Case Weight Ranges

[scatterbrain]

What would be the weight range of a group of brass needed to produce SD's of say, 15 consistantly? Maybe even 10?
I am trying to establish a range to use to presort brass before processing. I have been using 1 grain as the group size and wonder what others are doing.

[F. Guffey]

I have been using 1 grain as the group size and wonder what others are doing.

"What others are going"?

I sort by head stamps and then I sort by weight when loading rifle cases on a progressive press. When it comes to different case head stamps I want as many different ones as possible. After sorting I separate into groups of 20.

Why 20? I want to sort once, after that I tumble, after tumbling I sort my cases back into groups of 20, that prevents me from having to start over everyday.

F. Guffey

[scatterbrain]

For some 50 years I didn' brother sorting at all, not by head stamps or weight. I did a lot of varmit hunting, most successful, always enjoyable.
Then, I purchases a $100 dollar chorongraph.
How I sort by head stamp, weight, measure bullet weight, length, trim outside necks, anneal, cut primer pockets to same depth, set primers to nearest 1/1000, check both case runout and loaded bullet runout and don't enjoy loading as much as I used to. I am trying to get my SD as low as possible. That is why I ask about the range of grouping case weight as I don't want to group them by volume.
Want a chorongraph? Cheap.

[Unclenick]

Unless they are from the same lot, case weight doesn't necessarily correspond well to internal capacity. There are different alloys used for different brands and the tolerances for width and relief angles in the head, which don't affect case capacity, can cause about 20% error in guessing capacity from weight. The reason the lot matters is makers change the specs over time. Winchester brand .308 Win brass I bought fifteen years ago is about seven grains lighter than some more recent stuff I got. Manufacturers swap around, too. Norma's 2013 databook says that happens when a contract ties one guy up. He then farms out what he can't handle to other guys. Norma said they've made brass for Remington, for example, with Remington's headstamp on it.

All that said, brass capacity is not usually the first place I look to improve velocity SD. Proper seating of the primer comes first. For some reason the idea you should stop when the primer just kisses the floor of the primer pocket persists. It leads to inconsistent ignition times. You want the primer to go in about three thousandths deeper. Dan Hackett wrote that he just seated hard, going past that kissing contact point, and that he was almost always able to get SD's below ten fps doing that, even in magnums and long cartridges based on the 30-06, and that he was not able to do it any other way.

Creighton Audette was the first to suggest primers were "analog" rather than digital and Naval Ordnance at Indian Head confirmed by testing that "reconsolidating" the primer with two to four thousandths compression of the anvil into the primer pellet, also known as "setting the bridge", is optimal.

A second factor is powder settling. Hackett also observed significant differences could occur in peak pressure depending on whether powder was settled by vibration or not. This is mainly true of stick powders. Spherical powder's don't settle much, though I generally can't get equal accuracy from spherical powders for various other reasons. I think one of the secrets to the success of Federal's GM308M load with the 168-grain SMK is that the load of IMR4064 in it is very slightly compressed (about half a percent) so that locks the grains in place against repacking during transport. Looking for an appropriate powder that does that can be worthwhile.

Absent actual compression, you want to look at which powder's the load data says are most consistent. A standard practice among manual authors is to load so the variability they get in pressure doesn't go over SAAMI MAP. Hodgson describes this in the print manual I have. They say that because of this practice, when you look at the pressures they list for maximum charges of different powder's with the same bullet in your cartridge, the highest listed pressure is for the powder that produces the least pressure variation. Using that one should help with SD.

I hope that information helps you with your quest for low SD. Note that some loads like some primers better than others, so be prepared to try a number of them. Try to have the same firing history for all the brass you are loading to test this, too. Also, note that the load with the lowest SD isn't always the most accurate because it doesn't necessarily hit a barrel time sweet spot as nicely. You can tweak that some by adjusting bullet seating depth.

Good shooting.

[Bart B.]

Case weight spread in a given lot has little effect on muzzle velocity. Powder and primer consistently plus how repeatable the rifle is held have a much greater effect than a few percent spread in case weight.

Sort to a 1 grain spread if you wish.

[CarJunkieLS1]

Case weight means nothing, I repeat case weight means nothing, case volume is everything. For low SD/ES there are many variables and factors but case volume means alot. I sort my cases into groups with a 5% variance in case volume.

For my precision long range shooting it matters, but for hunting, and general plinking I'm not near as precise. For hunting if my ES is less than 30fps I don't worry.

[Don Fischer]

I weighted case's many years ago. What a waste of time!

[F. Guffey]

Old Yesterday, 01:10 PM #2
F. Guffey
Senior Member


Join Date: July 18, 2008
Posts: 6,969 Quote:
I have been using 1 grain as the group size and wonder what others are doing.

"What others are going"?

I sort by head stamps and then I sort by weight when loading rifle cases on a progressive press.

F. Guffey

And then one day a reloader claimed military cases are thicker, and then they claimed because the cases were thicker they were heavier. After that? All reloaders went into automatic response when comparing military cases to commercial cases; they then came up with a cute little saying about reducing the powder charge 10% .

So? Instead of weighing the cases I started measuring the cases, the measurements included inside measurements. I found 30/06 R/P cases with case head thickness of .260", and I found most military case heads thicknesses of .200".

What did that mean? The military case head was thinner and should have weighed less. BUT! if the military case weighed more it meant the case body had to be heavier. I know, SO WHAT?

I decided the powder column in the military case was smaller in diameter but longer than the power column in the 30/06 R-P cases. The powder column in the R-P case was larger in diameter and shorter than the powder column in the military case.

And then there is the unsupported case head/case head protrusion: I decided the R-P case with the thick case head was safer if there was a remove chance the chamber had too much case head protrusion or if there was a chance of catastrophic failure or case head separation.

But it is all about volume

F. Guffey

And back to tumbling: I want to keep my cases sorted, when sorting cases after tumbling I match the case heads. The cases go back in the same box they started in.

But there is that cute little saying about "volume is all that matters"

F. Guffey

[Jim Watson]

There are different alloys used for different brands and the tolerances for width and relief angles in the head, which don't affect case capacity, can cause about 20% error in guessing capacity from weight.

Which different alloys? Cartridge brass is traditionally 70% copper, 30% zinc; the current UNS 26000 spec calls for only 28.5% zinc with some odds and ends making the copper content 71.5% or less. Density is 8.53 gm/cm3 or .308 lb/in3

I finally figured out how slop in external head dimensions can cause volume to not track with weight.

Me?
For my foray into F-t/R I weight sorted WW .223 of the same lot number. I shot one half grain group and kept the other half grain group in reserve. There were not many outside that one grain spread.
I loaded Lapua .308 out of the box

[T. O'Heir]

The weight range of a group of brass doesn't make enough difference unless you're Bench Rest shooting. You can sort by brand if you really want to spend the time doing it, but you won't find any difference worth worrying about. Brass cases are made to SAAMI spec.
"...different alloys used for different brands..." No there aren't.

[F. Guffey]

The weight range of a group of brass doesn't make enough difference unless you're Bench Rest shooting. You can sort by brand if you really want to spend the time doing it, but you won't find any difference worth worrying about. Brass cases are made to SAAMI spec.
"...different alloys used for different brands..." No there aren't.

And that reminded me

I have an old catalog that has to be at least 15 years older than the Internet. The publisher of the catalog was offering a life time rifle. The deal? Purchase one of out rifle; when it wares out we will chamber and bore the barrel to the next size up for as long as you own the rifle. they included a price list meaning it will never cost more than the price listed.

I thought the rifles were magnificent and reasonable priced. I did not purchase one of the rifles but I did find some of the information in the catalog interesting. They included information about fire forming, the information is not worth of Internet mention because it came from P.O. Ackley.

F. Guffey

[Bart B.]

Originally Posted by T. O'Heir

Brass cases are made to SAAMI spec.

There is no SAAMI spec for case wall thickness or inside dimensions behind the neck, just outside.

Lightest weight new 308 case I weighed was 149 grains, average about 152 from WCC made in 1958. Heaviest was 199, average 195 from someplace unknown.

[F. Guffey]

Which different alloys? Cartridge brass is traditionally 70% copper, 30% zinc;

I am going to go way out there and say different alloys have nothing to do with the diameter of the powder column and the alloy has nothing to do with the length of the powder column.

And I liked the ideal the case head was .060" thicker from the bottom of the cup above the web to the chase head. I also like the ideal of having a thick case head because at the time reloaders did not measure case head protrusion, most of them did not know what it was.

On my Mausers I was the fan of having .110" case head protrusion. When firing 8mm57 cases that were formed from 30/06 military cases I had 90." case head protrusion + head space clearance. Even then I was the fan of .003" clearance.

F. Guffey

[Unclenick]

Originally Posted by Jim Watson

Which different alloys?…

Everything from Muntz Metal to 20:80 brass seems to have been used or to be in use. This article describes X-ray spectrographic analysis of several different makes.

	
	
Copper:Zinc   Density at 68°F    (notes)
   60:40        8.39 gm/cc       (aka, Muntz Metal)
   70:30        8.53 gm/cc       (aka, Cartridge Brass or 760 Brass)
   80:20        8.67 gm/cc       (aka, Low Brass)

Variation in tooling seems to make the most difference. I got some bulk Winchester .308 Win cases about 15 or 20 years ago that ranged in weight from 153.5 to 159.5 grains. Today they seem to be in the 160s. I made a ruler for case weight in tenths of a grain and stacked the cases in front of their weight on the rule to create a histogram of weights. Four distinct peaks showed up indicating the lot was comprised of the output of four different sets of tools likely running simultaneously on four different forming machines. After removing a small number of outliers, it looked like this:



But the four sets of tooling formed heads slightly differently, so it doesn't follow that capacity matched those numbers exactly. The difference in capacity could have been more or less. I didn't measure them all that carefully because, as per other comments, case capacity is just not the dominant source of error in velocity consistency.

[Bart B.]

Some ammo plants have made a production lot of ammo with bullets from 3 or 4 sets of dies. All USA arsenal lots of 30-06 M72 and 7.62 M118 match ammo were that way. No wonder their best lots used for the Nationals tested about 2 MOA at 600 yards. Rebulleting them with Sierra HPMK bullets and 2/3 MOA at 600 was common for M118, 1 MOA for M72, with 3/10 grain spread in charge weights and 4 grain spread in case weights

[F. Guffey]

Some ammo plants have made a production lot of ammo with bullets from 3 or 4 sets of dies. All USA arsenal lots of 30-06 M72 and 7.62 M118 match ammo were that way. No wonder their best lots used for the Nationals tested about 2 MOA at 600 yards. Rebulleting them with Sierra HPMK bullets and 2/3 MOA at 600 was common for M118, 1 MOA for M72, with 3/10 grain spread in charge weights and 4 grain spread in case weights

It seems it is always about something you can do nothing about. I had thousands of cases to sort for length from the end of the neck to the case head. For me? Not a problem, I thought about it for a few seconds and then put a gage together that was the fastest case gage I have ever seen. And, it sorted cases by length in thousandths as fast as [I] could pick them up and put them down.

One more time: what they do at the factory does not lock me up but when I find case heads that with a difference of .060" it does not take me long to find disadvantages and advantages.

I also decide if there was any truth in in one case being heavier and or thinner I decided the military cases had thin case heads and thick case bodies. Going the other way I decide if the P-P case head was thicker the case bodies were thinner.

And that leaves the part to be decided; that would be the diameter of the powder column and the length of the powder column. After that comes the auto response about the percentage of alloy.

F. Guffey

[hounddawg]

For the OP I never sort cases by weight or volume and get consistent SD's and ES's of below 10. Get the right powder, charge weight, and primer and single digit SD's are easy to get.

I weigh the powder within .3 gns (target weight plus or minus .1 gns), trim after each firing for consistent case length and always chamfer the necks before loading. I use a primer pocket uniformer on new cases and seat the primer between .002 and .006 below flush. This stuff ain't rocket surgery

[F. Guffey]

For the OP I never sort cases by weight or volume and get consistent SD's and ES's of below 10. Get the right powder, charge weight, and primer and single digit SD's are easy to get.

Reminds me of Wallace Beery's "It's OK there little buddy because nothing matters". One day I loaded 250 30/06 cases on a progressive press. After I finished loaded the cases I weighed all 250 cases. From the heavies to the lightest there was 27 grains difference in weight. A difference of 27 grains is a lot of difference when it comes to powder but I used 5 different case manufacturers (5 different headstamps). I sorted the cases after loading by headstamp and weighed again. the difference in weight was caused by the weight of the cases.

Again: I was at the pistol range shooting next to a Wallis Beery type shooter. He could not pull the trigger, he could not rotate the cylinder, he could not open the cylinder, he had a bullet stuck between the cylinder and barrel throat/forcing cone. the last round he fired had no powder. My friend and I put our stuff up and helped him. We placed a short stick down his barrel and then drove the bullet back into the case. We cleared his pistol.

After returning the pistol, he immediately started loading his pistol with his reloads. We offered him all the ammo he could shoot but he had his mind made up he was going to shoot his reloads.

We suggested there was a chance if one of his cases fired in his pistol had no powder there was a chance one of the other cases had all of the powder from two loads. But, to him, it was OK because there was no way to check his cases for double charges or no charges.

We told him there was no way he was going to stand between us whole firing ammo that could destroy his Model 66 S&W 357 magnum. We offered to check his ammo, we offered to loan and or give him equipment for checking the weight of his ammo; instead, he got mad and left the range, given the opportunity I would have volunteered to leave if that was a choice.

F. Guffey

[LineStretcher]

Originally Posted by Unclenick

Unless they are from the same lot, case weight doesn't necessarily correspond well to internal capacity. There are different alloys used for different brands and the tolerances for width and relief angles in the head, which don't affect case capacity, can cause about 20% error in guessing capacity from weight. The reason the lot matters is makers change the specs over time. Winchester brand .308 Win brass I bought fifteen years ago is about seven grains lighter than some more recent stuff I got. Manufacturers swap around, too. Norma's 2013 databook says that happens when a contract ties one guy up. He then farms out what he can't handle to other guys. Norma said they've made brass for Remington, for example, with Remington's headstamp on it.

All that said, brass capacity is not usually the first place I look to improve velocity SD. Proper seating of the primer comes first. For some reason the idea you should stop when the primer just kisses the floor of the primer pocket persists. It leads to inconsistent ignition times. You want the primer to go in about three thousandths deeper. Dan Hackett wrote that he just seated hard, going past that kissing contact point, and that he was almost always able to get SD's below ten fps doing that, even in magnums and long cartridges based on the 30-06, and that he was not able to do it any other way.

Creighton Audette was the first to suggest primers were "analog" rather than digital and Naval Ordnance at Indian Head confirmed by testing that "reconsolidating" the primer with two to four thousandths compression of the anvil into the primer pellet, also known as "setting the bridge", is optimal.

A second factor is powder settling. Hackett also observed significant differences could occur in peak pressure depending on whether powder was settled by vibration or not. This is mainly true of stick powders. Spherical powder's don't settle much, though I generally can't get equal accuracy from spherical powders for various other reasons. I think one of the secrets to the success of Federal's GM308M load with the 168-grain SMK is that the load of IMR4064 in it is very slightly compressed (about half a percent) so that locks the grains in place against repacking during transport. Looking for an appropriate powder that does that can be worthwhile.

Absent actual compression, you want to look at which powder's the load data says are most consistent. A standard practice among manual authors is to load so the variability they get in pressure doesn't go over SAAMI MAP. Hodgson describes this in the print manual I have. They say that because of this practice, when you look at the pressures they list for maximum charges of different powder's with the same bullet in your cartridge, the highest listed pressure is for the powder that produces the least pressure variation. Using that one should help with SD.

I hope that information helps you with your quest for low SD. Note that some loads like some primers better than others, so be prepared to try a number of them. Try to have the same firing history for all the brass you are loading to test this, too. Also, note that the load with the lowest SD isn't always the most accurate because it doesn't necessarily hit a barrel time sweet spot as nicely. You can tweak that some by adjusting bullet seating depth.

Good shooting.

Well stated and 100 percent correct.

[Bart B.]

Unclenick's best info:

"Also, note that the load with the lowest SD isn't always the most accurate because it doesn't necessarily hit a barrel time sweet spot as nicely."

That sweet spot is on the muzzle axis upswing near the top so slower bullets leave at higher angles than faster ones to the LOS to compensate for their greater drop at target range.

[hounddawg]

Also, note that the load with the lowest SD isn't always the most accurate because it doesn't necessarily hit a barrel time sweet spot as nicely."

I have to respectfully disagree there, in particular at ranges from 500 yards and out. Simple ballistics tell me that a 25FPS extreme spread can cost you .5 MOA or more at 1000. Then factor in shooter error and wind/mirage issues and you have the makings of a low score. Shooting a high ES/SD load is like running a marathon wearing a 50 pound backpack. You have lost before you take the first step

[LineStretcher]

Originally Posted by hounddawg

I have to respectfully disagree there, in particular at ranges from 500 yards and out. Simple ballistics tell me that a 25FPS extreme spread can cost you .5 MOA or more at 1000. Then factor in shooter error and wind/mirage issues and you have the makings of a low score. Shooting a high ES/SD load is like running a marathon wearing a 50 pound backpack. You have lost before you take the first step

You would be wrong to disagree because it's true. Today it seems that everyone puts so much emphasis on Velocity when in fact it is most important only to those that expect the bullet to do something upon impact other than punch a hole in a piece of paper. A precision hand loader will work his loads up for one rifle very slowly, optimizing each and every aspect. The primer, case, bullet, seating depth, COAL, etc., are all optimized for the one rifle which goes to what Bart B say's. if you simply grab numbers out of a book you are not handloading for your rifle, you're just reloading and hoping for the best.

When cases are made in a production environment they tend to be different by lot. When you weigh a case, you do it to sort out anomalies. A case that weighs different then the rest of the cases in the lot my have a defect so you discard it because it's impossible to correct the problem. Once you have all of your cases sorted by weight what you accomplished was to set a standard for the lot that will tell you that the powder in each case should burn in approximately the same manner. If you are just reloading then weighing cases is a waste of time but if you're hand loading then you are probably more interested in trying to get to a standard.

[scatterbrain]

Let me rephrase that question, what is the weight range of the bag/box of brass that you pay $70 to $100 bucks for? When you take them out of bag/box and use them they have already been sorted, according to Nosler and Hornady, Uncle Nick will probably have that answer.
Up until about 15 years ago I sorted by caliber. Having been involved QA/QC on the jobs, I decided to see what could be done to get to 0 SD. I will again say, weight sorting has helped, try it. I know it's not as excate as volume, but more practical.
As to primers, I trim all holes to one depth, and like Mr. Guffey, I made a gage that lets me know that my feel is the same, everytime.

[hounddawg]

You would be wrong to disagree because it's true.

The physics of how gravity and laws of motion affect the bullets travel is not a opinion, it's a scientific fact. If you like to start the match shooting loads with a half MOA vertical dispersion then feel free. If you shoot long range competition the other shooters won't mind either

Today it seems that everyone puts so much emphasis on Velocity when in fact it is most important only to those that expect the bullet to do something upon impact other than punch a hole in a piece of paper.

I have no idea on what you mean by that, bullet drop variance and resulting POI differences due to velocity spread occur from the time the bullet leaves the muzzle and until it impacts the target. If you had a 1000 yard windless tunnel and a machine rest firing bullets with more than 20 FPS differences will result in a larger vertical spread than a well developed load. Finding the sweet spot of the right powder, the right bullet and primer to get low SD's is the hard part. Then all you have to do is find the set spot on seating depth.

I can get sub MOA groups out to 800 and 1000 easy, just getting them in the centered in the X ring is what is kicking my butt. I bet 90% of the flyers all of us get is more due to the shooter than the ammo

[Unclenick]

Hounddawg,

It is perfectly possible for a load with an SD of 12 fps to outshoot one with an SD of 6 fps even at 1000 yards. With the #2156 Sierra Palma bullet launched at 2,900 fps, the drop difference for the typical extreme spread is about half an MOA and it takes very little shift in the angle of departure to make that up. If a 32" Palma barrel has its bending node about 10" back from the muzzle, it's about 0.7 thousandths of an inch of upward bend (see barrel bending FEA animated output on Varmint Al's site).

The limitation of exterior ballistics programs is they only describe what will happen to trajectory if you have a perfectly rigid barrel mounted to a perfectly rigid base. A real rifle with its bore line above the butt of the stock's contact point with a shooter's shoulder sees recoil induce the barrel flexing Varmint Al's animation shows. This contributes to the flat spots you see on an Audette ladder. It isn't just from velocity nodes.

The day will come when software will exist that lets you plug in your gun's weight and barrel dimensions, as well as your load data and shooting position and rest information, and have it work out all elements of the firing event. We just aren't there yet. The main drawback? It will demand to know the shooter's weight.