Bullet Seating Depth and Rifling

[Patriot_1776]

I have heard alot on the issue of seating bullets just off the rifling which can help improve accuracy.  I've read about having it so many thousandths of an inch off the rifling, and so on.  How does that work?  And do charges have to be altered down somewhat to accomodate the extra closeness to the rifling?  Patriot

[Muddyboots]

Patriot,
Seating depth and accuracy can vary from rifle to rifle just like the perfect load can do. Generally speaking seating depth of 0.005 to 0.010 will provide best accuracy for most rifles. When you start getting 0.005 you better be pretty good at your measurements since pressure can spike immensely if you oops and were right on the lands. I very rarely go less than 0.010 for my hunting rifles and in fact I have one that shoots best at 0.030. When you develop your loads you need to recognize that you have to back off if you change seating depth since pressure will always be lurking due to shorter buller jump etc. Stoney Point has a very good tool for this purpose and I would recommend using it or something similar (Sinclair has one too) before I started to adjust seating depths. Don't be fooled into thinking best accuracy is less than 0.010 since many rifles shoot better farther off the lands. Plus if you are hunting back in there you want to make sure the round feeds perfectly when you need it. Varying seating depths for same load can usually show you the best one to use. Again watch pressure very very closely since seating depth will change it dramatically the closer you get to the lands.
Muddyboots

[Darrell Davis]

Welcome aboard Patriot_1776,

As to the question of seating depth, you should get ahold of some of the info from Rick Jamison, a writter for one of the magizines. I would give you the name of the mag. but the system keeps deleating the word. Maybe if I tell you the first word starts with "S" and the second word is Times, you can figure it out.

Rick writes, and seems to well document his writting, that bullet seating depth can have the same effect as found in the adjustment of the "BOSS" found on some Winchester and Browning rifles.

In my relatively limited testing, I have found changing seating depth can have a positive/negative effect on groups, allowing my load development to take on an additional step.

As indicated on the above post, watch those pressures.

On my A-Bolt 300 Win. Mag., I have found that the "sweet spot" is at a length slightly longer then will work through the magazine. Thankfully, the Browning magazine could be modified enough to allow for these loads.

At one time, I followed the old rule of thumb that the bullet needed to be set just short of the lands, however, even if this is true in many rifle/load combinations, it has been proven to not be true in all rifles.

Keep em coming! :wink:

[tuck2]

Darrel Davis---How did you modify the Browning rifle magazine (clips) for longer reloads ? I have a Browning varmint rifle in a 223 Rem.with a boss. Shoots .4 -- .8 inch groups but I load it single shot with some reloads.

[Darrell Davis]

Morn'in Tuck2,

I can not recomend this operation, as it for sure is not "factory."

However, On the mag. which my rifle uses. there is a piece of what I think is alum. on the bullet end of the mag. This is held in by a rivet about in the center of this piece.

With careful reshaping on both sides of the rivet, the length of the box can be increased on both sides of this rivet. This metal IS SOFT, so take care how you go about it.

Keep em coming! :wink:

[Iowegan]

When you are dealing with seating depth, you must use the proper approach. First you set your seating depth, then you adjust your powder charge. If you reverse this process, you'll chase your tail. As the bullet depth is changed, the pressure curve also changes. It's like changing two variables at the same time.

I manufacture bullet seating depth tools and did a lot of testing with various calibers and guns. With few exceptions, when the bullet depth was set .010 off the lands, best accuracy was achieved. See: http://www.cactustactical.com/reloading.html

Sako, Tikka, and Mausers were exceptions. Sako and Tikka use a tapered throat that acts much like a forcing cone. If you try to seat the bullets out to the lands, they will almost fall out of the case. All Mausers, especially the 6.5 Swedes, are the same way. With standard production Ruger, Winchester, Remington, and Savage guns, seating the bullets out improves accuracy.

As Darrell Davis stated, unfortunately the magazine doesn't always accommodate the longer OALs. In that case, either seat to the max length that will work in your magazine or single load.

There is another thing that will help. Bullets with blunt noses don't have to be seated as far out. So if your shooting requirements can deal with blunt nose bullets, you'll see accuracy improvements. Of course you may sacrifice a little with ballistic coefficient.