M4A1 Upper Reciever - Geometry help/advice

Hi all,

 I'm currently creating an M4A1 and I've become stuck on a certain part of the upper receiver. The M4A1 upper receiver is basically a cylindrical piece of metal that merges seamlessly with other components around it. I'm not entirely sure if it's creating via welding then machining or molded from the get go - but the finished result is seamless.

I've searched the Polycount forums and can't find anything similar - I don't know if my keywords are off to prompt the right result. And I've also tried searching online. There's not much reference/tutorial for the upper receiver but there is plenty for the lower receiver which I didn't have any issues with.

Anyway, here's some pictures, I've sat and stared at it for hours and I've tried some different methods for terminating the geometry but I just can't seem to get it right. Apologies if the answer is staring me in the face!

The offending part of the reciever;


My version








I've only recently taken up modelling so go easy on me and as said prior, if the answer is staring me in the face I apologise in advance for wasting anybody's time. I'm pretty sure that the problem is with the area I've terminated the geometry below this part of the receiver as seen in the pictures. But this is the only way (I could manage) to stop the line running the length of the cylinder and distorting the curve/making a crease.

To add, I'm using maya 2018.

Best,
Griz