How much bearing surface is needed

[sdupontjr]

I'm looking to see if I can get a little more velocity out of my 20" CTR 308. Currently I'm using 155 scenar, 47.5g Varget, CCI-200, R-P brass, 2.810", 2840fps avg. This load shoots very well but is also a good bit compressed. I do however have 1lb of 8208xbr left and after talking to the local shop, he'll be getting some in. Figure I could try it out, possibly seat out further and not have a compressed load. I have messed with 8208 before and the recoil feels snappier and pressure came on about 45g in my T3 lite, but haven't tried it on the CTR. It's also very stable and similar to Varget. I do have TAC as well, but have heard of swings in varying temps.

I read several threads on seating depth and such on sniper hide, campfire, here and others. Some were seating them as long as 2.910" and some even further with those long-throated barrels. At what point do you not have enough bearing surface to properly hold the round?

I FL size and anneal every time. I have about 200 R-P brass, some Win, but I usually go through all of them, them FL size and anneal all in one go. Is it overkill, probably, but it's been working great. My max COAL is 2.888" for both my CTR and T3. And yes, I have LA bolt stop and different mag.

At 2.860"


At 2.835"


Hell at 2.860", there is .215" of bearing surface left while still being .028" off lands. Those guys who were running 2.910" had only .165" of bearing surface. The CTR that I'm playing with has less than 50 rounds through it, so I'm not interested in chasing the lands, but more after trying not to run a compressed load / possibly more velo. So is there a point at which it's not seated enough? Or is it more of, having enough so the round dopesn't fall out while cycling it from mag to chamber? OR something I'm not thinking about?

Or is there anything in the VV line that I'm missing? Local shop has lots of it.

 

[Vern400]

Not sure there's an answer to this. I pulled my barrel and rechambered to shorten the throat so I can only load out to 2.85 with similar bullets.

But if you dont bear on all the neck it's easy to bump the bullet over feeding it.

 

[TaperPin]

If it shoots well, who cares how much of the neck grips the bullet.

Even with full neck contact, simply feeding a cartridge from the magazine can increase runout a tiny bit as the bullet hits the receiver on the way in. As neck contact is reduced the chances go up. With a smooth feeding magazine chances of a problem go down. This would be easy to test - just fire one group fed from the magazine and another single fed.

In some barrels, more neck grip pressure helps accuracy, and a bullet barely in the neck won’t have much.

There have been many wildcats with super short necks and they never became popular even though it maximized the case capacity.

 

[wind gypsy]

"How much is enough" - I dont know, but i wouldn't have any concerns with 0.215" bearing surface in the neck. H4895 is another that'll take up less space but good luck finding it!

 

[sdupontjr]

Yeah I'm was gonna try the 8208xbr this week but now it looks like I'll get hit with this tropical storm in the gulf and tons of rain. I'll just have to see if weather allows.