Seating depth

R

RedSkyFarm

New member
Hi all. Still trying to learn how to get the most out of my rounds. I have a couple rifles that I reload. 25-06 and .223 at this point. I am trying to develop a good accurate hunting load. I read of you guys seating as far out as the lands and close to the lands. In the seating depth part of the accuracy of the rounds, it seems to be common on a hunting round to start at .010-.015" off the lands and work your way back in .040" increments initially to find a node to adjust from there. In either of these rifles, going .010-.015 off the lands, the bullet will pretty much fall out. Obviously can't seat there. As a rule of thumb, how much depth or seating contact is necessary? Is there a certain percentage of diameter of bullet that is sufficient? Also, why doesn't my rifles allow to seat out further? The .223 is fairly new, the 25-06 could be worn. At this point the .223, I'm using Sierra 55 gr. HPBT and the 25-06 Sierra 90 gr HPBT and Barnes 100 gr TTSX. Any info will be appreciated.
 
If I have the room, I like to seat rifle bullet's just off the lands. Don't know the distance off the lads, never mattered much to me. Normally I can seat the bullet so the base of the bullet is right at the junction of the neck and shoulder. If I shot heavier bullet's I'd have to invade the powder space. Had a 7mm mag years ago than shot the 140 gr bullets really well but not so well with the 160 gr that I wanted to use. I figured it was probably the 160 gr was seated to deep. So I loaded up a 160 gr with the base right at the bottom of the neck. Took it and the rifle to a gun smith and had it long throated the load the round just off the lands. Just off the lands is to me the best measurement I have. haven't a clue how to measure it and don't really care. Turned that rifle into a great shooter. Also increased the case capacity and ended up increasing the powder charge 2 gr's. Today most of the rifles will shoot right with that old 7mm mag ane same measurement, just off the lands.today I still use that measurement.
 
For hunting rounds the most common issue will be the magazine length.

You can not load longer than that or the rounds will not feed from the magazine and you will not get a second round off. Check that length first.

At a minimum they say you need at least one bullet diameter inside the case neck.
 
Work up a load using the max OAL given in your manual first. The off-the-lands stuff is a 100%, trial and error, load tweaking technique you can forget about altogether or fiddle with the OAL after you've worked up the load. Isn't necessary for a hunting load anyway. There is no magical math formula as every chamber is slightly different. So every rifle has a different preference.
And don't try to work up two cartridges at the same time.
 
All the reloading books that I have provide an overall length at which the load was worked up. I always start there for my rifles and revolvers.
 
I have some room left in the magazine. I have been seating to the length recommended in the manual. The manual recommends an OAL of 3.100 for the 90 gr HPBT for the 25-06. This gives a seat contact of .132". That's .125 less than the diameter of the bullet. The 5.56 recommended OAL is 2.250 for the 55 gr HPBT. This gives a seat contact of .153". .070" less than the diameter of the bullet. Can't help but think I'm missing something. Don't see seating deeper. That would make for an even bigger jump than I already have. Is the diameter of the bullet really the rule???
 
The most accurate rifle that I have gets the bullet seated 0.204" off the lands.

I had an accident once. My seating die got knocked off by 0.021" and naturally in the wrong direction. The bullet was jammed into the lands. The first round showed modest high pressure signs. The second round blew the primer out of the pocket.

The case head expanded 0.006" over normal. I know this because I measure before firing and after firing as our friend Mr. Guffey preaches. I have been doing this for prolly close to 42 years.

The differences in bullet tolerances precludes me from wanting to seat closer than 0.020" to the lands.
 
Good advice here already. The one thing I'd say is the Barnes TTSX bullets you mention like a jump of around .050. I believe that's what Barnes recommends. I screwed up and loaded some close to the lands (.005) and they didn't shoot well at all.

I assume on the HPBTs you aren't measuring the tail of the bullet which is why your measurements are so short?

Also, I usually start at .020 off the lands and move around in .010 increments. .040 seems like a lot.

Finally, some rifles just have long throats and you can't get bullets close to the lands.

One thing with light (for caliber) bullets is they are just shorter than heavier (for caliber) bullets so you don't have as much room to mess around with seating depth. Also, you loose some seating depth ability with boat tails.



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When I started messing with this concept in my .308 FNAR, I found out the seating depth makes about as much difference in group size as powder charge. I found that groups could go from 12" (at 200 yards) to less than 2" by changing only the seating depth. And the big groups were with bullets seated 0.02" off the rifling, while the small groups in that case were seated much shorter, at standard length. I had no idea it had that much impact on things.

In my case, after I ended up buying another .308 rifle, I decided to stick with SAAMI max COAL so I wouldn't get into danger if I (or someone else) grabbed the wrong rounds. And I still found a satisfactory load by adjusting the powder charge, and keeping the seating depth the same.

In your case, I would recommend the same for now. Stick with the standard COAL and do a ladder test with various powder charges, and I bet you'll find a load that makes you happy. I would not worry about messing the with the seating depth unless you just can't find a good load otherwise, or if you want to become a serious competitor in long range target competitions.
 
If I have the room, I like to seat rifle bullet's just off the lands. Don't know the distance off the lads, never mattered much to me. Normally I can seat the bullet so the base of the bullet is right at the junction of the neck and shoulder. If I shot heavier bullet's I'd have to invade the powder space. Had a 7mm mag years ago than shot the 140 gr bullets really well but not so well with the 160 gr that I wanted to use. I figured it was probably the 160 gr was seated to deep. So I loaded up a 160 gr with the base right at the bottom of the neck. Took it and the rifle to a gun smith and had it long throated the load the round just off the lands. Just off the lands is to me the best measurement I have. haven't a clue how to measure it and don't really care. Turned that rifle into a great shooter. Also increased the case capacity and ended up increasing the powder charge 2 gr's. Today most of the rifles will shoot right with that old 7mm mag ane same measurement, just off the lands.today I still use that measurement.
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I have to express deep puzzlement on this response.

While you state you like to seat just off the lands, you don't know where they are and you don't care.

How do you then determine you are seating just off the lands?

Obviously a gun smith did the one. You are aware you are eroding your throat (7mm is one of the worst) and its moving away from you?
 
I have measured with a comparator how far off the lands I am. In the 25-06, the 90 gr. with an OAL of 3.100" is .099" off the lands. The 5.56, the 55 gr with an OAL of 2.250" is .086" off the lands. I did not include the length of the boat tail as part of the bearing surface. Should I be? I have considered trying a heavier, non-boat tail bullet.
 
Red,
What kind of accuracy ae looking for? Will 1" 5 shot groups at 100 yards be ok or are you looking for 1/4" groups at 100 yards?
I get groups that are closer to 1/2" groups than they are to 1 inch groups and I just use the seating depth listed with the load. I adjust the powder charge to get the best groups.
I don't have any argument with seating the bullets close to the lands but I have never found it necessary with hunting bullets. In the field you won't be shooting from a bench (normally) so you should really work on the shooting positions you will have available during the hunt.
I understand working up the loads on a bench because that is the best way to see how accurate the load is in your gun. Just so you understand how important it is to be close to the lands, in my 30-06 (03A3 1942) I can't get any bullet (that will stabilize in that rifle) closer than about 1/4 inch from the lands and still have the bullet in the cartridge. It still shoots sub MOA 5 shot groups. Yes, it's a tired old rifle that probably ought to have a new barrel on it but as long as I have the accuracy I don't want to change out the barrel. I suggest that you use the COAL listed for the load and find an accurate load at that length. You'll get a lot more hunting done with a lot less trouble. I bet that with the right load your rifle will shoot 1/2 groups easily.
These long range target guys have to push their ammo more than a hunter does in order to keep the velocities above the speed of sound at the long ranges they punch paper. You aren't likely to shoot at more than 300 yards when hunting so you can stay inside the normal loads to get that done.
 
There is a lot of good information above. This is what I've found:

As a rule of thumb, how much depth or seating contact is necessary? Is there a certain percentage of diameter of bullet that is sufficient?
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I once read that contact should be at least the diameter of the bullet. I don't know where this person came up with that figure but he had written a book, and I bought it, so I'm sure he knows more than me. On the other hand I've shot and reloaded for both the 300 Win Mag and the 7WSM, both of which don't have enough neck to allow for that, and both of those rifles shot/shoot fine for hunting purposes. I don't crimp and I've never had an issue with either cartridge.

Also, why doesn't my rifle allow to seat out further?
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Some rifles have long throats, Weatherby rifles are known for it. In your case you need to find out how far out the lands are so you can know exactly how much you need seat out.

With all that said I have to agree with what I read above, for hunting purposes you are not going to gain enough accuracy to matter in the end or at least I've never found a rifle that it did.
 
ShootistPRS. Thanks for the info. I am currently on the 25-06 using the recommended OAL and have adjusted the powder charge to a best group of 5/8". More consistently between 11/16 and 3/4". Was looking to improve on it by changing the seating depth. Would like to get under 1/2". The 5.56 groups are at 3/8" consistently. I arrived at it by mistake. I was loading to the recommended OAL of 2.250 and was getting 5/8-3/4" groups. I seated some to 2.260 by accident, shot 3 5-shot groups at 3/8". Didn't realize until I got home and checked some lengths that they were .010" longer than intended. This "mistake" is what got me researching the seating depth. I understand these are hunting rounds, but would like for them to be as accurate as possible.
 
Ah. Didn't realize you were already that far along with testing. Yeah, if 5/8" groups at 100 yards don't satisfy you, then by all means go ahead and play with the seating depth. Keep everything else the same for now.

You definitely do not want to seat into the lands without dropping your powder charge below the listed min and working back up. The bullet has to be moving before it hits the constriction, or pressures will spike dramatically. Doesn't sound like that will be a problem in your case, but just keep it in mind for future reference.

How are you measuring your freebore? I've used the poor man's method by splitting a case neck (to reduce tension) with a jeweler's saw, and barely seating a bullet (by hand) in it. Then when I close the bolt, the bullet is pushed back into the case when it contacts the rifling. But again, if you've got that much free bore, this method won't work. Unless maybe you have some really long/heavy bullets to try.
 
I broke down and bought a Hornady OAL gauge. Had made/used something similar to what you have and thought I wasn't accurate in the measurements. Turns out the Hornady gauge just verified what my home made set up got. I'll make some slight changes in my seating depth and see what I get. Appreciate everyone's input.
 
RedSkyFarm said:
I broke down and bought a Hornady OAL gauge. Had made/used something similar to what you have and thought I wasn't accurate in the measurements. Turns out the Hornady gauge just verified what my home made set up got. I'll make some slight changes in my seating depth and see what I get. Appreciate everyone's input.
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If you haven't already, you could try changing primers. I usually monkey with primers last but in your case where you have (apparently) long throats and short bullets it might be easier to try a few different primers first.


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Off the lands: I am the fan of bullet jump, I want my bullets to have that running start. I want my bullet past the rifling before it knows it is there. There is nothing entertaining about having a bullet setting at the lands wondering if it is going to get very serious behind it if it decides not to go. Meaning? Consider adjustments to the maximum length (bullet and case) if you are seating into or at the lands.

F. Guffey
 
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