Your M48 is probably not feeding correctly. That is usually due to rough surfaces on the underside of the magazine feed lips (which are actually part of the receiver) and the feed ramp itself. One particular portion to have a close look at is the transition from the mag feed lips to the feed ramp, at the front edge of the feed lips. On every M48 series rifle I've seen, this area (on both sides) is usually not smooth. These areas should be smooth.... as should the feed ramp.
Do understand that most M48s won't feed round-nose bullets, or will barely do so. So, the rounder and blunter the profile of the bullet, the less likely it will feed well. These rifles were set up for heavy, long, spitzer FMJ's.
The solution is to smooth and re-profile the feed lip/ feed ramp transition and the feed ramp itself. I did this to my M48, years ago, specifically to get it to feed the short little Hornady 170 grain round-nose bullets. Well, I succeeded. Mine will feed almost any round-nose shape just fine now. It has a bit more trouble with flat-nose bullets, but will feed those if I seat them deeply enough.
It isn't really that difficult, if you understand the mechanics of how the rifle feeds....and make a study of the exact geometry of your rifle. I simply made a careful study of this, by test feeding (very slowly) regular FMJ rounds and the round-nose loads I wanted to use. Once I figured out exactly what was needed, it was a simple matter with a Dremel tool and several fine stones. After re-profiling, I polished the areas I'd worked over to a glossy surface.
However, if one is NOT patient, mechanically inclined and knowledgeable about guns..... I would NOT recommend trying this. It is exacting work and requires skill. This is NOT something I can teach someone to do over the internet. (I tried several times, in the past....and it never worked out well.) Pictures won't help, if you don't understand it already (so I won't post any - don't ask). I am simply saying that overcoming this problem IS quite possible, not even very complicated. But, it falls into the realm of "custom gunsmithing".....and I believe, should be left to those with such skills.
So, what is the solution (for the OP) ? Find a good gunsmith, who is willing to tackle this project. That won't be cheap. Or, take up hand loading for your M48. Then, you will be able to load whatever bullets work in your rifle - and play with seating depths to be sure they work.
