Seating Depth

[3potscreamer]

I've always seated the projectile 20 thou of the lands ( it's how I was taught ) and I've always had good results. However I'm working on a load at the moment that I can't get inside an inch at 100.
Would bringing the projectile out help make the difference. And if so do I use the most accurate load so far and start creeping out .005" at a time or do I have to drop the charge and work up again every time I move out.
You guys must be making me fussy nowadays.

[Seddo]

I have only seriously played with oal's once and it was surprising. I loaded up 8 rounds with 0.005" jumps in OAL and went to 300y and used a Farley rest and rear bag. It was a 243 win with 105gr amax. The best group was 0.010" off and measured 1.090" with 0.9" vertical. The best vertical was 0.010 in to the lands and it was 0.500" but the wind smashed the group and it was around 3". The end result was I now load the 0.010" into the lands.

Don't take what I have said as gospel as I'm sure every projectile is different. If I had the time I would do it for every rifle I own but I don't so the rest will have to wait.

[CZ550]

Most of my rifles prefer a jump of 40 thou. During load development I test my preferred powder load at 5, 20 and 40 thou off the lands to see which shoots best. The 30-06 had a huge improvement in accuracy just by seating the projie a bit further in.

Having said that, never tried seating into the lands like Seddo said...might be worth a go!

Regards,

CZ550

[Ned Kelly]

G'day all,
FWIW, I would only load into the lands with a varminter or target rifle (where you can usually shoot off the offending beasty), NEVER with a walkabout goat/pig/deer rifle. You need to ensure the rounds can be removed without the risk of a stuck bullet in the barrel miles away from either a gunsmith to remove the stuck case or a cleaning rod to remove the stuck projectile.
Fencing wire and quality rifle barrels DO NOT play well together!
Cheerio Ned

[Plowboy]

I just load as long as the mag will take. I am not really sure of the jump but for me, I am never going to be single loading while shooting bleeding things and that all I do. I did once make up a case to have a look at seating depth while touching the lands looked like and they don't fit in the mag.

[Teepee]

I have played with seating depth for all of my 20's
My conclusion is you need to do it once you have settled on a load that gives the best accuracy with that given rifle, projectile and primer.
As I only use CCI primers, that's one variable that stays constant.
It's amazing how much difference there is in just comparing say the 32g projectiles available as they are all different shapes. If you seat one to be .010" of the lands , you could find the next one will be .020" of the lands, simply by swapping from a vmax to say a Sierra bk.
I use a bullet comparator which I obtained from Pro cal trading (peter van muer) in bannockburn, vic.
Great little gadget which really takes out the guess work.

[stinkitup]

Lots of good advice, like Ned said horses for course as far as jammed or not jammed but OAL def can make a difference.

It is funny as I have my 6.5x55 50 thou for 140's that I hunt with can prob go closer but they always seem to shoot good and the 95 vmax well its probably more like 150. Just seat enough in the case to hold onto the bullet.

Vary in 10thous try seater 10 off and if you've already tried 20 go 30 and 40 and just see what happens if one of those shines then can go say 25 30 35 but usually you may not see a real difference.

Does the gun shoot sub inch with another combo?

Ryan

[aaronraad]

I use seating depth more as a fine/micro adjustment of a final load, but I've got a few reservations (brace for short rant):

1. Effectively you're changing the case volume/pressure curve, so why wouldn't we go back and redo our powder weights or even powder types
2. So we start at 0.020" and move closer to the lands effectively reducing pressure, then we get to <0.005" and you spike the pressure back up anyway, why does this work soemtimes
3. From 0.005" jump to 0.005" jam is pretty much no-man's land and getting a true measurement IMHO is near impossible, so we have to adjust our neck tension...another pressure adjustment
4. Going to something like a 0.010" jam requires minimal neck tension unless we've got one tough bullet jacket. BR shooters use this as a constant alignment technique more than a load adjustment, because their load is already good (<0.3 MOA) to begin with.
5. The closer we get with less neck tension the more we risk pulling the case out and leaving the projectile and powder behind. Ruined the day for many a target shooter and hunter.

I agree with starting at 0.020" and I don't go less than 0.007" myself. If the load (and the development loads either side of it) aren't showing signs of <1" @ 100y, then I don't expect seating adjustment will get you there.

I'd suggest doing the simple checks first, like scope mounts, bedding/action screws, a previous sub-MOA load, the nut behind the gun (give someone else a crack at a group), proper cross-hair/parallax focus, excess/unusual powder/copper fouling. Maybe move onto checking consistency of case/neck sizing, neck tension and loaded ammunition concentricity. VLD projectiles will sometimes require a VLD seating stem for consistent seating. If the brass has been reloaded a few times, do I need to consider annealing the necks again or new brass? Check the flash holes, trim length chamfer etc. I'd suggest being a little methodical here, because if you make too many changes here at once from your current regime you may not actually identify the cause.

If I'm confident with the simple stuff then I can justify going back to square one with load development by changing primer, projectile or powder to push for a significant/macro group reduction. This is the bit that keeps barrel makers in business so I'm only prepared to do one or two changes to re-develop a load, otherwise it's a warranty job or something I've done and I'm better off spending my time on another project.

Here is a link to Groups and Group Diagnosis, which might be of use to you now or in the future, all be it for small-bore shooting: http://www.rifleman.org.uk/Fuller_group_diagnosis.htm

Hope that was helpful and good luck.

PS: Tight throat (frree-bore) diameter tolerances in your chamber and higher neck tension can assist light projectiles in fast twist barrels, with long free-bores deliverer good accuracy...like the standard 6.5x55mm M38/M96 military spec. chambers, but very good throat tolerances. You don't want the projectile rattling around the throat any more than it has to before getting to the lands

[Ned Kelly]

G'day All,
nice one aaronraad, very well written.
That pressure spike at < 0.005" I believe is due to bullet jam being actually jammed into the rifling, in effect it is about 0.005-0.008 thou INTO the rifling, hence the pressure spike. Throw in variable dimensions on some mass produce bullets and you can off the lands or into them when using a seating die. I, too, do not like being at the jam figure because of the inconsistencies that you can get. It either 0.010" less than jam or 0.010" more than jam figure to be certain I am either jammed into or well off the rifling.
There are two excellent books that are well worth a precision shooters time to read, they may not exactly explain what is happening but they certainly illustrate the current BR tuning techniques.
They are:
* Extreme Rifle Accuracy by Mike Ratigan
* The Book of Rifle Accuracy by Tony Boyer
The two books cover just about all you could possibly need to know about tuning a rifle, and from two of the USA's top BR shooters.
But on the whole you nailed it, good read.
Cheerio Ned

[3potscreamer]

Thanks for the info guys I'll try going 10 thou either way with my best load and see what happens. I hadn't thought of going further from the lands.
Was talking to mick 762 he reckons trying a different projectile so that might be next.

[Ned Kelly]

G'day all,
DONT lengthen your pet load and try shooting them jammed ESPECIALLY if you are jumping the pet load.
You HAVE to reduce the load by 10% and work it up again with a jammed bullet.
The extra resistance of the bullet jammed into the rifling and not jumping forward can cause a dangerous pressure spike that NO-ONE here wants to experience.
Stay Safe
Cheerio Ned

[3potscreamer]

Thanks For the advice Ned.
I was going to stay well clear of the lands until I had more experience or some one with more experience looking over my shoulder.

[trevort]

3pot going into the lands is no problem as long as you work up to it for exactly the reason Ned says.

The only drawback of going into the lands is unloading and having a pill in the barrel and a chamber full of powder.

Its happened to me three times. Always have more than one rifle on a trip!


Now as far as critical nature of seating depth, the last time it happened to me was with the JAB 20, I don't think I screwed the seater down far enough when setting it up in the press. I came home, turned it down quarter of a turn and ran all the loaded rounds through again. It still put three shots in the same hole next time out.

[Ned Kelly]

G'day All,
there was an article in the now defunct "Precision Shooting" magazine a few years back that looked at the bullet position based on various jam settings, the conclusion from memory, was that with light neck tension i.e. bushing around 2 thou smaller than loaded neck diameter, the bullet would always push back to the same position in the barrel for a consistent jam.
So think of your throat as a secondary bullet seater. Where the bullet starts to push against the rifling and at some point it will move back into the case and that depends on the amount of bullet grip from the neck tension (AND the length of the case neck) of the resized case.
This is why I prefer jamming bullets and using moly bullets as I feel moly helps to prevent stuck bullets in the rifling and powder through the action.
Food for thought
Cheerio Ned

[justjeff]

Guys,

From a purely benchrest perspective, here's how I do it. Neck thickness is 11thou, neck tension 1 thou. Ladder test with 3 shot groups starting low, and working up, 10 Thou jammed. I use 0.5gr increments, but i am working with a big case (85gr H2O capacity). Look for the groups to open then contract, these are the nodes. Once you have identified the node that is accurate without excess pressure, load more cases at that powder charge, then try 10 thou jammed, 10 thou jumped, 30thou jumped, 50 thou jumped. Look at the results, you will find one is better, or if two consecutive, then reload for the half way point between them and see if it's better, but always load some similar to the last test for reference. This process will give you the optimum setting depth, and because the powder charge was set for jammed, you won't get any pressure issues.

All this is great, BUT, if the seating depth won't work in your mag, tough luck. This seating depth should remain constant in the bullet/barrel combination, regardless of the type and amount of powder, so if you want to try a different powder, you shouldn't need to go through it all, just ladder test for the nodes.

My 2 bob's worth.

Jeff