question re O.A.C.length & how much off the rifling

[roberto mervicini]

Hi, I reload a rem .300 ultra mag. (New rifle out of the box)

-brass once fired ( in my own rifle ) RP neck size trim to lenght.
-bullet Sierra 180 grain spitzer BT #2160
-rem primer 9 1/2 M
-Retumbo 102grain
COAL 3,574"
First Results at 200 yrds poor with rem factory load and my reload also... group 3 to 3.5 " .

I tooke one empty brass and set in the bullet half way and use the cam of the bolt to seat on the rifling, COAL 3.700".

My question: How much a bullet should be off the rifling, without increasing the pressure or how much should I decrease the powder load to compensate

Got available H1000 powder, Fed 215 and WW mag primers, Nosler 180 Partition and Hornady SST and Interbond bullets 180 gr. as well, if some one experience a good results with this components and care to share I will be thankfull.

Also if some one has a Sierra new edition reloading manual I would like to know data from mid to max for the 180and 200 grain tip in combination with H1000 and Retumbo powder.
Thanks
_______
roberto

 

[Unclenick]

Unfortunately there is no correct answer to your question as the result varies chamber to chamber, bullet-to-bullet. You find some that shoot most accurately with the bullet touching the lands and the load about 10% below what you expect when seated to a normal length. There are those that want the bullet much further back. Berger has examples of as much as 0.165" off the lands being best with some of their VLD bullets.

Most people talk about running bullets about 0.015"-0.030" off the lands, but it's not a magic number range, either, just a common one. It's also not uncommon to find more than one good seating depth. One near the lands and another with the bullet bearing surface around one caliber into the case mouth.

A basic method is to take a starting load (10% below your normal maximum) and try the bullets touching the lands. Pressure should still be safe with a starting load 10% below maximum. Shoot a group (I shoot at least 6 and more often 9 or 10 because I don't trust 3 to be meaningful, but suit yourself; overlay two or three groups of 3 if you prefer). Then back out and try just 0.010" off the lands with the same load. Then, following Berger's approach, back up in 0.030" steps to 0.060", 0.090", 0.120", 0.150", 0.0180" (about where you are now, or keep going deeper if you want to), firing groups each time. See if you get anything noticeably tighter in that range. If you do, you can try going in 0.010" steps either side of that tighter spot to learn where the middle of the best seating depth range is. Once you have that seating depth established in your gun, then tune the powder charge up to tighten the group further. Dan Newberry's method is good for that.

 

[roberto mervicini]

Thanks Unclenick, I will follow the procedure till found the sweet spot.... I was hoping for a kwik fix, and try to avoiding all the multiple loads even if I know kwik fix do not exist ....!

 

[243winxb]

For a hunting rifle you want to stay .010" off the rifling. This way you know the rounds will always chamber. When you measure the COL from case head to bullet meplat/nose, you dont take into consideration the difference in ogive between bullet lots. A tool that measure COL on the ogive may be more accurate.

 

[Unclenick]

Am I correct that you meant "at least" 0.010 inches off the lands for hunting? I agree you don't want throat contact for that, though some magazines may need rounds even shorter for rapid follow-up shots to go smoothly.

 

[243winxb]

Yes, the COL must fit the magazine.

 

[Jim243]

I can't tell you what will work in your rifle, but for me I use the Hornady LNL guage and measure the bullet in the chamber for MAX OAL and back off that by 0.050 for the jump to lands. I adjust the powder accourdingly to the OAL I will be using. This works for me 99.995 % of the time. HOWEVER I am using Savages and they seem to really like it. It may or may not work in your Remington. And I am not sure Hornady makes a case for the 300 ultra mag to use with the gauge?


Good Luck
Jim

This is how it works in a Savage 270.