Hi I'm a Nooby reloader using a Dillon 550b. I've just loaded and tested my first warm 10mm rounds using New Starline Brass. I'm shooting these rounds through a G-20 SF with a 20lb recoil spring and a Kimber Eclipse 10mm with a 20 lb recoil spring. All my testing went well- rounds started at .4215-.422 at the base and swelled to .433 in the Glock and .427 around the base in the Kimber using Longshot COAL 1.255. I didn't see any glock smiles or signs of over pressure in any of the spent cases. My question is at what point do you toss the brass? How many times can "new" brass be reloaded? Resizng .433 all the way back down to .422 in a resizing die seems quite a bit to me. Your help and remarks would be greatly appreciated.

I don't believe in a set number of reloads
When the Primer Pocket loosens is one sign
Signs of Web separation is another
And of course, Case splitting
Just my $0.02

As a new reloader I also had the same question. So far I have some Starline brass that is on its fifth or sixth full power loading out of my stock Glock barrel and is still looking great! I also have some Underwood (also Starline) brass that I've reloaded several times. I have had a few pieces of Underwood brass that I tossed after the first firing because it had either a full on smiley or a tiny stress line, but the majority I have reloaded several times and still look good.

I can't remember the exact number but I know that taterhead on Glocktalk kept track of how many loads he got out of his 10mm brass before it split or was worn out, I think it was 8+ loads on average out of the stock G20 barrel, but it could have been more.

In my experience if the brass looks good and holds the bullet and primer tight, load it and shoot it until it doesn't anymore!

Of course when loading "nuclear" loads (usually way above book) it is usually wise to use either new brass or brass that you know the history of (I. E. your own once fired).

Stkx66, welcome to the forum and the world of handloading!  I will say that the looser chambers of the Glock guns do allow for more case expansion than that some of the other makes, as you have seen with your Kimber.  As the brass is being worked at each sizing it will get harder and more brittle.

Careful, inspections are needed and I recommend "Pas-Thru" sizing to recondition any and all 10mm brass.  Why do I say that?
Please read these two sticky topics...
http://10mm-firearms.com/reloading-10mm-ammo/pass-thru-sizing-using-lee-fcd/

http://10mm-firearms.com/reloading-10mm-ammo/cross-section-of-a-smiley/

However these steps don't set well trying to utilize the speed of a progressive press. 

Thank you for the help. Today I bought the Redding GRX carbide pass thru resizing die and bottle from Unique Tek in Arizona. I have an extra die holder plate so I hope to use the 550 in a separate operation to resize the brass.
Thanks again.
Steve

I got the GRX resizing die  but it seemed to put to much load on my Dillon 550b so I ordered a Reddng Boss single stage and viola! Worked like a charm. Pass thru sizing was easy and I'm not putting needless stress on my 550b. 

Working with the sizing die as high up as will still allow the push pin to run the brass up past the carbide ring or in the case of steel dies the sizing portion, will allow you to take advantage of the most leverage of your press.

Cool. I'll play with the adjustments. Thank you