300 Win Mag reloading question

[Bang4theBuck]

Ok guys I just acquired a 300 Win Mag in a Bergara B-14 HMR. Now I know initially I will have to full length size all my brass but what about after I fire it in my rifle?
Should I partially size my brass (back out the FL sizing die a bit), neck size only or FL resize for longer case life.
Inquiring minds want to know.

That won't work woth the full length sizing die as the last part of the stroke actually reduces the length of the case so that it will chamber. You might, and I stress might get 2 firings out of the brass before it will no longer fit in the chamber, but why mess with it?

Also, all of the world class shooters full length size, even for competition. It is exponentially more important for hunters to full length resize brass as without it, and amount of dust or debris will preclude those rounds from chambering.

I would not recommend skipping the full length sizing.

 

[Tiny Tim]

Read what magnum maniac said. Belted mag cases are notoriously short and will stretch a lot on the first few firings. As stated, fire enough time to fully form to your chamber and you notice resistance to closing the bolt. Then full length resize using .002-.003" of shoulder bump.

This is why Peterson makes "long" brass for belted cartridges.

 

[MagnumManiac]

This is why Peterson makes "long" brass for belted cartridges.

This is why the US Military came up with the A191 chamber and the pressures that go along with it. Normal 300WM brass only expands .010" over case length, not .020" like a normal chamber.
I have both SAAMI and A191 chambers, never had a case head separation in either.
As to other posters saying do not neck size, no one is telling you to do that, you need to neck size so that you get CORRECT fired brass headspace numbers, once that is established, you Partial FL Size from then on bumping no more than .002".

Cheers.

 

[slick Nick]

I always full length size, has worked for me the last 60 years so I'll keep doing that. It's like all the cool kid ideas and I'm glad people try different things but I try not to jump on a following if what I have been doing works or has worked for a while. Having said that I enjoy these threads for the information you can get from them.

 

[memtb]

Do not run belted cases into a FL sizing before being fired. Period.

Thank You MagnumManiac……that was a "glaring omission" in my answer. As all of reloading (with the exception being my wife's rifle) is for my hunting rifle which is an AI, I failed to consider the cases "not" being fire-formed to the chamber! memtb

 

[Tiny Tim]

When I first started reloading my 7RM,I thought I was FL sizing (setting up die per manufacturer), then after a few reloads, my "sized" brass wouldn't chamber. That's when I learned about how to properly size them. Didn't have all the fancy measuring tools I have today.

 

[Alibiiv]

So you're only resizing a portion of the neck and not really neck sizing. A neck sizing die will only size the case neck. Doing what you're doing is still working the body.
There are two schools of thought on this. One is for neck sizing and the other for shoulder bumping.
I guess I'll try both and see what works for me.

I'm not a neck sizing kinda guy, don't own any neck sizing dies in over 60 years. Before I start this process I anneal my brass. After the first firing I take a measurement with a comparator then FL resize with the expander plug removed. I use a universal depriming die for depriming. I leave a .002 thousandths bump on the shoulder, essentially removing headspacing off the belt. I then neck size using a Sinclair mandrel die and turn the necks.

 

[FEENIX]

This is why the US Military came up with the A191 chamber and the pressures that go along with it. Normal 300WM brass only expands .010" over case length, not .020" like a normal chamber.
I have both SAAMI and A191 chambers, never had a case head separation in either.
As to other posters saying do not neck size, no one is telling you to do that, you need to neck size so that you get CORRECT fired brass headspace numbers, once that is established, you Partial FL Size from then on bumping no more than .002".

Cheers.

Tony,

I hope all is well with you. I load 6 belted magnums, 3 of which are .300 WMs, I, too, have never had any case separations. I have tried neck sizing only for a while, but went back to full sizing.

Cheers!

Ed

 

[cajun]

Make sure you have a head space comparator. After the first firing you can back the die out and just size the neck if it will chamber. Going forward from there measure the head space and adjust the die to bump the shoulder .002. It's important to know how much you are sizing. I've had dies that when adjuster per the instructions bumped the shoulder .010-.015. That's a recipe for a case head separation.

 

[Clem Bronkoski]

Do not run belted cases into a FL sizing before being fired. Period.
If you want to change interference fit in the neck, get a Neck only die. More advanced measures is what I do, but you won't have the same tools.
Neck size only until the bolt is hard to close, then measure the brass and set your FL die to size .0015-.002". If you don't wait until the brass is hard to chamber, you WILL get erroneous readings and end up bumping too much and wind up with case head separations.
Belted cases NEED to be allowed to settle by firing them in the chamber a few times, it is necessary.

Cheers.

Mag, I would need to run new brass through a FL sizer at least one time. Sometimes they come with obvious problems like out of round case mouths and who knows what else. After firing I can see your point. I thank you guys for posting those videos on how to set up your FL die to bump back the shoulder.
That is my next step once my cases are fired to fit my chamber. I do have some once fired brass that I have to FL size which I'll probably anneal before I do. Then go through the bumping process..
What I'm likely going to do is just use the purchased once fired brass for trigger time and then use all new virgin brass sized to my chamber and bumped for serious LR shooting.
Its been about 45 years since I had a belted cased cartridge so I FL sized everything. After getting responses from this post I'm only going to bum my shoulders back on my target rifles, this 300WM, my 6.5CM and my 308. All my other rifles which are for close range hunting (<200 yds) such as my 45-70, 30-30, 30-06 7-08 etc. get FL sized.

 

[cajun]

Mag, I would need to run new brass through a FL sizer at least one time. Sometimes they come with obvious problems like out of round case mouths and who knows what else. After firing I can see your point. I thank you guys for posting those videos on how to set up your FL die to bump back the shoulder.
That is my next step once my cases are fired to fit my chamber. I do have some once fired brass that I have to FL size which I'll probably anneal before I do. Then go through the bumping process..
What I'm likely going to do is just use the purchased once fired brass for trigger time and then use all new virgin brass sized to my chamber and bumped for serious LR shooting.

If the necks are out of round back the die way out so it's not touching the shoulder and just let the sizing button hit the neck.