I have worked with 6.8 cats for years and on anything larger than about .30 caliber, feeding can sometimes be iffy, especially when you get more than about 10 rounds in the magazine.  The front side ribs in the magazine tend to throw things a little off.  Some mags work OK, such as the PRI, and some need tweaking and some just won't work, period.  I have been having a hell of a time on two wildcats of mine based on the 6.8 case, one .33 caliber and one .37 caliber.  They just don't want to stack well in any 6.8 mag due to those side ribs.  A couple of weeks ago I noticed the .400 Legend was only slightly larger than the 6.8 case and since the .400 L is straight walled, the front side ribs are absent, or very minimal.  I bought a 10 R mag and it feeds the .30 HRT, .338 Spectre, my two cats, and I imagine any 6.8 based wildcat flawlessly.  If you have similar cats based on 6.8, and maybe 6.5 G cases, and you want a magazine you don't have to do any mods to to make it work, try the Duramag .400 Legend magazine.  Of course, cats based on the 6.8 that are smaller in caliber than the 6.8, normal 6.8 mags work just fine.  I have no trouble at all with PRI 6.8 mags for my .22, .24, and .26 caliber cats, and usually the .30 cals don't give me any trouble either.

A letter to Duramag also revealed that if you trim the follower, you can get one or two extra rounds in the magazine.  I have not tried that yet.  But there two down sides.  Duramag said that sales have been very slow on magazines for the .400 L and plans for higher capacity magazines has been shelved for now.   The other, COAL is shorter than with the PRI mags, 2.270 IIRC verses 2.300 for the PRI mags, but that's no hill for a climber.

I know it's a pipe dream, but if all of us wildcatters with our special rounds based on the 6.8, and possibly the 6.5 G case (I have not tried any 6.5 based rounds in the mag) then maybe if there is enough interest Duramag will put their plans for higher capacity .400 L mags back in the schedule.  Maybe?

Did the 338 Spectre have issues? I thought they worked well in the high cap 6.8 mags.

For the most part 6.8 mags work just fine with the .338 Spectre, and if your 6.8 mags are not giving you any trouble I see no reason to switch.  On my .338 Spectre, I did have to do some adjusting of feed lips VERY SLIGHTLY on PRI 30R mags but they were OK on PRI 20 R mags.  I mainly got the .400 L mag because of the two .338 and .375 cats.  My .338 cat is quite a bit longer in the body than the .338 Spectre so that was what caused issues with the front side ribs.  The only mag I had found before the .400 L mag to let me load and feed 10 rounds (state limit for private land hunting cartridges) was the CProducts (old company) 6.5 Grendel magazine, and it balked once in a while.  The .400 L mags feed it and the .375 as slick as a puppy's nose.