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7mmRUM & Retumbo

 
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  #1  
Old 02-05-2003, 08:14 PM
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Join Date: Mar 2002
Location: Southern Illinois
Posts: 397
7mmRUM & Retumbo

I was able to do a modified 'Audette ladder test' the other day with Retumbo in a 7mm Remington Ultra Mag. The powder itself is somewhat finer than many boomer powders, so it should meter fairly well. It did take 1 1/2 months to arrive on backorder, but that's life.

WEATHER:

Temperature: 62*F
Wind: 10-20 from 5:00 to shooter
Humidity: 98% with light rain
Sky: Overcast

RIFLE:

Action: Remington LA
Barrel: Kreiger 30" 1:9" twist heavy Palma taper, no muzzle brake
Stock: McMillain Prone w/3 way buttplate
Trigger: Jewell set @ 1 lb.
Scope: Nightforce 12-42x56mm,set on 40X
Bases: Champion's Choice 30MOA
Rings: Badger Ordnance 30mm

AMMUNITION:

Brass: Remington 300RUM necked down to 7mm & fireformed, prepped but unweighed
Primers: FC215Ms
Bullets: Cauterucio 176gr VLDs seated .005" into the lands

LOADS:

86.5 Starting load - fouler
87.0
87.5
88.0
88.5
89.0
89.5
90.0
90.5 Stiff recoil, primer cratered, minor stamping
91.0 Stiff recoil, primer flattened & badly cratered, heavy stamping & bolt lift - TIME TO QUIT & BACK DOWN!!!

All shooting was done at 200 yards. The total size of the group (excluding the fouler was 2.049." The three rounds at 87.0, 87.5, & 88.0 grouped at .570." The three from 89.0, 89.5, & 90.0 grouped at .984."

Recoil & muzzle blast was noticably heavier than max loads of 5010 that I'd used last year with good results. Obviously, the next phase of testing will involve groups at longer distances with powder charges of 87.5gr & 89.5gr, in addition to a chronograph to check velocity.

All in all, inconclusive, but promising... This rifle is primarlty used in conventional LR competition, but will occasionally be used in LR coyote & deer plinking. The 5010 pulldown standard goes out at 3,360 & ES & SDs in the low teens. Average 500 yards groups for it with 5010 were @ 3.25" last year. At $4/lb, the 5010 is tough to beat for that performance, as opposed to $18/lb for Retumbo.

Your thoughts & comments???
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  #2  
Old 02-05-2003, 08:51 PM
 
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Re: 7mmRUM & Retumbo

With that heavy a bullet, I would look hard at 50 bmg, if high velocity, throat and case life were important
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  #3  
Old 02-05-2003, 09:12 PM
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Join Date: Mar 2002
Location: Southern Illinois
Posts: 397
Re: 7mmRUM & Retumbo

S1,

I tried 50BMG last year, & unfortunately it did poorly. Some of my buds have had good luck with it in different species of RUMs, but this 7RUM hated it. There's not much 7mmRUM data out there for ANY powders.

Others I've tried are: RE22, RE25, WC860, MRP-2, IMR7828, & H1000. The 7828 wasn't bad, but only the 5010 did well enough to go the distance. I tried Caut 156s & 176s, JLK 180s, & Sierra 130s for kicks.

BTW, who does your danzac coating for you?
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  #4  
Old 02-05-2003, 09:46 PM
 
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Re: 7mmRUM & Retumbo

I do my own coating. Have you tried AA8700?
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  #5  
Old 02-05-2003, 09:53 PM
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Join Date: Mar 2002
Location: McNeal, AZ
Posts: 368
Re: 7mmRUM & Retumbo

Just curious, how does the 7 RUM differ from the 7 Rem. Mag.?

How many grains of water will the RUM case hold?
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  #6  
Old 02-06-2003, 01:06 AM
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Join Date: Dec 2002
Posts: 374
Re: 7mmRUM & Retumbo

My comment is...

I'm surprised that you find the retumbo to be a powder of choice in that gun. I'd say H4831, H414, N160, W760, IMR-4831 would be better choices. How in the devil are you getting that much powder in the case? I would have guessed that 65-70gr of say, 4831 would be full or compressed, is retumbo that much more dense?

Shoot the gun at night and see how much flame exits the muzzle. If it's a foot or more, I'd choose a faster powder and less of it.
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  #7  
Old 02-06-2003, 07:05 AM
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Join Date: Jun 2007
Location: Wilmington NC
Posts: 4,167
Re: 7mmRUM & Retumbo

Speedbump

200 yards is the absolute low end to try and do a ladder test. You can really tell the differences when you go to around 300-400. If you do it late in evening or early morning (no wind condition) it really makes the stringing and grouping definitive.

If you have the distance try it and see the difference.

Good Luck

BH
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