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338-300 RUM (Edge) vs 338 RUM, the Real Story??

 
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Old 06-11-2011, 12:01 AM
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338-300 RUM (Edge) vs 338 RUM, the Real Story??

I have searched several times and can't quite find the info I am looking for.

I just finished measuring case capacities between the 338 RUM and the 338-300 RUM. I am deciding which one I'm going to use, and the RUM cases are as large as I want to use for an M-70 action.

I started by using my 33 caliber Sinclair expander mandrel on both a new 300 RUM case and a new 338 RUM case. The OD of the necks measured the same after I expanded them. I then primed each with an intact spent primer. I didn't do any trimming or sizing.

The 338 RUM will hold 106.1 grains of H-1000 and 109 grains of water. The 338-300 RUM will hold 110.4 grains of H-1000 and 113.9 grains of water. I measured the powder charges five times each being as consistent as possible in everything I did. I measured the case of water three times each, also being as consistent as I could.

The 300-338 will hold 4.3 grains more of H-1000 and 5 grains more water. Five grains more water is a 4.4% increase in capacity, which should yeild a 1.1% increase in velocity. Given the 300 grain SMKs typically chrono around 2800 fps, that would give the 338-300 a 31 fps velocity advantage. However, many guys claim a 100-150 fps increase. At least that is what I have found from all the searches I have done, though I have seen no actual chrono results for a 28-30" barreled 338 RUM with a 300 grain SMK.

To get a 100 fps increase in velocity at around 2800 fps we need a 14% increase in capacity. Given I already know a 338-300 RUM holds 114 grains of water, that would mean the 338 RUM's capcity would have to be 100 grains. I suppose if we are comparing a 3.6" COL 338 RUM to a 4" COL 338-300 we might get there, but if both chamberings are long throated a similar amount there just isn't enough case capacity to get a 100 fps plus advatange to the 338-300 RUM.

For the 338-300 RUM (Edge), I have seen Shawn Carlock's velocities of 2800-2950 fps, with the standard load being 2800-2830 fps, from a 30" barrel. Like I just mentioned, I haven't seen RUM data for the 300 grain SMK from a 28-30" barrel

What does the 338 RUM with a 300 SMK in a 28-30" barrel usually chrono?

Is the comparison as I suspect--3.6 COL 338 RUM vs a 4.0 COL 338-300, are the Edge guys just loading hot, or is there something else going on?

Thanks.

Last edited by afp1; 06-11-2011 at 02:48 AM.
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Old 06-11-2011, 09:40 AM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

I have both.
A .338RUM at COAL of 3.700" and a .338 Edge at COAL of 3.970"
The RUM is loaded from the mag but the Edge is single loaded and long throated.
I found that the accuracy node of the Edge with 300gn SMK was back at 2840 fps so I don't use it at its full velocity potential anyway. I can get over 2900 fps.

Not much difference between them. Maybe 50 yards practical difference in range? I wouldn't like to be hit by either of them!
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Old 06-12-2011, 12:23 PM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

locally i find 300 RUM brass on shelves and NO 338 RUM. I had to choose an EDGE just for brass avalibility. I didn't mind it being 50fps faster it was the ease of reloading for me personally.

I push the 300gr smk to 2770-2780fps 90gr H1000. I don't seem to see pressure signs yet with H1000 at 90grs. Im happy about that. No need to push it faster for me.
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Old 06-12-2011, 01:44 PM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

Do and advance search and search for Long Time Long Range, he's covered this topic at length and detail based on building a bunch of each and shooting them.

I'm building the 338 RUM's for the reasons he sets out, just an easier road to go down IMO for equal performance.
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Old 06-12-2011, 02:12 PM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

So, it appears that if the tubes for both rounds are throated in such a way that a 250-300 gr. bullet is seated to mag length in a Mod. 700 rifle, the vel. diff. is less than 100fps, is that what I am hearing?
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Old 06-12-2011, 09:44 PM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

Quote:
Originally Posted by Nomosendero View Post
So, it appears that if the tubes for both rounds are throated in such a way that a 250-300 gr. bullet is seated to mag length in a Mod. 700 rifle, the vel. diff. is less than 100fps, is that what I am hearing?
That is what I suspect. 100 fps needs a 14% increase in case capacity, and even though I have since learned the Edge is a slighly blown out 300-338, there is no way we can get to a 14% difference in case capacity when both are throated the same. Even if we can find an 8% increase in case capacity, as many have mentioned with the Edge, we only get a 56 fps increase. I think the other 6 grains in case capacity come from most Edges being seated long and most RUMs being seated at 3.6 to 3.7"

I have decided to go with the 338-300 RUM. Not because I think there is any real performance difference, but it is exceedingly simple to run 300 RUM brass though my Sinclair 338 expander mandrel. I'd have to do that with 338 RUM cases before I could neck turn them anyway. 300 RUM brass is easy to find, and the die mod is simple. Take a FL Type-S Redding sizer, ream it out, and run the appropriate sized bushing.
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Old 06-12-2011, 10:01 PM
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Re: 338-300 RUM (Edge) vs 338 RUM, the Real Story??

Quote:
Originally Posted by bigngreen View Post
Do and advance search and search for Long Time Long Range, he's covered this topic at length and detail based on building a bunch of each and shooting them.

I'm building the 338 RUM's for the reasons he sets out, just an easier road to go down IMO for equal performance.
Thanks. When I did a search and included "Long Time Long Ranger" I found what I was looking for. Looks like the 338-300 is worth 50-75 fps over the RUM, which makes sense.
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