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| Shortround |
 Posted: Fri Oct 30, 2009 5:26 pm Post subject: Mil-spec brass |
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Joined: 14 Jul 2009
Posts: 80
Location: Avilla, Arkansas
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Being bored, more or less, during the lengthy gully washers of the past couple of weeks, I decided to lock myself in the “inner sanctum” and continue to organize what I had packed up 20 years ago.
Since I have a significant quantity of mil-spec .308/7.62 stuff I went to work there. Typical clean, prep, sort, cull, and clean some more. As this project nears completion, I have discovered that I have usable quantities of three types of commercial brass and ten types of mil-spec.
Knowing that different head stamps tend to have different internal capacities, I decided to take a sampling and compare against a “known” benchmark.
Using current manufacture Winchester brass as the benchmark, I give you this bit of possibly insignificant information to be used as you may deem necessary.
All brass was once fired and cleaned. They were full length resized, trimmed to 2.005”, primer pocket trued, flash hole deburred, case mouth cleaned up, and cases primed. WW 748 powder was used as the test media. The same process to settle the powder was used for all cases. All capacity weights are an average of five cases and are rounded to the nearest .1 gr. and .1%.
Winchester commercial - 57.0 gr. (100%)
Federal commercial - 55.0 gr. (96.5%)
Remington commercial - 56.7 gr. (99.5%)
WCC 60 - 56.0 gr. (98.2%)
WRA 64 - 55.7 gr. (97.7%)
WRA 67 - 54.6 gr. (95.8%)
RA 61 - 54.0 gr. (94.7%)
LC 77 Match - 54.9 gr. (96.3%)
LC 74 - 55.1 gr. (96.7%)
LC 81 - 55.2 gr. (96.8%)
LC 84 - 54.8 gr. (96.1%)
LC 85 - 54.0 gr. (94.7%)
LC 86 - 54.2 gr. (95.1%)
All of the Lake City brass within a given lot was very consistent. Typical internal capacities varied by no more than 1% and for the most part, less than .65%.
The LC Match was even better with less than .5% variance overall. Looks like real good stuff. Need to scrounge a bunch more of it.
As part of my learning process, I am thinking of taking a known accurate load with the Winchester brass and duplicate that load with the mil-spec. For example, if 50 gr. of XXX powder, along with ABC primer and bullet gives me a set accuracy level, then 47.6 gr. (95.1% of 50 gr.) in a LC 86 case with the same components should give me the same performance level. Of course I would start at a lower charge weight and work up to that point.
Am I making the right assumption? Or am I not factoring in some other unknown or sets of unknowns? At least ya’ll can pick something apart and not hurt feelings.
I just hate to see this much brass go to waste. I have already culled 50- 60 pounds that I felt was not good enough. Money saved on brass can go on powder, primers, bullets, and other necessary stuff (chronograph, QL, tools, shooting house). A lot of people do not care to use mil-spec brass. Other than an extraction issue with a batch some time back, I have had good luck with it. As to the extraction issue, I may have that figured out and will report on that later.
NEWS FLASH!!!!!!!!! Either the sun has come out or we have been nuked. I am guessing that it is the sun since there is no sign of an EMP. There is even a certain blueness to the sky. Guess I’ll take the cover off the scooter and let it soak up some of the brightness and air out. Both of us need to be ridden.
Shortround out |
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| dannewberry |
| Posted: Fri Oct 30, 2009 6:43 pm Post subject: |
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Site Admin
Joined: 26 Jan 2005
Posts: 2181
Location: Southwest Virginia
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Thanks for the info, this will be very helpful to many...
You're right to presume that you can extrapolate the charge to a smaller volume case by using the calculated percentage of powder.
For what it's worth, you can also extrapolate a 3rd OCW load with a 3rd bullet weight and a given powder, based on two other known OCW loads with two other bullet weights and that same powder.
Thanks again for the data. 
Dan
_________________
Don't develop "a" load. Develop THE load! http://optimalchargeweight.embarqspace.com/ |
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| Shortround |
| Posted: Fri Oct 30, 2009 8:28 pm Post subject: |
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Joined: 14 Jul 2009
Posts: 80
Location: Avilla, Arkansas
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Dan, if I understand you right, then if I have a load that uses a 175 grain bullet and 40 grains of brand X powder, and a 150 grain bullet using 45 grains of the same powder, then 50 grains would be correct for a 125 grain bullet?
In other words, if the bullet weight increases/decreases by X%, then the powder charge will decrease/increase by the same percentage?
(example: 51.5 grains of WW 748 with a 125 grain bullet is listed as an accurate load. If going to a 130 grain bullet, the OCW would be at 49.4/49.5 grains).
Interesting. |
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| dannewberry |
| Posted: Sat Oct 31, 2009 10:26 am Post subject: |
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Site Admin
Joined: 26 Jan 2005
Posts: 2181
Location: Southwest Virginia
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You have to have 2 known OCW loads with different bullet weights and the same powder, then, to determine the OCW with that same powder for a third bullet weight...
(I am indebted to Chris Long for writing this equation for me, as my own extrapolation method was a huge mess!) 
C=charge weight of new load
C1=charge weight of 1st load
C2=charge weight of 2nd load
B=bullet weight of new load
B1=bullet weight of 1st load
B2=bullet weight of 2nd load
C=C1+[(C2-C1)*(B-B1)/(B2-B1)]
...and that's pretty much it.
There are limitations to this method, as it can take you to unsafe charge levels as you run up the bullet weight--so always check published data, and of course always work up to the suspected new OCW.
This method has always revealed the new bullet's OCW, every time I've tried it.
Dan
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Don't develop "a" load. Develop THE load! http://optimalchargeweight.embarqspace.com/ |
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| Shortround |
| Posted: Tue Nov 03, 2009 10:23 am Post subject: |
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Joined: 14 Jul 2009
Posts: 80
Location: Avilla, Arkansas
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Dan, that formula works out pretty nice. It will be useful. Thanks for that info.
After sorting and prepping several hundred Lake City 84 7.62mm cases, I decided to take a sampling and see how close they were on weight.
I took 50 random samples and this is what I came up with.
High – 178.9 grains
Low – 175.8 grains
Average – 177.2 grains
How does this compare with commercial brass as to consistency? This had less than 1% difference on either side of the average. I think this percentage would tighten up if all of the cases were exactly the same length. Length varied from 2.003” to 2.008”.
I did load up a few, reducing the load to the 96.1% level I came up with earlier, and noticed that the pressures seemed a bit lower. I used 43.6 grains of RL-15 with a 150 Hornady as compared to 45.5 in the Winchester case. Even bumping up to 45 grains extraction was not an issue. Gonna do an OCW work up today.
I think the mil-spec extraction issue is fixed. The secret? Clean, clean, clean!!!!! Just fill the tumbler up with brass and let her run until they are real shiny. To test the theory I had, I loaded up an identical load in a couple that were a bit dull. They shot fine but were a bit sticky. I think the military stuff is a bit”rough” and the extended tumbling smoothes up the surface to more like the commercial stuff. I sure wasn’t looking forward to trashing a couple of five gallon buckets of once fire brass and having to buy new stuff. Guess I’ll start on the .30-06 next. Got one ammo can full of National Match and a couple cans of LC 75. This is beginning to turn into WORK! At least this bunch is nice and clean from being sealed up.
Again,I appreciate all the info I'm able to get from this site.
Shortround out |
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| dannewberry |
| Posted: Tue Nov 03, 2009 10:33 am Post subject: |
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Site Admin
Joined: 26 Jan 2005
Posts: 2181
Location: Southwest Virginia
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Thanks for the update, and I hope the load testing goes well. Let us know.
And thanks again for the volume references... that will be helpful to many in the future.
Dan
_________________
Don't develop "a" load. Develop THE load! http://optimalchargeweight.embarqspace.com/ |
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| RePete |
| Posted: Wed Nov 04, 2009 9:22 am Post subject: |
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Joined: 24 Oct 2007
Posts: 35
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I had 2 boxes (40) of new unfired Winchesterbrass that I weighed (about 20 years ago). 2 different lot numbers.
The first batch weighed in at
High - 155.5gr
Low - 151.5gr
Average - 152.5gr
The second batch was
High - 165.0gr
Low - 158.0
Average - 162.625gr.
I found the results disappointing for supposingly good brass (batch to batch)
I hope that these number help shortround and Dan. |
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