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300 Mag 150 to 180 gr grouping issues

 
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  #1  
Old 03-06-2012, 05:33 PM
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Join Date: May 2011
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300 Mag 150 to 180 gr grouping issues

Okay here's the deal.

I am trying to develop a load for my fathers 300 win mag and I thought I would run this by you guys before I go outside and waste more time and ammo and blood pressure.

I have the gun shooting 150 gr ballistic tips under an inch. Africa being the destination and wildebeest x 2 on his list of animals, a harder hitting round is obviously needed.

So today I loaded up 180 gr Accubonds with 76 gr of 4831 and seated the bullet the same as factory Winchester round to get started. I shot a 5 round 4.8 inch grouping. I put 3 ballistic tip rounds in and shot under an inch group. According to Remington the gun has a 1:10 twist rate. It's a model 700 sps buckmaster edition. I got annoyed last year with the rifle and when I figured out 150 gr bt shot so well out of it, i settled for the lighter bullet on mulies. I can't get away with that now. Where the hell should I start. Whats the issue? My .308 is a 1:10 and I put the accubonds down it today in a 3/4 inch group on my first load attempt. So ya....
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Old 03-06-2012, 06:45 PM
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Location: Allen, TX
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Re: 300 Mag 150 to 180 gr grouping issues

Quote:
Originally Posted by twiedenh View Post
So today I loaded up 180 gr Accubonds with 76 gr of 4831 and seated the bullet the same as factory Winchester round to get started.
Perhaps you ommitted details... But, that's not load development. That's a shot in the dark.

A common method goes something like this...

Try seating the bullets .010" from the lands. Or, as long as you can while still able to feed cleanly from the magazine.

Then, load 3 rounds each in .5 gr increments from near min to book max load.

Allow the barrel to cool sufficently between shots and/or groups.

Verify that you're not flattening primers, marking the case head with the ejector, sticky bolt lift or other signs of excess pressure.

Choose the best group or two and load 5 rounds each to confirm that you repeat similar performance.

Then, stick with that powder charge and load 24 rounds with 3 rounds each varying seating depth by .005" step sizes. One or more of those groups should yield good results.

Confirm your final load with additional groups.

Chrony everything if possible and confirm actual trajectory/drops at various distances to confirm/compare against your ballistics software.

Happy hunting!
-- richard
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  #3  
Old 03-06-2012, 06:57 PM
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Join Date: Feb 2008
Posts: 446
Re: 300 Mag 150 to 180 gr grouping issues

Quote:
Originally Posted by twiedenh View Post
Okay here's the deal.

I am trying to develop a load for my fathers 300 win mag and I thought I would run this by you guys before I go outside and waste more time and ammo and blood pressure.

I have the gun shooting 150 gr ballistic tips under an inch. Africa being the destination and wildebeest x 2 on his list of animals, a harder hitting round is obviously needed.

So today I loaded up 180 gr Accubonds with 76 gr of 4831 and seated the bullet the same as factory Winchester round to get started. I shot a 5 round 4.8 inch grouping. I put 3 ballistic tip rounds in and shot under an inch group. According to Remington the gun has a 1:10 twist rate. It's a model 700 sps buckmaster edition. I got annoyed last year with the rifle and when I figured out 150 gr bt shot so well out of it, i settled for the lighter bullet on mulies. I can't get away with that now. Where the hell should I start. Whats the issue? My .308 is a 1:10 and I put the accubonds down it today in a 3/4 inch group on my first load attempt. So ya....
Trying just one powder weight is NOT the way to find accuracy. Load 3 rounds each starting 5% below the max listed charge weight and go up in either .5gr or 1gr increments and shoot for groups, once you have an accurate powder weight, adjust seating depth in .005"-.010" increments back from .010" off the lands, or maximum magazine length. I would load 5 rounds .3gr above/below the most accurate powder weight, then find the most accurate node, only change seating depth once you have found the most accurate load. Rule of thumb: Only change one thing at a time and compare results.
This has always worked for me to get me 'in the ballpark'.

In my own 300WM, I get the best accuracy with RE25 and 200gr AB's, but also run 180gr AB's with the same powder. I run 81gr with 180gr AB's in Rem brass and a COAL of 3.390". (WARNING! This COAL may NOT work in your rifle.)

How far off the lands are you with that 180gr pill?

What is the COAL of that round?

Factory ammo COAL's do not always gel with handloads, you need to know how far off the lands you are and adjust seating depth to 'tune' the load.

The twist rate is not the problem.

If you give me the above info needed, I can help get you started with your load development.

Cheers.
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  #4  
Old 03-06-2012, 07:14 PM
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Re: 300 Mag 150 to 180 gr grouping issues

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  #5  
Old 03-06-2012, 07:24 PM
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Join Date: May 2011
Posts: 45
Re: 300 Mag 150 to 180 gr grouping issues

I'll get the exact load information on here tomorrow, I don't have it with me. I develop loads by going over the powder spectrum on the higher end(hunting load) till I find the most accurate charge and then play with the seating depth. I have never run into issues like this with any other rifle. I can bounce all over the spectrum of seating depths and powder charges with the 150's and get something respectable for a hunting rifle. As soon as I shoot 180's with it, it's all over.
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Old 03-06-2012, 07:24 PM
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Join Date: May 2010
Location: Central Ohio
Posts: 253
Re: 300 Mag 150 to 180 gr grouping issues

My advice: (I load for 3 300wm)
Stick with seating at 3.34, manufacturer standard oal. This rifle is going on a hunting trip and you will probably want ammo to fit in magazine.
Try RL-22, I think the 4831 is too slow burning for the 180gr bullet.
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  #7  
Old 03-06-2012, 07:32 PM
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Join Date: May 2011
Posts: 45
Re: 300 Mag 150 to 180 gr grouping issues

I'll try some rl-22. I originally bought rl-22 for his rifle but the 4831 worked better with the 150 bt.
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