300 Sherman Shortmag (SS)

[Bucks4me2]

I got the 300 SS back from Rhian with the new throat and the brake. It looks awesome with the brake and it is extremely tame now (not that it was bad at all before). I hurried and put the scope and stock back on last night and ran out to send a few fire forming loads down to smooth everything back out. After the fire forming loads I ran 3 of my most used load of 63.3 grains of Superformance down with the magneto attached. I was somewhat disappointed with the results until I started thinking about it and consulted with Rich. My fist shot gave me an error but next two were 2942 and 2953. Very good ES. This was the exact same speed as before and the bolt was super hard to get open, maybe more so than before. The case head has a very pronounced extractor mark and flattened primer. With a little collaborative brainstorming we hit on the idea of trying some new brass and see how that worked (the brass I used with the Superformance load was on its 12th firing!!! All with full throttle loads.

The results with the newly formed brass was just what we were expecting. Pressure dropped due to the brass being able to contract when sized and not spring back near the web.

I'll post a picture of my results from this morning comparing the initial testing with the new throat. All loads except MRP were one shot over the magnetospeed.

My next session out I will try a load of RL 17 and N560 to see how it compares to before the throating. I will also run higher with Hybrid 100V and see where I max out now.

As of now I am leaning towards 100V, Superformance, or RL22-MRP being the winners. Out of those I'm hoping for 100V since it is the most temp stable of the powders I listed.

Sorry for the long read but lots of information to get out there!

That's smoking hot! Congratulation on a gorgeous rifle. I'm also impressed with bigngreen, the dedication and interest he is showing in your success. The efficiency that cartridge is showing is off the scale.

 

[elkaholic]

Good stuff Ryan. I knew this 300 version was going to be a keeper and Rhian has been awesome in making it all come together. I will give you some Ramshot Hunter when we hook up. I think it may work too. I am still expecting something to work at close to the (MAGIC) 3000 level......Rich

 

[shawnb]

Things are looking up for you. What is your oal with the 215s? I found that i have a really short throat. I am looking at getting it lengthened 100thou.

And what do you know about n165? Is that a powder that might work?

 

[elkaholic]

Things are looking up for you. What is your oal with the 215s? I found that i have a really short throat. I am looking at getting it lengthened 100thou.

And what do you know about n165? Is that a powder that might work?

I think N165 would be close to 4831 in my experience with it. Good accuracy and es but not top velocity. You could try it though?...Rich

 

[Idaho Trecker]

Things are looking up for you. What is your oal with the 215s? I found that i have a really short throat. I am looking at getting it lengthened 100thou.

And what do you know about n165? Is that a powder that might work?

Things are definitely looking up but it's a big learning curve being the guinea pig haha few more things to try still. If I remember right the col is 3.010"

 

[elkaholic]

Shawn....You would need about 3.1" coal to have the same length throat.....Rich

 

[shawnb]

Ya that about what i came up with. Im extending the 215 to touch at 3.14 and the 208eldm will touch at 3.1. I rechecked and am currently touching at 3.045 with the 215s and 3.005 with the 208s

Im on a short action and have the ptg 3b bainey box on order. When i get it i will do a short write up on it. Its supposed to allow a 3.11 oal.

 

[Idaho Trecker]

Ran one load of 63 grains of N560 and got 2795 which was 52 fps slower and way less pressure than before with the big speed drop. 1 load of Rl 17 was ran with 59 grains and gave me 2907 which was a lot of pressure and 11 fps faster than before the throating.

Tried one load with 65 grains of N560 which showed 2916 and was what I will call max useable. Did one more with 63.6 grains of Superformance and got 2957 which was basically no different than the 63.3 grain load I had been shooting.

Also finished out my Hybrid 100V pressure test with
59 2860
60 2918
61 2960
62 3000

The 62 grain load was the absolute max with this rifle. I'm going to try and keep the 100V load as my go to since it has been the best for temp stability for what works in here so far. Next I will see how it groups and run really close to the 60 grain and 2920 fps area. That seems to be where every powder likes to run without excessive pressure.

 

[shawnb]

Good info. This is sure an awesome little round. Cant waitto get my throat lengthened and try some 100v haha.

 

[Idaho Trecker]

After a restless night of trying to figure out a powder to try next (or again) I revisited my notes on RL 26 from my first outings with this rifle and had to get out of bed to see how much I could fit to the base of the neck again. To my surprise I was able to get 67 grains to just a few thousandths below the neck!!! I loaded up 65, 66, and 67 grains under a 215 berger. A quick trip to the field started off with an error on the magneto but quickly turned around when the next round (66 grains) gave me a reading of 2960!!! The last gave me exactly what I expected at 3010 FPS!!!!

The pressure on the 67 load was somewhat stiff but the primer was still pretty round with a slight crater. There was an extractor mark but not bad. It looks like RL 26 will be my powder in this cartridge also. As long as accuracy is good (it always is ) there should be a good useable load around 2940fps or so.

 

[elkaholic]

After a restless night of trying to figure out a powder to try next (or again) I revisited my notes on RL 26 from my first outings with this rifle and had to get out of bed to see how much I could fit to the base of the neck again. To my surprise I was able to get 67 grains to just a few thousandths below the neck!!! I loaded up 65, 66, and 67 grains under a 215 berger. A quick trip to the field started off with an error on the magneto but quickly turned around when the next round (66 grains) gave me a reading of 2960!!! The last gave me exactly what I expected at 3010 FPS!!!!

The pressure on the 67 load was somewhat stiff but the primer was still pretty round with a slight crater. There was an extractor mark but not bad. It looks like RL 26 will be my powder in this cartridge also. As long as accuracy is good (it always is ) there should be a good useable load around 2940fps or so.

Now your talkin'! RL26 is the best I have found in both the Sherman AND SS cases with just about any bullet. There was some ?? as to whether the 300 had too much bore, but it looks like it's the champ again. Good job with testing Ryan. 3010' with 67 grs. of powder. HOTDANG!............Rich

 

[Idaho Trecker]

Thanks Rich! Now that my wedding is over I'll work on some accuracy loads with 26. Looks like it's time to order some more 215 berger. Just for fun I ordered a couple boxes of 212 eld x to possibly mess with.

 

[tbrice23]

Thanks Rich! Now that my wedding is over I'll work on some accuracy loads with 26

Your shooting career is over. Lol

 

[Idaho Trecker]

It's amazing how rl 26 has been so great through the Sherman and SS cartridges for speed and accuracy! This rifle has shown me that it can shoot better than I am capable throughout all of my testing. Here is what I came up with at 100 yards with 215 grain Berger and 65.8 grains of rl 26.

This group came in at .350" (3 shots)
Magneto was attached for 4th shot (not shot at target) and read 2978 fps.
I feel if I had a little more magnification I might have been able to hold up my end since this rifle does.
I'm going to leave this load alone until after hunting this year but will back it down a little after season as this load is a little stiff.