Powder load volume/ muzzle velocities?

[Alan Warner]

OK. so I'm asking to know what one might see for velocity variations due strictly from variable thrown weights. Seeing as 10 fps @ the muzzle will yield a full minute @3520, (my given load/bullet combo)
I would like to work with one factor at a time.
Sample lot of thrown and trickled charges (12) show a max ES of .06g, and an SD of minuscule amounts. Charge weight is 196g. Percent variation @.06 = .0003% (.06g is about one kernel)
Can anyone equate velocity variables from this info?
I have not yet placed these known loads in line with the Lab Radar
Thanks
Alan
PS. A note of interest --- I load at home using a Denver 410D and a Gunderson. The DI floats a lot and constantly needs to be zeroed. Not a problem ( and no, air and electrical interference is not an issue) . I had doubts about the DI, so I ran some at home and weighed them @ the shop on our Sartorius. The results are above. Interesting though, the Denver, even after Cal. showed a standard weight of 196.00 to be 195.77. The standard was made using the Sartorius.
thank s again.

 

[Quickshot]

Hi Alan,

I agree that modern analytical balances have solved the issue of inconsistent charge weight. I trickle to +/- 0.5 kernel; just because it's fast and easy. Brass prep was the key to low Es and Sd. It is still critical to tune the load and seating to match the barrel harmonics. A well tuned load will hold the sweet spot better over environmental and charge weight variations.

But, it is possible for BC variation to spoil a well tuned load. I've had 1 out of ten bullets leave the muzzle with in 3 FPS of the other 9 and by 55 yards it's lost 30 FPS more than the other 9. Those rouge rounds always impact way low. The deviant POI is easy to spot at 2000+'yards. I have started culling rounds with a concentricity gauge.

Cheers,

 

[Greyfox]

I estimate my muzzle velocity variation to my thrown weights to be in the 2/3FPS range. I did some work with my 6.5x284 MV(2975) and my 6,5x47 MV(2880). Using Retumbo and H4350 respectively. Each .1gr for these loads is 5-6FPS. 10 FPS impacts elevation .1Mil(.36MOA) at 1000 yards. My RCBS Chargemaster throws to within .05grs. I estimate my variation due to charge weight at 1000 yards to be 1-.2 MOA. This is very close to a study performed by the US military that I read many years ago. Their data for the 30-06 yards indicated that .1gr variation in charge weight would approximately result in a .1MOA varaiation in POI at 1000 yards.

 

[Greyfox]

My 6.5x284 at 3000FPS and 6.5x47 at 2880FPS using Retumbo and H4350 respectively will register a 5-6FPS change in velocity per .1gr of powder variation of my loads. This velocity change at 1000 yards is approximately a .1-.2 MOA point of impact change. I control my charge weights to +/- .05grs. I like my overall ES to be under 12 FPS for hunting and Tactical/PRS competition.

 

[Deleted member 71114]

A while back we did a little work on this and came to the conclusion that there are variations in the end result due to burn rates, type of extrusion - kernel size, and case volume. Without getting to in depth the fps spread can be different from one powder to the next because of the kernel surface area then combined with the case volume of a certain load. There will be averages that folks can go off of but the bottom line is case volume and powder type in each individual set up has a different end result in which is more noticed in the ELR world.

Repeatable load charge is the most common issue and challenge and one that most folks overlook because they believe that their system is dumping charges at the upmost accuracy when in reality it's not.

Case prep and consistency in powder charges are two key players in low ES's

Just passing along the info we have worked through.


Cheers
Jeff