I just realized I used large rifle Primers in my 300 mag Brass.. so do I knock them out and reprise with mag Primers or used them this once?

What's your load? Or what powder are you using?

Loading a standard primer should still work just fine, given the powder you are running. But if you had a load worked up in it, it will be a little slower by 10-30 fps. Going from a standard to a magnum primer usually acts like about .3 to .5 grains of powder. So, vice versa, and your load now acts like it's .3 to .5 grains less on powder.

If you are using a very slow powder and plan on shooting them in below freezing weather I would use a magnum primer. If the cases are not charged yet, depriming is not bad. A hang fire will scare the snot out of you!

I’ve done that.

I have done the opposite, CCI 450 instead of CCI 400s in some Grendel brass. Reduced load by .3gr and it shot well.

I've also know a shooter who forgot to change out his pistol powder, and loaded 42+ grains of pistol powder in his 260 Rem. NEedless to say, his 260 had catastrophic disassembly.

And people wonder about the warnings and why they exist

Ain't no thang to punch out live primers. Wear eye pro and go slow.

I got a batch of cci lr mag recently by accident. Them alone with the same load data in my 6mm creed increased speeds by 20fps.

I hate to waste Primers, but I hate wasting the bullets and powder too to shoot loads that aren’t right...ugh! I’m gonna punch them out. Is there a way to do it without running them thru the resizer?

Just lower the expanding ball/decapping rod inside the sizing die, where the case will not go high enough to size. You can knock it out easily. Just do easy and don't hit the primer fast when removing.

Or use a Lee decapping die.

https://leeprecision.com/decapping-die.html

^^^ Yes, that would be easiest, but requires purchasing another die (I have 2 of them, myself).

I’ve got 2 RCBS decapping dies, one for large and one for small calibers. If you are close to Argyle/Roanoke in DFW, I’d be happy to let you borrow one!

I appreciate the offer but I'm quite a ways from you. I need to buy a recapping tool but will probably just go with Chad's recommendation.

I seem to deprime a lot. I use the Lee Universal DeCapping Die the others have mentioned on a Lee single stage press. I even keep a clean spent primer tube to catch them.

A lot of the old school brass was primed from the factory, stuff like 300 Savage and 35 Remington. Never understood that, and have always punched it out and at the appropriate time & place, pushed it back in.