Rifle Tuning Sr/Lr

[brantfredrickson]

This graph from Brownell's book, Firearms Pressure factors suggests there is an optimal seating depth where that change in seating depth produces a zero change in maximum chamber pressure. When a load prints well on a tuning target over a range of seating depths, perhaps I have found the optimal seating depth. Again this is not what I am looking for. And again I am looking for a seating depth that performs well over a variation is charge weight. Any thoughts...

 

[Ggmac]

I would think data would be better if each was a 5 or ten shot group . At a min 3 shot groups repeated a few times to eliminate human , error . Unless of course it's in a shooting machine in a very specialized tunnel .

 

[Tim Singleton]

Great information, Tom
Lots of people always asking questions about staring loads. Asking about Powder load info
I'm saying looks to me likr seating depth is the factor in tuning a gun short or long range
Not what some want to hear because it means they have to go out and shoot their gun and figure it out themselves

 

[Cool Tool]

There is know doubt tuning at the distance you are competing is very important.PS good job Tom

 

[Martin52]

Interesting, my powder ladder shows very little vertical with loads between between 44.2 and 44.8gr H4895 (155.5 Bergers) but I'm struggling with the horizontal spread.....sounds like more work is needed on seating depth.

 

[Canadian bushman]

I dont shoot nearly as small as others here but this is what ive done lately.

1. I do a real quick powder ladder (.5-1gn) working up to find where a safe/comfortable charge is and also where i start to get too hot.

2. Then i do some group shooting with different seating depths (.01-.02) to look for a window that looks like its shooting more of a round consistent group than other depths.

3. Now i will typically shoot another powder ladder at distance (600-800yds) as well as some groups with smaller changes in powder (.2-.5gns) trying to find the middle of a sweet spot.

4. Here i go back to seating depth, creeping forward and back in small increments (.005") looking for small groups and waiting to see where the groups open back up.

Usually by this point i know if i wanna chase neck tension and primers, or if im going to try a different bullet or powder.

 

[Alex Wheeler]

View attachment 994827

Hopefully when all aspects have been worked out, it looks like this.

Red is .005 jump
Blue is .007 jump
Yellow is .009 jump
Window found! unfortunately not all barrels will put ten down there at 2.570", but you get the point.

Tom

If you did this ladder at 600 or 300, or shot groups at 100 I would bet the farm you would end up with a different result. Unfortunately I dont know a way to get around tuning at the range you want to shoot if you need top accuracy.

 

[Rust]

As I mentioned in a previous post, I use Lapua Scenars (6.5 140 gr) which I put lightly into the lands. I've found the Scenars to be a very tolerant bullet regarding seating depth into a 1-1/2 degree leade. The latest hybrids not nearly so much.

Seating into the lands does result in higher initial pressure but I use a lighter load than a lot of folks and still get a very respectable 2940 fps which is the sweet spot with single digit ES/SD numbers.

For finding a load I check to see what commonly works. The three recommended powders were RL-22, H-4831 and H4350. H4350 worked best and the only time I've done any further testing was with a new barrel or a different lot number of powder, primers or bullets.

I'm not one for chasing magic combinations any more, they don't exist in the first place. If you've got something that works leave it alone and practice. If you've got an F-Open rifle that will hold the bull at 1,000 in mild conditions run with it.

 

[DHD]

A question about seating depth here.

When a barrel ages, do you find that the preferred seating depth remains similar? You guys shoot out many more barrels than I, so I figured I'd ask for your experiences here.

FWIW, I find my rifles tend to prefer the same seating depth even as the throat moves out. I have a Bartlein in 6×47L that groups opened up some and decided to check the seating depth. I used the new depth and it started to shoot great again. I did not change the powder charge. This was at 600 yards.

I have similar experiences with my other calibers.

 

[mikecr]

This graph from Brownell's book, Firearms Pressure factors suggests there is an optimal seating depth where that change in seating depth produces a zero change in maximum chamber pressure. When a load prints well on a tuning target over a range of seating depths, perhaps I have found the optimal seating depth. Again this is not what I am looking for. And again I am looking for a seating depth that performs well over a variation is charge weight. Any thoughts...

The graph is simply showing a case of seating depth affecting peak pressure. On contact side due to powder timing with higher earlier starting pressure, on the other due to load density. But we can compensate with any one, for any other, and it still does not change the fact of where best tested seating is.
That is, I can test for best coarse seating at several different loads, and it will always end up in the same place. It's just easiest to see it when we are far enough from powder or barrel nodes that seating changes do not take us in/out of them while we're trying to see only seating. So when I test, I back the charge away from any suspected best/intended powder charge, and while the grouping is larger, seating affect itself is easier to see.

With a 6.5wssm Imp & 28" barrel, I knew intended mid node would be ~2950-3050fps. There would be a high node ~3200, and a low node ~2800. I did full seating testing during fire forming in two segments. ITL testing with a load producing ~2825, OTL at 2850. This kept me out of any nodes even while moving within a pressure curve, similar to Brownell's example. This is basically Berger's recommended seating testing. I do 3 shot groupings at 300yds. It's relatively bad grouping the whole time, and I'm talking 1moa at times, but I could clearly see best at ~10thou OTL, and 90thou OTL. Nothing good ITL. These areas brought my worst to 1/2moa. I chose 10thou OTL, and now with fire formed brass, I go to work on powder with ladder testing and chosen seating. This got me to 3/8moa, and with tweaking of seating to define it's window, providing best group shaping, and a couple primer swaps & firing pin setting testing, I reached 1/4moa. My seating window ended up 8thou OTL +/- 3thou.
Around 250 shots I guess, IMO not bad for a new wildcat, with nothing really known there. It was easy and made sense all the way.
With every shooting system of mine, seating has shown to be the biggest adjustment to results, by far. Way more than powder. I believe tension has the potential to at least hurt us more than powder itself. I know primers and primer striking can. Powder seems to me the finest adjustment. If I could, I would move to powder/ladder testing at 1kyd. But I would always work out everything else, the coarse adjustments, closer.

The fine tweaking of seating shot in earlier mentioned ladders is only shaping,, and possibly evidence that OTL works better with the load than ITL. Well, probably, but that's all. This is not the opening/closing seating nodes that come out in full seating testing. So if that's all that was done for seating, 5thou off could actually be a terrible place. 17thou off might be better, for all anyone knows there. But an excellent demonstration in seating shaping.

 

[Mulligan]

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[Titan700]

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