Separate names with a comma.
Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bjlooper, Mar 10, 2008.
I think A carry weight 270 RUM will be my next project, Any advice on barrel length and twist ?
Twist and bbl length depend on what you want to do with it.
Very fast twist for very long range bullets for big game. 30" bbl would maybe be a schoche bit too long for that cartridge. Be careful with powder bridging. The RUM shoulder may reduce the probability of powder bridging but I'd start out w/ball powders just to be save.
I think that a better choice, if you wish to stick w/the standard RUM case, it the 7mm RUM. No bridging problems. Good selection of heavier bullets, including WC 200s. Twist would be something like 1-7 as w/the 270.
Just a thought......
What is the dffrence in the 270 AM and the 270 RUM?
The AM is improved.
How much additional capacity and velocity do yo get with the AM. What barrel length do you recomend.
150 gr Ballistic tips or Accubonds > 3500 FPS. (I stopped at 3500)
169.5 gr Wildcat RBBT bullet (.7+ BC) 3200 FPS (Again I stopped at 3200)
195 gr Wildcat RBBT - BC out of sight high - >3000 FPS
I had powder bridging problems with stick powders w/the 150s. I wouldn't even attempt a stick powder w/the heavier bullets.
I use US-869 exclusively. 101 gr for the 150s. 95.6gr for the 169 and 93 for the 195s. If considering a 270 AM check w/Kirby regarding interior barrel design.
If I were doing the 270 again I'd go with the 277 AM. Its based on the 338 Lapua case. Much, much better brass. Nosler is not nearly as good as Remington in my experience in the 270 AM cartridge.
What is "powder bridging"?
I have reloaded for years, but I have only loaded for regular everyday cartiages. I'm not really into the teckno stuff so I don't read much more than what powder and how much is max....gun)
Here's the brief nontechnical version, as I understand it. The powder charge in the case is ignited from the base. Thus unburned powder it sent into the neck of the case as the bullet exits.
When there is too much powder for the small bore get out of the case quickly pressure skyrockets until there is sufficient volume for the powder to begin flowing.
It's just like pouring 60 grains of 4350 in a powder funnel made for the 17 REM. Except without an ignited primer behind it. It just isn't going to go through that little hole in a reasonable fashion.
After 30+ years I never experienced it either. But I blew some primers and described what was going on to Kirby who diagnosed it as powder bridging.
ball powders flow smother thus no bridging.
I've been working on a frontal ignition where the powder is ignited at the base of the bullet. Its a lot of work but bridging isn't a problem and recoil is reduced due to not sending that weight of powder down the bore.