Calculated velocity change caused by a single granule of Varget in a .308/175gr.

[BoydAllen]

Recently I have been working with a friend who is working up loads for his .308 and is at the stage where he is trying to minimize the extreme spread of velocity for loads using Varget, and 175 gr. SMKs.
Toward that end, wanting to give him some sense of the relative importance of a given variance in powder weight, I got out my No. 27 Hodgdon manual and looked the minimum and maximum loads for that combination. Once I had those I subtracted the low values for velocity and charge weight from the high ones and found that for a three grain difference, the difference in velocity was 107 FPS. Dividing that by 3 gave me the change per grain, and dividing that by 10 gave a velocity change per tenth grain of 3.7 FPS. An earlier experiment had showed me that there are approximately four granules of Varget per tenth grain, dividing 3.7 by 4 rounded off to .9 FPS/granule.

 

[Dusty Stevens]

In your experience is this real world? I mean is one kernel the same as every other kernel as far as heating value or however its measured. Do you think every kernel is .9fps or is some 1.2 and others .4? Ive always wondered that since each kernel is a different weight

 

[M14AMU]

That's akin to counting hairs on a cats back!!

 

[BoydAllen]

Perhaps I should dig into some ballistic software and come up with vertical at 1,000 yd. per grain, tenth grain and granule for the same load. My point is when you are working with multiple variables, you need to know how to weight them, otherwise you can end up expending a lot of effort on something that is not the biggest part of your problem.

 

[Lapua40X]

Perhaps I should dig into some ballistic software and come up with vertical at 1,000 yd. per grain, tenth grain and granule for the same load. My point is when you are working with multiple variables, you need to know how to weight them, otherwise you can end up expending a lot of effort on something that is not the biggest part of your problem.

Well, Boyd, as much as I appreciate your sharing the information. I think you've expended a lot of effort for something that is not the biggest part of a reloader's problems.

 

[rduckwor]

On my scale, a single granule of Varget weighs 0.02 Gr. Pretty consistent as well. H4350 kills me when I trickle it as it isn't nearly as consistent as Varget on weight per granule. I pick one out and the weight drops 0.02-0.04. Probably my scale but the Varget makes it easy to hit the target weight. Does 0.02 Gr matter? Not they way I shoot!

RMD

 

[watercam]

I appreciate the thought process involved. I then think back to watching a benchrest competition where no one weighed any charge weights and simply used thrown charges at the range to adjust their loads between strings.
Not a long range match by any means but group sizes approaching the mid-1s were impressive.
None the less, I weigh every charge to within a lines width of my balance beam scale to the best of my ability without taking too much time to do it. SDs in the 4-5 range seem to work.

 

[JFM33]

Thanks Mr Boyd,I recently had the opportunity to shoot on some electronic targets at 1000 Yrds for an F-class regional and was amazed how they record the velocity as the bullet impacts the target.I scored for a gentleman shooting a 308 with 200 grain bergers and could watch how his velocity went from 1437 to 1453 fps took up all the verticle @ 1000 approximately 10". Thats just 16fps difference.
If the charge weights are the same would you look at neck tension next to eliminate the es.
I saved a screen shot of his recorded string it was a learning event.
John

 

[BoydAllen]

MTM,
I am more of an ES fan than SD. What sort of ESs are you getting?
JFM33,
It would have been nice to see the 100 yard velocities as well, to see if the source of the velocity differences at 1,000 yd. were from bullet to bullet differences in BC.

 

[BoydAllen]

Dusty,
The thought was to give my friend some idea of the the maximum improvement that is possible by using more accurate powder weights than he is currently using, to encourage him to look elsewhere first. He has an ES of about 40, and IMO getting his bullet pulls more even is a bigger part of his problem. He is about to do a test to look at what more accurate charges do, which pleases me, since that is the approach that I favor...testing.

My point in doing the math was to come up with a general range, not to calculate an actual outcome. He has a chronograph for measuring that. What kind of scale are you weighing granules on? My setup was probably less precise, but it still got me close enough for this purpose.

 

[JFM33]

Ok, now you have got me thinking the next time I go to pratice on the electronic targets I need to bring my conograph and at least get muzzle velocity at 10' to go with the down range velocity.
I dont know if the shooter sorted and pointed his bullets so I guess thats another variable.

 

[amlevin]

That's akin to counting hairs on a cats back!!

Especially while they're shedding 8)

 

[amlevin]

Boyd--

Do you know of any "affordable" chronograph that's capable of measuring bullet speeds down to that amount accurately? They may show a tenth of a fps variation on the readout but that assumes that the chronograph is "triggering" of the same part of the bullet with every shot. If one sensor triggers off the tip and the other sensor is a little slow, triggering off the main body, that 1/2" difference can give as much variation as a change in a single granule of Varget.

I'm waiting for the day that someone actually counts out the granules to get a set of loads or let's say 43.5 grains for a 175 gr bullet. Wonder if his speeds will be as close as expected and more importantly, the groups as small on the target.

 

[BoydAllen]

No, I do not know of such a chronograph. I was trying to show the potential improvement of going from the accuracy of a Chargemaster to that of charges trickled onto something like a Gempro 250. If we estimate the Chargemaster as being at +- .1 grain, and the Gempro at +-.02 the difference would be around 6 FPS in ES. That will not get you to low double digits from around 40.

 

[CharlieNC]

Quickload is an excellent tool for evaluating this question and it can also incorporate similar parameters such as case capacity, bullet weight, etc. I have always found it to be reasonably accurate, at least in the relative sense to reflect changes. The program also comes with a ballistic calculator to evaluate the downrange effects.

 

[SHootSTraight22]

Quickload is an excellent tool for evaluating this question and it can also incorporate similar parameters such as case capacity, bullet weight, etc. I have always found it to be reasonably accurate, at least in the relative sense to reflect changes. The program also comes with a ballistic calculator to evaluate the downrange effects.

I wish someone could run QuickLoad for me!!?? I want 3,230fps with a 6SLR and a 6mmCreed, using Palma brass... .237 bore, and H4350... 24in-28in. barrel, using any primer and coated bullets if I have to...

 

[jlow]

Recently I have been working with a friend who is working up loads for his .308 and is at the stage where he is trying to minimize the extreme spread of velocity for loads using Varget, and 175 gr. SMKs.
Toward that end, wanting to give him some sense of the relative importance of a given variance in powder weight, I got out my No. 27 Hodgdon manual and looked the minimum and maximum loads for that combination. Once I had those I subtracted the low values for velocity and charge weight from the high ones and found that for a three grain difference, the difference in velocity was 107 FPS. Dividing that by 3 gave me the change per grain, and dividing that by 10 gave a velocity change per tenth grain of 3.7 FPS. An earlier experiment had showed me that there are approximately four granules of Varget per tenth grain, dividing 3.7 by 4 rounded off to .9 FPS/granule.

Boyd – I think you are very close. I did a quick check for you on QuickLoad using the tuned data for my AI AT shooting 185 Berger Jugg with Varget. At 70 degrees, going from 43.5 grains to 43.52 grains increased my predicted MV from 2604 fps to 2,605 fps so around 1 fps for that one 0.2 grain weight kernel of Varget.

 

[BoydAllen]

Thanks.

 

[savagedasher]

I think you're getting the cart ahead of the horse till the case capacity is all the same it can't be determined accurate. Larry

 

[BoydAllen]

No argument here. I just wanted to put some numbers on what powder variation was likely to do. He is shooting Lapua brass that has been very lightly turned. Personally, from my discussions with him, I think that he will see results from careful annealing, and perhaps playing with neck tension. I would only worry about small amounts of powder variance after all of the bullets had the same feel when seating, and my ogive to head dimensions were very close to perfect.