Home Forums Reloading Big Game Rifles New brass vs once fired...all else being equal.....do they yield same pressure?

All else being equal, will the same load produce same pressures if loaded in new vs once fired, neck sized brass? If not, which will be higher. I am looking at working up loads for my 264 win in new brass. I am wondering if my results will be valid with once fired brass, from my gun, later. What say you? I know the new brass has more room to expand to fit my chamber, but I don't know the implications of that regarding changes in pressure.

I think you're over thinking things. There is a diffence but I don't don't think it's enough to cause any dramatic changes in anything. While I wouldn't shoot a match or even go hunting with a mix of new and 1x loaded ammo, I have worked up a load with new brass and then reloaded it and gone hunting. the fact remains that there is a limited amount of space in the chamber. When that is filled, it is filled.

IME the decreased case capacity increases velocity, hence it probably increases pressure. I've heard other guy claim they've had the opposite experience, and the soft new brass absorbes some of the shock, reducing pressures. I have a feeling the reality is actually pretty complex and may vary according to brand of brass, and where you are on the pressure scale.

If component prices ever return to a reasonable level, it would be fun to run some controlled experiments and see what variables a guy can isolate.

I have never found there to be a noticeable difference in pressure with new brass vs once fired brass of the same brand. Accuracy can be different and usually in favor of new brass in my experience.

Once fired neck sized brass usually fires like loads FASTER for me than virgin.

Since the chamber volume is the same, if the powder charge, seating depth, etc... are all equal, pressures will be equal as well.

I don't know if I'm reading this right. I assume we are talking about the same brand of brass? The case is only a way to hold components together. It will expand to the chamber dimension. The dimension of the case, walls ect, take away from the dimension of the chamber. Both the once fired and new case will expand as far as the chamber will allow. The only difference will be the case wall thickness.

Never develop loads with new, unfired brass

Fire form it first either with bullets or Cream Of Wheat.

I would say that once you work up your loads with new brass and get one that shoots well, the second firing will be more accurate especially with just neck sizing. If you are concerned about more pressure, drop your charge by a half of grain and see what it does. Personally, I believe the pressure difference will be nill between new brass or once fired, at least not enough to worry about.

I am always glad to get all my new brass fire formed. My second firings always are more consistant in all repects, especially nowadays when most new brass is has little uniformaty.

There's an easy way to answer the question. Load some up in new brass, fire it over a chronograph, and then do the same with once-fired.

That won't prove anything, as results by a few fps from day to day for several reasons, including light conditions, temperature and chance.

Pressure will be the same with either now or used brass of the same lot. This has been proven umpteen zillion times in pressure labs.

Obviously. So if he did that, and got a variance of only a few fps, he'd have his answer. Plus, who said he has to do it over two or more days, he could do it on the same day, and even alternate shots to account for variation in environmental conditions and fouling/temperature of the chamber and barrel.

My only point was, why ask a question and get a bunch of answers based on what people think might happen, when you can easily find the answer yourself.

Exactly, physics hasn't changed much....lol

This is my xperience, also !
Kraky is correct, IMO.
Jim

I believe that`s due to their being closer to chamber size and not wasting pressure on expanding the case and instead pushing on the bullet with more it.

Fired brass gives slightly lower velocities for me, hence the need for sizing dies, the case is larger after it's fired so pressure with the same powder charge is less.

Gunner

So now we have conflicting evidence from personal chronographs in different conditions.

Looks like "tastes great, less filling" to me.

Let's hear some more evidence from various people who use various chronographs under various conditions. That ought to settle the question once and for all.

May be that i only slightly neck size?

Gunner

I fondly remember the late Bob Milek writing about his Remington XP100 chambered in .250 Savage and its favorite load of a 100 grain Nosler BT with H335. Without fail he always cited the velocity as exactly 2705 fps, as if that 5 fps meant something. When I chrono loads, I usually only view the first two digits as significant figures, whereas the latter two are often vagaries attributable to living in a random universe. For example, when I test loads in my Swift using 55-grain bullets, if I get really good accuracy and the chronograph shows 38XX fps, I call it good. It doesn't matter to me if the average of several shots is 3789 or 3814, I still read it as 3800 and go on my merry way; because I know tomorrow it might be 3825 or 3794 or whatever and I'll be just as happy and the groundhogs just as dead.

Some may insist on extreme spreads less than 25 fps and s.d.'s in single digits, but I've got more important things to worry about. I try to keep track of the number of times my brass has been fired and relegate them to the same lots, but I don't think the difference in speed or accuracy (or pressure) is measurable within my limitations.

Does this mean that for the average guy with the average chronograph, pressure does not equal velocity?

If you're referring to my post above, I wasn't talking about "various" anything. it was one person, with one chronograph, under one set of conditions.