Originally Posted by Long Time Long Ranger
Nesika, I am trying to understand what you are saying. I have a degree in applied math along with the engineering so I don't mind you throwing the boring math at me to help me understand more. Are you saying the loads I quoted are not suppose to be shooting 1/2" to 1" groups at the 300 yard target like they do so well. Do you have your 30-338 lapua twisted with a 1-14 or 16 to shoot the 125 accurately at over 4300. You said it also shot the heavy bullets well so it must be a 1-10 or so. Talk to me and tell me what you are doing. I am here to learn like everybody else so let me know what you are saying. Those loads I mentioned will rarely miss a prarie dog at 500 yards if the wind is right so I am trying to figure out this brick wall you are talking about. Evidently I haven't hit it yet pushing 3600 fps with the 107's and 4300 with the 55's in the same twist barrel. I know my 30-378 blew up the 125 BT when I took it over 4300 with a 1-10 twist so I understand there is a brick wall there. I guess a guy just works up the top load for his rifle and sticks with it. Some shoot and some don't. Your big 30 shoots it but mine didn't. I was just wondering if you had a 1-14 twist for the light bullets. Why does the 55 BT shoot at 4300 fps with a 1-9 twist and the 125BT blew up at 4300 with a 1-10? My engineering tells me it is probably the larger diameter of the soft, heavy lead in relation to the jacket giving all that heavy lead more momentum to outspin the jacket. But I don't know.
I have a 1-12 in my 300-338. It's 34" long and I use somewhere between 95-105 grains of powder. I have fiddled with RL22 and some others but RL25 seems to work best. (I'm not in front of my computer at home and I don't have my load data here and I have not shot this rifle since May of 2006) I use a GM215 Federal Primer and my cases are Lapua. With the extremely heavy loads I have to resort to my "vibromatic drop tube" method of hand loading.
vibrate the case as I dump powder down a 29" long drop tube made from an old Easton arrow shaft that screws into my reloading press. (trick set up) Then you "stand" on the press to get the bullet in there. I swear I can almost see the cases swell.
The chrono work was done in the test tunnel at COR BON ammunition. Pete Pi Jr. is a personal friend and when I worked for Nesika we leased their tunnel for our accuracy testing and load development. I believe they have a Oehler brand chrono. Tests were done on several different occassions over the span of a couple weeks. Mainly because I was having a very difficult time accepting the velocity being that fast. It always checked in that range though so I have to assume it's accurate.
With a thin jacketed (J-4) bullet in 6mm the "brick wall" (for me and for quite a few others) has been right about 3300-3400. This is in a 1-8 barrel. Obviously there are probably bullets out there that will tolerate more. The Barnes stuff would be a good candidate since they are made from one solid piece of material.
Yes, slowing the twist and cranking up the velocity will allow you to go a bit further, but as I've mentioned in other posts/threads this can be dicey and potentially harmful.
If your getting 3600 out of 107's DON'T CHANGE A THING!! It's workin and that's awesome.
In no way should anything I said be taken as a personal crack towards anyone or anything. It's just my experiences after doing this (building guns) for close to a decade.
Hope this helped.