[velocette]

For my .308 AR rifle. 18" bull barrel. My primary load is 41 gr of IMR 4895 behind a Sierra 168 gr HPBT match bullet in Federal brass. Excellent accuracy, sub moa. (Just below the Sierra manual's max of 41.3) All loads seated to magazine length of 2.8"
Chronographed at 2450 fps by a fellow shooter at my local range.
Now many months later, I do not have a chronograph available & am curious about using brass of larger powder capacity. The Fed case is the heaviest .308 brass (182 gr. average) with the least internal capacity.
If I were to use a case with larger internal capacity such as a Winchester or Hornady (160 grain average) and use the Hornady reloading manual's charge data for a 168 grain bullet which is 2 grains higher for max, is it reasonable to expect a 50 ~ 100 fps increase in velocity? Or would the larger case dimension obviate the difference? Obviously, all loads to be worked up to being observant of pressure signs.

Roger

[Steve C]

What will happen with a change in components is unknown. The only way to find out is to get a chrono and try the changes.

Personally if I have a sub MOA load I stick with it. I wouldn't worry about a small gain in velocity. You are just as likely to loose your accuracy as increasing your velocity.

[AR15barrels]

Using quickload to model your question, I come up with the following results:

Cartridge : .308 Win. (52gr water capacity)
Bullet : .308, 168, Sierra HPBT MatchK 2200
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length : 18.0 inch or 457.2 mm
Powder : IMR 4895

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.595% 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
-02.4 103 41.00 2451 2240 53814 9458 94.2 0.992 ! Near Maximum !

Cartridge : .308 Win. (55gr water capacity)
Bullet : .308, 168, Sierra HPBT MatchK 2200
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length : 18.0 inch or 457.2 mm
Powder : IMR 4895

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.595% 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
-02.4 96 41.00 2379 2111 47123 9493 93.1 1.056
-01.8 97 41.25 2393 2137 47967 9558 93.4 1.047
-01.2 97 41.50 2408 2163 48828 9622 93.6 1.038
-00.6 98 41.75 2422 2189 49705 9685 93.9 1.030
+00.0 99 42.00 2437 2215 50599 9748 94.1 1.021
+00.6 99 42.25 2451 2242 51508 9810 94.4 1.013 ! Near Maximum !
+01.2 100 42.50 2466 2268 52432 9871 94.6 1.005 ! Near Maximum !
+01.8 100 42.75 2480 2295 53381 9931 94.9 0.997 ! Near Maximum !
+02.4 101 43.00 2495 2322 54344 9991 95.1 0.989 ! Near Maximum !

Cartridge : .308 Win. (58gr water capacity)
Bullet : .308, 168, Sierra HPBT MatchK 2200
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length : 18.0 inch or 457.2 mm
Powder : IMR 4895

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.61% 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
-02.4 91 41.00 2315 1999 42035 9494 92.0 1.116
-01.8 91 41.25 2329 2023 42746 9563 92.3 1.107
-01.2 92 41.50 2343 2047 43470 9631 92.6 1.098
-00.6 92 41.75 2357 2072 44205 9698 92.9 1.090
+00.0 93 42.00 2371 2096 44954 9765 93.1 1.081
+00.6 93 42.25 2384 2121 45715 9831 93.4 1.072
+01.2 94 42.50 2398 2146 46489 9896 93.6 1.064
+01.8 94 42.75 2412 2171 47278 9961 93.9 1.056
+02.4 95 43.00 2426 2196 48079 10025 94.1 1.048
-01.7 96 43.25 2440 2221 48894 10089 94.4 1.039
-01.1 96 43.50 2454 2246 49724 10151 94.6 1.031
-00.6 97 43.75 2468 2272 50569 10213 94.8 1.023
+00.0 97 44.00 2482 2298 51428 10274 95.0 1.015 ! Near Maximum !
+00.6 98 44.25 2496 2323 52301 10335 95.3 1.008 ! Near Maximum !
+01.1 98 44.50 2510 2349 53191 10394 95.5 1.000 ! Near Maximum !
+01.7 99 44.75 2524 2376 54095 10453 95.7 0.992 ! Near Maximum !
+02.3 99 45.00 2537 2402 55018 10511 95.9 0.985 ! Near Maximum !

[boommer]

Hey FOR A BUCK @ QUARTER YOU CAN GET a Crony! and learn how to read pressures, in the real world each chamber is different the bore is different every thing has as effect and somethings looks good on paper but in the world of pressures, has to have all volumes and expansions have to be exact, powders have to be exact to what is tested. I'm not saying that load charts and such are not road maps but don't set them in stone.

[Grumulkin]

I spent some decades happily reloading without a chronograph. Frequently a different brand of brass will give different results on the target. If using different brass it would be prudent to see if the point of bullet impact and accuracy is similar between them and if not, do some load adjustment.

[velocette]

Randall;
Thank you very much for your work. Rather apparently, IMR 4895, no matter what case volume is used results in about the same results.
Do you think if I used Alliant Reloader 15, I could improve the results with larger volume cases?

Thanks
Roger

[AR15barrels]

Randall;
Thank you very much for your work. Rather apparently, IMR 4895, no matter what case volume is used results in about the same results.
Do you think if I used Alliant Reloader 15, I could improve the results with larger volume cases?

Thanks
Roger

Actually, there is some gain there, but it is small.

Look at the pressures and velocities in each of the three different case volumes.

At 52gr water capacity and 2450fps, you are at 53,800psi
At 55gr water capacity and 2450fps, you are at 51,500psi
If you bump the charge up to match the pressure, you actually have more velocity by about 35fps.

[velocette]

Randall;
Thank you very much. You have answered my questions very well.
Your help is very much appreciated.

Roger