Compressed loads and accuracy

[whoami-72]

Hi reloading gang. Still asking complete rookie questions.

Setup: reloading .308 win with 150gr cx and 150gr ttsx bullets using norma brass and staball match.

Question 1: what do you guys consider a compressed load? I always thought it was based upon when the bullet would get pushed back by the powder and not seat at the correct depth without a little extra umph. However, tonight I was loading up 45.5,46.0, and 46.5gr increments under the cx bullet and looked into the case mouth and realized that the case is full and would compress under all of them. In previous loads I would've only counted the 46.5 because it's the only one I had to adjust seating depth for. None of the rattle if you shake them. I'm obviously now realizing that compression is variable and not a hard answer.

Question 2: I've always heard to load for full case capacity or slightly compressed to get a likely accuracy potential due to the powder burning more consistently. My question is, what happens to velocity and accuracy if you're way over compressed? Say like my earlier example where 45.5 is the beginning of compression but I loaded to 46.5. Does velocity/powder charge stay a roughly linear relationship? Does it go exponential? Does it plateau? How about accuracy?

 

[sdupontjr]

1) There isn't a consider in my compressed load for my CTR 308. 49.5 g of varget with a 155 scenar gets plenty of crunch, so much that it leaves a mark on the tip of my bullet from the seating stem. Very accurate, but when 8208xbr starting hitting the shelves, I swapped to it. Same accuracy, better SD/ES and not compressed. I have read where some put so much Varget where they just seat the bullet until it won't go anymore. So yeah, very compressed.

2) The only thing that I noticed was my groups opened up some. I have a T3 lite 308 and a CTR 308 and 2 Rem 700 308's the boy's use. Both of my Tikkas use a similar load. Velocity was pretty damn close, CTR is 20" barrel. at 49g of varget, both shot very well with same particular load. At 49.5, the Lite group opened up and when I mean opened up it went from about .5-.625 moa to about 1.5 moa. Very repeatable and it also showed svery slight pressure signs. The CTR however still shot the same accuracy, slightly more velocity than the 49g load with no pressure signs. I didn't go anymore because I decided to swap powders.

If your after velocity and worried or have questions about compressed loads, try TAC, 8202xbr and other powders. TAC was too temp sensitive for me. I'd rather slight slower velo's but more accuracy. But to each their own.

 

[wind gypsy]

I have loaded a bunch pretty heavily compressed that shot well. 223 77tmk Varget at AR mag length and 300 wsm h4831 and 200 ELDx @ 2.9" come to mind. The thing I hate most about it is that unless you're real anal about things, you get inconsistent resistance to seating from inconsistent compression case to case. You can get inconsistent seating depth and inconsistent rings from the seating stem on the bullets too. Generally loads work but it's just something that can be avoided by using a powder with lower case fill so thats what I try to do.

 

[whoami-72]

1) There isn't a consider in my compressed load for my CTR 308. 49.5 g of varget with a 155 scenar gets plenty of crunch, so much that it leaves a mark on the tip of my bullet from the seating stem. Very accurate, but when 8208xbr starting hitting the shelves, I swapped to it. Same accuracy, better SD/ES and not compressed. I have read where some put so much Varget where they just seat the bullet until it won't go anymore. So yeah, very compressed.

2) The only thing that I noticed was my groups opened up some. I have a T3 lite 308 and a CTR 308 and 2 Rem 700 308's the boy's use. Both of my Tikkas use a similar load. Velocity was pretty damn close, CTR is 20" barrel. at 49g of varget, both shot very well with same particular load. At 49.5, the Lite group opened up and when I mean opened up it went from about .5-.625 moa to about 1.5 moa. Very repeatable and it also showed svery slight pressure signs. The CTR however still shot the same accuracy, slightly more velocity than the 49g load with no pressure signs. I didn't go anymore because I decided to swap powders.

If your after velocity and worried or have questions about compressed loads, try TAC, 8202xbr and other powders. TAC was too temp sensitive for me. I'd rather slight slower velo's but more accuracy. But to each their own.

Gotcha, thanks for the info. I hope to never be at the point where I have a deformation on the bullet lol. I'm pushing pressure with the 46.5gr load so maybe I'll drop it back down. velocity was hovering around 2910 with 46.5 so I can definitely drop it and still have room to spare.

 

[whoami-72]

I have loaded a bunch pretty heavily compressed that shot well. 223 77tmk Varget at AR mag length and 300 wsm h4831 and 200 ELDx @ 2.9" come to mind. The thing I hate most about it is that unless you're real anal about things, you get inconsistent resistance to seating from inconsistent compression case to case. You can get inconsistent seating depth and inconsistent rings from the seating stem on the bullets too. Generally loads work but it's just something that can be avoided by using a powder with lower case fill so thats what I try to do.

Yeah, that's why I stopped at 46.5. The 45.5 charge weights were tracking with the micrometer and all bullets were within 2 thousands or less. When I went up in charge weights I noticed I was getting 6 thousands or more variance and the seating depth went from 2.810 to 2.815+. So, I had to really fenagle those. Definitely not worth it if I'll be doing a few hundred loads for hunting season.

 

[sdupontjr]

I have loaded a bunch pretty heavily compressed that shot well. 223 77tmk Varget at AR mag length and 300 wsm h4831 and 200 ELDx @ 2.9" come to mind. The thing I hate most about it is that unless you're real anal about things, you get inconsistent resistance to seating from inconsistent compression case to case. You can get inconsistent seating depth and inconsistent rings from the seating stem on the bullets too. Generally loads work but it's just something that can be avoided by using a powder with lower case fill so thats what I try to do.

exactly. That's why I swapped powders.