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Guesses on muzzle velocity, 300 RUM

 
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  #22  
Old 12-09-2009, 12:19 AM
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Re: Guesses on muzzle velocity, 300 RUM

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Originally Posted by Crop Damage View Post
I'm very, very new to reloading. I do not have a chronograph, I could probably use one if I called several people. I've got a hunting load that's working really well for me, and I'm not sure what kind of velocity I'm getting. Was hoping some more experienced people on here might have some better guesses at it than I do. Trying to make a rough ballistics card out to 700 yards.

Load is

300 RUM
190 Berger VLD Hunting Bullet
88.0 gr 7828
Rem Brass
CCI Magnum Primer

Rifle is Remington 700 APR w/ 26" barrel
Temps average 50 degrees
About ten feet above sea level, on the high ground.
I modeled that load in QuickLoad as well as I can with out knowing the COL at which you are seating the bullet. The COL has a noticable effect on both pressure and velocity. The model is not a replacement for a chronograph but it is a good place to go for an estimate if one doesn't have a chronograph. I use IMR7828 in my .243 with 95g Nosler BT bullets and the QuickLoad models are for that cartridge are within 2% on MV.

Results of modeling your load:

First, at least in QuickLoad, that looks like a pretty hot load. At 50F the calculated peak pressure is within 600 psi of max at 64,400 psi in a rifle that has a 65,000 psi maximum. The muzzle velocity is predicted to be 3,082 ft/sec.

At 70F the predicted pressure goes up to 66,790 psi and the MV goes to 3107 fps.

At 90F (not an uncommon summer temperature) the pressure goes up to 69,215 psi with a muzzle velocity of 3,131 fps.

I have two recommendations: First, definitely shoot that load through a chronograph and compare your measured MV with the predicted values in the manual for the bullets. If you are higher than the velocity predictions in the manual for your powder charge using the same length barrel, you might consider backing off on the powder charge.

Second, make darn sure your bullet is not touching or seated into the lands. That will increase the peak pressure another 6,000 to 7,000 psi.

Fitch
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  #23  
Old 12-09-2009, 12:54 PM
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Re: Guesses on muzzle velocity, 300 RUM

Thank you Fitch. Now I'm slightly concerned! My COAL is 3.70". I don't know what pressures the barrel can withstand, the rifle is the african plains rifle from the remington custom shop, and the barrel is 26" long, if that helps.

As far as I can tell the bullet is not touching the lands. I marked the bullet with black marker and ejected the cartridge without seeing any marks. There is probably a better way to check that though.

I have not got any load data from Berger, which is why I'm having to guess the figures for this load. Looks like the chronograph will tell me a lot, and I'm going to have to get a ballsitics program.

I definitely do not want to have the rifle blow up in my face later this summer. I can step it down some, but how are there people claiming to get 3400 + FPS from this bullet using different powders, when I'm maxed out at 3100? Longer barrels maybe? I think I saw those loads on another reloaders website. I don't really need any more speed or power out of this round, if I can get it to group well at 700 yards. Thats as far as I want or need to shoot, and more speed won't help me too much I don't think. Thank you for the good info, that's very helpful.

Last edited by Crop Damage; 12-09-2009 at 01:44 PM.
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  #24  
Old 12-09-2009, 01:42 PM
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Re: Guesses on muzzle velocity, 300 RUM

Quote:
Originally Posted by Crop Damage View Post
Thank you Fitch. Now I'm slightly concerned! My COAL is 3.70". I don't know what pressures the barrel can withstand, the rifle is the african plains rifle from the remington custom shop, and the barrel is 26" long, if that helps.

As far as I can tell the bullet is not touching the lands. I marked the bullet with black marker and ejected the cartridge without seeing any marks. There is probably a better way to check that though.

I have not got any load data from Berger, which is why I'm having to guess the figures for this load. Looks like the chronograph will tell me a lot, and I'm going to have to get a ballsitics program.

I definitely do not want to have the rifle blow up in my face later this summer. I can step it down some, but how are there people claiming to get 3400 + FPS from this bullet using different powders, when I'm maxed out at 3100? Longer barrels maybe? Thank you for the good info.
The load you have calculates as over pressure in 70F and warmer conditions, or if you let a cartridge soak in a hot chamber. But it would be good to get chronotraph data to see if my predicted velocities are correct. If the predicted velocities are correct, the predicted pressure probably isn't far off either.

The 3.7" COL is longer than I used and acts to reduce pressures significantly because it increases the initial chamber volume behind the bullet. The only data that would improve my prediction now is an accurate water grain capacity for your as-fired brass. The capacity I'm using now is 112.5g which is the QuickLoad default value for that cartridge.

The updated results I get with that COL and a 26" barrel:

90F 66,617 psi 3.101 fps
70F 64,294 psi 3,077 fps
50F 62,000 psi 3,051 fps

I have no explanation for anybody else's data. I only go by what I measure myself. I will say that there are a lot of folks on the internet that are getting higher muzzle velocities and smaller groups than I am.

Getting yourself a good chronograph, like a CED M2 will let you get your own data. If it were me, I'd definitly e-mail Berger as they suggest on this page

http://www.bergerbullets.com/Information/FAQ.html

and ask them about load data for the bullet in your cartridge (besure and give them the COL you are using) and get starting and max loads from them. \

The best powders, according to QuickLoad in descending order of maximum muzzle velocity (which says nothing about accuracy), are Vihtavouri N570, Hodgdon H870, Hodgdon Retumbo, Vihtavouri N560, Accurate MAGPRO, IMR7828 and IMR7828SSC.

I hesitate to recommend it with out knowing your background but the QuickLoad software, which my estimates above are based on, used correctly (it comes with an excellent manual), can be a huge assett when it comes to understanding internal ballistics (that which happens between the time the primer fires and the bullet leaves the muzzle). It comes with two excellent external ballistics programs as well. Like any other simulation modeling tool it's output is only as good as the input. I treat it's output like I do the load maps in reloading manuals which means I never start at a QuickLoad predicted max load. I start 10% low and work up while documenting the chronotraph readings, looking at primers, checking for sticky extraction, etc. This SW is one of the better investments I made in reloading equipment.

I have come up with a lot of good starting load and probable max load for a lot of cartridge bullet combinations using QuickLoad. I've selected cartridges, bullets, powders, barrel lengths and a number of other things based on combining QuickLoad studies, QuickTarget external ballistic results, data and equations in EXCEL from "Applied Ballistics for Long Range Shooting" by Bryan Litz. The result allows comparison of optimum game weights, point blank ranges on different game, for the various cartridges of interest.

However, if you aren't an analytical type (I'm a retired engineer) you may not find that approach to be your best approach to learning.

A few rainy/snowy days at the computer with some good coffee, pencil paper, and calculator, doing what-if studies on powders and experimenting with the effect of seating depth and bullet selection has given me the opportunity to learn and gain mor indepth understanding. I'm definitely not an expert, but I'm finally at the point of appreciating how much I don't know.

Fitch

Last edited by Fitch; 12-09-2009 at 02:04 PM.
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  #25  
Old 12-09-2009, 02:09 PM
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Re: Guesses on muzzle velocity, 300 RUM

"...I don't know what pressures the barrel can withstand, the rifle is the african plains rifle from the remington custom shop, and the barrel is 26" long, if that helps."

And you don't want to find out by pushing it too far!!

"...I can step it down some, but how are there people claiming to get 3400 + FPS from this bullet using different powders, when I'm maxed out at 3100? Longer barrels maybe?"

Every gun is different, usually pretty close, but still different and thus will shoot at different speeds. Because of this (in part) you can not depend on a chronograph to tell you when you are at max pressure. You need to examine your fired cases very carefully, if you use a hand primer seater like the Lee, you will notice less effort to seat the primers when loading a case that was shot with fairly high pressures. Don't forget that you will usually, not always, but usually find your most accurate load is not the fastest. Bullet placement is much more important than an extra 50 to 100 fps that you might get by pushing your gun to the limit. Also your brass will last much longer if you back it down some, and as you know, brass aint cheap.

Your cartridge started out life at what some would consider (me included) to be over-bore capacity, which tends to make them less inherently accurate and not as forgiving at close to max pressure (notice how accurate most .308 Win. Rifles are, same bore less capacity = more efficient). That doesn't mean it won't be accurate, some guy's are shooting really good with this round, but you should be very careful, because a round that is over-bore capacity may tend to spike pressures near max rather than climb up consistently and predictably.

You are ultimately the judge, but I vote for less pressure, more accuracy and longer brass life.

Good luck and keep us posted!
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  #26  
Old 12-09-2009, 06:04 PM
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Re: Guesses on muzzle velocity, 300 RUM

You guys are great. Thanks for all the info, I've learned a lot from this thread. I will contact berger for load advice, as recommended. I've been cleared by my "war dept" to get a chronograph, and I'm comparing exbal vs loadbase vs quickload.

Thanks for the warning about the chamber pressures, I had no idea that temperature could affect it that much. I'll have to come up with a summer load for this rifle. You're right about accuracy and lower pressures being better than higher velocity and a rifle bolt through your face. I think I'm now more aware of these issues than my buddy who is helping me with the reloading. He usually starts off at max and works down. Don't think I'll be doing that.
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  #27  
Old 12-10-2009, 07:05 AM
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Re: Guesses on muzzle velocity, 300 RUM

Quote:
Originally Posted by Crop Damage View Post
I think I'm now more aware of these issues than my buddy who is helping me with the reloading. He usually starts off at max and works down. Don't think I'll be doing that.
Right on.

+1 for what TyIdaho wrote.

The .300RUM is a very overbore cartridge. In addition to what TI wrote, be aware that overvore cartridges, especially severly overbore cartridges suffer from significantly reduced barrel life. The .300 RUM has an overbore index of ~1510 which places it significantly above even a .220Swift or a .22-250 (both at 1218) or a 7mmMag (1326). For more on overbore see

Defining “Overbore” Cartridges via Comparative Index AccurateShooter.com Bulletin

That link isn't anything "official" in terms of being a standard but it is quite useful. I experimented with it for a while and find it to be a rather useful predictor of barrel life. Barrel life is affected by more factors than the geometry however, bullet weight (powder burn rate), loading at less than maximum, and a number of other things have an effect. The .300RUM is a Big Game hunting rifle so it doesn't get shot as much as a varmint rifle, PD rifle, or target rifle. At a dozen rounds a year 1200 rounds of barrel life is good for a 100 years. But be advised there is some motivation to find your accurate load with out putting 300 rounds down range.

Keys to this are picking the bullet with care to match the game that will be hunted, and being systematic and organized about load development. The experience, skill and ability to do what-if analysis on the computer to narrow down choices will help with this. If you have a .223, it is a nice high barrel life rifle to use as a teaching aid for the load development process.

This isn't anything to worry about, but it is a factor to keep in mind. It says if you are efficient and manage to get to your desired hunting load in a hundred rounds or so you will have plenty of hunting barrel life "in the bank" so to speak.

Fitch
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