Seating depth? what's the limit?

[Al8095]

Seating depth? what\'s the limit?

Hey guys, I just got my box of A-max's and when I check the lands with my stoney point the bullet is not even in the neck when it contacts. I know this bullet likes to be really close to the lands but it doesn't look like that's going to be an option without rechambering. I was going to seat the bullet out really far and my question was what is the minimum contact needed between the neck and bullet? If I seat it out to where less than half of the neck is contacting the bullet what problems could I have. It has to make a difference with pressures and I'm sure it will run the risk of collapsing cases way up. Even with it seated like that I have over a .150 jump, can this bullet shoot well with that much? So what would be a minimum portion of the neck that has to be gripping the bullet? Thanks a lot Sorry forgot to say, the gun is a sendero 7mm ultra mag

 

[Al8095]

Re: Seating depth? what\'s the limit?

Sorry about sending that twice, I didn't know if it would delete my whole topic or what, but I just had forgotten to add that it was a sendero 7mm ultra if that helps.

 

[Budman]

Re: Seating depth? what\'s the limit?

Al you can't get close to the lands with the factory rifle in the RUM. I seen you posted looking for loads but I wasn't around my data or am I now. Are you going to feed from the mag.? If so seating depth will be col of 3.60 max I believe. The free bore is really not a problem with loads I have used but I didn't try that bullet. Went with Sirroccos (sp) and seated at 3.60 any went from there.

 

[QuietHunter]

Re: Seating depth? what\'s the limit?

I remember reading once that a minimum seating depth should be equal to the diameter of the bullet. That being said for a 7mm RUM, you would have .284 of the bearing surface of the bullet in the brass.

Can anyone else confirm?

 

[Al8095]

Re: Seating depth? what\'s the limit?

Thanks guys, no I am just loading one shot at a time so I have been exceeding the 3.6 col. I was reading something about how bullets with a tangent ogive, like the matchking, accept a jump better, and those with the secant ogive need to be closer to the lands to shoot well. I didn't know if it would even make a difference in my factory rifle with a lot of jump. I guess the only thing to do is shoot what works, since I won't rebarrel until the factory barrel is burned out. Does anyone know if the bullet diameter depth rule is a good guideline? Thanks

 

[Len Backus]

Re: Seating depth? what\'s the limit?

I have read on Benchrest.com that many accuracy nuts may only have half a bullet diameter's worth of bearing surface in the case neck.

 

[MAELTY]

Re: Seating depth? what\'s the limit?

I just dealt with the same problem in My Model 70 Coyote 7MM WSM. I smoked the bullets and found that the 162 grn AMAX's just touched the land at 3.075. Using identical loads and only changing the seating depth this gun shoots the best at 3.045. It seems to like the jump because it went from .6 down to .3/.4 @ 100yds.

I don't know if this will help you or not as it surprised me as well.

My theory with this gun is to let the bullet jump as long as it keeps shooting as it is.

 

[johnny k.]

Re: Seating depth? what\'s the limit?

Al,
The "rule" that I go by on seating bullets out to meet the lands and groove is to keep at least half a caliber in the case neck. In the 7mm that would be .142". This should provide good neck tension and also keep your runout to an acceptable level ( under .003 for me).
I have had some bullets (40gr Nosler BT in my .22-250) that would never make it to .010" off the LaG. Accuracy suffered because I tried to run the bullet out as far as they would go. What I was doing was creating too much runout. When I seated the bullets deep enough in the case neck to eliminate runout I found accuracy was pretty darn good anyway, go figure. Keep us posted. Johnny K.

 

[Al8095]

Re: Seating depth? what\'s the limit?

Thanks everyone, that helps a lot. I guess now the only thing I can do is head to the range. I will seat them out pretty far but keep over the 1/2 diameter rule. I will probably get to shoot a little tomorrow and then tuesday I will have enough time to shoot some at 500. Tuesday night I will have some results to let everyone know. Thanks everyone!

 

[Al8095]

Re: Seating depth? what\'s the limit?

Hey guys, well I have not had the weather to get the testing done that I had hoped. One day after work I had time for one group at 100 that was .9" which is good for me. That was with 91.5 gr retumbo behind it. Yesterday there were 15 mph winds. I was off so I just couldn't stand it and went to the range. Shot groups with 92 and 92.5 before I made myself quit. Needless to say they were terrible. I might be able to get out there tomorrow or Friday morning so I will keep you posted when I get some good weather.