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CDM vs Starline case capacity?

Printed From: AMT Guns information
Category: Auto Mag Pistol
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Printed Date: 18 Jul 2019 at 1:27pm
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Topic: CDM vs Starline case capacity?
Posted By: Pantera Mike
Subject: CDM vs Starline case capacity?
Date Posted: 08 Aug 2018 at 8:31am
Does anybody know for sure how the capacity of Starline cases compares to that of CDM, Norma, and typical rifle brass?

I ask because period load data is all over the map, and it’s suggested that case capacity can vary considerably. The impression I get is that for a given amount of powder, pressures will be higher in cases with a smaller capacity, and loads need to be adjusted accordingly.

Grains of water seems to be the typical method of measuring case volume. Somewhere I remember reading a comparison between several different types of brass but for the life of me I can’t remember where it was.

If somebody had some Starline and CDM cases and could produce the comparative volumes of each (either using water or gunpowder, filling each case up to the brim and then measuring the weight of the measuring medium) that would be great!

Posted By: Benny123
Date Posted: 08 Aug 2018 at 3:39pm
I recall the articles of Lee Jurras comparing different brass types for the 44AMP. I only have Starline. I would expect the rifle parent case with increased wall thickness to have the least capacity, and CDM, the greatest of the bunch . The impression that you got that pressure will be greater with smaller capacity is spelled out many years ago by the ideal gas law PV=nRT. ......volume decreases, pressure goes up

There are a lot of collectors of that old stuff around . Hopefully someone will chime in. If memory serves I felt like, Lee referenced CDM as having the greatest case capacity, albeit nominal

Posted By: jw4570
Date Posted: 08 Aug 2018 at 10:20pm
Look no further than Ian's Site for an article by Barry Duckworth and Bruce Stark.

The case capacity is actually compared using grains of WW296, but I think it's the relative capacities you are looking for:


Posted By: CrazyLarry
Date Posted: 08 Aug 2018 at 10:50pm
From what I have seen measured:

(lowest to highest resized 308 brass capacities)

NATO brass is nearly all identical, but, there are lot-2-lot differences anyhow.

Cut down military brass has the thickest amount of metal around the bottom, therefore it "should" last longer.

Starline brass is made "thicker" than 44mag brass at the web/primer pocket, but, not by much.

If I were going for 1300fps with a 240gr bullet, an 8.5" barrel is needed.
From what I have read else where with 308 based loads, there is not that much of a difference in capacities for pistol rounds that end up with significant changes to velocity.

Now, in a rifle, that is a different story. I used to cut down 30-06 REM brass to make 300SAV before I scored a bag of once fired REM cases at a gun show. Cut down 30-06 was 100fps consistently slower than resized original 300SAV brass.

Posted By: Benny123
Date Posted: 08 Aug 2018 at 11:04pm
That’s a really informative article by B Stark. And I forgot about it, when I first saw the title I really didn’t understand the need to search for a moderate load and how one could use a slow-burn pistol based powder for an otherwise slow moderate load. Charges of w296/h110, and mp300 are designed to be almost at capacity. And the part that states that no pressure testing has been done with respect to the cartridge. Didn’t Lee Jurras produce his own line of ammo , Supervel, and was the first to commisison a pressure gun for this cartridge, he’s stated in the articles around a 40- 45K max pressure range, with charge details for his own line of bullets and others. I dunno maybe I’m wrong. As Ive mentioned before anything Detailed oriented about the automag I learned from this Ian site and forum .

Posted By: jw4570
Date Posted: 08 Aug 2018 at 11:24pm
Lee Did Pressure test something like 6 loads of SuperVel.  I have the pages somewhere.  He had them up on his site when he had it.

Posted By: jw4570
Date Posted: 08 Aug 2018 at 11:34pm
I uploaded the files but can't figure how to link them here...

It says Error inserting it in current location

And I can't access the FAQ again.


Posted By: jw4570
Date Posted: 08 Aug 2018 at 11:39pm" rel="nofollow -" rel="nofollow -" rel="nofollow -" rel="nofollow -" rel="nofollow -" rel="nofollow -

not how I wanted to do it, but I think you can at least click and see them?

Someone confirm it works from their end

Posted By: jw4570
Date Posted: 08 Aug 2018 at 11:45pm
I forgot one was with discontinued 630 powder.  296 and Blue dot still around.  3 44's and 3 357's pressure tested.

Maybe Ian can add this to his info page?

Posted By: Benny123
Date Posted: 09 Aug 2018 at 12:00am
Nice job—all came through

Posted By: Benny123
Date Posted: 09 Aug 2018 at 12:04am
Yeah, I didn’t know what 630 was. Not sure when that was produced. 680 I’d see a bit and was replaced by aa1680 which is a fav for keeping the pressure down on hot loads for large for caliber bullets in magnum cartridges. Presuming it shines for the 265 in the 44amp

Posted By: Pantera Mike
Date Posted: 09 Aug 2018 at 4:35pm
Thanks to all, especially Bruce. Great information here!

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