The effects of case volume

[Snakeoil]

As I was getting ready to test some breech seating loads in my .38-55 on Wed., I ran some numbers in GRT to confirm expected MV from the loads so I'd know if I had enought scope adjustment to get me out to 500 yds. What was very striking was what small differences in case volume would have on MV. I realize that case volume is a variable that has to be considered in developing a load. But I guess I never looked hard at the numbers until I started playing with GRT.

At Wilton, I was talking to another member who is a die-hard single shot shooter. He is the impetus behind the NRA .22 BPCR matches held twice a month on Saturdays at the club. We were talking about breech seating and he asked if I was planning on having a powder measure on the bench and using just one case. I said no. He said Dave Hicks said there is really something to using just one case. For those who do not know Dave, he was on the US BPCR team and set and I believe still holds a few records out to 1500 yds with his High Wall in .45-70 that is throated to be more like a .45-120. I can see Dave's point. The breech seater is fixed in how far it places the bullet in the bore. With one case, the case volume never changes. So, bullet density, powder charge accuracy (smokeless) and primer consistency are you only 3 mechanical variables. Weigh your bullets, use match primers and use a powder that meters like 2400 and given you find a load that the rifle likes, you have the potential to shoot some bad-ass groups, at extended distances, range conditions notwithstanding.

Just might try this one case technique as a winter therapy project. Of course that means I'll need to bring a powder measure to the range, long with my scale. I keep trying to make shooting easier. But if this keeps up, I'm gonna need a wheelbarrow to bring all my crapola to the range.

 

[Ian]

Somewhere on this board I posted a thread about pistol cartridge case volume and how small changes can have huge consequences to peak pressure. There is very good reason to use only 2.7 grains of Bullseye under a .38 wadcutter while 3.2 grains is the norm under an SWC of the same weight. Same goes for any cartridge but the effect often is not as dramatic. The only "blow up" I've experienced from my own handloads was a 1911 and inadequate case tension on the thin Winchester brass from a mixed-headstamp lot; I had increased sizer diameter to reduce brass being worked for cast bullets and it was fine....except for the Win headstamps. Bullet got seated deeper and deeper while in the magazine under recoil and probably more when hitting the ramp and hood, then blew a hole in the case head and primer due to the confined powder space. Only lost a magazine and set of stock panels, luckily.

So again, yes case volume matters and small differences have an effect, but this is definitely a factor that "only matters if it does", and everything matters in competition.

 

[popper]

Case volume (for a cartridge) isn't that important for most of us. Unfilled case volume is very important. case volume never changes - well, that depends. If the case fits exactly in the chamber - can't expand due to repeated firing pressure, yup. But then, what case do you practice with - same as the event? What happens to neck tension after 10 firings? I suppose breach seating doesn't care about neck tension? Or there isn't any? Jam the bullet and no neck tension! Military does it all the time in BIG guns.

 

[Tomme boy]

You don't need to bring a scale or measure. Just bring pre measured charges. I bought a bunch of vials to hold my black powder that is weighed out on my scales. I think I ordered 10ml glass vials with a screw top. The largest I have weighed out was 90 gr of FFg and only fill about half of the vial.

I first used the black powder measure and was varying about 3-4grs going by volume then weighed. I was surprised by the amount of variance.

 

[358156 hp]

My interest is piqued. If you breech-seat the bullet when using black powder, how do you get the necessary powder compression necessary for BP to burn properly? It would seem to me that you'd have excessive space if the powder is introduced in a case.

 

[glassparman]

As far as case volume, i have always tried to use the same brand and era of cases when I load a batch of ammo. This helps emilinate some of these issues.

 

[RBHarter]

Well lemme tell ya about 140 pieces of LC43 ..........
That didn't work out really well . Fortunately I had a bone stock special order 1965 Savage 110LH to set me straight........
In a picky rifle case volume can be gigantic.

A buddy gave me 100 pieces of 1995 Rem brass from 1 lot of factory ammo . It only varied from 187-205 gr case weight vs the LC43 at 178-207 gr
25 gr of soft lead is what's sticking out of a 22LR .
25 gr of steel shot is about 5 pellets of B air rifle shot .
So 25 gr of brass is someplace in between .

 

[Joshua]

Well lemme tell ya about 140 pieces of LC43 ..........
That didn't work out really well . Fortunately I had a bone stock special order 1965 Savage 110LH to set me straight........
In a picky rifle case volume can be gigantic.

A buddy gave me 100 pieces of 1995 Rem brass from 1 lot of factory ammo . It only varied from 187-205 gr case weight vs the LC43 at 178-207 gr
25 gr of soft lead is what's sticking out of a 22LR .
25 gr of steel shot is about 5 pellets of B air rifle shot .
So 25 gr of brass is someplace in between .

It’s posts like this that make me wonder why I even sort my rifle brass by headstamp!

Oh yeah, neck tension! Consistent neck tension, that’s why I keep batches of brass together.

 

[Snakeoil]

My interest is piqued. If you breech-seat the bullet when using black powder, how do you get the necessary powder compression necessary for BP to burn properly? It would seem to me that you'd have excessive space if the powder is introduced in a case.

I'm new to breech seating. So, I'm no expert by a long shot.

I suspect it was a technique that was developed with the advent of smokeless powder. Prior to breech seating, shooters like Harry Pope would muzzle load the bullet using a false muzzle and push the bullet all the way down the bore. If they were using BP, I could see them pushing until the bullet stopped on top of the powder charge. When I shot BPCR, my bullets were slipped into the cases with my fingers and rested on top of a BP charge that had already been compressed about 1/16". When the cartridge was inserted, it would engrave the rifling and closing the breech block would create a small "crunch" as the bullet compressed the powder a tad more. So, for breech seating with BP, you could seat the bullet into the rifling such that the base would enter the case and compress the powder when the action was closed. The key to breech seating with smokeless is to seal the bore. Now you can do this with the first band on a bullet if sized right. I prefer to put the entire bullet into the bore. The base on the bullet I'll be testing tomorrow was a gas check bullet. The GC shank was machined to match the last driving band of the bullet. The result is a PB that is probably about 3/16" wide. I suspect that will provide superior sealing to a narrower last band/base.

After typing the above, I was curious when breech seating first started. I did a quick search and although I did not find a date, I found reference to Harry Pope which jives with my memory on the subject. Here is a link to a discussion on the CBA site if anyone is curious. They argue the improved accuracy point. Another reason to breech seat today is to save cases. A friend at the club is shooting a .28-30-120 Stevens in a vintage High Wall. The cases were big bucks. And half his cases were formed and the other half made on a CNC machine. The weights of the two types vary by a lot indicating that volumes are more than likely very different. He's going to BS because he wants the cases to last forever.

BREECH SEATING NOTES

On Breech Seating There is at least a hint that something happens during the leap of the bullet

forum.castbulletassoc.org

As a sidenote on BP and breech seating, if you'll remember, the 1859 Sharps rifle which was the basis for the 1874, was originally a breech loaded rifle that used separate bullet and BP in the form of a paper cartridge.

You don't need to bring a scale or measure. Just bring pre measured charges. I bought a bunch of vials to hold my black powder that is weighed out on my scales. I think I ordered 10ml glass vials with a screw top.

Yup, good point. I was thinking about doing that. I did the same as you and ordered a box of them off of fleabay for ML matches. I think I bought 100. They were dirt cheap.

 

[popper]

If you run the numbers on a 308 case with case brass density of 0.308#/cu", you find 25gr case weight diff is ~0.001" case wall thickness variation. I.E. you'll never notice. Yup, 43 brass was during war time and tolerances were not that important. Like weighing powder to 0.001gr or bullets to 0.1 gr - won't matter. You can prove me wrong by taking the high/low cases, cut and prep - measure, repeat lower on the case (tapered of course). Or weigh the cases, fill with water and weigh again with accurate scale. If Pope and his like could do what they did with rudimentary equipment, we should have much better performance with our handloads.
Eliminating variables is what it's about, finding the larger variables is more important. In most cases it's the shooter. Like all sports, when you find what works for you, you will NOT change.
I will repeat what I said before, it's not diff case volume but empty space that makes the difference.

 

[Snakeoil]

You piqued my curiosity. I ran the numbers. For the cylindrical portion of a .308 case (yeah, I know, it isn't) to make it easy. It is 0.002 cubic inches of volume.

I will repeat what I said before, it's not diff case volume but empty space that makes the difference.

So, are you saying that too much empty space creates excessive variability in pressures?

 

[popper]

Not exactly. Seating depth determines(?) burn rate. Seating depth varies empty space, just like wall thickness. Wall thickness variation is very small. Kinda hard to put to words, hope you understand.

 

[Joshua]

This is a great visual example of how seating depth changes pressure.

 

[Snakeoil]

This is pretty common knowledge. I thought you were saying something else about empty space.

 

[RBHarter]

I had this rifle ........
Everything as close per case as I could get it , seriously I got so deep into this that I now know that IMR 4350 has 9 kernels per 1/10 of a grain and they aren't all identical and had 2.5 gr of case weight which translated to something like .4 gr of water volume that was throwing bullets out 12" into a different zip code at 100 yd .

I also had a 308 that would shoot 2.5" within 4" of POH as long as the bullet weighed less that 175 gr ........I shot 180 RN from Hornady, Speer and Sierra shorter than 150 SPBT and tossed them around like marbles on a sidewalk in San Francisco. Yeah everywhere and running away down hill . The 301-318 @172 gr worked great right off .

I have closed as many serviceable groups into great groups with weigh lots as primer changes .

I don't know what 5 gr of brass looks but I would venture that it's about the volume of 1 pellet of #2 shot . That ain't much space and it's a lot more than 2 gr . If the physical space inside the case is different from case to case it doesn't matter where the bullet is or how precisely it is placed there that "BB" sized difference in case volume is still going to be there. It's also going to change the amount of air space in the complete chamber dimensions.

The only way to delete air space would be assuming friction and neck tension displacement are identical is to have a compressed load torqued to it's final compression which is going to screw with the OAL by the difference in chamber/case volume .

Mechanically we can eliminate the chamber and mechanically seat to depth and compression with the case deleted there by reducing the possible error in volume to that of the peculiar shapes of individual powder kernels and the resulting nth of barrel length . If what I read once about Harry Pope's loading techniques is accurate that's exactly what he was doing having less than .1 length of the cases available for the bullet base to enter and seating the bullet in the case from the muzzle end with a breach loaded rifle . If the bullet isn't pressed down onto the load with uniform pressure then the case/chamber variations will still exist. If case #1 has .009 left and just kisses the breach seated bullet base it won't have the same air value as case #2 that with .008 that has 6psi against the bullet base nor will #3 with.0095 that is in contact but only by up ended kernels in the neck .

In this case there might not be an even measurable pressure difference but the rifle might react to it . Apply caliber and and that pellet of #2 brass shot can be huge , in 25,6.5,27 or 28 in an 06' case , we're looking at a functional difference on .06-.09 in seating depth . In a 45-70,90,100,110,120 , 458 , 460 Weatherby or really any 308+ case in 35 cal and up we're looking at more like a gas check depth and twice the escape hole passing 4 times the volume. Which would to a greater or lesser degree negate the case to case variations.

In shot shells because a 12 ga is a big enough case to really examine the changes of base shape from case to case is why we sort by Headstamp not to control case volume differences .
At some point , because I no longer retain the names , Springfield Armory conducted testing with flash tubes in 06' case like those found in artillery shells to place the primer flash at the front/top of the powder column . It did result in positive advancement of the desired reductions of pressure and velocity variations but wasn't practical for production in such small cases . Imagine threading a #10 wire ga horse needle and screwing it into a large rifle boxer primer pocket ........I suppose it could just be flared and held in place with the staked primer .

Look to the old schools when looking at the 2.5-4 inches in front of the bolt/breach face for solutions to and the problems causing the need for the solutions .

I also once dabbled in how to make a flammable gas gun work and that stumble was how to consistently seal the barrel end of the combustion chamber and deliver a consistent gas mixture that wasn't a bomb . Lot of mechanics there that high power potato gun can't cover ..... It was however a worthy investigation.

 

[glassparman]

Of course empty space is totally a no-no with black powder.

 

[Tomme boy]

Maybe with black. It is a HUGE wives tale in regular black powder muzzle loaders. It won't do anything to the gun. Maybe the old Damascus twisted iron barrels but it does not hurt a modern rifle at all. Only way it will blow up is if the bullet in the gun hits a barrel obstruction. Its been proven time and again that not seating a ball or whatever will do nothing.

Hell I have done it several times on accident. Certain alternative powders create a huge rock hard carbon ring from using it. Well it keeps moving forward after each shot. Noticed it after I did not need my extension anymore to seat the bullet. Or what I thought was seating. And this was with 150gr of powder. I don't use that powder anymore. I stick with real black.

 

[popper]

It's like weighing cast bullets. Cast one, and the next one is slightly heavier - due to dia being miniscule larger. Same with brass, miniscule difference in ID causes what seems to be a large weight difference. Volume of .001" thick hollow cylinder (2" long) is 0.0005 cu". one gr h2o= 8gr brass = 0.03cu". A 308 case is ~1.68 cu" internal volume. So 4% variation of internal volume for 20 gr weight diff (assume all difference is due to case volume - big assumption). So say you have 1% variation of internal volume for decent brass. This controls the actual powder burn, enough to make a difference? Consider a 0.1gr powder error (/40gr load) is .25% error. But powder has energy.
Not an argument, just numbers so you can decide for yourself.

 

[RBHarter]

Let me try this a different way a 350 GM is a 350 GM you can .1 of the deck and .1 off the head and run it up to 14-1 compression but it's still a 350 . Take .030 out of the walls now it's 355. It goes over 360 , 362 I think if you take .060 out of it . The difference between a 345 and 392 IHC is .128 bore . It's the same in the case you're just raising and lowering the compression within the window . If you stroke it IE drop a 400 crank and rods in the 350 now it's 388 ...... Kinda like adding a 1/4" to a 7×57 and now it's 7×64 or 280 .

 

[Barra]

I take a powder measure to the range and load a case and use it all day.
sometimes I might load 5 at a time.
I’m lazy and save the 50 I have in the box So I don’t have to do all that stuff at home.
I also tinker so I can try things.
This way I can tweak a load without loading extras Etc.
sometimes I’ll breachseat using one case.
slows down my shooting cadence.
I enjoy it more.

large case shooters say that the small differences in case volume and powder charges evens out in the case pressures.
‘Small case shooters belief they have more constant ingnition because the powder is more uniformly laying in the case.
with say a 30-30 and a few grains of bullseye you will get different velocities from the power orientation And poi. Sometimes tighter groups sometimes not.
Once case shooting eliminates a lot of variables and benchrest case preparation.
Early cases were not as uniform.
Plus it bugs the heck out of benchrest shooters and the like to see you use a de-re prime tool and no sizing. No neck tension.
cast bullets that are finger lubed at the time and pushed into the lands with a pencil or Biro
To test your seal of the bullet.
just pop a primer.
it will shove the bullet a little way in and it will hold pressure till you let the case self extract.
if it does that then your golden to more onward.