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-   -   Case Head Expansion (http://glocktalk.com/forums/showthread.php?t=1242124)

99blkta 07-13-2010 15:16

Case Head Expansion
 
I'm still quite new to reloading and was wondering at what point is case head expansion too much? So far most of most of my cases are around .424, after being fired through a KKM barrel (IMR 800X 10.1gr). At what point would yall trash the brass?

Forgive me if some of these questions seem elementary, I'm trying to read and learn as much as possible.

Aloxite 07-13-2010 22:59

Now I'm certainly no expert. So take my post with a grain of salt.

My understanding is that the idea is to start with some rounds that you know are within pressure specs. Fire those rounds in your pistol. Then measure those rounds and use that figure for your load development.

So take some hot factory rounds like Buffalo Bore or Double Tap and fire those in your weapon. Measure that. If your reloads show the same or lower case head expansion then you are within the same pressure range.

Otherwise it seems like the individual chamber of the barrel is going to influence how much expansion you see.

99blkta 07-13-2010 23:23

Thanks for the information, makes logical sense. I'll have to give that a try tomorrow!

MSgt Dotson 07-14-2010 09:21

With what bullet? Hodgdon's website shows 9.8 gr of 800x as max with 155 gr XTP, 8.7 gr with 180 gr, and 7.8 gr max with 200 gr FMJ....; other loading sources may give higher loading data with other bullets, but, depending on your chosen bullet, you certainly don't have unlimited headroom left...

The KKM is usually known as a quality bbl, but, I'd avoid trying to duplicate .41 mag ballistics in it, and would reserve your max loads/hunting loads to brass relegated to using only once or twice... (Case head seps are no fun at all....)

Brass will only expand to fill the chamber; attempting to gauge pressure solely by case expansion by compare DT loadings in one case with custom powder blendings with your loadings in another could quickly lead to a blowout/destroyed frame, lost fingers, etc....

99blkta 07-14-2010 10:33

Quote:

Originally Posted by MSgt Dotson (Post 15636851)
With what bullet? Hodgdon's website shows 9.8 gr of 800x as max with 155 gr XTP, 8.7 gr with 180 gr, and 7.8 gr max with 200 gr FMJ....; other loading sources may give higher loading data with other bullets, but, depending on your chosen bullet, you certainly don't have unlimited headroom left...

The KKM is usually known as a quality bbl, but, I'd avoid trying to duplicate .41 mag ballistics in it, and would reserve your max loads/hunting loads to brass relegated to using only once or twice... (Case head seps are no fun at all....)

Brass will only expand to fill the chamber; attempting to gauge pressure solely by case expansion by compare DT loadings in one case with custom powder blendings with your loadings in another could quickly lead to a blowout/destroyed frame, lost fingers, etc....

The bullet used is a hornady 180gr FMJ, the load data was taken from Hornady's manual 7th edition. All loads were worked up from the starting load. There was no evidence of primer flatting. I just measure all the brass I've fired to get an idea. The brass used was also brand new brass from DT. I didnt just throw it together per say.

Taterhead 07-15-2010 10:10

Quote:

Originally Posted by Aloxite (Post 15635500)
Now I'm certainly no expert. So take my post with a grain of salt.

My understanding is that the idea is to start with some rounds that you know are within pressure specs. Fire those rounds in your pistol. Then measure those rounds and use that figure for your load development.

So take some hot factory rounds like Buffalo Bore or Double Tap and fire those in your weapon. Measure that. If your reloads show the same or lower case head expansion then you are within the same pressure range.

Otherwise it seems like the individual chamber of the barrel is going to influence how much expansion you see.

I agree. To tighten this up even further, look up the Ken Waters method if you have not done so already. MMA10 has a great summary that is found here:

http://www.glocktalk.com/forums/showthread.php?t=179485

Benchmarking with hot factory stuff is especially useful if the intent is to load in brass of the same type and manufacturer. Different metallurgical properties of different brass makes - even regular Starline vs. nickel Starline like DT uses - will yield different expansion characteristics.

Many of us use Starline brass so Buffalo Bore is a good data point for these purposes.

In a loose Glock chamber, it is easy to see a trend of max case expansion from min to max. Mine trend very consistently with Starline brass. IMO, this is the single most important part of analyzine loads during workups.

MSgt Dotson 07-18-2010 20:41

If new brass, I'd use max loads only 'a few' times with it, i.e, two or three....perhaps two more times as plinking/target/reduced loads (ie., at .40S&W velocities), then toss it.

Others may disagree, but, I'd prefer to buy new brass than have a case head separation at the 7th or 10th reloading...(which I have seen occur with folks using 'too many times reloaded' .40 brass)

99blkta 07-19-2010 12:24

I'd be more than happy with the approx. 6 reloads you speak of. You answered the questions I had in mind MSGT Dotson, thanks for all the information.


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