Charge weight in fired brass vs new

[efm77]

I'm still fairly new to reloading so pardon my ignorance and/or overthinking. I've been loading for my 338 Lapua. Haven't shot a lot in it and have been using the same cases. Got a pretty good load for it and am wondering if when I have to get new brass, as long as it's from the same manufacturer, will I have to start all over again or can I use the same load I've been using. I always hear any time you change a component, you should start load development all over. But I've always taken that to mean if you change brand of brass, primer, or powder brand/type, bullet make, weight, etc. I was hoping that as long as it's the same manufacturer and everything else being the same, I wouldn't have to waste time, money, and components starting all over again. Any input would be appreciated.

[mikeinco]

probably depends on how close to max/full case you are at.
very big case will not respond much to a small change.
i would still measure case vol of an average new and average sized used case.

[yobuck]

With a little luck this one could last as long as the resizing question. lol

[efm77]

I'm 3.5 grains below the listed max charge. My first thought is it shouldn't make much, if any, difference if I use the same manufacturer that I've been using. But I'm sure there's slight variances in case capacity from lot to lot, I'm just not sure if it's enough to be potentially dangerous or now. Push come to shove I could back it off a grain or two, but it would just suck to have to completely start all over again just because it's time for new brass. If that's the case, to play it completely safe, it makes me wanna just load 10% off of max and leave it there lol.

[CFJunkie]

I have loaded over 50,000 rounds for 8 target rifles in 3 different calibers over the last 10 years.
For those rifles, I use only Lapua brass and have obviously gone through quite a number of different lots of brass.
One thing I have noticed is that Lapua brass is extremely consistent and high quality so I am comfortable when I introduce a new lot to replace brass that is at then end of its useful life.
I keep meticulous records of all the variables and regularly measure each rifle’s chamber depth to maintain consistent jump.
That said, from lot to lot of brass, I have never noticed any indication that the change in brass has caused significant enough change to warrant any concern over safety.
I load like you do.
I don’t push Pmax and concentrate on loads that are tuned to each rifle’s performance, especially harmonics.
I have never measured any difference in performance that I could attribute to changing to a new lot of brass.
I don’t doubt that there is a theoretical basis for your concern, but I believe that the impact is so small that the effect is masked by ‘shooter induced variations’.

[efm77]

Thanks for that info! Yeah I'm not real keen on pushing it to the very max for several reasons. I like speed, but don't see the need in pushing my luck nor being too hard on my equipment. I've worked up from starting loads but found a charge I was comfortable with at a velocity that I'm fine with that's still below the listed max charge. I thought by switching to new brass of the same brand, I should be ok, and it shouldn't cause any noticeable difference to be at a dangerous level. Nevertheless, me being a newbie, it started playing in the back of my mind and got me second guessing. Thought it wouldn't hurt to ask for others' experience.

[CFJunkie]

A belated welcome to serious reloading. Sounds like you have a nice rifle.

If I may be so forward, one thing that I would recommend that you do is to keep good records of your loads, including powder, charge weight, brass manufacturer, and primers used, as well as seating depth, trim length, velocity, & ambient temperature for each load shot.
Keeping good records from the start is of great value because I have often gone back to data from years ago to study the potential impact of a particular factor.
I have over 10 years of records in a giant spread sheet that allows me to analyze my results in as many different views as seem to make sense to me.
I admit that some views turned out to be a waste of effort, but many of them gave me insight into what would improve each rifle's performance.

I have temperature tapes on each of my barrels to guard against letting the barrel heat up too much.
I find that at some point each barrel begins to show the effect of high barrel temperatures (group POI drops about 1/4 inch).
That messes up my group sizes so I monitor barrel temperature and let the barrel cool when it gets close to the point the drop begins.

It also helps to measure your chamber when your rifle is new and then measure it regularly (every 500 to 1000 rounds) to monitor throat erosion.
I modify the seating depth to maintain the jump that has shown the best accuracy as the throat erodes.

[efm77]

Thank you for the advice. I'm doing a lot of what you suggest. I have not kept temperature or weather data yet though I'll likely start. Been shooting and building rifles for quite a number of years, but just recently got in to reloading so still learning as always.

[CFJunkie]

I got into monitoring temperature when I realized that hunting in the morning at near or below freezing in November was going result in much different muzzle velocities than testing on a range in September.
Temperature data especially helps if you are not using extreme powders, that is, powders that are temperature insensitive.
The best extreme powders change only 4 to 8 fps over a range from 0 to 125 deg. F.
Most stay under 20 fps changes over that range.

Some of the older powders are very sensitive to temperature.
A load can change up to 155 fps over a range from 0 to 125 deg. F.

Shooting from an uncovered position on a range in the sun, especially in Virginia or North Carolina in the summer, with temperature sensitive powders can result in considerable temperature changes for the ammo in just a few hours.
So what you load for early morning temperatures will result in quite a few fps faster muzzle velocities by Noon time.
Now I load for the forecast temperature for each hour that I expect to be at the range, especially if I am using a temperature sensitive powder.
And I never let a round sit in a hot chamber for very long before I pull the trigger.

OK, I admit I am anal when it comes to reloading for accuracy.

[charlie b]

LOL, yep.

I have to admit I have a large umbrella I take to the range on summer days out here. Just the sun on the barrel will heat it up a lot, and, keep it from cooling. Same for the ammo.

[yobuck]

I got into monitoring temperature when I realized that hunting in the morning at near or below freezing in November was going result in much different muzzle velocities than testing on a range in September.
Temperature data especially helps if you are not using extreme powders, that is, powders that are temperature insensitive.
The best extreme powders change only 4 to 8 fps over a range from 0 to 125 deg. F.
Most stay under 20 fps changes over that range.

Some of the older powders are very sensitive to temperature.
A load can change up to 155 fps over a range from 0 to 125 deg. F.

Shooting from an uncovered position on a range in the sun, especially in Virginia or North Carolina in the summer, with temperature sensitive powders can result in considerable temperature changes for the ammo in just a few hours.
So what you load for early morning temperatures will result in quite a few fps faster muzzle velocities by Noon time.
Now I load for the forecast temperature for each hour that I expect to be at the range, especially if I am using a temperature sensitive powder.
And I never let a round sit in a hot chamber for very long before I pull the trigger.

OK, I admit I am anal when it comes to reloading for accuracy.
Thats what dials on scopes are for, fine tuning as various conditions change.
Based on information gathered as a result of a sighter shot, and yes even (some) L/R hunters take sighter shots whenever possible.

[243winxb]

Compare weight of new lot to old. Same trim length and clean. New brass will have less volume, till fired. The little 5.56 is 4% difference.

Keep good notes. Give every component a lot number if it doesnt have one.

[efm77]

OK so I get that the new brass will have a little less volume, but how much does that affect pressure when it's fired in the same chamber with all else being equal (seating depth, powder, primer, trim length, etc)? Chamber volume doesn't change. Does the extra expansion of the brass cause the pressure to spike more? Not trying to argue, just trying to learn.

[darkker]

1) OK so I get that the new brass will have a little less volume, but how much does that affect pressure when it's fired in the same chamber with all else being equal (seating depth, powder, primer, trim length, etc)?
2) Chamber volume doesn't change. Does the extra expansion of the brass cause the pressure to spike more? Not trying to argue, just trying to learn.
1) It depends.
2) Essentially no.

So there is A LOT of really vad info out there, 99.99% of the time it comes from people who never measured anything other than "signs"...

I've been using a strain gauge pressure system for close to a decade, here's some things the cool kids don't know, and can't tell you.
"Extreme" powders, as get advertised and praised; are B.S. Powders are only "stable" when used in designed for applications, used outside of those parameters, they aren't magic. Ever see Hodgdon post advertisements from General Dynamics, or Thales? Nope.
Continuing with that, the fault isn't in the powders themselves, it's the primer output that varies and fools with resultant burning curves. Dr. Denton Bramwell has done some excellent work showing this.

As far as the pressure changes you asked about, it really depends on the cartridge, but for a generality: the bigger they are, the less it matters.
A couple years ago I pressure tested and shared the traces from a 6.5 Creedmoor test. Small primers and large pocket brass. Regardless of the brass weight, or measured capacity, magnum or regular primers; the pressure was....??? If you guessed "the same", you win a cookie.
Short of doing a proper sample size of a few hundred rounds for statistical accuracy; a dozen of each gives a general indication. Any difference was statistically noise, and nothing of consequence.

Now, that isn't to say a primer swap "won't" change things, or that a brass change "can't" affect something; is not what I'm saying.
Merely that in the 308 sized case family, when within the pressure ranges that a powder is operating normally, differences as described, just don't matter nearly as much as most people think they do.

Cheers

[charlie b]

It's about like powder charges. Most people won't see a 0.1gn or 0.2gn change in powder charge on their targets, especially at shorter ranges, while others will. Depends the quality of your reloads, rifle, shooter and range. If you can see a POI change from a 40fps change in velocity then some of these things do matter. Most people will not see any difference.

[Robinhood]

It's about like powder charges. Most people won't see a 0.1gn or 0.2gn change in powder charge on their targets, especially at shorter ranges, while others will. Depends the quality of your reloads, rifle, shooter and range. If you can see a POI change from a 40fps change in velocity then some of these things do matter. Most people will not see any difference.


This may be true at 100 yards but at 1000 it does have an effect. Also if you are using a lighter barrel you ill see it as harmonics change. None of it means crap if your neck tension is all over the place or you have bullet r.o..

[charlie b]

Just the point I was trying to make. Most people don't shoot at 1000yd and few shoot past 200yd.

[243winxb]

OK so I get that the new brass will have a little less volume, but how much does that affect pressure when it's fired in the same chamber with all else being equal (seating depth, powder, primer, trim length, etc)? Chamber volume doesn't change. Does the extra expansion of the brass cause the pressure to spike more? Not trying to argue, just trying to learn.

New brass keeps changing for about 3 firings, till ifs fully fire forms to chamber and fl bushing die is adjusted correctly. Does it matter at 100 yards. Yes. Factory brass when compared to full BR prepped brass difference is about 1/4', but its not all from the volume change.

Factory guns may never see any difference.