Seating depth

[hookr88]

I'm new to reloading and am getting ready to reload some 7mm-08 rounds. I have different grain bullets, from 140gr to 175 gr. Do I set the overall length the same and let the seating depth vary or do I adjust the seating depth the same and vary the overall length? The latter method doesn't seem right, but I thought I'd just double check. Thanks.

[JackOfAllTrades]

The reloading manual for the bullet you are using should give you the OAL for the cartridge. Knowing this, you should be able to set your seating depth accordingly.  Bullets of the same design that weigh less are usually shorter, but they could also have a different taper forward of the ogive. Thus, your seating die will need to be adjusted nearly any time you change the bullets you're using. Even for a same weight bullet from a different manufacture. So always start with the manufactures spec for the bullet which will follow sammi spec for the cartridge.  That said, for single shots or bolt guns I seat my bullets to be ~.002" from the lands of barrel/chamber I'm loading cartridges for and work my loads up for performance and accuracy using my chronograph data and watching for high pressure signs.  I suggest that all new reloaders use the specs in the books provided by the bullet manufacture though.

-Steve

[hookr88]

Steve, thanks. I was looking at the specs from Sierra's reloading manual and getting ready to load Nosler bullets. Brian

[shaneman153D]

That said, for single shots or bolt guns I seat my bullets to be ~.002" from the lands of barrel/chamber I'm loading cartridges for

-Steve

Sorry to hijack, but how do you measure this?  Would you do the same for an auto?  If not, why?

[Intruder]

Seating depth will definitely change.  The max COL doesn't vary from bullet to bullet.  Now, your particular gun and magazine may like cartridges slightly longer/shorter than established COLs and even that may change from bullet to bullet.  That's where the trial and error of loading for your particular gun comes into play..... figuring out what it really likes.

Be very careful having significant variance from the published COLs.... seating and feeding problems can arise as well as pressure variances.  Starting out, probably best to stay at or near specified COLs.
  

[carpsniperg2]

the max col for bullets can vary, but there is a max col which will fit "chamber in the gun" the col of my 7mm-08 loads are 2.730 with the bullets i shot if i went to 175g bullets it goes up to 2.800 so it can change depending on the bullet but there is a max col that will work in the guns hope this helps aslo if you go to hodgons they have there basic loading manual on there for you to use.

[hookr88]

I plan on sticking to the charts. Okay, but another newbie question is "COL" cartridge overall length? I.E. as referred to in the charts as max overall length? I couldn't find COL in any of my books. I looked before asking.

[Red Dawg]

The best way to find your true col is insert a bullet in some brass that has been shot but not re-sized. Color desired bullet with a sharpie. Put the round in your chamber and lock the bolt.  When you eject you will most likely just get the brass so use a cleaning rod and lightly tap the bullet out of the chamber. Insert bullet into brass until you are all the way to your mark. Then you measure with a caliper. That is the length all the way to lands of the rifle. I like to back it off a bit from the lands but some like to be right on it. Sometimes it will fit in your magazine and sometimes it wont but that is where I start and compare to data in my reloading books. Your col will vary greatly with different bullets and it sometimes does take a lot of trial and error depending on your gun.

[hookr88]

Thanks for the info, you guys have been a big help. I think that also answers Shanemans question. Brian

[shaneman153D]

The best way to find your true col is insert a bullet in some brass that has been shot but not re-sized. Color desired bullet with a sharpie. Put the round in your chamber and lock the bolt.  When you eject you will most likely just get the brass so use a cleaning rod and lightly tap the bullet out of the chamber. Insert bullet into brass until you are all the way to your mark. Then you measure with a caliper. That is the length all the way to lands of the rifle. I like to back it off a bit from the lands but some like to be right on it. Sometimes it will fit in your magazine and sometimes it wont but that is where I start and compare to data in my reloading books. Your col will vary greatly with different bullets and it sometimes does take a lot of trial and error depending on your gun.

Thanks red dawg, I'll give it a try, but IIRC, with an AR, it won't fit the magazine so most guys load to mag length.

[JackOfAllTrades]

That said, for single shots or bolt guns I seat my bullets to be ~.002" from the lands of barrel/chamber I'm loading cartridges for

-Steve

Sorry to hijack, but how do you measure this?  Would you do the same for an auto?  If not, why?

A precision mic like this one will help you get that just perfect.   https://shop.rcbs.com/WebConnect/MainServlet?storeId=webconnect&catalogId=webconnect&langId=en_US&action=ProductDisplay&screenlabel=index&productId=3186&route=C11J149

But Reddawgs method has been used by many reloaders for years.

Steve, thanks. I was looking at the specs from Sierra's reloading manual and getting ready to load Nosler bullets. Brian

If you're going to use Nosler bullets, use Noslers manual.

For an AR or other semi-auto, Load to max OAL listed in the book minus just a tad and load a few to function test. Once you know what functionsw well in your gun then load a bunch and blast some Yotes!

-Steve

[fremont]

Insert bullet into brass until you are all the way to your mark.

Sorry to be dense, but this is where I get lost.  What mark are we talking about?

[Red Dawg]

this would be the mark that the brass leaves on the bullet. Maybe a little scratch or sometimes it will scrape all of the marker off the bullet.

[fremont]

Thanks, RedDawg.

I have always done it this way.  Take bolt out of gun.  Drop desired bullet into chamber and have a friend hold it firmly against the lands with a pencil's eraser (a new pencil works best....long enough and no sharp point!).  Run an appropriately sized wooden dowel down barrel and carefully mark it at the muzzle with a pencil when it contacts bullet's point.  Remove pressue on bullet and tap out.  Replace bolt and lock down.  Run wooden dowel down again and mark at the muzzle when it contacts bolt face.  The difference between those two marks is your max. COAL for that particular bullet.  Then, there's the debate about how far off that max. length should you load.

This said, it's always best to confirm with reloading manuals.  You also have the issue of magazine length.

[Intruder]

This can be kinda a confusing concept.  Even some of us on here tend to use different terminology for the same thing.  Starting out I'd just stick to using the published COLs for the particular bullet based on what your manual says.  Depending on the manual and how it list things it will show COLs for each bullet and possibly the overall Max COL... which represent the longest that a cartridge should be (regardless of bullet) to fit the specs for that round.... specs being the tolerances that you'd expect off the shelf stuff is loaded to conform to.   

As many have pointed out specs don't always match guns.  That's were figuring the COL (and subsequent seating depths) to achieve the best fit and potentially best accuracy for a particular gun comes into play.  There are several methods for doing this, as folks have described.  There are actually tools that help with this too.

This concept is similiar to why you'd  fire form your brass... so it conforms to your guns chamber better.  It may be out of spec when fire formed but it will often lead to more accurate loads. 

Fire formed brass and COLs that are out of spec are essentially specific to a particular gun.  If you full length size and stick to published COLs then the rounds would be considered usable in another firearm of the same cal.   

[Skinnyman]

I use the method that Red Dawg describes. Once I have that measurement, I subtract .015 to .030 from the case overall length just determined for that gun. Once you subtract that, load your re-loads to that new shortened length. You want the bullet just off of the lands (Rifling), not touching them. I am sure some reloaders do not subtract as much as I do, .015 to .030 is what Nosler recommends.

The new COL that you just found for your gun might not fit in your magazine, COL is too long. So load to your new COL and run a magazine full of ammo through (not firing it) to make sure it operates smooothly in your magazine. My 30-06 has a longer COL than the magazine will allow, but my 338WM it works just fine. If it is too long then keep slowly shortening the COL until it will run smoothly through the magazine.

If you use this method, you will get better tighter groups than using NAAMI published COL (at least that has been my experience). NAAMI is what all of the reloading manuals (at least the ones I know of) use to publish their measurements of cases.

[C-Money]

I have always just made my ammo a little under the max C.O.L. listed in my Nosler or Hornady book. I make sure with a dummy round that it goes in and the bolt closes before mass production. Getting out right on the lands is from what I hear to be best for accuracy. I am very pleased with my accuracy sticking with what the book sais.