Difference in case capacity.

[JNG3]

I've been using Federal Match wadcutter brass for a load I shoot from my 38spl Ruger LCRX +p. I only have 50 of this brass. I have a bunch of Remington 38spl brass. I trimmed a Rem case to the same length as a Fed case and carefully measured case capacity with water. I came up with a repeatable .6 grain difference. The Rem cases have less capacity. I load 3.5 grs of Bullseye under a 150gr button nose wadcutters. This is a max normal pressure load. I'm not sure how much difference .6 grains in case capacity matters. I guess I'm being lazy and not wanting to start at the minimum charge of Bullseye and work my way up again. Will .6 grains capacity matter to any great extent? Is there a formula to figure out how much to drop the powder charge? Just start over and work my way up???

[ioon44]

Any time you change a component you should just start over and work my way up.

[JNG3]

I understand that this is for bottleneck rifle cases but all I could find on this subject is this portion of a thread from another forum I've copied and pasted.

"No. Not volume. But weight has a remarkable stable relationship, depending on the powder. Back in the 1960's, Wm. C. Davis, Jr. writing for the American Rifleman, worked out that you could estimate you needed to change the powder charge 1 grain for every 16 grains of additional brass weight, assuming that weight difference was all in the sides of the case so that with the bullet seated the same depth in both instances and with the head having identical dimensions, that brass weight difference was all in the powder space under the bullet. Since cartridge brass has a density of 8.53 g/cc, that's the equivalent of saying 1 grain change in powder charge for ever 1.87 grains of water capacity, or 0.53 grains of powder for each grain of water capacity. This was for IMR single-base powders of that day. The change is about right for keeping velocity fairly constant and letting pressure vary a little. It actually seems to be a compromise between these points.

What I would like is to do is keep the barrel time the same, so a sweet spot load with one case is still a sweet spot load with another. I find changing the charge about 0.7 grains for each additional grain of water capacity is often close to that."


Based on this I would need to reduce the powder charge by .42 grains or to make it easy .5 grains. Which would put me at the starting load according to Lyman. So I guess I need to start over.

[Dusty Bannister]

At some point those Federal cases will need to be retired. Maybe it would be better to just buy several hundred cases of new brass (Starline?). Work up your load again and not have to trim, and otherwise overthink what you are doing.

[PaulG67]

"Just start over and work my way up??? "

Yes

[jsizemore]

If your using a powder charge at the upper limit of the recommended charge then I would work up a load for each lot of cases not just manufacturer. If your near the lower end of the powder charge range then it shouldn't make much difference.

It's your gun and body. Do as you see fit. If other folks are around take a bit of care.

[JNG3]

OK, this was stupid. I know better! I guess as we all get older we tend to think we know too much and look for shortcuts. I had an "idiot moment' and I'm sorry I wasted folks time. I WILL start at the minimum powder charge and work my way up.

[44MAG#1]

Since it is a "normal pressure load" you are using I would use it.
It is a +P gun, right?
.6 of a grain difference in water weight will mean very little difference in powder charge weight. There will probably be more difference in two different lots of powder that that.
What you need is the water weight with the bullet seated. That is easy to figure if you are capable of using simple math. Water weight 252.89 grains to a cubic inch. How much does the Bullet displace??? Total case volumn in water minus the weight the bullet displaces equal actual water weight one has to relationship to powder weight.
If you have even just a simple education you can figure the rest. I can and I am about as simple as they come.

[reddog81]

What is working up a load in 38 Special going to tell you regarding pressure or anything safety related? It's a low pressure round. If you see any pressure signs you're way past .357 pressures.

If you want to work up the load to find the most accurate powder charge that's another story but I wouldn't be too worried about hurting the gun assuming it's a modern revolver in good condition.

The gun in question can handle +P rounds and we're talking about a load that runnning 16,400 PSI according to my Lyman manual. The load is already 20% below the pressure of what the gun can handle.

[tazman]

I would drop the charge slightly, say .2 grains and run it over a chronograph and see how well it matches up with what you have been shooting. If it doesn't match, adjust the charge weight until it does.
This assumes you have a chronograph and have tested/or can test the loads you currently shoot.

[JNG3]

Yes I own a chronograph. I consider it indispensable for reloading. I would want the Rem loads to basically duplicate the velocity of the Fed loads.

[USSR]

My only question is: "Why are you using so much Bullseye with a wadcutter load"? With 3.5gr of Bullseye, your velocity is going to be much higher than the original Federal Match Wadcutter load no matter what brass you use.

Don

[tazman]

My only question is: "Why are you using so much Bullseye with a wadcutter load"? With 3.5gr of Bullseye, your velocity is going to be much higher than the original Federal Match Wadcutter load no matter what brass you use.

Don

Some guns just shoot better with a higher charge of powder. I have seen that myself in a couple of my revolvers and a semi-auto.

[lightman]

Theres nothing stupid about this, so don't beat yourself up. Your chronograph can tell you when you duplicate your favorite load. If you want to juggle some numbers, calculate the % difference in the 2 cases and reduce your powder charge by the same. Or just knock it back .3 grain and clock it. Getting a new lot of cases is a good suggestion.

[Bigslug]

OK. . .I think we've pretty well established that a simple change in brass with the existing load is highly unlikely to hurt the revolver in question.

We're also dealing with a 2 or 3 inch belly gun that's unlikely to see the 50 yard line at Camp Perry.

In the interests of keeping it real - drop your preferred charge, seat your preferred bullet, and return to your regularly scheduled program.

[earlmck]

For what its worth I put this question to QuickLoad. First came up with a 150 grain wadcutter load of COAL 1.25" with the 3.5 grains bullseye, giving 15k psi. Then I reduced the water capacity of the case with no other changes and got 16k psi. So an additional 1000 psi with that capacity reduction. This was virtually cancelled out by reducing the charge to 3.4 grains.

I'd bet that is not far off.

[tazman]

Sounds like you have a plan.

[dubber123]

6 tenths I wouldn't expect to amount to much, probably less than powder lot variation as noted by 44MAG#1 above, especially on a low pressure load. I have run into troubles with this in a 357 Mag load, but it was an "adventurous" load to begin with, and the brass I switched to weighed a full 6 grains more. And yes, I knew better, and should have checked first before swapping components. Its good you are considering it, but I doubt it will amount to a lot.

[JNG3]

In response to USSR's question. I am using 3.5 grs of Bullseye with the wadcutter because-

A. It is a 1.875" barrel snubnose and 3.5grs of this powder gave the best velocity. Actually this charge of powder and this wadcutter gave the best consistent accuracy.

B. The revolver is more accurate with the max charge than it is with the starting charge of powder.

C. I did some testing with jhp's and virtually none expanded in wet newspaper with one layer of denim. All but one did not even exit. I then tried swc's cast from 1-20. There was little bullet upset, but all exited and produced more damage to the newspaper pack than the jhp. On a lark I tried the button nose wadcutters. All exited and produced the largest hole in the newspaper pack. The wadcutters were also the most accurate when shooting at targets for accuracy. This is my carry gun, so in the unlikely event it is needed and hopefully NEVER, I wanted the most effective cartridge I could find for it.

[tazman]

All well thought out results with good test data.
Do a ladder test with the different brass over the chronograph to get the powder charge you need to duplicate your current load. That should give you the results you want.
Ladder tests are a pain in the backside but you only need to do it once.