.500 S&W velocity mystery

[plinky]

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.

I took the Chrony with me today and both .500s. I also loaded up two loads in excess of the Hodgdon manual and hotter than what I have fired before. The results were not what I expected. Loads A and B below are my standards. Load A is a mild and fairly inexpensive plinker. Load B is Hodgdons max for the Sierra 400 and it has always been a good shooter. But since load B is no where near compressed and I'd found some data online using 42 gr of H110, I had to try it.

My results in the 4" gun are within 2 fps of the online data for load D. The odd part is that with each grain of powder added, the velocity dropped. Even at 42 gr, it is not a compressed load. I used heavier than normal crimps on the new ammo...actually buckled 3 cases before I realized it.

All brass is Starline except load D which is Cor-bon. So any ideas on why the "hotter" loads are slower? I have a theory but I'd rather hear from someone who has been through this (or something like this) before.

6/14/08 S&W .500 Mag. 4" bbl and 8.375" bbl
3 shots each load in each gun
70 deg. F and humid

Load A: Speer 325 gr JHP, WLR primer, Titegroup 20gr. loaded in 2005

8.3" bbl. 1552 fps/ 1738 fpe SD 16.37 fps
4" bbl. 1268 fps/ 1160 fpe SD 14.2 fps

Load B: Sierra 400 gr JSP, WLR primer, H110 40gr. loaded in 2005

8.3" bbl. 1617 fps/ 2322 fpe SD 17.9 fps
4" bbl. 1469 fps/ 1917 fpe SD 27.4 fps

*******************************************************************************************************************
Loads below this line are in excess of some published data. I do not reccomend that anyone use them. I include them only for the sake of discussion.

Load C: Sierra 400 gr JSP, WLR primer, H110 41gr. loaded 6/12/08 different can of H110

8.3" bbl. 1590 fps 1550, 1608, 1613 SD 28.6
4" bbl. 1467 fps 1393, 1473, 1536 SD 58.5

Load D Sierra 400 gr JSP, WLR primer, H110 42gr. loaded 6/12/08 different can of H110

8.3" bbl. 1569 fps 1546, 1569, 1601 SD 23.3
4" bbl. 1435 fps 1401, 1446, 1459 SD 24.8

Thanks for any insight you can lend.

 

[janobles14]

how long is your barrel and are you using magnum primers?

i think if you arent burning all of your powder up then you can lose some velocity.

also, you can lose some if your primer isnt firing hot enough to start a good burn on compressed loads.

edit: k i see an 8 inch barrel listed. i dont think that is it. sounds like the pressures are dropping due to less case space. just my guess

 

[Bullet]

While this was in reference to rifles maybe it is true for your loads. Copied from another forum -

In fact, lack of increased velocity even with increased powder charge or even loss of velocity with increased powder charge and pressure, are standard high pressure signs watched for in load development. It is the one pressure sign a chronograph can give you.

You might look here -

http://www.customsixguns.com/writings/high_pressure_loads.htm

.

 

[RecoilRob]

Your 'heavier than normal crimp' might be coming into play here too.

You can only crimp SO tight. Applying more will swage the bullet down and actually make the crimp looser.

Other thought is the powder column pushing the bullet out before being ignited completely. More powder can move the bullet sooner....which can negate the increased charge. But, you should see increased SD (which it looks like you have).

 

[plinky]

Thanks guys for your thoughts, some of which I hadn't considered.

Janobles14, yeah, I had considered working up with magnum rifle primers (and might yet) but several sources say they are not needed so if it did work it would probably be a bandaid for another problem.

Bullet, Your quote and the great link point to what I believe is the main problem. I had gotten used to piling W296 and H110 into a case until no more would fit. Not chronographing a lot of loads, I wanted to believe that it was very hard to overload a magnum pistol with these powders and if more powder went in, velocities had to be higher. I'd wager that a lot of folks want to believe this. But apparently Hodgdon know what they are doing and their maximums are not there just to spoil my fun. Now that is probably not a revelation to advanced ballisticians but it was to me.

Recoil Rob, I am certainly going to look at the crimp. It definately is hard on cases and may also have hampered ignition. It was odd that on the "overloads" the cases were a bit sooty like you get with a very light load and it could be that the bullet left the case before the powder was well lit.

Again, Thank you all for you time and insights.