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300 RUM and 230 Hybrid Twist Rate

 
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  #1  
Old 03-01-2013, 09:48 PM
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300 RUM and 230 Hybrid Twist Rate

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
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Old 03-01-2013, 10:42 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

Berger says a 10 twist will stabilize the 230, I have a 30 X 338 Lapua Imp. and it has an 8 twist, I am pushing the 230 out of it at 3340, they are not blowing up and accuracy is great.
I think you will be fine with a 9 twist.

Dave
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Old 03-02-2013, 12:27 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

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Originally Posted by dirtball View Post
Berger says a 10 twist will stabilize the 230, I have a 30 X 338 Lapua Imp. and it has an 8 twist, I am pushing the 230 out of it at 3340, they are not blowing up and accuracy is great.
I think you will be fine with a 9 twist.

Dave
Thanks Dave. 3,340, Wow! That's some ballistics there! Right in there with the .338 edge and Lapua using 300 grainers. I just want to make sure I'm not unnecessarily giving up velocity anywhere. With what my gunsmith and I are putting together he feels that I should get 3,200fps with the 230's when we're done. If more, that's a bonus. With the design I will not have to sacrifice any accuracy either.
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Old 03-02-2013, 06:46 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

3200 with a 230gr may be a little optimistic for the 300 Rum, I was getting about 3230 in my Lapua Imp with Retumbo, but gained 100 to 120 FPS in both my 30 and 338 Lapua Improved cartridges when I switched to RL33.
It would also be worth a try in the 300 RUM with that heavy bullet.

GOOD LUCK with the project.

Dave
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Old 03-02-2013, 07:04 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

Quote:
Originally Posted by dirtball View Post
3200 with a 230gr may be a little optimistic for the 300 Rum, I was getting about 3230 in my Lapua Imp with Retumbo, but gained 100 to 120 FPS in both my 30 and 338 Lapua Improved cartridges when I switched to RL33.
It would also be worth a try in the 300 RUM with that heavy bullet.

GOOD LUCK with the project.


Dave
Dave. With the long barrel, canted lands and unique chamber design I think 3200 is very do able, but we will see. I gotta stay with an extreme powder that will not fluctuate with temp. RL33 sounds great but if it's like the rest of Alliant's powders it can get crazy with big temp changes. I don't want to have to worry about POI changes at long distances because of temp changes.
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Old 03-03-2013, 04:53 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

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.
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  #7  
Old 03-03-2013, 06:52 PM
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Re: 300 RUM and 230 Hybrid Twist Rate

Well, I'll wade in on this since I'm using a 300 rum with the 225 hornady hpbt and both rl33 and rl50. I can get 3000 fps out of my factory 26" barreled 300 rum with 102 rl50 and the 225 hornady in rem 7rum(reformed)brass with a 215 lighting the fire. I've run out of case capacity though so I've been working with rl33 lately with the rum. It shoots well to 95 grains rl33 but I haven't chrono'd yet as it was windy when testing. AZ shooter has run a bit heavier charges with the berger; his results can be found on the rl33 thread.
If only I could find some I5010; I was running 3320 fps with 180's with I5010 several grains below top charge. It would haul well here too. If only I could get more 225's for my rum too; I'm under 100 left and everyone's out for the year.
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