I have several L5 mags that will not seat in my SCAR with 30rds loaded. Only one will seat with 29rds. That's with the bolt forward. Bolt locked back, they all seat fine.
All of my L5s are version black mod 1. The black followers replaced the green followers to allow them to work in Bushmasters. Catching and holding the bolt back. Other than that they will work fine in every other AR I have.
I loaded 28 rds and tried to seat them in the SCAR, no luck. I called Scott Vilardi (Small Arms Business Manager) and we discussed at length the issues I had with the SCAR. Scott sent me the black version mod 1s to cure the problems I was having with my BM patrol carbine. Scott said that some of the earlier black mod 1s got out and will not work in the SCAR. He sent me new mod 2 followers. In comparing the followers, mod 2 has a shorter spring leg. Mod 2 are mfg date stamped '09. The only one that I had that seated with 29 rds was also stamped '09 but a few months earlier. I replaced all the mod 1s with mod 2s and they will all seat fine with 30rds on a closed bolt. I also cut 1/16" off a mod 1 spring leg and was able to get it to seat with 30rds on closed bolt too.
That was fine and dandy until I racked the bolt back. Seems that the L5 rear mag body has extra material that will not let the bolt catch function.
Directions to modify an L5 to work in a SCAR
Problem: The opening in the rear of the magazine is too narrow impedeing the bolt catch.
Fix: Remove a small amount of material from one side of the opening
1. Empty the magazine
2. Remove the bottom and dissassemble
3. Remove the material from the left side of the opening, see the photo below (remove the area highlighted in yellow). You"ll need something like a dremel tool or coping saw.
4. Reassemble, check.
Works fine now.
Also, as a side note......the SCAR has an ambi mag release. On the left side, it pivots off of the flat latch. With Pmags, & Lancers, the depth of the mag catch cutout has an affect on that release.
Meaning that there is some "looseness" (flop) with the left mag release lever. Compare the fit with a HK mag or GI mag (D&H) and there is no looseness or flop. The depth of the HK mag mag catch is very small, but deep enough that there is no flop to the mag release lever.
Pmags seem to work with the bolt catch, but could be modified in the same way to insure functionality like the L5s.
I believe the Beta C mags can be also modified like the L5s to get them to work. (Just haven't got around to it yet)
I'll have to chat with Scott regarding this issue as he was surprised to hear that the military SCAR lower is different from the "commercial" SCAR lower.
ETA: Scott also said that the mod 2 followers also have a slightly shorter front section by 1mm, since all the new L5s now have a beefed up rubber baseplate from the inside. The SCAR L5 mags will have the modification that I posted and will no longer have the raised magwell ridge. Seems that it caused problems with the EGLM launcher. Hopefully, my SCAR demo mag will arrive soon for pics and shooting. Scott just sent quite a few of the SCAR L5 mags to Crane for testing.