300 RUM Help Please

[Mr6.5]

I have a 300 RUM I built on a Savage 110 action awhile back. I have noticed that when I take it to the range the first two shots impact the same point 5 inches above the bullseye (where it was zeroed when the barrel was already warm), then there after all the other rounds punch the X center. The FIRST TWO rounds are 5 Inches higher than the others, I am assuming this is due to temperature increase in the barrel. This is a 100% deer rifle not a bench gun, ONLY the first COLD BORE SHOT matters to me. If my thinking is correct I should ZERO the gun cold on the first round, let it cool completely down and check zero. Right?

The thing that is confusing me is I have seen plenty of barrels throw shots after they get hot, but these barrels usually start throwing them all over the place, this rifle just changes impact point by 5 inches and shoots one hole from then on, no matter how warm it gets.

The barrel is not a large barrel, I think it is like .680 at the muzzle, just a nice SS X-Caliber hunting barrel, 27" long.
Using Retumbo Powder
Firing 180gr Maker T-Rex Bullet
Peterson Cases and Federal 9 1/2 Magnum primers
The barrel is free floated and glassed into a Bell and Carlson stock

I simply have no reference for this large fire breathing round, I wonder if anyone ese has experienced this? My 30 Nosler does not do this but it is a heavy barrel. Is it that this rifle is going to be good for two shots and then have to cool off? That is not a problem as it is a deer rifle, I only need one shot.

 

[Guy Miner]

Interesting. The only rifle I used that did such a thing badly needed proper bedding. It was a 308 Win with a varmint weight barrel in an injection molded stock.

That rifle would put the cold bore about 1.5" high, the second shot about an inch high, then cluster the rest in a tight group where it was zeroed... I put it in an HS Precision stock with the aluminum bedding block and made sure the barrel was truly free floated. Problem solved.

I don't know that you have a bedding problem. Just saying that the rifle I used needed a bedding fix to cure the issue.

Regards, Guy

 

[Mr6.5]

Interesting. The only rifle I used that did such a thing badly needed proper bedding. It was a 308 Win with a varmint weight barrel in an injection molded stock.

That rifle would put the cold bore about 1.5" high, the second shot about an inch high, then cluster the rest in a tight group where it was zeroed... I put it in an HS Precision stock with the aluminum bedding block and made sure the barrel was truly free floated. Problem solved.

I don't know that you have a bedding problem. Just saying that the rifle I used needed a bedding fix to cure the issue.

Regards, Guy

I took the rifle apart and noticed the action screws had loosened. I opened up the barrel channel to ensure a true free float with full expansion. I also glassed in the lug tightly with DevCon. I used Blue locktite and torqued the action screws to 50 Inch pounds. I also double checked all scope mounts. Hopefully this will improve the situation.

 

[Guy Miner]

I took the rifle apart and noticed the action screws had loosened. I opened up the barrel channel to ensure a true free float with full expansion. I also glassed in the lug tightly with DevCon. I used Blue locktite and torqued the action screws to 50 Inch pounds. I also double checked all scope mounts. Hopefully this will improve the situation.

I hope your rifle does a fine job! The 300 RUM is a serious cartridge.

Regards, Guy

 

[JD338]

I have a 338 RUM in a HS Precision Hunter stock. Cold bore and warm barrel shoot to the same POI.

JD338

 

[jjs405]

... the action screws had loosened... I used Blue locktite and torqued the action screws to 50 Inch pounds....

A trick I have done for decades is using a witness mark on my action screws to detect any movement. You can use a silver/gold sharpie or a paint pen. I started doing this after I had accuracy problems because of the screws loosening up without me noticing ... all it takes is a quick glance to verify that the marks line up & nothing has moved.

I only do this on my go-to hunting rifle & one more important rifle to make sure that nothing has changed ....

 

[Mr6.5]

I have a 338 RUM in a HS Precision Hunter stock. Cold bore and warm barrel shoot to the same POI.

JD338

That is good to know! Hopefully I can get to the range this week and see if the problem is resolved.

 

[RL338]

Were you starting out with a clean barrel each time by chance?

 

[Mr6.5]

Just an update, it ended being the muzzle brake causing the issue, so much for the high dollar brake! Pulled it off and issue went away.

 

[JD338]

Glad you got it figured out. I didn't realize you had a muzzle brake on it. Sometimes they work their way loose which will change the barrel harmonics.

JD338