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Success! First time out on the range and my semi auto M53 runs great! (once i figured out that i loaded the belts backwards lol)
The only issue is every once in a while itll crank off a couple extra on its own. It might be the fire control or someone said it might be because im not using milsurp ammo and commercial primers are too soft.

Its still not finished.... gotta finish welding the front receiver bushing, lots of cosmetics, and tightening up the stock to receiver fit.
I'll get up a few pics and vids when I can. Thanks to those who helped with advise!

Sounds like a good start that is going to need some fine tuning. Keep up the good work. Post a few pics as you can. I have a few ideas about the extra few bangs here and there. Tell us more about the bolt and fire control group.

Later 42rocker

The fire control is a BRP semi auto grip stick. I had to trim the hammer and disconnector slightly. The bolt and carrier i modified using using BRP and Robert MFG parts. Using a one piece firing pin and drilled out the wedge.

The firing pin seemed to protrude from the bolt face slightly so im wondering if i need to knock a few thousandths off somewhere. The whole conversion was easy and smooth. I did not use their roller bearing / pin assembly. I drilled and re used the original stud that controls all the belt feeding gizmos. I destroyed too many carbide mills and reamers trying to enlarge the hole in the carrier.

Hits on the primer are dead center and solid

I have some pics and a vid on my IG page @ajsarms but ill get more up on here

The firing pin should not protrude from the bolt face when the firing pin is fully rearward. If it does, that's a good place to start for fixing things. Excess protrusion causes blown primers, so you need to check the protrusion. Protrusion should be between 1.35 and 1.65 mm.

https://youtu.be/6wcvgSkyBtE

Going for the 3rd test fire this AM. Ive already been given advice on how to load and make ready easier lol. learning learning.
I had only fired 3 rounds before this video. I have done more work since this video. Hopefully I solved the issue. Ill know shortly!

Yes, That is a bit of bacon. Call it a pre range snack

Youtube link doesn't work.

https://www.youtube.com/watch?v=6wcvgSkyBtE

huh.... try this.

SO....I tried filing the firing pin down a few thousandths and it still runs away even with barely visible primer strikes (commercial PPU ammo)
A buddy gave me some milsurp stuff (corrosive) with hard primers that im going to try with a new firing pin.

Though it was a little better with the shorter firing pin.... got through about 15 rounds before it ran away with 3 or 4.
I really think the BRP firing pin spring is just a little weak. I may even try a small spacer behind it to act as sort of a pre-load.

We shall see

(i am shocked at how little it takes to set off the primers in the PPU ammo. Im thinking that might be a big issue)