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300 RUM and 230 Hybrid Twist Rate

 
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  #8  
Old 03-03-2013, 08:40 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

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Originally Posted by Fiftydriver View Post
Remember that you are comparing the RUM case to the Lapua case. Two different animals. I have many wildcats developed on both. THe standard RUM case and the standard Lapua case are nearly identical in case capacity, within 1 grain either way most of the time.

When loaded to identical chamber pressures, they will make nearly identical velocity.

The improved version of the Lapua will give you 10-12% case volume increase but that does not translate into 10-12% velocity increase, in fact its more like 2-3% increase in velocity.

The main advantage that the Lapua wildcat has is dramatically stronger case strength. If you load the RUM up to a point where you will start to loosen primer pockets in 4-5 firings per case, you will likely be in the 3100 fps range with the 300 RUM and the 230 gr bullet weight even in a 31" barrel. May be a bit more then this but if your looking for legit 3200 fps, I suspect your going to really cut your brass life.

The Lapua parent case however will take 70,000 psi of chamber pressure and not complain one bit so right there you will get a significant boost in performance over the RUM.

In all my testing, which compares the 7mm RUM vs my 7mm Allen Magnum, 300 RUM vs my 300 Allen Xpress, the 338 Edge vs my 338 Allen Xpress and the 375 RUM vs my 375 Allen Xpress. In every case, when using heavy for caliber bullets, the improved version of the Lapua case will add 150 fps on top of what the RUM case will produce.

I would be a bit suspect of the claims of nearly 3350 fps with the 230 gr in a 30-338 Lapua Improved. Must be a very fast barrel. Out of a 1-8 twist, that throws some red flags up. In a 30", 1-8 twist barrel, my 300 Allen Xpress will drive a 230 gr to just shy of 3300 fps and it will drive a 240 gr SMK to 3225 fps using Retumbo. I have not tested RL-33, mainly because its nowhere to be found.

Now, that said, all of my loads were loaded to a pressure level that NEVER loosened a primer pocket even after 10 firings. In my load development, I did push things over 3300 fps easily but chamber pressures were to the point where primer pockets were loosening after 3-4 firings on the Lapua parent case.

If your loosening a primer pocket on a 338 Lapua case, your pushing chamber pressures over 70K psi. I would not recommend that.

As far as the twist rate you should use for the 230 gr . I would say use what Berger recommends. A commercial bullet maker is going error on the conservative side for recommended twist rate. Remember that this bullet could be used in anything from a 30-06 up so they are going to recommend what has been proven by them to work on the less rounds as its clear that the faster magnums will need slightly less velocity to maintain stability.

I work with Berger alot on new bullets. They send me prototypes and ask me to try to destroy them with velocity out of my Allen Xpress and Allen Magnum chamberings. I was sent the 230 gr Hybrid when it was new and I tested it out of my 300 AX and pushed it to 3400 fps with proof loads (far higher then what should ever be used) and out of a 1-8 twist barrel at that. Accuracy was better at around 3300 fps but there were no bullet failures of any kind.

I also tested them in a 1-10 twist 300 AX with a 27" barrel length and performance and accuracy was great so I would think that in the slightly slower 300 RUM, you will see no issues.

They have proven themselves to me in twist rates from 1-8 to 1-10 and at velocities from 3000 to 3400 fps so in all reality, I do not think it will matter at all if you go with a 1-9 or 1-10 twist barrels.

Just stay realistic with your velocity goals. Personally, I would not expect to see much over 3100 fps with this bullet weight on average out of a 31" barreled RUM. Not saying you can not get more, just saying you will give up brass life by doing so.
Thanks for chiming in Kirby. I am having a reamer made with a very long but match diameter throat. With this and the long, canted rifling barrel my gunsmith feels that I should be in the 3200fps neighborhood. He has built many Rums with set up for the 230's as well. If it turns out it will do 3100-3150 that's just fine. I am not out to destroy brass and certainly not going to throw away any accuracy for top velocity. My main concern was just whether one would encounter a velocity decrease in a 9 twist compared to a 10 twist. From what I'm hearing it doesn't really sound like it.
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Old 03-03-2013, 08:48 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

Tumbleweed, are you going to neck down the bertram 338 edge brass?? If so, kinda ironic. thats what i am considering doing.
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Old 03-03-2013, 09:18 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

I would be a bit suspect of the claims of nearly 3350 fps with the 230 gr in a 30-338 Lapua Improved. Must be a very fast barrel. Out of a 1-8 twist, that throws some red flags up. In a 30", 1-8 twist barrel, my 300 Allen Xpress will drive a 230 gr to just shy of 3300 fps and it will drive a 240 gr SMK to 3225 fps using Retumbo. I have not tested RL-33, mainly because its nowhere to be found.

Kirby
A year ago I would have said exactly the same thing, in fact I was getting slightly less velocity that you with Retumbo, probably not pushing them as hard.
I had read all of the hype about RL33, so I decided to give it a try, Two Ohler 35's cant be wrong, Easy bolt lift and no ejector marks.
I think you will be pleasantly surprised when you get a chance to try some.
It should be a great powder in a lot of your cartridges.
What I have read is that it is made by a different company than the other Alliant powders, all I can tell you is that I found it less temperature sensitive and a whole lot cleaner than RL 25.

Dave
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Old 03-03-2013, 11:08 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

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Originally Posted by barnesuser28 View Post
Tumbleweed, are you going to neck down the bertram 338 edge brass?? If so, kinda ironic. thats what i am considering doing.
Had not thought about it until now but that's a possiblity
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Old 03-05-2013, 02:13 AM
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Re: 300 RUM and 230 Hybrid Twist Rate

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Originally Posted by Tumbleweed View Post
Hi guys, could use some of your experience on the question of rifling twist rate for an upcoming build that I am preparing for. It is a 300 RUM using only the 230 Hybrid Targets and a 31" Broughten 5C heavy palma barrel. Tim North of Broughten recommended I go with a 9 twist for better stability out to extreme distances. I will use this out to a mile possibly. Also, I am at sea level and the highest altitude at which I would need to use the rifle in hunting situations would be about 3,000 feet. I understand that a 10 twist should stabilize the 230's fine and I know that a little much twist shouldn't hurt anything. My main concern is will "too much" twist cause me to lose velocity? I designed a unique chamber for this and with the long barrel I am trying to set this up for maximum velocity. Thanks
A 10 twist should be fine. That's what Berger recommends and bullet makers are usually conservative. Putting the numbers in Bergers twist calc. length 1.602: conservative vel, 3100 fps, 0 elevation... the calculated SF is 1.59

Target Bullets | Berger Bullets

If you have a question, Berger would be the best ones to ask.

I'm having a Broughton 5C with 10 twist chambered in 300 RUM as I type this. I plan on shooting the 230's through it along with some other bullets.
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Old 03-05-2013, 07:06 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

I have a rum with 26 inch barrel.. 92 grains of h1000 getting around 2900 for velocities. Shoots very well also so ima stick with that. Retumbo had pressure at 91.5 grains so I quit trying it.. The 230 bullets r awesome and even 2900fps will kill and elk well past 1000 yards!!!
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