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Poll: Better off using a 300 RUM or 7mm 180 bergers at 3000 fps
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Better off using a 300 RUM or 7mm 180 bergers at 3000 fps

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300 RUM or 7mm with 180 bergers at 3000 fps

 
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  #134  
Old 01-29-2013, 08:03 PM
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

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Originally Posted by Jordan Smith View Post
Just so you know, QL is showing 99.5gr of Retumbo at 3122fps in a 26" barrel with the RUM and 210gr VLD. It is saying that the load produces an estimated 80k psi. I've also seen guys that push over 3200fps with a 160gr bullet in the 7RM, and 3100fps with the 180. I don't think I'm brave enough to push that hard. The problem with traditional pressure signs, is that they often don't show up until well over 70k psi of chamber pressure, if using strong brass and hard primer cups. A strain gauge would be a useful tool to tell how much pressure you're actually running to get that 210 to 3130fps, just for your own safety, if nothing else.

I don't mean to preach, but I thought I'd at least mention it. We may not know each other, but I'd hate for your hide to get peppered by shrapnel from the barrel or action. The load may not have any negative side effects right now, but metal fatigue is a cumulative process, and enough 80k psi loads will eventually weaken the action (assuming that's what you're running- only a strain gauge or other pressure testing equipment will tell the true story).

BTW, your signature is awesome and very true.
I appreciate the heads up. Here are 3 of my loads with Retumbo, all without any visible pressure signs.

180 E-Tip, 98 gr, 3400 +
200 AB, 94 gr, 3200
210 Berger, 93 gr 3130

Not sure why QL is showing 99.5 gr for 3122, but I was nowhere near that charge and never expected to get near it with the 210's. I did a lot of research in both online manuals and threads in this and other forums before working up these loads. I had a good idea of the start and max range and the expected velocities. If you search the threads for 300 RUM load data, you'll find my charges and velocities are similar to a lot of others.
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  #135  
Old 01-29-2013, 08:42 PM
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Join Date: Mar 2012
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

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Originally Posted by MontanaRifleman View Post
I appreciate the heads up. Here are 3 of my loads with Retumbo, all without any visible pressure signs.

180 E-Tip, 98 gr, 3400 +
200 AB, 94 gr, 3200
210 Berger, 93 gr 3130

Not sure why QL is showing 99.5 gr for 3122, but I was nowhere near that charge and never expected to get near it with the 210's. I did a lot of research in both online manuals and threads in this and other forums before working up these loads. I had a good idea of the start and max range and the expected velocities. If you search the threads for 300 RUM load data, you'll find my charges and velocities are similar to a lot of others.
Yeah, there are lots of variables that QL factors in, and I just did the default values for most of them, not knowing your actual numbers. That could be part of the reason why there is so much disparity between the two numbers. Assuming an OAL of 3.598", usable case capacity of 99.8gr, and a 26" barrel, it's saying that 93gr of Retumbo should be around 63k psi and 2940fps. Lot to lot variation in the powder also plays a part here, and it's saying that a lot that is 10% faster than average would produce 3041fps.

This is also assuming a SAAMI chamber and throat, which you may not have, and your land and groove diameters could vary from what QL assumes, as well. Lots of factors involved, but it serves to give a ballpark. Strain gauge data would be very interesting to compare to what QL is saying.
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  #136  
Old 02-24-2013, 10:42 AM
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Join Date: Dec 2006
Location: New Mexico
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

Just got my 7mm mag rifle from Travis at Rbros and it's at 3050fps with the 180 Berger VLD's, 27" barrel and Retumbo. The rifle shoots this load under a 1/2"

Chronoed 12' from the muzzle
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  #137  
Old 02-25-2013, 12:30 PM
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

RBROS is who I went with also for my 7 mag build. I'm the OP and Im not regretting my decision to go with a 7mag vs the 300 RUM. I went with a 26" rock creek barrel and Im getting 3060 (verified drops out 1100 yards)with 71.5 grains of retumbo using the 180 berger vlds. I am using norma brass vs the winchester he normally recommends. The norma is great but the problem with it is the brass neck nickness is a little more so I have to neck turn all my brass. I love my RBROS 7 rem mag. I've shoot groups down to .308 CTC. It shoot every load I tested to pretty much 1/2" groups, he builds a great rifle.
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  #138  
Old 02-25-2013, 05:44 PM
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Location: New Mexico
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

I agree, my Rbros 7 mag rifle is shooting the 180 VLD's under 1/2" at 3056 fps. It's a very accurate rifle, just like my Rbros 7 WSM. These rifle are tac drivers! I can't wait to take a game animal with it.
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  #139  
Old 02-25-2013, 09:54 PM
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

The 7mmRM/Retumbo combo seems to like running in the 3060 range with adequate bbl length and the right chamber. That's where my rebarreled Rem 700 runs too. I've also gotten great accuracy from 69 grains of H1000 running up to 3000 fps.
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  #140  
Old 02-26-2013, 02:27 AM
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Re: 300 RUM or 7mm with 180 bergers at 3000 fps

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Originally Posted by pyroducksx3 View Post
RBROS is who I went with also for my 7 mag build. I'm the OP and Im not regretting my decision to go with a 7mag vs the 300 RUM. I went with a 26" rock creek barrel and Im getting 3060 (verified drops out 1100 yards)with 71.5 grains of retumbo using the 180 berger vlds. I am using norma brass vs the winchester he normally recommends. The norma is great but the problem with it is the brass neck nickness is a little more so I have to neck turn all my brass. I love my RBROS 7 rem mag. I've shoot groups down to .308 CTC. It shoot every load I tested to pretty much 1/2" groups, he builds a great rifle.
I hunted with a 7 RM many years and killed a lot of critters with it. It's a fine cartridge. That said it is no where near a 300 RUM. I've shot both. Your 7 mag can push 180's with a G7 BC of .345 @ 3060 fps and a 300 RUM can push 215's with a G7 BC of .356 @ 3100 fps. The RUM is pushing a heavier bullet with a higher BC at a greater velocity. In other words, it is leaving the 7mm bullet behind in all categories. Flatness, TOF, Windage, and Energy. Not a slam on the 7mm, just putting things in perspective.
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