Sound like the infamous melting g36. But the receiver don't get so hot only the mount point for the barrel. You could still have a aluminum receiver combined with a steel/titanium insert around the barrel. Aluminum is also 8 times better heat conductor and could aid cooling as long as it don't melt.
First it didn’t melt. The polymer expanded under sustained heating. The degree of expansion was however overstated often used as an excuse for poor marksmanship. Second remarkably on point. The G36 wasn’t designed for long sustained fire much like M4 or other assault rifles (particularly carbines) are not. The heat build up is shorter. Pressure and vibration peaks are designed to be less. Repeated mag dumps will heat the barrel to heat treat.
Heat and pressure as well as vibration are the issues. MGs are subjected to much higher limits on all of them. The KAC LAMG and FN Evolys are not designed for long mounted sustained fire. They are designed for infantry mobility well offering belt advantages of longer bursts. This is why KAC Branded it as “Light
Assault Machine gun”. They were pushing a system oriented specifically to Infantry only (even more so SF predominantly ) in an assault role. This differs from FN Minimi or HK MG4 which as weapons are heavier and have a number of feature not found on the LAMG and Evolys like quick change barrels. Minimi, Negev and MG4 have those as they are intended for more than just infantry use but also mounted. So it’s a question of where you place the 201. Is it a LAMG or a LMG? proper? If the former okay Aluminum though I think Titanium would be better. It’s characteristics make it better all around. If the latter steel. The construction of the Minimi and Negev was the basis of comparison made in the quote I was commenting on I add in the MG4 as it’s very similar all three have iterations in both the 7.62x51mm and 5.56x45mm class. All three operate as infantry arms yet have a weight of between 7-8kg. All have quick change barrel mechanisms.
Put another way. FN Minimi (M249) & Maximi (M240), HK MG4 & MG5, Negev 5 & Negev 7, PKM, even the QJY88 are descendants of the M60, FN MAG 58 (M240), (MG3) MG42 and MG34. They are universal Machine gun builds. Okay as infantry weapons but designed for mounted and as such are heavier than they could be as they are meant to be operated in any number of ways demanding higher stress tolerance and there for heavier build.
FN Mk46 & Mk 48, Negev 5 SF & Negev 7 SF, M240L, PKP Pecheneg are an attempt at a hybrid. Striping the Universal to bare bones but with limited success. They have the higher stress of their base model but have been stripped as much as possible. They will have shorter lives and are no longer mountable.
FN EVOLYS, Utlimax, KAC LAMG & AMG, HK M27, HK21, QBB95, RPK, RPD, NGSW IAR variants these are the descendants of Browning Automatic rifles, Lewis guns and other Infantry oriented Machine guns. They make more concessions to weight trading off ruggedness for man portability and accuracy of firing by infantry.
So Where does the 201 sit? If you are saying it’s a M249 equivalent than it’s going to have to have some heft, a Steel or Titanium receiver set. If it’s a LAMG then you can go with aluminum or titanium.
(Did you notice I said Titanium on both sides? Because it’s a material that allows the best of both if you compensate for vibration it’s a very good material for a lighter Universal LMG. if you use it on a LAMG it’s got good heat characteristics. It’s just expensive and requires supply and the machinery to work it.)