Your friend is telling you information that is not true! I have loaded 10mm for my G20 for several years with Lee 40S&W dies. I can also adjust them down for loading 40 to use in my G29 with a Lone Wolf barrel that I use for IDPA.

 

I use RCBS dies with no issues

 

Your friend might be referring to the Redding GX-R sizing die. This die can be used after you size and decap your 10mm or 40s&w brass.

If you re-size and case gage 100 40s&w cases you may get one or two that will not sit flush with the gage! Break out your Redding sizer die and run it through. Presto! Case sits flush with case gage!

 

The Redding G-RX die is fairly popular, for good reason, amongst 10mm reloaders. It is a push-through die that sizes the base of the case. Redding makes a steel (lube needed) and carbide (no lube needed) version. Get the bottle adapter and use any 2 litre bottle as your collection bin.

 

The OEM glock barrel chamber is well oversized for reliable feeding, .436", so doubtful a base sizing die would be needed for chambering/RTB. I use the RCBS Carbide .40/10mm die set without any chambering/FTF/RTB issues in both the OEM Glock G40 barrel and a KKM Precision barrel, .428" chamber.

However, if loading for a revolver or some after-market 10mm Auto barrels with tight chambers, there could be issues. Either use a case gauge or a 'plunk' test to determine if a base-sizing die is needed.

 

May have been referring to the Lee Bulge Buster die, which is basically the Lee 40SW/10mm FCD die with a special attachment to push an unsized case all the way through die. I use this when brass has been fired in Glock 10mm barrels as there is a small bulge in brass area that isn't supported by chamber. With Storm Lake, Lone Wolf or other barrels, bulge busting isn't needed.

 

Here's what I'd do before getting a G-Rx Die or Bulge buster die:

Hit the spent cases with touch of Hornady One Shot (makes the whole resizing experience so much dreamier). Set the sizing die so that it just touches the shell holder. Or if using a progressive, make sure that the die is screwed in sufficiently to lift the tool head so that all of the slack is removed. Not looking to "cam over" with a carbide die, but making sure it is screwed in all the way.

Then size a few cases. If the brass drops into your case gauge and/or kerplunks into your barrels, there is no issue requiring special brass prep equipment. This is true for pretty much any auto-loading cartridge.

I have a G-Rx carbide die, but rarely use it because I don't need it. Where I do like it is after several reloads where my G20 chews up the rims a bit. That cleans up the edges of the rims where the sizer won't reach. Otherwise, my 40 and 10mm Glock-shot high impulse loads resize without issues passing my case gauges.

 

I have loaded for both .40 S&W and 10mm, used just the Lee 3 die set, no problems encountered!

 

Like others have said, They were either talking about the Lee bulge buster or the Redding G-RX. I have a bulge buster but have never used it. If brass on my fired loads has stretched to the shape of a smilie it toss it. If a smilied case is de bulged, reloaded hot, and the fatiged area re indexed over the non supported area - you have a potential probem. A bulge just above the case head is normal on Glock brass in .40/10. If it is just bulged, I run it through my Dillon sizer die and they feed no prob. I am against over working brass. Glock chambers are already large.
By using a smaller base die for a larger chamber the brass works itself to death quickly.
You won't have a problem using normal dies with the brass even using Dillon dies with large entry radius.

 

I have the G-RX and use it on every 10mm case. I have other 10mm pistols with tighter chambers than my G20. All brass goes in same bin.