Explain to me how you open up the boltface and make it a push feed?
The 6,5x55 case is larger in diameter than the 8x57 the M38 was made to feed. Chances are, the mag box is too narrow or the feed rails need attending to. Could be that the extractor is too tight as well since the rim is also larger. So as you can see, it could be any number of things or a combination of things.
z1r is right on ! As usual
Good morning to you sir, I hope that this Labor Day Weekend had been good to you so far and you're well.
In my experience, the suggestions offered by z1r and greydog are spot on. I'll note that I do know greydog both through chatting on the phone and from his reputation as a very fine gunsmith.
Off the top of my head, issues with feeding with 98 actions were what they suggested as well as sometimes the shape of the magazine follower.
While it wasn't a Mauser, a Ruger 77 Liberty Model tanger in .338 refused to feed reliably for me. When a wonderfully crusty gunsmith in Tonasket described his usual fix to me for what he called, "those jammers", it worked most of the time, but not 100%. Later on I had it rebarreled to .308 Norma which is nearly an identical case shape as far as the degree of body taper and the same as when it was a .338 Win Mag, it didn't always feed.
Fast forward a few years and I was tearing my little remaining hair out trying to get a 98 barreled to .22-250AI 40° to feed reliably and it resisted my best efforts.
I had on the bench, about 5 followers from different rifles and at least that many magazine springs. As I was playing with the .22-250AI anyways, I also pulled out that 77 and began swapping parts to see what I could learn.
Strange as it might seem to relate, a follower out of a 96 Swede with a modified brand new Ruger magazine spring made the Ruger 77 feed perfectly! Weird as it might seem too, along with fooling with the feed rails a wee bit at a time, the magnum follower out of the Ruger 77 along with a fairly fresh surplus Mauser mag spring worked in the .22-250AI.
As z1r says, it's mostly a combination of things.
Lastly Pappy 348 asked about Swede rims - that is if they had thicker rims. In the Swede brass that we've played with, "usually" the European stuff is slightly larger in diameter - usually. They seem to have the same thickness as say '06 or .270 brass though. It'll depend upon a few things though I'm guessing. My usual walking around rifle made from a Mauser roll marked action fed .30-06 brass from many sources, then about that many varieties of .270 brass with that barrel and when I had a 6.5x55 barrel put on it fed even better than the previous two.
Another sample of one bolt face and how it gets along with the extractor, which is a commercial FN one that lightly polished before installing it when I first made the '06.
Hopefully that's useful to someone out there.
All the best to you and everyone this Labor Day Long Weekend.