Brass thickness, capacity and pressures...

Keller

Keller

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I've been reloading for years using mainly Winchester brass for my .308 (M1A) and have had no issues at all. Recently, I wasn't able to purchase Winchester brass and went with a bag of Remington and I've noticed that with my standard load (155 Grain Hornady A-Max and 45.9 Grains Win748) there is less "space" in the casing. The load is not compressed and is still 3 grains short of the max load, but I'm concerned that the lower capacity of the thicker Remington brass might be increasing pressure.

Am I being paranoid?
 
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This is where it hits the fan..............

You'll notice that no manufacturer ever provides brass type, brass volume, powder lot, outside temperature, rifle leade length, chamber or bore "tightness" (all things that affect pressure) - nothing except a powder, powder quantity, bullet weight and type, and OAL, yet they list pressures to within a few hundred psi, and this load is then used in hundreds of slightly different brass-barrel combinations and is still deemed "safe". Those who cling to load tables count on that. Some will say "look for pressure signs", but none can use them to predict actual pressure, and few understand how utterly unreliable most are.

All to say that the pressure listed in published "safe" loads are only going to approximate what you use. There is a margin of error. With the laod you used, what was safe in the Winchester brass will be safe in the Remington brass.
 
Below are Quickload examples, .308 maximum rated chamber pressure is 60,191 psi

Winchester .308 case with a internal case capacity of 55.8 grains of water.
155 Grain Hornady A-Max and 45.9 Grains Win748, 56,414 psi, 2901 fps (3,777 psi under maximum rated chamber pressure)

U.S. Military Lake City case with internal case capacity of 53.45 grains of water.
155 Grain Hornady A-Max and 45.9 Grains Win748, 62,884 psi 2957 fps (2,693 psi over maximum rated chamber pressure)

2.35 grains of water less case capacity with the Lake City cases caused a over pressure condition.

The default case capacity setting of Quickload is 56.00 grains of water
155 Grain Hornady A-Max and 45.9 Grains Win748, 56,310 psi, 2900 fps

Cartridge : .308 Win.
Bullet : .308, 155, Hornady A-MAX 30312
Useable Case Capaci: 48.911 grain H2O = 3.176 cm³
Cartridge O.A.L. L6: 2.800 inch = 71.12 mm
Barrel Length : 26.0 inch = 660.4 mm
Powder : Winchester 748

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-20.0 76 36.72 2360 1917 29569 5685 93.9 1.545
-18.0 78 37.64 2415 2008 31520 5839 94.9 1.506
-16.0 79 38.56 2470 2100 33592 5985 95.8 1.468
-14.0 81 39.47 2525 2194 35821 6123 96.6 1.432
-12.0 83 40.39 2579 2290 38192 6252 97.4 1.394
-10.0 85 41.31 2634 2387 40723 6372 98.0 1.354
-08.0 87 42.23 2688 2486 43431 6483 98.6 1.316
-06.0 89 43.15 2741 2586 46326 6583 99.0 1.280
-04.0 91 44.06 2795 2688 49426 6672 99.4 1.245
-02.0 93 44.98 2847 2790 52747 6751 99.7 1.211 ! Near Maximum !
+00.0 95 45.90 2900 2894 56310 6818 99.9 1.178 ! Near Maximum !
+02.0 96 46.82 2952 2999 60128 6873 100.0 1.147 !DANGEROUS LOAD-DO NOT USE!
+04.0 98 47.74 3003 3104 64199 6917 100.0 1.116 !DANGEROUS LOAD-DO NOT USE!
+06.0 100 48.65 3054 3210 68557 6956 100.0 1.087 !DANGEROUS LOAD-DO NOT USE!
+08.0 102 49.57 3104 3317 73234 6993 100.0 1.059 !DANGEROUS LOAD-DO NOT USE!
+10.0 104 50.49 3155 3425 78262 7027 100.0 1.032 !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 95 45.90 3006 3111 67919 6498 100.0 1.099 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 95 45.90 2741 2586 45545 6890 96.3 1.283

Cartridges: 1000 Yard .308 Case Capacity and Other Problems
by Germán A. Salazar
http://riflemansjournal.########.com/2011/01/cartridges-1000-yard-308-case-capacity.html
 
Out of an abundance of caution you could download by a grain and see how it shoots. You can always go up from there. I notice that with some loads, which it stands to reason are lower pressure, the m14s action cycles much more gently and the brass fall to my side. These loads shoot well at 300-600 yards despite being a bit downloaded from max. So for me, pushing the limits of pressure and velocity doesn't seem to produce benefits.
 
Andy said:
This is where it hits the fan..............

There is a margin of error. With the laod you used, what was safe in the Winchester brass will be safe in the Remington brass.
Click to expand...

Your statement is totally wrong, as an example if the Hornady reloading manual lists a Winchester Model 70 rifle and Hornady/Frontier cases the pressure readings were taken with a strain gauge. And this means the pressures were specific to that rifle and load and the internal case capacity of the cases being used in testing.

The manuals state clearly to start low and work up to maximum load and any time you switch components you start over and work up again. Just switching cases can put you over maximum pressure and the majority of Remington cases have less case capacity than Winchester.

Below are what just two grains less in case capacity can do with the same bullet and powder charge in a .223 case.





 
Andy said:
This is where it hits the fan..............

You'll notice that no manufacturer ever provides brass type, brass volume, powder lot, outside temperature, rifle leade length, chamber or bore "tightness" (all things that affect pressure) - nothing except a powder, powder quantity, bullet weight and type, and OAL, yet they list pressures to within a few hundred psi, and this load is then used in hundreds of slightly different brass-barrel combinations and is still deemed "safe". Those who cling to load tables count on that. Some will say "look for pressure signs", but none can use them to predict actual pressure, and few understand how utterly unreliable most are.

All to say that the pressure listed in published "safe" loads are only going to approximate what you use. There is a margin of error. With the laod you used, what was safe in the Winchester brass will be safe in the Remington brass.
Click to expand...
Contrary to what some people choose to believe, all loads listed in a loading manual, may not be safe in all firearms. By the same token, substituting components,or changing lots of powder can result in a load that is no longer safe in the firearm. That is the reason for the disclaimers in the manuals, that warn people to watch for signs of excessive pressure.
 
Why don't you first measure the volume of water (in grains of water) of your cases. That's where you should start, anyways. I always make comparative capacity measurement of different brand / batches (of at least once fired cases) before loading them.
Then, adjust the powder charge with the case capacity.
 
bigedp51 said:
Below are what just two grains less in case capacity can do with the same bullet and powder charge in a .223 case.
Click to expand...

I'm not doubting what you've posted, but 2 grains in a .223 cartridge is not equal to 2 grains in a .308, unless the case capacity is similar. One of my books shows the .223 having 1.87cc useful case capacity, and the .308 3.43cc useful case capacity.



.
 
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Thicker Bass with firm meat is my favorite. Ones from deep water seems to have firmer meat from the higher water pressure. Fishing season just arrive here in the warm West Coast.
 
Keller said:
Winchester - 55.6 Gr Water
Remington - 54.4 Gr Water
Click to expand...
NOTE: NO Bass fishing allowed :rey2

Quickload data on these two cases and there capacity below.

1. Winchester case - 55.6 Gr Water - 155 Grain Hornady A-Max and 45.9 Grains Win748 - 56,876 psi - 2811 fps - 93% of case capacity

2. Remington - 54.4 Gr Water - 155 Grain Hornady A-Max and 45.9 Grains Win748 - 60,039 psi - 2841 fps - 97% of case capacity

Switching to the Remington case with less cass capacity will cause a 3,163 increase in chamber pressure and be very near the maximum rated pressure of 60,191 psi.
 
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saskgunowner101 said:
I'm not doubting what you've posted, but 2 grains in a .223 cartridge is not equal to 2 grains in a .308, unless the case capacity is similar. One of my books shows the .223 having 1.87cc useful case capacity, and the .308 3.43cc useful case capacity.
Click to expand...

The following pressure data is from Quickload software and is approximate.

You are correct, two grains difference in case capacity in the .223 can change the chamber pressure 6,914 psi.
Two grains difference in case capacity in the .308 can change the chamber pressure 3,163 psi.

I wasn't trying to confuse the issue, I simply used the .223 reference photos from Quickload because I was too lazy to upload new .308 photos to photobucket.

The major point being I would never mix brands of brass with the same load, I would use them with different bullets or a different powder and mark them as such and even color code them to avoid confusion. In 46 years of reloading I have NEVER shot mixed brands of cases and always tried to use brass from the same lot number or by weight/case capacity.

Also different brands of cases will have varying shoulder and neck wall thicknesses and will rebound differently when resized. Meaning the cartridge case headspace length could vary and could caused chambering problems on the OPs M1A. The Op will need a Hornady cartridge case headspace gauge to accurately check for correct shoulder bump on his resized cases.
 
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Ed, I think our mate decided to lower is powder charge of at leat .75 grains... with the fast, basic rule of thumb the equivalent load should be around 45 grains for the Remington brass.. I don't run it through QL I am out of spare time for now...
 
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