Interesting COL findings
I played with the COL on an already good load for my custom 300 RUM today. I shot it early on with the COL of 3.600 to SAMMI spec. It shot real good, under an inch. I then adjusted the COL to as long as my box would hold, 3.650 and it shot maybe a little better. My chrony went kaput, so I do not know what the velocity differences were, but the point of impact were about the same. The few readings I got were about 3320 fps. I then tried 3.625 and my group sucked. So, I have two groups under the magic 1", not a bad dilemma eh? I think I will stick with the 3.650 since it seems to group better, at least in my mind. My die is set up that way now and I won't have to change anything. The picture is of the 3.650 load with 95.4g and 95.2g of retumbo. The other one is 3.625 with 95.2g Retumbo.
Nosler neck sized brass 2.840
Federal large rifle magnum match primers
3.650 COL or .138" off the lands
Reminigton action 300 RUM
Zeis 4.5x14 rapidZ 800 scope.
shot off a lead sled 100 yards.
I played around with other bullets and they did not do well. My gun does not like the 180g etip. I am under the nosler recommended start load by 2 grains and I still have a sticky bolt, so they are out. Too bad, because I like them a lot. My new gun seems to have a lot to say about bearing surface. The Barnes 168g TTSX is whizzing along at 3320fps without a care so I guess I have my load.
That's a bummer, mine does wonderful with the 180gr E-Tip. I took a young bull elk the Sunday after Thanksgiving with an E-Tip from the 300RUM.
Originally Posted by Daved
I started at 94.5 and went up in .07gr increments until I hit 98.0gr of Retumbo, no issues along the way. I picked a load that gave 3339fps as it perfectly matches the Boone and Crockett reticle holds for 300, 400 and 500 yards as tested. My COL was 3.636". Quite a jump but very accurate and it feeds from the magazine.
Make absolutely sure your bore is copper free prior to testing. Any fouling you may have can cause pressure issues in your testing. The E-Tips leave a clean bore in my RUM. After shooting 30 rounds in testing I had a clean bore only requiring a couple of wet patches with virtually no blue copper fouling.
I knew you would be the first to chime in on the 300 RUM and the Etip. Ya, my bore was pretty clean. It was spotless, I took my fouling shots and then tested. Who knows, maybe the load will work with a totally clean bore, but that is not practical.
The 3320 for the 168ttsx matches up with my rapidz reticle just barely. The 400, 500 and 600 yard marks in the scope equate to about 15 yards further for each distance, so the bullet will be a bit high. I don't think it will matter much. Of course that is on paper. I will see about real life 400+ yard shots when the snow clears. It is no fun checking targets while slogging through the snow. Prone is not as practical either. I can check real time 100 to 300 yards here at the range.
You think you had a jump. I had well under sub MOA with 3.600 or .188 off the lands with the ttsx. I adjusted the Etips around some and there was still pressure signs. I switched to remington cases and non match primers too. No go. I am afraid to see what happens if I put a really long bullet in there, like maybe the 200 TTSX or the LRX Barnes bullets. The 220 partition is quite long too.
I have been doing my own C.O.A.L test with a 30-06 that I have. I started at .015 off the lands and I have to dhit my last string that will be .030 off the lands. I will post it later this week. I found some pretty neat affects.