every shooting. Keep track of the speed associated with each case. See if the same cases yield the same variances (high,low speed) after several shooting cycles.

Something to do on a rainy day I guess. 8)

 

[jlow]

I like amlevin’s idea of the case test a bit more.

Throwing charge variation may or may not affect precision/accuracy but at least to me, it is easy enough to hand weight charges to make sure that they are consistent and as Heavies stated so well, my OCD will make me cringe at the thought of only throwing.

Busdriver is also spot on in saying that unless you got all the other noise under control, the data might drive you crazy and IMHO, the case is where most of the uncontrolled, unrecognized error resides.

Case volume on the other hand is also harder to deal with on a one by one basis since it requires that (at least to me) not so accurate volume determination with water and having to keep track of cases unless you cull them upfront and only use a limited number of cases.

 

[Bradley Walker]

With the powders you suggest, they meter very well in good throwers.
Put Varget or H350 size kernels in to the mix and whole different story.

Yah, the large kernel stuff would not work.

 

[BoydAllen]

By and large, in the target shooting game, the BR is a long range cartridge, and in that game, ES can be very important. Also, the way that matches are run does not make it convenient to load at the range ( I am told) so with preloading the rule, there is no reason not to weigh loads. In addition, the powders that are commonly used for high BC bullets are not as easy to throw to a narrow ES of charge weights as those typical of short range benchrest.

On the other hand, in short range benchrest, a very high percentage (almost 100%) of the competitors load at the range, between matches, making adjustments as needed. At 1-200 yards, ES has much less of an impact on group size, and the difficulties of weighing every charge outdoors, and the additional time that it would take are considerations that cannot be ignored.

It has bee pretty well established that weighing charges with a scale that is more accurate than +-.1 grain will improve vertical dispersion at 600 and 1,000 yards because of the reduction in the ES of velocities that it produces (as compared to thrown charges) when coarser powders are used. On the other hand, many short range matches continue to be won with throw charges, and I think that this speaks for itself.

If you want to do this test, and wish to avoid the variable of case volume and neck tension variations, all you have to do is to use one case for all shots, reloading it at the range. The issue of operating a scale outdoors, can be handled by using preweighed charges from suitable individual containers. There will be some change in neck tension as the case work hardens, but this could be reduced by using different cases for weighed and thrown charges.

 

[Bradley Walker]

I don't think it will work for large kernels.

Anyone ever try AA2520 for 6 BR?