How is this possible?

[Qtiphky]

In my recent trip to the range, I discovered another anomaly that I am confused by. As I was sighting in my 300 WSM and my 308 Win, I noticed the velocities didn't seem right. The 308 had higher velocities than the 300 WSM with less powder. The 308 was shooting a 15 grain lighter bullet, but it also had 7 grains less of the same powder. Here are the results:

300 WSM
165 grain Nosler Ballistic Tip
52 grains of H4895
2780 fps

308 Win
150 grain Barnes Tipped TSX
45 grains of H4895
2822 fps

Does this seem right?

 

[William T. Watts]

While H4895 is usable it certainly isn't an optimum powder for the 300 WSM with a 165 gr Ballistic tip, on the other hand H4895 is an ideal powder for the 308 Win with a 150 gr Barnes TSX.. Frequently when a powder is used that isn't a good match for the caliber and bullet weight low velocity isn't all that unusual. William

 

[jimbob86]

Seems a bit slow..... my Lee 2nd ed lists a start load of 51 grains for a vleocity of 2800 ......

...but I agree, H4895 is not the optimum powder for that cartridge...... something slower, like RL-19 or H-4831 .....

 

[mrawesome22]

Yep. Need a slower powder. Try some H4350.

 

[old roper]

Not sure where your getting reloading data but Hodgdon has a start load of 55gr/H-4895(2839fps) to a max of 59gr( 2977fps) with a 165gr bullets.

H-43540 and R-17 have been good powders in my 300WSM with 165gr bullets 3100 to 3200fps.

 

[William T. Watts]

IMR Powder.com lists 54 grns of H4895 with a Nosler Partition and 51 grns with a Hornady GMX with both being a maximum charge. I believe this to be a Hodgdon website. My advice would be seek out several loading sources and use the lowest start load and work up looking for the usual pressure signs.. William

 

[Unclenick]

Qtiphky,

Your results are what QuickLOAD predicts using 24" barrels.

QuickLOAD says the .308 with a Winchester case should send the Barnes bullet out at 2813 fps, right at 60,500 psi, getting 33.2% ballistic efficiency. The .300 WSM with 52 grains of H4895 it predicts to get 2762 fps from the Nosler BT, peaking at 45,600 psi and getting about 27.7% ballistic efficiency. It's in good enough agreement with the real results to consider the model's analysis valid.

So, 16% more powder is trumped by 20% more efficient use of the powder. The WSM case is only 79% filled with powder under the bullet, so the pressure is lower which burns the powder less quickly. This is what makes the powder usage less efficient in the WSM load.

 

[black mamba]

Yep, what nick said. It's all because the case is so much larger on the WSM.

 

[Qtiphky]

Sounds logical

Thanks for the replies. As for where I got the load, I don't remember as I worked it up last year after deer season and shot it in the cold so I know it should be fine with temp swings and what not. I thought I got it from the Hodgdon website, but I must be remembering that incorrectly. Seems to make sense though as there does seem to be more room in the case.

 

[mrawesome22]

A lot more case capacity.

When choosing a powder, case fill should be a big part of the decision process. Ideally, a powder that gives good velocity and is slightly compressed.

 

[Qtiphky]

Hodgdon's Website

I went back to their website and found two different combos for 165 grain bullets. For a 165 GMX bullet, it says to start at 47 and not to exceed 51 grains. For a 165 Nosler Partition, starting at 51 and not to exceed 54. I thought that was where I got my ranges from, I started at 51 and at 52 it settled right in to a nice tight group that didn't really kill my shoulder. Above 52, the groups opened up again, so I loaded up a bunch at the 52 for sighting in and chronographing this fall.

 

[Unclenick]

Qtiphky,

Try this experiment when you get out there. Before firing each shot, point the muzzle in the air or, if your range doesn't allow that (mine no longer does), tip up very slightly (not over the berm) and slap the buttplate a couple of times to settle the powder over the primer before rotating the bolt down and firing. Get an average of 10 shots taken that way. Then reverse the process and tip the muzzle down before slowly coming level to fire each shot and take another average.

In the M1 Garand with loads of similar charge density to yours, but shooting IMR4895, I've seen about 80 fps difference in velocity and watched the primers go from starting to flatten to well-rounded. I'd be interested to hear what sort of range that produces in your gun. You may find that getting the powder over the primer makes the front of the powder column act enough like a projectile of its own mass to get you the performance of a slightly smaller case. It did with the .30-06, anyway. The shorter aspect ratio of your case should be less sensitive to it, but some effect is still likely to occur.