New Load Is Inconsistent

[Shooter Fred]

I recently loaded up a test batch for my 300 RUM...I shot 5 shots with 5 different loads...the best load was the hottest, which at the time only showed minor signs of pressure (a slightly flattened primer and ejector mark).

I reloaded the exact same load and went to the range this AM and I could not get the groups tight for the life of me...also the pressure seemed to be a bit higher as I had one case crack at the end the bullet goes in (1 out of 50 that I shot).

Just so you know, I calibrated my scale prior to measuring the loads and I was very cautious to make sure the exact amount of powder was in each case. I made sure to drop the powder the same way into each case as well. I seated every bullet to the exact ogive measurement of 2.970. Every primer was seated carefully and correctly.

The only thing that was different today is it was about 5-10 degrees warmer, more humid and a slight breeze (5-10mph). I was shooting at a range of 100 yards. My best group of 5 would be two almost touching then the other three around 2 or so inches away in multiple directions.

I was wondering if anyone has any suggestions on where to go from here...I obviously need to back off the powder a bit but I am not sure what to do at all. Any suggestions would be appreciated.

Just so you know, it was not me shooting poorly as i was able to get a few loads someone else made up for me to group well (they are target not hunting loads).

Thanks,
Fred

 

[MTBULLET]

what powder?
what amount?
what bullet?
what primer?
how rapid are you firing the groups?
is the bbl clean ?

 

[Shooter Fred]

what powder?
what amount?
what bullet?
what primer?
how rapid are you firing the groups?
is the bbl clean ?

Retumbo -- 99 grains
Federal Primer -- Gold Medal 215M
180 Grain Accubond -- weight sorted to +or- 0.2 grains (actual spread min to max was 179.8-180.1)

I started off firing once ever minute or so (even my first groups would not group well). Then I sped up and slowed down to see if the temp of the barrell made a difference. I even cooled the barrell down in between cleanings and the cool barrell still would not group well.

The rounds that someone made for me that were grouping well grouped just fine no matter if the barrell had 10 rounds or 1 round down it, or if it was hot or cold. Totally night and day. The powder that is in the target loads that grouped well is spherical powder...anyone have a clue what powder that could be?

Also, I started out with a clean barrell. I put two target rounds down it to then started my shooting of the test loads. I would clean it after about 10 rounds.

Thanks for any help you can offer!

 

[T3-OleMan]

'Nellie' taught me not to clean the barrel so much. Don't change anything but the cleaning. Just don't clean for 20 rounds......5 min between shots = cool barrel and you will know one valuable fact.....What SHE likes. {:>) All it will cost is time and one box! Then you will for ever know. Worked for me.

 

[Greyfox]

A valuble price of information is that your rifle grouped well with you friend's target load. What was your friends load, particularly, what bullet and what powder? I'd work from that basis. My experience when the groups are as you described, I would g try a change of bullet first. Barrel/bullet is generally the predominate accuracy factor.

 

[Shooter Fred]

A valuble price of information is that your rifle grouped well with you friend's target load. What was your friends load, particularly, what bullet and what powder? I'd work from that basis. My experience when the groups are as you described, I would g try a change of bullet first. Barrel/bullet is generally the predominate accuracy factor.

I paid someone to make up a load for me...so they are not going to tell me what the load recipe is as they want to make money and sell more loads to me

I did try to reverse engineer the load and weighed powder etc...it used a spherical powder but I have no clue what kind of powder that may be. The velocities of the target loads using this spherical powder were so **** tight...they shot 4 out of 5 at the same exact FPS and the 5th was only 5 FPS difference. Do you know what spherical powder may be used for a 300 RUM?

So you think try a different bullet?

 

[Shooter Fred]

Any other suggestions or know what spherical powder may have been used?

I really appreciate the help as I am really new to this...thank you!

 

[Greyfox]

It is possible the spherical powder could be Hybrid 100V. I have not used it, but have heard of shooters getting excellent results with it.

 

[backwoods83]

When you say spherical, I think ball powder, if that's what you mean it could be W760, Supreme 780, US869, H870, WC872, or old school H450 but not likely. With an ES that tight my guess is US869.

 

[RockZ]

For the RUM case I would think US869 would be a good choice

 

[MTBULLET]

have the best results in my 300 RUM's with H-1000

 

[Shooter Fred]

I was thinking possible US869 as well but I cant be sure (unless I try it...which may not be a bad idea).

Thanks for the help guys

One last question...do you think if the case lengths were not all the exact same it could have played a roll in the inconsistencies of my groups? This was once fired brass so I figured I didn't need to trim them at all but I got thinking that maybe some were a .001 or .002 difference...are these loads that sensitive?

 

[backwoods83]

You may wanna try US869, I thing hogdons has data for it on their page, should be insensitivve to temp as it was designed for the .50bmg. And I have never seen 1-2 thousands neck length make that much difference, if any at all.

 

[MTBULLET]

from my experience, us869 in the .300 RUM will put you more in the .300 win mag velocity category.