Heavy (long) bullets in 308 size cases - question

[mdesign]

Assuming your magazine and throat lengths allow. Is there any velocity benefit to seating the bullet further out of the case to create more powder capacity or is it usually a wash in the end because the amount of powder capacity gained is small or pressure signs do not allow you increase powder amount?

Have ran 162 gr in my 7-08 for a long time but they use up a lot of capacity. Was just interested if there was much to be gained by doing what is needed so that I could seat the bullets out of the case further and free up some case capacity.

 

[HousePlant]

Go until you run the bullet into the lands or it isn't really held in securely... whatever ends up being accurate. Typically a lot of space in a 308 magazine for longer tips IME.

 

[Rockdoc173]

I always start at 0.010" off the lands after locating those lands with my Hornady OAL tool. With the Hybrid/ATip-type bullets I rarely have need to go elsewhere since they're more forgiving than VLD/tangent-types. If you run the bullet further out of the case, you have more powder capacity which may increase your velocity. However, if you run them out so far that you contact the lands or (as with many benchrest guys) actually seat them into the lands, you may see pressure spikes that are undesirable- especially if you're already at the top end of pressure with a big charge. As stated, I think starting at 10-off is a happy medium in target chambers. If we're talking factory guns with long throats, well, that's different because 10-off will often put you well outside of the magazine constraints. In this case it depends on the bullet as to where you end up in jump length. For VLDs, Berger has a good article on their website about seating depth for those specific bullets.

 

[918v]

Assuming your magazine and throat lengths allow. Is there any velocity benefit to seating the bullet further out of the case to create more powder capacity or is it usually a wash in the end because the amount of powder capacity gained is small or pressure signs do not allow you increase powder amount?

Have ran 162 gr in my 7-08 for a long time but they use up a lot of capacity. Was just interested if there was much to be gained by doing what is needed so that I could seat the bullets out of the case further and free up some case capacity.

It really depends on the specific powder. Also consider feeding geometry. What powder are you using? I’ve read Staball can produce great velocities with your combo.

 

[6MT]

I always start at 0.010" off the lands after locating those lands with my Hornady OAL tool. With the Hybrid/ATip-type bullets I rarely have need to go elsewhere since they're more forgiving than VLD/tangent-types. If you run the bullet further out of the case, you have more powder capacity which may increase your velocity. However, if you run them out so far that you contact the lands or (as with many benchrest guys) actually seat them into the lands, you may see pressure spikes that are undesirable- especially if you're already at the top end of pressure with a big charge. As stated, I think starting at 10-off is a happy medium in target chambers. If we're talking factory guns with long throats, well, that's different because 10-off will often put you well outside of the magazine constraints. In this case it depends on the bullet as to where you end up in jump length. For VLDs, Berger has a good article on their website about seating depth for those specific bullets.

^this!

I do this exactly. For the .308 with 185gr Juggernaughts, my chambering has an extra .170” of free bore. Seating them long does give more room in the case for powder. And thus increasing the velocity. My accuracy node is a .010” jump. Speeds are around 2750fps.

The only downside, I need to single feed. I don’t really mind though. (My rifle is not a factory offering.)

 

[mdesign]

I run 41.5gr of Varget at .015 off the lands for a velocity of 2625fps out of a 22 inch barrel. There is about .100 more room in the magazine so the throat length is the limiting factor. Was just wondering if the throat was longer and I could seat the bullet out further to take advantage of the mag length would the additional case capacity be enough to make a meaningful difference.

 

[918v]

I would go forward with your plan, but get some Staball. You‘ll prolly pick up 150 FPS.

 

[mdesign]

I was not aware of the powder. I see the burn rate is slower than H4350 but it is a ball powder so probably fill better. The load was very compressed when I used H4350 due to the deep seating depth so Staball might give me some FPS.

It appears to be newer on the market so there is not a lot of load date out there but I do some looking around and see if I can find a starting point