Seating depth

[Ralph Littlefield]

I'm trying out some Barnes Match Burner 6.5 140 gn bullets and read on a forum that they generally perform best with a .005 to .015 jump to the lands.

Reading that made me wonder if such a statement could be accurate. Is it possible that a bullet, barrel, or caliber will be likely to have a specific jump that is likely to provide more desirable results?

Are there any "rule of thumb" that can be used when deciding on a seating depth?

 

[BenPerfected]

Start with finding touch. The rest is trial and error. Do you have the tools to find touch?
Ben

 

[Ralph Littlefield]

Start with finding touch. The rest is trial and error. Do you have the tools to find touch?
Ben

Yes, I have the tools for that, but my question is not specific to my situation, it is a general question.

 

[rsmithsr50]

yes some combinations have windows where they work well. but all guns are individuals.

 

[David Christian]

@Ralph Littlefield, generalities are just that. Depending on your idea or desire for accuracy, you should perform a progressive seating depth starting at some distance from “touch” and work your ways backwards at .003 increments. Somewhere over a .030 distance you will find a jump distance that sings for your particular, barrel, bullet, powder, primer combo.

 

[Ned Ludd]

There are usually a lot of "ifs" involved in making generalizations about things such as optimal seating depth for a given type of bullet in different rifles, especially if you are jumping the bullets (i.e. bullets seated off the lands). IF the barrel length is similar, IF the rifling is similar, IF the velocity is comparable, IF you're hitting the same node, etc., etc., etc., it wouldn't be all that shocking shocking to see two similar rifles tune in with a given bullet seated at a similar distance off the lands. In fact, it is quite common to see loads for .308 Win F-TR rifles, which by design tend to be quite similar, if not almost identical, tune in at very close to the same seating depth with a given bullet and powder.

Nonetheless, as David suggested, it should be a standard practice during load development to determine optimal seating depth for your specific setup. Like David, I generally test from about .003" to .030" off the lands in .003" increments. Of the various 0.224" and 0.308" bullets I use, I have yet to find one that didn't tune in within that window. For that reason, I typically start charge weight testing with a new bullet at .015" off the lands, which is basically halfway in between the two seating depth test bookend measurements (.003" to .030" off the lands). That way, if you test seating depth after optimizing charge weight, you're not moving the bullet more than half the total seating depth test range in either direction. In my hands, that is not enough to appreciably change effective case volume or velocity, so I don't have to re-optimize charge again after doing a seating depth test.

In any event, a generalization about the preferred seating depth for a given bullet might be useful in terms of choosing a starting point, but seating depth is such a critical part of optimizing precision that you always want to test it yourself. Further, optimal seating depth will likely change over the life of a barrel as land erosion occurs, so you need to check it periodically. Carrying out a fine increment seating depth test is really not very painful in the grand scheme of things, and once it's done, then you know for sure, until it's time test and adjust it again.

 

[Murray Brook]

In most of my varmint barreled rifles accuracy with most bullets that grouped good came from somewhere between a slight touch to .060 off. In my 7mm/08 I was having trouble getting a load to shoot the way I wanted. Tried several different bullets with different powders got the same .75 results. One of these bullets was the 171 Barnes match burner which showed promise. I decided to do the Berger ladder seating depth test out to .130 off. Had never gone this far before. Well at .120 off the lands I was averaging .3-.4 for five shot groups. . Finally got what I was looking for, although I would have never dreamed .120 off would be the sweet spot. I guess as others have posted all barrels are different, you never know till you try. JME

 

[std7mag]

Are the Match Burners a monolithic bullet?

If so Barnes, Nosler, Hornady all recomment a 0.050" off the lands for their monolithic bullets..

Cutting Edge is the only monolithic bullet that i know of with different seating depth.

 

[pintopete]

Ned Ludd, I enjoyed your post above, especially the second paragraph. Makes good sense as to which comes first & why; seating depth or charge.

Thanks! Peter.

 

[Murray Brook]

The Match burners are a regular cup and core bullet.

 

[JEFFPPC]

Start with finding touch. The rest is trial and error. Do you have the tools to find touch?
Ben

Good advice but no special tools required. I constantly read about finding touch then working back into the case .003 at a time. Good advice but limited. I have found as many barrels that shoot best with a seating depth at or just slighty less than a square mark from the rifling. Don't limit yourself, start at a square mark rather than touch.

 

[AJC]

Good advice but no special tools required. I constantly read about finding touch then working back into the case .003 at a time. Good advice but limited. I have found as many barrels that shoot best with a seating depth at or just slighty less than a square mark from the rifling. Don't limit yourself, start at a square mark rather than touch.

Okay I'll play what is a square mark

 

[Mikemci]

Okay I'll play what is a square mark

When the length and width of the rifling marks on the bullet are equal, making a square mark, rather than a rectangular mark.

 

[AJC]

When the length and width of the rifling marks on the bullet are equal, making a square mark, rather than a rectangular mark.

So then you measure that square Mark with a caliber and that is your initial seating depth off the lands

 

[FiftyOuts]

Or You can use a Hornady COL gauge...

 

[Richard Coody]

For me it totally depends on what is the intended use of the rifle.

Bench gun i start with a hard jam and work up a powder charge. With berger vld's often that is it for load development. With the hybrids or matchkings start at a jam and work up a powder charge. Then back out ,010 at a time until something shows. Then fine tune seating depth and powder charge.

Hunting or any other mag fed rifle. I use the berger method to find a rough seating depth mag length or less then fine tune seating depth and powder charge

Easy to miss that best seating depth or powder charge but i want neither without as large a window as i can find. If your window is too small every change in conditions will have you getting out of tune. With a precise bench gun it is easy to see when your rifle goes out of tune but many shooters scratch their heads wondering what.happened when their rifle was shooting great.last.weekend.

 

[mikecr]

Here's your rule of thumb:
You'll never know best seating until you do FULL seating testing to find it.

 

[Mikemci]

So then you measure that square Mark with a caliber and that is your initial seating depth off the lands

That is a starting point only, for some shooters.
I was only defining what a square mark is referring to. That was your question.

 

[Iowa Fox]

Maybe its Monday and I've had to much coffee but a question for the experts way beyond me. What about throat leade as it relates to seating depth and accuracy? Is there a optimum degree most reamer grinders use?

 

[rsmithsr50]

do not limit yourself to one opinion, start at the touch, and work in and out from there,'
without an optical comparator, "square" is NOT a real value, but an opinion, with no numeric value.'
work from facts

Good advice but no special tools required. I constantly read about finding touch then working back into the case .003 at a time. Good advice but limited. I have found as many barrels that shoot best with a seating depth at or just slighty less than a square mark from the rifling. Don't limit yourself, start at a square mark rather than touch.