9mm reloads - scuffs on cases


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k9kev88
February 6, 2012, 05:05 PM
I started reloading 9mm recently and have had success - my reloads with HP-38 and Berry's plated 115 grains were shooting around 1090-1130 fps, which is right at the factory load speed.

I noticed that the cases coming out of my S&W have a certain look to them - but also, I noticed that other 9mm brass from the range (shot by someone else) had the same look - almost like the cases are being scuffed as they expand and are ejected from the chamber.

Only one of the cases below came from my S&W - the others were picked up.

Can someone enlighten me - what causes this, and is it a problem??

http://www.hagasys.com/cdn00201/9mm_casing_scuffs_01w.jpg

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rcmodel
February 6, 2012, 05:33 PM
As you suspect, pressure causes it.
The 9mm is a high-pressure round.
If you are getting 1,130 out of a 115, you are running 34,000+ PSI.

More specifically, the case expands and grips the chamber tightly.

Then the slide recoils, the barrel unlocks, and the case is yanked violently from the chamber before the pressure has dropped enough for it to contract and release it's grip.

A dirty carbon fouled chamber, or a rough factory finish in the chamber can also cause it.

rc

k9kev88
February 6, 2012, 05:37 PM
As you suspect, pressure causes it.
The 9mm is a high-pressure round.
If you are getting 1,130 out of a 115, you are running 34,000+ PSI. rc

OK, thanks - my concern is - is this an indication of too much pressure in the reloads? The speed is right on... if this is rather common, then no worries, but I want to understand. The Hodgdon data for HP-38 indicates that 1135 fps for the powder loaded is only 32,000 CUP. Most loads were around 1080 - 1090, so there were a few spikes.

The Federal Champion factory loads were all running over 1100, but I'm sure they have a different powder.

My S&W only has 600-700 rounds through it and I clean it every time it is used - I don't see anything weird in the chamber.

Walkalong
February 6, 2012, 06:02 PM
A 115 Gr bullet can be safely pushed to 1130 FPS with the proper speed powders. Hodgdon data says HP-38 is one of them.

Cases look normal. Polishing the chamber could help, but it hurts nothing.

ReloaderFred
February 6, 2012, 09:49 PM
k9kev88,

It's normal to see that slight scuffing on high pressure semi-auto cases. As rc said, you can lightly polish the chamber with a tight fitting cloth swab and some Flitz or J-B Bore Cleaner. Just don't get carried away with the polishing, as it only takes a minute or two. And as Walkalong said, it's won't hurt anything.

The other thing is, rc gave you pressure in PSI (Pounds per Square Inch), whereas Hodgdon gave you pressure in CUP (Copper Units of Pressure). The PSI reading is obtained with a strain gauge, while the CUP reading is obtained with a copper crusher method, which is the amount a copper pellet is crushed by the pressure in the chamber. They're different and there isn't a direct table of reference between them.

Hope this helps.

Fred

k9kev88
February 6, 2012, 10:22 PM
OK, thanks guys. They shot really well, but I wanted to make sure they were OK before I reload 500 at that same pressure.

I'm thinking I could use about .2 grains less of HP-38 powder than I have with the Autodisk measure, which means I may have to make a custom scoop for the 115 grain bullets. The variance in the Lee Pro Autodisk was more than I expected - it was within acceptable tolerance, but the FPS varied from a low of 1048 up to 1159 over 20 cartridges, which seems like quite a bit.

1SOW
February 6, 2012, 11:09 PM
I'm thinking I could use about .2 grains less of HP-38 powder than I have with the Autodisk measure, which means I may have to make a custom scoop for the 115 grain bullets.

There is a LEE micro adjustable disc you can buy. Some like it. I don't. I never got it to be consistent with my loads.
Some with the LEE disc system modify unused disc holes for "specific" powder drops between the existing holes. I renumber the modified holes to a number "between the existing numbers". EG. I have a "hole number 47.5". This modified hole can be used with any powder, just like the regular holes.The discs are $5 each for spares.

J_McLeod
February 6, 2012, 11:17 PM
I've had good results with the micro disk. I only have one and I leave it set for 4.8gr of HP-38. Everytime I check it's +/- .1gr. Worth the $10.

gamestalker
February 7, 2012, 03:05 AM
To add to RC's on target explanation, case sieze is a necessary element and is the cause of the scuffing you describe. And with certain cases such as the 9mm, pressures are significantly higher and this scuffing is a bit mroe noticable. Nothing to be concerned about, and it will certainly tumble away.

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