Need advice on primers backing out Marlin 30TK

[strangwn]

I have primers backing out slightly with light loads in my “new to me” Marlin 30TK 30-30. I had full length sized some range pickup (once-fired?) Win HS brass and loaded with 110 gr RN jbullets and starter load of 31 gr 3031. Since then I have read here about dealing with this common issue.

So I went back to my supply of unsized Win range pickups and tried chambering about 20 of them in the Marlin. I was surprised that I was able to fully chamber all of them, although some required some slight extra pressure to fully return the lever. My plan now is to try neck sizing and loading some of these, but expect that I may have some chambering issues. I do want to be able to shoot light loads with the 110 gr jbullets, lightish loads with 150 gr jbullets, and loads with cast 311041 and similar, all without having the primer-backout issue. I can segregate brass for light-only use.
Can anyone help with some expert advice on all this?

[fouronesix]

Almost all guns/cartridges will do it with light loads and it's normal if it's not extreme. You are seeing the result of some headspace. For guns to function properly there needs to be some plus some gun designs have a little more lash in the lock-up as in many of the lever actions. You can back the FL sizer out a little- which allows the fire formed shoulder to "assist" the headspacing. That will help if you can still chamber the round smoothly enough. While the rimmed cartridge relies on the rim for primary headspacing- there is enough shoulder on the 30-30 to help the headspace control.

[Baron von Trollwhack]

Since the tried cases fit before sizing, and you know the case headspaces on the RIM, that's where the extra headspace originated and allowed the primers to back out a bit. Neck size only to get some better fitting cases after you shoot them by seating the bullets so there is a little tightness closing the lever fully, and thereafter as long as the cases fit, only size the neck partially.

One of the major concerns accuracy wise in 30-30 is that you trim to uniform length, in addition to a modest FCD crimp. Varget works very well with the 31141 at full velocity loads assuming your casting, loading, and case prep is uniform. No mixing cases for the best accuracy.

Bvt

[Wayne Smith]

All primers slide out and the recoil of the round re-seats them against the bolt. This is so reliable that one of John Garand's first auto rifle designs used this as an actuator. Then the military began crimping primers and he went to a gas design.

Your light loads simply do not have enough recoil energy to re-seat the primers. That is why many people will have special cases for light loads with an enlarged primer vent hole so that the primer won't come out.

[Scharfschuetze]

Proper head space precludes primers from backing out. Excess head space dimensions with loads that have a higher primer pocket pressure than powder chamber pressure (light or squib loads) will back the primers out by the pressure in the primer pocket pushing the case forward if it is unrestrained by the rim, shoulder, belt, lip or extractor. Higher pressure loads that back the case back over the primer for a flush fit against the bolt face are just obfuscating or hiding the fact that there is a little play in the rifle's HS tolerance or the cases's rim.

It's a common enough affliction. I have two turn of the century Marlin 1893s that both exhibit some slop in the HS, yet both have been shooting for something like 113 years without issues. Both have been in family since they were originally purchased three generations ago. Knowing that they have generous HS, I reload for them accordingly by neck sizing and as Wayne suggests above, enlarging the flash holes to reduce the primer pocket pressure to less than the powder chamber pressure when shooting plain base boolits in squib loads. For more powerful loads using the Lyman 311041 mould I just fire away and don't worry about it. Cases thus fired may very well have a shorter life span in a rifle with some HS slop as the cases after a few reloading cycles will thin near the web after obturating on firing and then stretching back to the bolt face and then getting full length sized back to original dimensions. Neck sizing ameliorates this to a large extent when using loads of adequate pressure.

My modern Marlins do not display any excess head space and primers will not back out no matter how light the charge or small the flash hole is. They were great rifles for the kids to learn on with light cast boolits over a few grains of Bullseye powder or for indoor gallery shooting. We fired many thousands of very light loads through them without a primer protruding due to their "to spec" head space.

[Geezer in NH]

Light load IMHO want to load that the primer pockets need to have the flashole opened. Make sure you mark that brass as light only by file in the head or somehow.

It is common for light loads to push prime out. They come out when fired but the load does not have enough power to reseat them.