Different brass, does this REALLY affect your load

JRose

JRose

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Jul 10, 2007
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#1
I have acquired a lot of .308 brass over the years and was wondering. If all your brass is mixed, but FL sized and trimmed equally, how much affect, if any, does it actually have on your pet load?

I have a great load for my 10FP using Lapua brass, theoretically I would think that using the same OAL/Powder/Primer/Bullet in a different case would yield the same results.

Am I wrong? Has anyone tested this between different brass? The only thing I could think of is a slight variance in neck tensions, but I have enough to sort into like head stamps for each outing, so it wouldn't be a mish-mash of different brass per string.
 
#2
Re: Different brass, does this REALLY affect your load

FL sizing the different brass is making the outside dimensions the same.. But internal volume will differ due to different thicknesses of case/neck Walls between brands.

HOW much this effects YOUR pet load, depends on your load and rifle.
Aside from neck tension, the different internal volume will increase/decrease pressure of the load, therefore alter the characteristics of the load.

Take some different brands, size them the same, seat a spent primer in them and weigh them. Then fill them with water, and (carefully) weigh them again, to give you an idea of the different amount of water (internal volume) there is between brands. (x5 cases of each brand to get an average).
 
#4
Re: Different brass, does this REALLY affect your load

I was just thinking about how much internal volume really matters. 42 grains of powder burns like 42 grains of powder, no?

I'll definitely try it out and see, side by side, but my simple mind things that it shouldn't matter.

Not trying to dispute what you guys are saying, just playing Devil's advocate...
 
#5
Re: Different brass, does this REALLY affect your load

Seems to me that the powder will burn pretty much the same, but the amount of pressure generated is very dependent on the internal volume of the case. If you light off 42gr in a 308 sized case you know the result... If you ignite 42grains of powder inside a cartridge the size of a 2 liter soda bottle i don't see you getting near the pressure, and that would lead to much lower velocity. Bad example i'm sure, but i believe the concept is there. I realize your talking a much smaller internal volume difference when comparing different brands of brass, as opposed to the example i used. I can't comment on "how much" of a difference it would make, only that i can see how it would definitely make some difference.
 
#6
Re: Different brass, does this REALLY affect your load

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JRose</div><div class="ubbcode-body">I was just thinking about how much internal volume really matters. 42 grains of powder burns like 42 grains of powder, no?

I'll definitely try it out and see, side by side, but my simple mind things that it shouldn't matter.

Not trying to dispute what you guys are saying, just playing Devil's advocate... </div></div>
No, because they are in different sized containers. For comparison's sake, say you had a water balloon filled with a cup of water and a trash bag containing a cup of water, and dropped them both on the driveway from your roof. The water balloon is going to make a larger spash than the garbage bag.

Now I realize the variances between the inner dimensions of two different cases is nowhere near the difference in a a water balloon vs trash bag, but I think the same principle would apply here. Think about how much of an effect miniscule differences in neck tension and seating depth can affect how the ammo shoots.

I am interested to see what you find though. Please let us know.
 
#7
Re: Different brass, does this REALLY affect your load

The biggest thing to watch out for when you use different brass is when you are near max fill/pressure. At that point small variations will have a greater impact based on the pressure curve. Pressure increases at a pretty linear rate until you start to compress things and then it increases exponentially.

If you are running 42 of Varget you should be pretty good (safe pressure wise). That being said your ES will be all over the place depending on the brass at hand. 42 of V in a R-P case will be very different than 42 in a LC Match case. It'll still be good for practice / short range ammo but nothing I'd like to use at distance during anything that mattered.

Cheers,

Doc
 
#8
Re: Different brass, does this REALLY affect your load

Does 42 grains of X powder "burn" the same in two different cartridges? No. Your pressures and peaks will be different, even with the same bore size.
When running max loads like a lot of people think they need OR running far above them (which is very common) due to the "lack" of signs (mostly guys too silly to know what they are seeing and feeling) a peak due to 5% or more volume change is bad news.

Why not try some simple tests? Or even use QL if you have it. That has a setting for case volume which should tell you something. Keep in mind some powders spike REALLY fast when pushing max loads.


Bit odd someone who seems to have a fair idea what is going on would ask this.....
 
#9
Re: Different brass, does this REALLY affect your load

YES

in my .224 from winchester > remington > ADI brass i have a differance in ES and the biggest differance is the change in POI about 1/2 in what ever direction depending on the brass used.

in my 308 from winchster, remington and lapua the biggest differance i see is ES in winchester is was in the 60's and with lapua its down to 10fps, its just down to the consistancy of the internas of the brass.

i have also noticed a differance in different lots of brass, winchester .223 using the h2O test i come up with a 2 grain differance.

also have noticed a differance in new brass to used brass, ive had 2 losts of 50 .308 brass from the same bag, one lot was a hot load the other was a more mild load and after a few firings on the brass there was a weight differance between the brass and so i assume a internal volume differance too due to one batch of brass (hot loads) being trimmed alot more then the more mild load.
 
#10
Re: Different brass, does this REALLY affect your load

I think the biggest difference between lots of brass will be found in the neck tensions. I also think these tension discrepancies are the biggest factor in dispersion.

Sort your brass. Keep your lots separate, and once separate, load them as separate batches, cycle after cycle. It should also be dedicated to an individual firearm. Once a batch is started, it shouldn't be subsequently comingled with other batches, or its own consistency will be lost.

Greg
 
#11
Re: Different brass, does this REALLY affect your load

The difference in case volume will change pressure and therefore change velocity and POI to some degree. At shorter ranges difference may be small but will increase at long range and become an important factor.
 
#12
Re: Different brass, does this REALLY affect your load

Not .308, but in .30-'06, I can shoot 49.5 gr Varget and 168 SMK in LC brass that shoots MOA, but try that in commercial WIN brass that is 20 gr. lighter, and it's about 3 MOA. No difference in prep.
 
#13
Re: Different brass, does this REALLY affect your load

I've tried chrono-ing varying different types of brass with the same load and have never been able to find an appreciable difference in the results with LC, Win, Rem, and Lapua 308 when shooting an accuracy load. Variation due to environmental changes (session to session) and/or SD within case types always greatly overshadowed differences introduced from case type to case type. I try to keep case types together, but I run the same load in all of them. But then I don't shoot BR, either.
 
#14
Re: Different brass, does this REALLY affect your load

Thanks for the imput guys. Luckily I have fairly large lots of each different kind, maybe I can just run em into the dirt, then move on to the next lot, and tweak the load a touch.


Loading is such a pain in my ass.... LOL
 
#16
Re: Different brass, does this REALLY affect your load

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JRose</div><div class="ubbcode-body">
Loading is such a pain in my ass.... LOL</div></div>

It's tons of fun if you listen to some around here. I agree with you
wink.gif


Example to your question, I use 45grns of Varget with the 178 AMAX in Win brass and 44.2grns in one lot and 44.4grns in another lot of Lapua and I get the same velocity with all of them. Internal capacity makes a difference.

Just work up a load with each type of brass. What types are they?
 
#17
Re: Different brass, does this REALLY affect your load

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">

Just work up a load with each type of brass. What types are they? </div></div>

Litterally all kinda stuff....

I have about 700-800 once fired Fed cases, 300-400 Hornady once fired, few hundred LC, and a mish mash of various range droppings...

I feel ya Todd, I just tend to think on a small scale here since I figured the inside dimensions could not possibly be that much different.
 
#18
Re: Different brass, does this REALLY affect your load

Fed will be close to the Lapua load, Hornady might need a few tenths more powder and LC maybe a few tenths less.
 
#20
Re: Different brass, does this REALLY affect your load

Rob and Rat are right on with my experience. Fed, LC and Lapue have all shot the same for me with a good OCW load. Win/BH needs a few tentchs more with everything else the same.
Maybe a better shooter can tell the difference, but I can't.
 
#21
Re: Different brass, does this REALLY affect your load

When working up our load for the 308/175 group buy in Winchester brass, I had to increase the propellant .8 to 1.0 grains to achive the same velocity and similar es/sd as the load in Lapua brass.
 
#22
Re: Different brass, does this REALLY affect your load

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MikeSWammo</div><div class="ubbcode-body">When working up our load for the 308/175 group buy in Winchester brass, I had to increase the propellant .8 to 1.0 grains to achive the same velocity and similar es/sd as the load in Lapua brass. </div></div>

Yep, I just went back and looked at my load log, and I see about the exact same difference between Win/BHA and Lapua/FC. Win brass needs about a full grain more propellant (RL-15 in my case) to get to the same MV as Lapua and FC.
 
#23
Re: Different brass, does this REALLY affect your load

Just tested this very thing yesterday with Lapua and Federal brass. Everything else, including brass prep was identical. The Federal brass shot 2" left at 100 yards. Yowza. I'm not sure I'd have believed it if I hadn't seen it myself. Accuracy seemed comparable, and I did not have the chrono set up.
 
#24
Re: Different brass, does this REALLY affect your load

1+

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gfunkUK</div><div class="ubbcode-body">FL sizing the different brass is making the outside dimensions the same.. But internal volume will differ due to different thicknesses of case/neck Walls between brands.

HOW much this effects YOUR pet load, depends on your load and rifle.
Aside from neck tension, the different internal volume will increase/decrease pressure of the load, therefore alter the characteristics of the load.

Take some different brands, size them the same, seat a spent primer in them and weigh them. Then fill them with water, and (carefully) weigh them again, to give you an idea of the different amount of water (internal volume) there is between brands. (x5 cases of each brand to get an average). </div></div>
 
#26
Re: Different brass, does this REALLY affect your load

I have shot a .46" 5 shot group at 100 yards with mixed 223 brass.

I think better matched brass could tighten that up to .45".

For hunting, who cares?

For competition shooting, the difference is to die for.
 
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