I've found more time shooting my 300WM and reloading for it. I'm noticing that my once-fired brass is so close to trim-time, in fact many of them are beyond the max case length that they actually need trimming. Compared to the 308, 243, 338Lapua, and even the 50BMG case, the 300WM brass seems to "grow" a lot faster. In these other calibers, I've reloaded the cases at least 3 times without trimming.

I'm using Winchester brass for the 300WM (the Federal cases even grow faster!!!). I've loaded them from hot to mild and it seems to make no difference. No difficult extraction or other pressure signs, no headspace problem that I'm aware of.

Is this normal for the 300WM?

I always seem to need to trim mine. I personally couldn't tell you why.

You are probably seeing the results of a loosely cut chamber and possibly a smallish sizing die. Loose chambers are very common in magnums to accommodate the belts, which are manufactured with widely varying dimensions by the different brass manufacturers. So in order to ensure that all factory ammo will chamber, chambers are often cut on the large side. Likewise, die manufacturers want to make sure cases sized with their dies will fit even the tightest of chambers. When expanded brass is sized, the difference only has one place to go - forward. This gets worse the larger the fired brass you size to a smaller size.

Options: neck size only, at least until the cases chamber stiffly, then FL size. Or set your FL sizing die up to partial FL size, that will ensure minimal sizing and no problems chambering in YOUR rifle. As a third alternative, measure the actual brass length YOUR chamber can handle. Sinclair sells a "case length gauge" for about 5$, you can use that to determine how long cases can become and still be safe in your chamber - most chambers are cut a good deal longer than the SAAMI min specs you see in reloading manuals.

- mike

art,

What mho said is correct. I might add that the expanding button on conventional sizing dies do drag some metal forward so be sure you lubricate the insides of the necks and wipe them out after sizing.

One could just neck size with Lee Collet dies but for a hunting rifle it's best to FL size. In particular for one that seems to have a large chamber as mentioned above.

You might consider the quite expensive FL dies that use bushings. They don't need an expanding button.

Make sure you feel inside each case down near the bottom all around for insipiant head separations. Make a tiny hook on the end of a piece of coat hangar wire for this and file an edge to it.

When brass is forced past it's elastic limit it will increase in some dimension. Thus when you size it back it will be longer in this situation.

Also the FL sizing for a break open gun must be enough so that the cartridge will drop into the chamber. Thus when fired it will stretch a little. This is ok as function is first.

Sounds like the perfect set up.

Order another bag of brass and shoot something with it.

mho/savage99, thanks for the suggestions.



As for sizing, I'm already "partial" full-sizing. What bothers me is the rate of growth - from 2.613 to 2.623 for many of them. That's a 10 thousandths growth. Maybe my barrel is like shilen30's. BTW, my barrel/rifle is a Blaser.



As for possible head separation, I did a cut-away for one from a hot- loaded case (because I thought there was a ring outside just in front of the belt) and found that the case wall near the belt had a normal thickness.



I'm sure to order a stoneypoint chamber gauge.



Art

Ten thousanths is a lot. Try to be happy. Just keep checking the insides of the cases and trim. If you like the rifle that's all that counts.

I have an old M70 in 264 WM that not only has a large chamber on the sides but it's out of round by .0005" as well. I just put up with it and FL everything. I finally got it shooting so I am happy.

Mine shoots touching holes at 100yards.



One other thing - I'm using non-cannelured bullets but I'm Lee-factory-crimping tight. Could that be the cause?



My rifle is a Blaser, i.e. interchangeable barrels, so I shoot also a .416rem with it in addition to the above-mentioned calibers. Not even the 416 case grows that fast.

I don't mind a longer neck for a 300WM!!! :-)

Art,

I doubt the factory crimp has anything to do with the stretch. But that one is easy to verify, simply don't crimp a bunch of cases. Shoot and resize, and see if the cases still grow as much.

I'm not sure that the Stoney Point chamber gauge is going to tell you the max length of the brass the chamber will accept, to avoid having to trim quite as much. As I stated above, to my knowledge, the only gizmo that does that is the Sinclair "chamber length gauge". Good thing is, it is pretty cheap.

I'm kind of a die-hard Blaser fan myself, unbeatable versatility - like you shooting a .300 WM and a .416 RM in basically the same rifle. The Blasers are also usually very accurate, so sometimes one sighs and lives with their idiosyncracies. And as much as I hate to admit it, I have also had Blasers with very generously cut (magnum) chambers. It sure does hurt to admit to this "wart on the nose" on what is otherwise one of my favourite factory rifles. Still if the barrel shoots well... Maybe the chamber is long enough that you won't need to trim every time. Get the Sinclair gauge and find out.

-mike