Seating depth-- more than one sweet point?

[WV1951]

If it matters, 12FV, .223, 69 SMK, front and rear bags.
Still working on loads and thought I had found the niche, but a bit inconsistent. MOA not a problem(if I do my part).
For s&g's, I loaded some to OAL to match some Australian Outback that shot well some time back.
My initial .030 jump is now being closely matched by a .075 jump.
The inconsistency I believe is on the trigger puller, but curious if you have found two seating depths so far apart that work?

[Texas10]

I've noticed that too in my 12FV, 223. Seating depth changes that large tend to change barrel time, max pressure, and velocity. It'd be interesting to chronograph those loads and see what kind of velocity change you're experiencing.

I performed a seating check using the .040 technique where you seat one group of loads touching or lightly into the lands, next one .040 off, next is .080 off, etc. and as I recall I went out to .140 off.

I started by shooting the group loaded to the lands, and worked my way off. All groups printed lower on the chart than the previous, with the exception of the last ones loaded to .140 off. Those printed much higher and tighter, but also cratered the snot out of the primer. I did not own a chronograph at the time, so I had no data to explain the higher POI.

Using this method, one of the groups will shoot much better than the rest, and that is the distance you begin to refine for that particular bullet.

Here is some interesting reading;

http://www.the-long-family.com/optimal%20barrel%20time.htm
http://bulletin.accurateshooter.com/2010/02/neck-tension-bullet-seating-and-the-time-factor/

And if you're really having trouble falling asleep some night: http://archive.org/stream/velocitypressure00culv/velocitypressure00culv_djvu.txt

[WV1951]

Yea, I can see where .140 off would probably trigger some pressure signs. Somewhere on here Darkker posted a graph showing the pressure close to the lands and far off the lands. I noticed more cratering as I got closer to the lands. Didn't pattern well anyway.
Based on your experience, I might try a few even seated deeper and go .085 off. Hate to try more with a 69 grainer. Too much bullet in the case neck. Funny thing, only thing that comes close with the 55's is nearly in the lands.

[Fotheringill]

Try this method from Berger.

It works with whatever bullet you are using.

http://bulletin.accurateshooter.com/2009/03/berger-tips-for-loading-vld-bullets/

[Texas10]

Today I shot a seating depth workup with 69 gr. Tipped Match King in 223 and 25.5 gr Varget out of my 26 inch CBI barrel with 8 twist. Loads started at -.015 and worked down to touch in .003 increments. Here's the results, all shot at 100 yds.
-.015, 5 shots, .604 mostly horizontal with one flyer (#1)
-.012, 5 shots, .492 2 separate bug holes with one flyer (#1)
-.009, 5 shots, .412 4 leaf clover group
-.006, 5 shots, .455
-.003, 5 shots, .362
-.000, 5 shots, .394, most vertical element

Flyers were my shooting, I was switching back and fourth between a 308, also working up a seating depth, and the 223 with it's much lighter trigger. I got a few shots off before I intended.

According to Sierra, the TMK has a longer bearing surface than the SMK, so a separate load work up is necessary. At my charge weight, I was getting a some significant cratering, but no blanking. I was using CCI400 primers, and can switch to BR-4 to help with the cratering.

Hope this helps.

[Deadshot2]

Several years ago I ran across a thread discussing charge weights and seating depths. The consensus was that one should start their load development with bullets seated out so they just contacted the lands. Starting low, work up the load for best group size, not changing seating depth. When you've found the best group that is as high as you can go without excessive pressure, you've now established an upper limit for that bullet/powder/primer combination in your rifle.
Now start shortening the COAL by .005" increments, shooting groups of 3 for each length. Stop when you reach the published Minimum COAL (or you reach that magic one-hole group :p. Of course you may be limited if you shoot from a short magazine and have a long leade (like Remington .308's). Then your maximum mag length is your starting point. One can keep fine tuning by raising or lowering the powder charge weight but not the seating depth. Only change one at a time of course. Soon you'll reach the point where any change in powder charge or seating depth will be less accurate. Just like tuning a radio by playing with antenna and tuning knob, one at a time, until the station is clearest.


If shooting VLD's (or the new ELD's from Hornady) you might want to make a pass through by shortening .020" for each increment and then work around the best groups you find then.

If you want "bughole" performance patience is the quickest path to that destination along with an organized path.

[390fe]

Apples and oranges, but on my .308, I can pick up about 50 fps by seating my bullets .055 deeper.

[Deadshot2]

Apples and oranges, but on my .308, I can pick up about 50 fps by seating my bullets .055 deeper.

Not really. Seating deeper reduces capacity of the case which raises pressure when the charge weight remains the same. "Playing" with seating depths can alter speeds in varying amounts. Also alters barrel timing, etc, etc.

As an example of how case capacity plays a big role, I am reforming .308 Palma (Lapua) brass into 6.5 CM brass so I can have both the benefit of the small primer AND leave $40+ in my wallet by not buying the Lapua 6.5 CM brass. The reformed cases hold about 2 grains less powder but I am shooting at the same speeds as published max with less powder. OK, part of it might be my barrel too (a hand lapped Benchmark) but volume and pressure, which sends the bullet down the bore, are closely related. A few thou, one way or another, is often an easier way to adjust than changing charge weights. Also a way to alter statistics like ES and SD as powders enjoy an optimum case fill ratio.

[WV1951]

Not sure I asked my question correctly. I am not asking for seating depth suggestions, but rather if anyone has experienced good/similar results between two seating depths. Obviously, the charge may be a bit different.

[short round]

The way I adjust for seating depth is to use target, made of target paper, not typing paper or printer paper. Load three rounds of each seating depth. Now fun part, shoot for group. Observe bullet hole size, some will be smaller than others. The larger hole shows that the bullet is not stabilized at that range. I want a small clean hole with no tearing around the edge.

[RC20]

Not sure I asked my question correctly. I am not asking for seating depth suggestions, but rather if anyone has experienced good/similar results between two seating depths. Obviously, the charge may be a bit different.



Yes I have. I did use the Berger method of .030 deeper at each step.

I am working with H208 ELD Ms. I got them pretty well down in the 1/2 MOA area, also got some 1/4 MOA but randomly.

I thought I would do the Berger method and I moved a group of 5 each back .030. I was back about .090 (total of .120) and it came in consistently under a half, more like a close 1/4 to 5/16.

Next two step back was far worse.

[WV1951]

So, RC
Did you settle on one or the other, or just keep looking for the magical one hole load, lol? My two looks to be .030 and .075 off. I may end up a little different when I try changing only .005 instead of .010.
Were the groups between the two seatings similar?

[Texas10]

The question of which of the two nodes to work with, .030 or .075 off is probably best answered with a chronograph. JMHO, YMMV.

[Deadshot2]

The question of which of the two nodes to work with, .030 or .075 off is probably best answered with a chronograph. JMHO, YMMV.


That or see which one is more consistent by shooting a series of groups using each seating depth. I might load a box of 50 and shoot 5 groups of 5 for each and at the end of the day look to see which one maintains the smallest group. That would be the go-to seating depth.

On the other hand, the one that fits the magazine would be the winner. If both do, see above.

[DT400]

I have. .002 and .062 off of the lands print the same in one of my guns. The .062 prints 1 MOA higher and I attribute that to the reduced case volume. I wasn't using the chrono at the time so I am not sure of the actual FPS difference.

Darrell

[WV1951]

After all of the above is worked out, haven't even got into the powder preference question. I have been trying Varget and H4895. Getting somewhat similar results, but probably an edge to the H4895 with the 69's and maybe(??) Varget with my 55's, but the 69's seem to be the best groups.
Geesh, this gets confusing. Had little idea of what I was getting into when I started chasing this.

[WV1951]

Well, after hemming and hawing around for a while, I think I found my niche. Picked up some IMR4895 and liked the initial results. Then tried two different cases and looks like FC is my choice for these 69 SMK's. I had several groups sub MOA with different seating and slightly different loads, but still thought I could do better.
Now I am going to move on to 55 SGK's, and see if I can find something that will work.
http://i55.photobucket.com/albums/g152/mandn1951/IMG_3013_zpsebneegiq.jpg (http://s55.photobucket.com/user/mandn1951/media/IMG_3013_zpsebneegiq.jpg.html)

[Texas10]

More grist for the mill...
Been having some trouble developing a good shooting load for my 22-250 using 80 SMK and H4350, not the least of which is availability of H4350..He he. Then I realized that I'd started load development using the OTC method first, and seat depth second. I have since change to the seating depth first crowd, so I decided to start over. (I'm getting there WV....I'm getting there)

I picked what looked like a good starting charge from previous range sessions, and seated bullets starting at .030 off and working forward in .005 increments. Interestingly, the .020 off load shot a 3 round group measuring .180 moa at 200 yds. But the .010 off and .000 (touch) were both in the low .2's so almost equally good.:cool:

So there you have it, 3 different sweet spots between .030 and .000 with all the others shooting about half a moa.

Now I just have to worry about availability of H4350 when I run out....:(

[rckendall]

I hope this isn't too far off the topic at hand, but I recently worked up a load for my 12FV in 223 also, using 69 gn SMK. I used both some old Federal Gold Metal Match and new, remanufactured Black Hills 68 gn ammo as a baseline for accuracy. Both of these were considerably shorter than mag length.

I found sweet spots with both Varget and 8208 using mag length seating and never did do any seating depth testing. I have gotten a 1/4" 5 shot group, many 1/2" 5 shot groups, and now average about 5/8" for 5 shot groups in most all conditions. I am happy with what I have, but, am I giving up anything? How much of a difference can be seen with these seating depth tests?

Thanks,
Richard