I have run out of large rifle primers, I am a month away from going into town to aquire some more.
I have 600 large pistol primers, can I use these as a substitute for rifle primers in mild loads, in a 375H&H and 450 marlin? I have used small pistol primers in 223 rounds before and vice versa, and found them no different, what say you guys?

This guy says please don't do that.If you were being attacked by space aliens and that was all you had ,mabe. Otherwise always use the proper components. Someone correct me if I'm wrong,but as I remember large rifle primers are taller than large pistol primers.
Covey16

I think Covey's right... the pistol primers may seat so deep you may not get them to fire. On the other hand, if you are experienced and absolutely positively know you won't exceed pistol pressures then theoretically it would be safe. That said, it's just not wise to play "Extreme Handloading" unless you have a true death wish.

I've read one is different from the other size wise, but with MILD loads I do it myself frequently because I gots lots of old Mag pistol primers but no mag pistols, least not large ones. Most common is 30-30 loads with lead bullets and about 12 gr SR4759. It works in my .358 Win too. I re-emphasize that the loads are very mild. My primers are about 30 years old so they're probably a different lot that yours. CCI's.

I have shot large rifle primers in 45acp cartridge in a Mauser with good results.
The large rifle are .000" or .001" larger in dia and .008" taller, and so the fit is not perfect, but good enough.

The brass is also thinner and has less explosive in the pistol primer. That could be a real problem getting good ingnition with ball powders in those huge cases of yours.
But if you are shooting stick or flake powder, you will probably never notice a difference with mild loads.

And I would WANT mild loads for 223 rounds of those calibers

There's been lots of discussion among knowledgeable gun people about detonation in large cases with small amounts of fast powder. I've never seen it and am not qualified to comment one way or the other,just throwing that out. Some of you on this forum are vastly experienced and are qualified to make your own judgements about odd combinations of components. I erred on the side of caution in the case of this poster since he was asking for opinions and may not be as experienced as some.If the rifle is properly headspaced and the load is mild enough, you certainly can make a shootable round with stick powder or especially flake powder. The judgement comes in at how much powder.
best wishes
Covey16

Small amounts of slow powders in big cases are where the detonation danger's usually reported. Very small amounts of fast pistol powders have been used in rifle cartridges for many decades for gallery loads. The maximum load for any of these in .30-06, for example, is around 15 grains. It's very easy to inadvertently double-charge one of these powders and seat a bullet, which would likely blow a gun. But the fast powders aren't likely to inexplicably detonate.

Ricochet
Double loads were one aspect of some of the discussions I have read. When several of the blow ups were tracked to their real source, it was human error with double or triple loads of fast powder, metal fatigue and a couple of "documented" cases of real detonation with slow powders. Not to get too far off topic,just thinking about that .375 H&H case,whatever powder and a pistol primer.
Covey16

Yeah.