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300rum, 200gr, 3200fps how???

 
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  #8  
Old 10-18-2011, 01:11 AM
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Re: 300rum, 200gr, 3200fps how???

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Originally Posted by dodgefreak8 View Post
Im kinda thinkin it's due to lower pressures from not trying to force that pressure through a 7mm hole. but I'm not sure.
that's not bad choice, I have to say.
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Old 10-18-2011, 11:40 AM
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Re: 300rum, 200gr, 3200fps how???

First off, 3200 fps with a 200 gr Accubond is certainly a practical load in a 300 RUM with at least a 26" barrel length. I have build dozens of these rifles using Lilja barrels which are not known to be fast barrels and most of them easily reach this level of velocity with that bullet weight.

Now to the WHY its possible.

Well, there are two schools of thought. One is the larger surface area on the bottom of the bullet allows more pressure to be applied to the base of the bullet which results in more velocity. There may be something to that but I generally fall into the second school of throught.

In my opinion, its all based on sectional density and bullet baring surface to the bore. If you take the same case capacity and two different caliber rifles, in this case 7mm and 30 cal and shoot bullets with the same sectional density, you will come up with nearly identical velocity results in most cases all else being equal. If you look at bullets in 30 cal and 7mm with the same sectional density, the 160 gr 7mm and 200 gr 30 caliber are very similiar. As such, you will get similiar results.

In my testing of the 7mm RUM with the 160 gr Accubond, in 26" barrel lengths it can easily be pushed to 3200 fps and often slightly faster. In fact I would say on average, from the rifles I have built and tested, 3250 fps is about right for the 7mm RUM with the 160 gr Accubond so it will get you a bit more velocity then the 300 RUM with the 200 gr Accubond but the 30 cal has a slight edge in Ballistic coefficent so its pretty much a wash in the end.

Barrel life is in the favor of the 30 cal but not dramatically. The 30 cal can be a bit less effected by enviornmental conditions simply because it has a higher expansion ratio compared to the 7mm.

Both can be made to work extremely well, both are extremely accurate in a good rifle. For heavier game at long range I would opt for the 30 cal personally but either will do very well.
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Old 10-18-2011, 02:09 PM
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Re: 300rum, 200gr, 3200fps how???

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Originally Posted by Fiftydriver View Post
First off, 3200 fps with a 200 gr Accubond is certainly a practical load in a 300 RUM with at least a 26" barrel length. I have build dozens of these rifles using Lilja barrels which are not known to be fast barrels and most of them easily reach this level of velocity with that bullet weight.

Now to the WHY its possible.

Well, there are two schools of thought. One is the larger surface area on the bottom of the bullet allows more pressure to be applied to the base of the bullet which results in more velocity. There may be something to that but I generally fall into the second school of throught.

In my opinion, its all based on sectional density and bullet baring surface to the bore. If you take the same case capacity and two different caliber rifles, in this case 7mm and 30 cal and shoot bullets with the same sectional density, you will come up with nearly identical velocity results in most cases all else being equal. If you look at bullets in 30 cal and 7mm with the same sectional density, the 160 gr 7mm and 200 gr 30 caliber are very similiar. As such, you will get similiar results.

In my testing of the 7mm RUM with the 160 gr Accubond, in 26" barrel lengths it can easily be pushed to 3200 fps and often slightly faster. In fact I would say on average, from the rifles I have built and tested, 3250 fps is about right for the 7mm RUM with the 160 gr Accubond so it will get you a bit more velocity then the 300 RUM with the 200 gr Accubond but the 30 cal has a slight edge in Ballistic coefficent so its pretty much a wash in the end.

Barrel life is in the favor of the 30 cal but not dramatically. The 30 cal can be a bit less effected by enviornmental conditions simply because it has a higher expansion ratio compared to the 7mm.

Both can be made to work extremely well, both are extremely accurate in a good rifle. For heavier game at long range I would opt for the 30 cal personally but either will do very well.
Thanks Fiftydriver,

Thanks for the great explination! So if my calculations are correct the 300 is the better caliber for one reason. At 1000 yards the 7rum has 955lb/ft of energy and the 300rum is still pushing 1381lb/ft. Since I am wanting to use this for elk, that to me sells the 300rum over the 7mm. Not to mention the fall is less by about 14 inches. I think I am sold on the 300rum!
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Old 10-18-2011, 03:03 PM
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Re: 300rum, 200gr, 3200fps how???

I was in the same boat as you with what cal to build. I went with the 300RUM I took in on a trade then sent off for work. i'm glad I did. I'm getting 3175FPS with a 210gr berger with 94gr of retumbo. This was the first load I tested. I also tested some 230gr bergers that did well also @ 2950. These load are really mild for this riflebut work really well . Here is the spec's to it.

The Optics Talk Forums - 300RUM upgrade - Page 1
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Old 10-18-2011, 03:27 PM
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Re: 300rum, 200gr, 3200fps how???

Comparing the 160 gr AB in the 7mm RUM to the 300 RUM with 200 gr AB will give the 30 cal an advantage in kenetic energy and also bullet frontal area. This means that it starts larger in diameter and it will expand to a larger diameter while retaining a good bullet shank length meaning that as it penetrates to roughly the same depth as the 7mm 160 gr, it will displace more vital tissue then the smaller caliber bullet. Just a simple fact. So, if your hunting larger game, certainly the larger caliber will effect more vital tissue then any smaller caliber bullet of same design, sectional density and at similiar impact velocity.

Now, lets look at a different bullet, if you look at the 180 gr Berger VLD, you get a dramatic boost in BC even over the 200 gr Accubond in 30 cal. The 7mm RUM will drive the 180 to 3100-3150 fps pretty easily. In a long barreled custom rifle, the 7mm RUM will get you up to 3200 fps. Throw that in with a BC in the .680 range, it really narrows the performance gap. Velocity is similiar, BC in favor of the 7mm and sectional density now in favor of the 7mm. So it makes the comparision much harder to pick a true winner.

The 30 cal still has the larger frontal area in its corner but all other areas are much closer when you use the best bullets in the 7mm family.
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  #13  
Old 10-18-2011, 03:45 PM
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Re: 300rum, 200gr, 3200fps how???

Great point! I entered that into my calculator and The 300rum accubond combo still has a slight advantage in energy until a little over 1000yrds. It does give up about 100fps in velocity to the 7rum with the 180gr bergers. Now to play devils advocate I put bigdaddy0381's 210gr berger load in the calculator and it ups the 180gr berger/7rum combo again. It gains about 50fps over the 300rum but the 300rum gains 200lb/ft over the 7rum. I really don't see an advantage to the 7rum worth considering UNLESS you are shooting beyond 1000yrds.
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Old 10-18-2011, 04:55 PM
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Re: 300rum, 200gr, 3200fps how???

Quote:
Originally Posted by BigDaddy0381 View Post
I was in the same boat as you with what cal to build. I went with the 300RUM I took in on a trade then sent off for work. i'm glad I did. I'm getting 3175FPS with a 210gr berger with 94gr of retumbo. This was the first load I tested. I also tested some 230gr bergers that did well also @ 2950. These load are really mild for this riflebut work really well . Here is the spec's to it.

The Optics Talk Forums - 300RUM upgrade - Page 1
This is what I'm talking about. Now this guy has a barrel 3" longer (Kirby--maybe you can give us a good estimate of extra fps per inch with the 300RUM and the 210 Berger between 26" and 29") than mine at 29", but my Retumbo load is 94.5g and chrono says about 3020fps MV, but using Litz's velocity banded G1 data and shooting on paper/steel out to 1k yds, Exbal gives me a trajectory validated MV of 2993 fps. I'd sure like to get well over 3100fps MV with a 210 Berger, but it's just not going to happen with my combination of components for whatever reason. I could probably up this load by .5 or so, but it's quite accurate as it is when I do my part.
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