Ejector mark on 3oo RUM need advice


Nov 24, 2011
I have a new Christensen Arms 300 RUM. Every once in a while I get a shot with a ejector mark. Primer never flattens. I am shooting new nosler brass. Federal primers. 95 grains of retumbo. nosler 180 accubond. Im not resizing brass at all. Im shooting between 3220 and 3265 fps. I shot 9 shots today and the very first one came out at 3222 fps and showed a good impression of a ejector mark. The rest were fine. I checked over all length on ever shell before I took to range. I double weighed all my powder. They were all the same. The bullet is .024 off the lands. This is brand new brass from nosler. I was having same problem with there old brass and they sent me new brass. Im at the low end with retumbo. My velocity's are not extreme. Why am I having this problem. HELP!
You said you are at the low end of Retumbo is that what you mean by the starting load ? the reason I ask is because I load Retumbo at 85.5 grains in my .300 Rum and if I remeber correctly thats my starting load and something like 91 grains was the upper end of the load data that I started with. I can say this for sure tho , I started reading off the net about how everyone was pushing retumbo in the 91 to 94 grains . When I tried to load my rifle with New Nosler brass at these charges I would have ejecter marks and sometimes stiff bolt lift. I was told when I asked a similar question as you have that this would happen as the nosler custom brass is softer than the Remington brass . In short I started using the remington brass again and havent had a problem this far but i am not loading on the HOT side either.

Just an ideah to think on:)
The 3200-3250 fps range for a 300 rum is rather mild but normal. I've seen over 3300 with a 180 and book loads with mine. I'd give the bullet a bit more run to the lands and your pressure symptoms will probably go away. I'm getting 1/2 moa at .15" to .2" run to the rifling. If not, switch to remmy brass like the other poster. It's what I use, but I've seen Nos. do well too.
Did you have any oil in the barrel for that first shot? That can really boost the pressure in a 300 RUM. Make sure that you clean all oil out before firing.
I run a light coat of oil after I clean. I moved it further away from lands when it happened first time. Didn't seem to help.
You are still close to the lands. This big of round needs .2" or so to smooth out the initial pressure spike; it's not a 308 where you can bury the bullet in the lands and get away with it. Get much more overbore and you'll need to be nearly 1/2" off the lands to smooth out the pressures(257 roy or 7 rum).
I would try a few rem rum cases if you can to see if it goes away too.
Light oil shouldn't be an issue; I have always used a light oil or hoppes and then run 1 dry patch afterwards leaving some in. I've Never had an issue.
I'm with everyone else on distance to the lands bein the culprit. Are you loading out of an 8 pound can of powder or a bunch of different 1lber's that could be from different lots??? Lot numbers on your powder is the only other thing I would look at if its not all from the same can.
I'm using same powder. I'm confused now with the distance to the lands. My Nosler reloading manual says to set bullet off of lands between .015 and .03 inches. I'm at .024. Does this not apply to a 300 RUM.
Folks shooting 30 caliber magnums in competition with max safe (normal) loads with bullets seated out to touch the lands have been getting excellent accuracy since the 1950's. I've no idea what the internal ballistics are with bullets so seated, but pressure's fine and accuracy has equaled what the long range benchresters get these days.

Ejector hole marks in case heads typically indicate pressure's too high. Cartridge brass starts to extrude into holes in the bolt face at about 65,000 to 70,000 CUP (80,000 to 89,000 PSI). Bore obstructions, tight bore and groove diameters for the bullet or the wrong powder type or charge weight are common causes. Regardless of the cause, it you see ejector hole marks on the case head, something's causing it. We all get to choose our own safety margins to shoot in.

It's best to remove anything you put in the bore after cleaning it before you shoot it.

There was an article in the American Rifleman many years ago on the pressure difference between bullet seating about 1/10th inch off the lands compared to touching them. It was only about 2,000 to 3,000 CUP difference in the .30-06 cartridge they used. Here's an example:


Note the two far right bars indicate the bullet was seated .001" and .021" long and was set back that far when chambered. And no pressure difference between bullets seated .019" off the lands and .001" long to push back that far.

Shame on those who put two different pressure measuring systems' charts together. The top one with bars is acutally CUP numbers and the bottom one with the curve is PSI. But they do show pretty well that pressure goes up a bit when a given load's bullet touches the lands when its fired.
If you really want to run just a few thousandths off the rifling, go for it. But don't expect to not have to drop a grain or three to run safely if you are getting ejector marks at current charges. I do run my 300 win .010" off the lands with one load, but it fits the mag even being a browning, and the load has been shot hundreds of times in all temps. without a hint of over-pressure. My 300 rum gets treated differently, partly because it's throated long enough that I'd be single loading, partly because it uses slower powder and a lot of it with some very tough bullets that like a run to the lands.
welcome to the "non-stock' .300 rum, each and every custom/semi-custom is different. load for YOUR rifle and forget all the "do this/try this/mine only likes" BS.
some of mine will shoot 180's, some 168's, i don't shoot over 180's, cause i have bigger rifles if i need more range/kill'em power, and i wont tell you what the loads are, cause your's will NOT be the same.
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