7-300 Win Mag questions

[JustBC]

I am having a 7-300 barrel done. I have a couple questions about loading.
1. What is the best 300 Win Mag brass to neck down? Has anyone used RWS brass?
2. What bushing sizes should I use?
3. How many steps do I need to go through between .300 and 7MM? (I am unfamiliar with necking brass down)
4. Will I need to neck turn to get good results?
5. Any gotchas I need to worry about?
6. Any extra tips for accuracy?

Last but not least, load recipes for 195 Bergers/197 SMKs?

Thanks!

 

[demolitionman]

tag

 

[mdmp5]

I don’t have a 7-300, but I have had a 300 up until recently, and I have necked down several hundred cases before.

Don’t know if there is a best brass per se, but I used to shoot Lapua/Norma brass and it lasted me quite a while.

For a standard 7mm case, your bushing size will be around 315. Now mind you, that’s for a 7mm case. In necking down, you will have a thicker neck, so probably add 3-5 thousandths. Then if you neck turn, you would use the smaller bushing after. You will know if you should neck turn if the case doesn’t chamber.

You will want to take your necks down in a stepwise fashion. For a 300, you are looking at a neck diameter of roughly 335. So you are gonna have to take that down to about 320. I would recommend 3 passes, which is 5 thou at a time. If you go too aggressive, you will get funneling in the brass, which will only be rectified from the first firing. So I would take them down 5 at a time, then see where you are in terms of neck tension and if the brass chambers. If the neck tension is fine and the brass doesn’t chamber, it’s time to neck turn. If the neck tension is too loose, take it down to the proper tension with a correct bushing

 

[18Echo]

I have a 7-300 from Robert Gradous. I haven't gone out to shoot it though...

A While ago 300WM brass was hard to find so I jumped at a good deal and bought 200 cases of Norma. One bag I kept for my 300 Barrel the other one I necked down for the 7-300 barrel (it's a switch barrel rifle on a Surgeon).

I used a Redding Bushing die to neck down, I think I did it in 2 steps. I went below diameter and then used a sinclair expander to neck up and then neck turned using a K&M set up to .014 (maybe .013) If I remember (it's been a while), then did final sizing. Seated the Berger 180 VLD with a Forster 300 seating die with a 7mm stem.

I have all my rounds loaded for OCW with 7828SSC, just need to find time to get out to the range.....

 

[JustBC]

Thanks guys. I use Norma brass for 223 and 6.5CM. I will give it a shot for 300 win mag.

 

[JustBC]

Norma brass ordered. I also picked up some pulled Federal Premium 300 Win Mag brass from Graf's. I think it was from pulled military ammo. I can make my mistakes on that before I get to the Norma.
Next stop is bushings. I will seat a bullet in the brass, take measurements then step down in .005 increments as suggested. I am waiting on the barrel so I won't know if i need to neck turn for a while. Thanks again guys.

 

[18Echo]

Neck turning for me is more about uniform tension versus anything else and you don’t need the barrel for that.

 

[JustBC]

So far everything seems to work. Went down in .005 increments down to .315. No doughnuts, no issues. I still need to figure out the correct neck tension.
So 2 questions though...
First, it doesn't seem like it is sizing all the way down to the shoulder. See attached photo. It is ALMOST there. My dies are down as far as they will go. Is this going to effect chambering or accuracy? Is it something I should worry about?

Second, how do you actually determine correct .001-.002 neck tension? Do you figure out the slip-fit then go down .002?

Thanks guys!

 

[mdmp5]

Bushing dies don't make it all the way to the shoulder - neck junction. What you have is normal.

To determine 1 to 2 thou of NT, you said you were at 315 now right? Seat a 284 bullet and make sure it doesn't just slide into the case. If it seats fine, then take that measurement and subtract 1-2 thou. Chamber that dummy cartridge to make sure it fits. If it is really tight, you have to turn the necks a bit.

 

[JustBC]

DOH! exactly like you would with any other setup ;-) Makes sense, thanks.