Experimenting with seating depth?

[RoughNeck182]

Hi guys. I'm new to reloading and I was wondering about experimenting with the seating depth of my loads for my new Rem 700 SPS Varmint in .243. I have measured the length to the lands with a homemade dummy round with low neck tension that gives me very repeatable measurements, confirmed with other dummy rounds marked with smoke/marker to confirm the length where contact is made on the ogive. I planned to start at 0.010" off the lands and move further away at first because I don't have a bullet comparator yet and didn't want to get any closer without a good way to check variations other than OAL which seems to vary quite a bit. BTW I'm using the Hornady 105 AMAX and retumbo powder. Does this sound safe enough for trying starting loads, and then working up in charge? Also, when I get my RCBS Mic set and have more confidence in my precision, what is the safest way to try 'touching' the lands or even 'jamming' my bullets, (starting loads okay to try jammed?) and is that even worth experimenting with? This rifle will be used for fun-target, plinking, varminting.

Thanks, any advice would be much appreciated!

 

[sailhertoo]

Re: Experimenting with seating depth?

I'm trying this now myself if the wind would stop blowing long enough to get to shoot!

I've got a stony point seat depth gauge that I use. Can only be real accurite if the head space measurement is the same on the cases. I use a stony point for that too.

I am going to start at 15 thous. and then 10 thou., 5 thous., then touching, then jamed a little. I"ll see which of the 5 groups are the best and maybe fine tune a few thous. from there.

 

[RoughNeck182]

Re: Experimenting with seating depth?

Sailhertoo, I had a similar plan. When you touch/jam will you just use a listed starting load and work back up to your preferred charge? I just wansn't too sure how much of a jump in pressure to expect, if normal starting loads would still be the recommended starting point with no bullet jump...

 

[sp388]

Re: Experimenting with seating depth?

I have read and experimented with the OCW and audette ladder methods for load development.

I am up to the part of the OCW that says charge weight is good to go and to start worki9ng on seating depth - - - in the OCW method he is against group sizes....

So when trying different overall length and seating depths do I look for POI to move like the OCW workup or can I go back to kicking myself for 'group sizes' ????

What do you look for ?

 

[Greg Langelius *]

Re: Experimenting with seating depth?

I find that seating depth's relationship with rifling contact will vary to the same extent that ogive lengths vary, and this is a very natural relationship.

For initial load development, I always produce ammo to an identical true OAL length, and I personally prefer to ensure that I have a definite jump, and will try to arrive at an initial depth that is greater than ogive length variances, and also add a small (.005"-.010") fudge factor, to essentially guarantee they <span style="font-style: italic">all</span> jump. I do this because contact pretty much guarantees at least a small pressure spike, and I would prefer to ensure that my load development gets done without any such added complexities.

It is only after all other aspects of load development have been reliably resolved that I will experiment with seating depths, and if I decide the load needs to be in contact, I will ensure it is in definite contact regardless of ogive length variations, and I will also do some minor load variations to deal with the potential for newly introduced pressure spikes. I believe such issues can alter the ideal charge level.

You don't need to shoot groups and you don't need to be kicking yourself either for shooting groups or not.

I produce a load development target using a word processing program. Using a large type style and bold print option, I create a target that has rows of five 'o's of roughly 1/2" in size. At 100yd, I fire one shot of the same charge weight increment at each one of the 'o's in a row, then do the same for the next charge level on the next row. This way I can tell how well/consistently each increment delivers a POI relative to the POA, and can isolate and keep track of each shot more easily in terms of called flyers or observed wind gusts. For statistical purposes I usually try to shoot at least 2 rows of each increment, but there are also practical limits to how many rounds I am willing to expend these days in load development.

Greg

 

[Mag 300]

Re: Experimenting with seating depth?

SP308

if your not looking at group sizes then what is the criteria???? that is the end state that your trying to get to correct?
I also have to look at the OCW and the audolette ladder.
hate to say it but when working up a load for a 308 gap stumbled on 44 gr of RL 15 with a 168 gr .010 off the lands "jump" and its shooting .25 moa.
Not trying anything else ????

just lazy I guess.
But interested in what you find and the theread in that I have 9 other rifles to perfect a load for .
Thanks Bill

 

[sailhertoo]

Re: Experimenting with seating depth?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RoughNeck182</div><div class="ubbcode-body">Sailhertoo, I had a similar plan. When you touch/jam will you just use a listed starting load and work back up to your preferred charge? I just wansn't too sure how much of a jump in pressure to expect, if normal starting loads would still be the recommended starting point with no bullet jump... </div></div>

Well I worked up to the best shooting load first and now I'm going to vary seat depth and leave the powder load the same. I will be watching for pressure signs as I load closer to the lands.

Don't know if this is the correct way to do it or not but its what I'm going to try.

 

[sp388]

Re: Experimenting with seating depth?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bill Stoffels</div><div class="ubbcode-body">SP308

if your not looking at group sizes then what is the criteria???? that is the end state that your trying to get to correct?
</div></div>

Bill, I agree 100 percent. This was put out as a question more out of curiousity. I have settled in on 43.5 varget which averages 2710fps and shoots pretty well. But like everyone, I wonder if it could do better, so seating depth is an option. I have seen over adn over here that everyone says to adjust your seating depth because each particular rifle may have its own ideal depth with different bullets... no arguement there.

Part of what caught my attention with this thread is because when I tried to use the ocw method last october (my ocw method was wrong because I didnt round robin) I settled in on 43.5 varget but there have been a few days it has shot awesome and a few times when it was mysteriously off. -- To me it seemed like a logical answer that my 43.5 varget was maybe the high end of the 3 ideal charges as described on newberry's OCW page.

I was just curious what everyone does to find the ideal depth because many say to do it but few say how.... I am a group size man and that will probably never change- probably due to an incurable form of OCD that many "precision" shooters have. - - - I threw in the part about dan newberrys OCW (similar to OCD by the way) for conversation purposes and curiousity.

So yesterday I went out and tried another OCW workup figuring this time I would follow directions. I was expecting that this would yield nearly the same results as october- 42.5 and 43.5 varget with my 175smk, in fed 1X neck sized on 210M's sent over the CED chrono.

My results were as expected..... different. My increments were 42.5, 42.8, 43.1, 43.3, 43.5, 43.7, 43.9. I expected 43.5 to shoot well and that is why I went in 0.2 increments there.

 

[KQguy]

Re: Experimenting with seating depth?

I would advise against seating the bullet in or even close to the lands,I would stay at least .010" off the lands.My reasoning is,since the ogive varies from bullet to bullet,you will get different amounts of pressure from round to round.Another reason to avoid seating bullet to the lands is because as the throat erodes,you will need to "chase the lands",in order to keep whatever pressure you developed from jamming the lands.So basically,you will alway's be retuning your load.I personally have never found any benefit in acccuracy to loading to,or into the lands.You will get much more consistancy by jumping.Just make sure you have good bullet runout,if you jump the lands though.

 

[eitmsmf]

Re: Experimenting with seating depth?

Jumping more will INCREASE pressure not decrease. Eric Stecker had a post on 6BR.com about depth and there were some pressure increase numbers listed and showed the increases as the bullet was jumped farther. I also have never seen properly loaded ammo "vary" at the ogive. The throat will stay sharper and not run as fast with a touch instead of being hit every time the gun is fired. Also ammo that has runout will not be corrected by jamming.

 

[glock24]

Re: Experimenting with seating depth?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eitmsmf</div><div class="ubbcode-body">Jumping more will INCREASE pressure not decrease. </div></div>

Be careful with this statement . . . I found myself in a knock-down, drag-out argument a few months ago regarding this;

http://www.snipershide.com/forum/ubbthre...3432#Post973432

Long story short, I learned that seating the bullet deeper (more jump) gives the bullet more of a running start into the lands, thus reducing the pressure generated.

Of course there is a point where seating the bullet too deeply will decrease the internal case volume to the point where pressure begins to rise again, but it is not a linear relationship starting from the lands and going deeper . . .

 

[KQguy]

Re: Experimenting with seating depth?

The actuall bullets vary,take 10 or so bullets and load them,then check and see what the rounds measure to the ogive.You will notice,they vary some.Or you could just measure to the ogive on just the bullet themselves,and see the variation.When you try to load to the lands,and have varying ogive dimensions,you can have some inconsistancy's in your loads.Also,throat erosion is not caused by bullets slamming into them,it is caused by powder burn.That is why magnums burn out barrels so much faster than non magnums.

 

[eitmsmf]

Re: Experimenting with seating depth?

glock24 is right. I should have put CAN in my statement. In the lands will increase start pressure but the jump CAN increase max pressure, velocity, and shorten time in the barrel.

I usually don't post here because I shot benchrest and trust me, the rituals I go through reloading would drive most people nuts.

 

[RoughNeck182]

Re: Experimenting with seating depth?

Well about the pressure debate - my first loads ~10 thou off the lands seemed to have less primer flattening than the original loads, which I expect would be the case until you actually touch, or come very close to the lands? Anyway seating 10 thou off the lands seemed to shrink the groups for sure in both loads I tried. With 37 gr IMR4350 the loads shot to the same POI just a tighter group, which seemed very handy, this way I can load mag length or 10 thou off the lands (or wherever turns out best for accuracy) for single loading depending on what I'm doing and with minimal changes.

SP308 - I'm planning to try the OCW and ladder tests as well, please keep me posted on how things are working out for you!