Determining Bullet Seat Depth

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ssmith1187

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Good evening!!

I am currently in the process of developing some hunting loads for my Ruger M77 Mark II rifle chambered in .30-06. I am not new to reloading but I am new to rifle cartridge reloading.

I am to the point in the process where I am determining the optimal bullet seating depth using a Hornady O.A.L. Gauge and Hornady Bullet Comparator.

As a point of reference I measured a Federal Fusion 165 grain factory loaded cartridge and came up with an ogive measurement of 2.603 inches.

I am using a dowel inserted into the muzzle end of the barrel and “feathering” the bullet back and forth to determine the point when it contacts the rifling in the barrel. Once this has been determined I then lock the thumb screw on my O.A.L. gauge and remove it from the chamber of my rifle and take the measurement using my bullet comparator.

The bullets I am interested in potentially developing a hunting load for are (also listed is the ogive measurement and the difference between it and the reference cartridge measurement):

Barnes 168 grain TSX: 2.719 inches (+.116 inches longer than the reference cartridge)
Berger 168 grain VLD – Hunting: 2.689 inches (+.086 inches longer than the reference cartridge)
Hornady 165 grain SST: 2.683 inches (+.080 inches longer than the reference cartridge)
Nosler 165 grain Ballistic Tip: 2.729 inches (+.126 inches longer than the reference cartridge)
Sierra 165 grain GK Spitzer Boat Tail: 2.733 inches (+.130 inches longer than the reference cartridge)
Speer 165 grain Boat Tail Soft Point: 2.724 inches (+.121 inches longer than the reference cartridge)

I understand I am comparing apples (a generic factory loaded cartridge) to oranges (potential hunting loads) but the difference seems to be larger than I would have expected. Even visually the new loads seem much longer than the factory loaded cartridge. I understand that factory loaded cartridges need to be manufactured to fit countless chambers, but I would not have thought the measurements would have been that different.

Hornady recommends a free-travel of between .020 to .040 inches. So taking the longest measurement (Sierra GK) of 2.733 inches and subtracting .040 inches (maximum recommended free-travel) gives me a bullet seat depth of 2.693 inches. That is still .09 inches longer than the reference cartridge.
Am I placing too much stock in the reference cartridge measurement? Should I not even be thinking in terms of that measurement or should I just be concerned with the my bullet comparator is telling me?

Thank you,
Steve

Attached are a few photos showing:
#1) The length of my reference cartridge
#2) The length of the Berger 168 grain VLD – Hunting cartridge
#3) The visual difference between the two
#4) The current seating depth of the bullets listed above (in that order from left to right). Note, the current seating depth does NOT take into account the additional .020 to .040 inch adjustment.
 

Attachments

  • Reference Cartridge.jpg
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  • Berger VLD Hunting.jpg
    Berger VLD Hunting.jpg
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  • Berger VLD Hunting #2.jpg
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  • Seat Depth.jpg
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Many factory rifles today have very long leades, or free-bore as it were, to satisfy the lawyers.
It reduces pressure.

How does your rifle shoot with the factory loads??

If it is unsatisfactory, you may or may not see some improvement by seating longer.

On the other hand, the most accurate factory ammo loaded, namely Match & Varmint ammo, is loaded to a "standard" length that shoots well in just about anything.
It's not unusual to get sub-MOA with that ammo in accurate rifles.

You can do what you want to do, but I load my hunting ammo to standard length, or to the crimp cannelure on the bullet just like the factory ammo would be loaded.

Perfect functioning and feeding in adverse hunting conditions is more important to me then gaining another 1/16" tighter group.

rc
 
Your questions are hard to pick out of a the info.

I took a bullet & seated it long in the neck with little press then forced the bullet into the lande. I then colored the bullet with a sharpie & seated it deeper in the press until it no longer rubed marks in the sharpie. I measure OAL & reduce another ~.020". I don't care what the ogive measurement is. I use the dumy round to set up the die. I do this for each bullet. There my be better seating depths but there is only so many of the unlimited possibilities you can try.
 
You need to stick with 1 bullet or you will jamb a different brand into the lands of your rifle. You will have to use a cleaning rod to knock it out and powder will dump in you magazine.
 
Thank you for the replies.

RC, it does not shoot horribly at all and truth be told it's probably more the shooter than the rifle at this point. But like most things in this hobby, we tend tweak this and turn that in hopes of squeezing out that last drop of accuracy. Perhaps it's as fruitless as a dog chasing its tail...but at least it fun to watch them try :)

King and tri, that is kind of what I am realizing at this point. At what point does one call it good enough versus trying different powder, charge weight and seating depth combinations? If I were a BR shooter then by all means it would make sense to pay attention to that level of detail but for hunting cartridges out to 200 yards...perhaps I'm overthinking this just a bit.

Thank you again,
Steve
 
Am I placing too much stock in the reference cartridge measurement? Should I not even be thinking in terms of that measurement or should I just be concerned with the my bullet comparator is telling me?
Click to expand...

ssmith1187,

For hunting/plinking ammo, I simply set my seating die up to seat the bullet so that 1 caliber (.308") of the bullet (not including the boattail) is in the neck. As rcmodel pointed out, factory chambers tend to be long throated, but with your AOL Gauge and comparator, you can confirm that such an OAL will not place the bullet ogive into the lands. For target loads, I tend to seat my bullets about .012" off the lands as determined by my AOL Gauge and comparator. The reason I do that is, even with match bullets such as Sierra MatchKings, the bullets come off of different machines, and the ogives will vary by up to .010". Hope that helps.

Don
 
At what point? When you decide you don't want to any more or you die. It really depends on which one comes first.

Even if you found that perfect match of bullet, powder, & everything else evolved what if there is another powder, primer, or bullet that would work? You may even get into making your own.
 
It all has to do with your rifle, for hunting or field type loads, .020-30 off the lands is fine, you will have to play with some differnt depths to fidn out what works for you. For competition loads people like to get closer than that, even touching the lands in some cases, the problem with this is the round may have to be too long for the magazine or too long to feed properly. Here is how I figure out my seating depth.

Take a case, and use a hacksaw or dremel to cut 2 slits down the neck of the case, place a bullet in the modified case, make sure it is loose enough to easily slide back and forth, then place it in the chamber and slowly close the bolt so that the lands push the bullet ogive back into the case. then carefully remove it and measure it at the ogive, this is the length to your lands, you can then subtract various amounts to find the seating depth that will work best for you.
 
Take a case, and use a hacksaw or dremel to cut 2 slits down the neck of the case, place a bullet in the modified case, make sure it is loose enough to easily slide back and forth, then place it in the chamber and slowly close the bolt so that the lands push the bullet ogive back into the case. then carefully remove it and measure it at the ogive, this is the length to your lands, you can then subtract various amounts to find the seating depth that will work best for you.
Click to expand...

spclpatrolgroup,

See the OP - he has tools specifically made to measure base to ogive dimensions.

Don
 
Why trash the case? If you seat a bullet in a sized case then pull it the second time in will be easy enough for the lande to shove it in. Just use the marker to know for sure it is no longer jamming into the lande.
 
USSR said:
spclpatrolgroup,

See the OP - he has tools specifically made to measure base to ogive dimensions.

Don
Click to expand...
The one he was talking about was specifically made for that also. It was just made by him & he got to save some money.
 
"Am I placing too much stock in the reference cartridge measurement?"

Yes.
It has no significance unless you were reloading the exact same bullet.
Otherwise, you can tinker with jump to lands all you like.
For a hunting rifle, they have to go into and feed out of the magazine, too.
I have one rifle that with the USSR target seating of .012" off the lands, the OAL is too long for the magazine. That's OK, it is a slowfire target rifle and the magazine is not needed.
 
I love test brands of different powder and bullets for the best combination, new and latest and greatest! I think it's safe to stay within the recommended col, I like the information in Nosler or Sierra for best book loads.
 
I use to pull my hair out over the issue of seating depth but i dont anymore. I use a Stoney point oal gage to find the lands then seat the bullets about .020off the lands. After that I can usually find a very accurate load by simply juggling components instead of stressing over seating depth. The only bullet that i seat differently is the barnes bullets that love alot of jump in my rifles so i start them at .050 and work from there.
 
What I do to find where the zero variance point to the lands is, I seat a bullet longer than will chamber. I then take the bolt out and hand feed the round into the chamber very lightly, this is so I don't get it jammed into the lands. Once I feel it contact the lands I stop and let it fall back out, seat it a deeper and continue until it will no longer stick to the lands when I push it as far in as possible. At this point I seat .010" deeper to allow for olgive inconsistencies of bullets, and then finish up my batch. I then document the die setting for that particular bullet so the next time I load them, I can get set up without having to do the above all over again. But I still do a chamber check to be sure that the new lot of bullets is getting them where I want them.

Using this method a guy can also seat them to a pretty precise distance off the lands if .010" isn't what your wanting and then know exactly where the olgive is in relation to the lands.

GS
 
Quote:
Originally Posted by USSR

See the OP - he has tools specifically made to measure base to ogive dimensions.

Don

The one he was talking about was specifically made for that also. It was just made by him & he got to save some money.
Click to expand...

Okay, kingmt, just to humor you, if he already has one tool to measure with, why would he need to construct a second one? Sheesh.

Don
 
I didn't say he needed another one but thanks for the humor anyways. He may tho because his does sound like such a pain for such a easy task.
 
kingmt said:
Your questions are hard to pick out of a the info.

I took a bullet & seated it long in the neck with little press then forced the bullet into the lande. I then colored the bullet with a sharpie & seated it deeper in the press until it no longer rubed marks in the sharpie. I measure OAL & reduce another ~.020". I don't care what the ogive measurement is. I use the dumy round to set up the die. I do this for each bullet. There my be better seating depths but there is only so many of the unlimited possibilities you can try.
Click to expand...
that's how I do it, too.
You have to do it again for each different weight and/or brand bullet, but then again.. isn't that why we hand load?
 
Again, thank you for all of the replies, recommendations and ideas. That’s why I asked these questions on THR!!!

I’ll be busy this weekend having a bit of fun in my workshop.

All the best,
Steve
 
Maybe a little late, but don't tear your hair out over this. I've been where you are and it really isn't that complicated. As has been mentioned, most over the counter rifles have really long leades and odds are that loading a round to get close to the lands and fitting into a magazine are going to be mutually exclusive.

Just find an OAL for your chosen projectile that functions reliably in the magazine of your rifle.
 
I have found that every rifle chamber is unique and the reference or SAMMI spec do not always reliably apply.

I have found Rugers, which I love, to have generally tight chambers for example.

You have your reality right in front of you.

Knowing your chamber spec with a particular bullet combo is the single most important thing a reloader can do in my NSHO.

Have you tried the optimum charge weight method for finding a particular load that works best with your rifle? You combine that with knowing your chamber spec and its pretty easy to come up with a great load.
 
Actually I have a much easier way to do this.

I will back down from a max charge in .2 or .3 grain increments and get a good 10% under a book max load to start.

So for example, 10 rounds would look like this:

42 42.2 42.4 42.6 42.8 43 43.2 43.4 43.6 43.8 44

This was grains of Varget in my .308. 42.6 and 42.8 and 43 grouped excellent. So I loaded another set only this time I added .1 grain to each load starting about a half a grain below my sweet spot and going about a half a grain above it.

The sweet spot for this particular brass/primer/bullet/powder and col turned out to be in the 42.6 to 42.8 range. That is one "node". You may find that you get two nodes in a set of rounds.

It is very important that you shoot at a target that is 200 yards out. That distance magnifies the barrel whip enough so that you can clearly watch the effect.

I generally wait about five minutes between each shot and I clean the barrel every 10 shots. I am trying to find a round that works great out of a one or two shot fouled cold hunting rifle.

If you want to do a little digging around check out http://www.varmintal.com/aflut.htm

Varmint Al is a genuine scientist from one of the national labs. And he is an avid reloader. He did an analysis of the barrel whip that occurs, in this case with a standard charge through a barrel of different diameters. He has done the same work with the optimum charge weight method of which he is a big fan.

When the round fires, a shock wave goes down the barrel, when it hits the end of the barrel it returns and so forth. It "rings" the barrel just like a bell. When the shock wave is at the end of the barrel it "whips" the barrel, actually it very minutely vibrates it. This changes bullet impact. What you are doing with optimum charge weight is finding the charge that has the shock wave back at the receiver as the bullet exits the barrel. No two rifles are exactly the same. So OCW lets you find the charge that is perfect for your particular rifle and ammo combination.
 
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