300 Sherman Shortmag (SS)

[tbrice23]

Speaking of powder; Ryan is learning what it is like to be the guinea pig for a brand new wildcat. Something very interesting though is the fact that the SS and saum act very differently.....Rich

It could be barrel/ bore temperament (preference) as much as cartridge differences.

 

[elkaholic]

It could be barrel/ bore temperament (preference) as much as cartridge differences.

Could be but it seems to be too pronounced even for that. We have decided N570 is a no go because the particles are so large you can't get enough in the case with the lower density.

 

[wilkup]

Has RL33 been tried? Would it work on this round?

 

[elkaholic]

Has RL33 been tried? Would it work on this round?

Way too slow!

 

[shawnb]

I would still like to see where you end up with r26. If you can stuff 66gr of that in there thats a lot more than where you started with it unless you have attempted this and didnt post it.

 

[elkaholic]

I would still like to see where you end up with r26. If you can stuff 66gr of that in there thats a lot more than where you started with it unless you have attempted this and didnt post it.

We tried that first and it didn't work.......Rich

 

[Idaho Trecker]

This has been one interesting cartridge to be the guinea pig for but definitely worth it. Once again it seems like the design of this cartridge has an effect on how burn rates of powders act differently.

H4831 should have been faster burn rate and no problem to pressure out according to the burn rate but it actually acted slower in this cartridge. I ran a pressure test from 62-65 grains

62- 2807
63- 2833
64- 2873
65- 2877

It looks like the H4831 is gaining about 30-35 fps per grain. I think this could explain the small difference between 64 and 65 grains if the ES was 10-15 and the 64 charge was on the top end and 65 at the bottom end of the ES that would make sense.

I was able to pick up some 7828ssc to give a try and again got a different result than expected. I loaded up 64.5-66.5 in 1 grain increments with 66.5 being all that would fit and compressed expecting to be able to easily shoot the top load. Again this powder actually acted much faster than RL 22. The 64.5 grain load was the only one I was able to shoot due to way to much pressure and barely being able to get the bolt open. This one shot went 2982 fps which gives hope to possibly use this one once the new throat is done after a little more testing without it.

 

[MudRunner2005]

This has been one interesting cartridge to be the guinea pig for but definitely worth it. Once again it seems like the design of this cartridge has an effect on how burn rates of powders act differently.

H4831 should have been faster burn rate and no problem to pressure out according to the burn rate but it actually acted slower in this cartridge. I ran a pressure test from 62-65 grains

62- 2807
63- 2833
64- 2873
65- 2877

It looks like the H4831 is gaining about 30-35 fps per grain. I think this could explain the small difference between 64 and 65 grains if the ES was 10-15 and the 64 charge was on the top end and 65 at the bottom end of the ES that would make sense.

I was able to pick up some 7828ssc to give a try and again got a different result than expected. I loaded up 64.5-66.5 in 1 grain increments with 66.5 being all that would fit and compressed expecting to be able to easily shoot the top load. Again this powder actually acted much faster than RL 22. The 64.5 grain load was the only one I was able to shoot due to way to much pressure and barely being able to get the bolt open. This one shot went 2982 fps which gives hope to possibly use this one once the new throat is done after a little more testing without it.

That's good that you found a couple powders that are giving you near full capacities with decent results. I'd back that 7828 load off a a grain and then work up in .1's and see where that pressure threshold actually is. Then you you can start doing some fine-tuning, once you know your absolute safe max. If you can get 2,940-2,950 out of that cartridge with a 215 Hybrid that's pretty **** solid.

Another one that might be worth trying, is Norma MRP. That stuff is supposed to be Norma's version of RL-22, but it's supposed to be VERY temp stable. I have never loaded anything with it, so I can't confirm 100%, but I can't recall reading anything negative about it. So, that might be worth looking into, also?

 

[Idaho Trecker]

Mudrunner...I have had the same thoughts about trying MRP but lately I've spent entirely to much on single pounds of powder for this rifle and need to slow down to meet my wages. For now I'm going to see how Superformance and RL 22 do at distance and how the ES and SD are with those powders. Soon after that it will probably be time to send the rifle back for the new throat.

 

[MudRunner2005]

I'd keep working with 7828 SSC since it has given you the best performance so far.

Look on the bright side, with all this experimenting with different powders, and keeping track of your velocities and powder charges, you're basically writing your own reloading manual for the .300 Sherman...Information that will also be very helpful for others in the future.

 

[Idaho Trecker]

Life has sure got away from me lately so I havent been able to post my latest data from over a week ago. Here it goes

I wanted to finally stretch out to some distance and do some temp sensitivity testing with Superformance since I couldnt find much data on it.
The load I felt would be pretty safe pressure wise led me to load up 4 rounds with 63.3 grains of Superformance and the 215 Berger. These first 4 were shot at 50 degrees. The first shot was done at 100 yards to make sure I was on with the Magneto attached and from there I moved to 680 yards. I had 1 shot error out on me but here are the other 3...

2937
2919
2943
average 2933

Not a terrible ES but being use to the single digit ES with RL 26 in other cartridges I was hoping for better. Even so I've had alot worse and this is still plenty acceptable. I'll post the target pictures shortly and they can speak for themselves. I'll say with my shooting abilities and the "low" power scope I am Extremely impressed with the rifle and cartridge!!!

The next trip out I shot the same load and did the same 100 yard setup to start with an outside temperature of 73 degrees.

2963
2980
2963
2973
average 2970 (average w/o 2980 fps shot 2966)

The second shot in the string was the first shot at my target after I set it up at 702 yards and I chambered it before I was really ready to fire and it sat in the chamber for a full minute or two which could explain the little bit higher speed. This time I had a very variable 3-9 mph wind from 290 degrees and was still very happy with the group I ended up with.

The temperature sensitive is still lacking at about 1.5 fps/degree change with superformance. I'm hoping once the "Special" throat is put in I will be able to possibly use a slightly different burn rate and put me in a range to use a more temp stable powder.

On another note the brass life on this case is unreal! I have been using the same 7 brass from the start of this project. I've rotated the order of the brass when doing the pressure tests so the same ones are not constantly fired with the highest charge. Every brass still holds primers with two being somewhat loose even after all of these pressure tests. I am at 10 firings even with all of these full bore loads!!!

After a little more testing I am going to send it off for the new throat and start the testing all over. Thats just terrible that I'll have to do some more gun)

 

[Idaho Trecker]

680 yards



702 yards

The 702 yard picture won't load right but it should be rotated clockwise so the writing on the target is legible.

 

[elkaholic]

680 yards
View attachment 62926


702 yards
View attachment 62927
The 702 yard picture won't load right but it should be rotated clockwise so the writing on the target is legible.

Sub 1/2 moa in a breeze is pretty good at that range. Lengthening that throat may change things enough so that you CAN use a different powder. We'll see?.....Rich

 

[shawnb]

What are you guys doing with the throat? Just lengthening? What are you going to end up with freebore?