Seating Depth Depth - Opinions Please

[ChocDog]

Here is my rough seating depth test for 120 gn Nosler Ballistic Tip over 44.3 gn of Varget.
Info
Rifle - Tikka T3x stainless light in 7mm-08, 22" barrel
Scope - Vortex Viper HST 4-16 X 44
Brass - Lapua, 4x fired, fl and neck sized to .002 neck tension, annealed after every firing
Primer - Fed 210
Dies - Redding - body, neck sizing, competition seater, instant indicator
Press - Redding T7
The rifle is for hunting and punching paper. My thoughts are I should focus on the node at group #5, even though group #2 is smaller. The reason being is the group #5 is horizontal and #2 has some vertical properties. Does this make sense? Am i on the right track? I was planning to try to fine tune on either side of #5 to try to tighten this up. I know this is a hunting rifle, but I do have plans to take this out to possibly 400 yards.

Any thoughts or comments would be greatly appreciated.
Thanks in advance!

 

[dsculley]

If it were me I would test a wider seating depth range. I like to use the Berger test. I have found that bullets that are not supposed to be sensitive to seating depth sometimes shoot better with some jump. In my 6.5x47 Berger 140's are jumped 0.075" and RDF 140's 0.070". If I read your target correctly, you tested from 0.006" jump to 0.006" jam. for me, that is a pretty narrow window.

 

[Richard Coody]

is 2.80 touching the lands?

is it mag length?

with a hunting rifle i usually go max mag length and then get shorter by .010. i have also used the berger seating depth test with great results. some seating depth nodes can be .030 wide.

 

[ChocDog]

If it were me I would test a wider seating depth range. I like to use the Berger test. I have found that bullets that are not supposed to be sensitive to seating depth sometimes shoot better with some jump. In my 6.5x47 Berger 140's are jumped 0.075" and RDF 140's 0.070". If I read your target correctly, you tested from 0.006" jump to 0.006" jam. for me, that is a pretty narrow window.

I agree the test was pretty narrow and I was limited on time and needed to start somewhere. Isn't the Berger test for VLD's? Do you think this would work for non VLD's? When I was measuring to the lands, using the Alex Wheeler's approach and the Hornady gauge using a modified case that I made from my fired cases, the 120 NBT does not leave enough bearing surface to start at the lands

Is the the test you are recommending (for Berger website)?
Load 24 rounds at the following COAL if you are a hunter (pulling a bullet out of the case with your rifling while in the field can be a hunt ending event which must be avoided) or a competition shooter who worries about pulling a bullet during a match:
1. .010 off the lands (jump) 6 rounds
2. .050 off the lands (jump) 6 rounds
3. .090 off the lands (jump) 6 rounds
4. .130 off the lands (jump) 6 rounds

Shoot 2 (separate) 3 shot groups in fair conditions to see how they group. The remarkable reality of this test is that one of these 4 COALs will outperform the other three by a considerable margin. Once you know which one of these 4 COAL shoots best then you can tweak the COAL +/- .002 or .005. Taking the time to set this test up will pay off when you find that your rifle is capable of shooting the VLD bullets very well (even at 100 yards).

 

[ChocDog]

is 2.80 touching the lands?

is it mag length?

with a hunting rifle i usually go max mag length and then get shorter by .010. i have also used the berger seating depth test with great results. some seating depth nodes can be .030 wide.

2.80 is (was) mag length. It was what was used for my initial OCW. I just swapped out the mag and bolt stop to allow for longer seating depth.
This small/short of a bullet does not allow enough bearing surface in the case to touch the lands. Offhand, I think at 2.80 it was .167 jump, i'll have to check my notes.

 

[Richard Coody]

2.80 is (was) mag length. It was what was used for my initial OCW. I just swapped out the mag and bolt stop to allow for longer seating depth.
This small/short of a bullet does not allow enough bearing surface in the case to touch the lands. Offhand, I think at 2.80 it was .167 jump, i'll have to check my notes.

unless you plan to single load at the range there is no sense in testing anything longer than mag length. if you do want to single load i would pick a different bullet. a match king or berger hybrid. both are easier to tune than VLD's.

i would test from mag length until you compress powder or the ogive starts into the neck at 0.010 increments. you can go 0.020 increments for a rough test and then fine tune at 0.005.

 

[ChocDog]

unless you plan to single load at the range there is no sense in testing anything longer than mag length. if you do want to single load i would pick a different bullet. a match king or berger hybrid. both are easier to tune than VLD's.

i would test from mag length until you compress powder or the ogive starts into the neck at 0.010 increments. you can go 0.020 increments for a rough test and then fine tune at 0.005.

I just swapped out the mag and bolt stop to allow for longer seating depth to have the flexibility to test/shoot longer bullets. That's the thing about Tikkas, their short action calibers are built on long actions and use a short bolt stop and a blocked mag. I am going to try a modified Berger test this week.

 

[FeMan]

I would recommend shooting more than three shots. After getting burned a few times by a small three shot group that wouldn't reliably repeat itself, I have gone to at least four if not five shot groups. I have had bergers hammer jumped from 3 thousandths to 250 thousandths. Most of my loads are 20 to 60 thousandths but that certainly isn't the limit.

 

[Dusty Stevens]

I would recommend shooting more than three shots. After getting burned a few times by a small three shot group that wouldn't reliably repeat itself, I have gone to at least four if not five shot groups. I have had bergers hammer jumped from 3 thousandths to 250 thousandths. Most of my loads are 20 to 60 thousandths but that certainly isn't the limit.

I dont think his barrel is gonna like 5 shot groups being a pencil barrel. I wouldnt even shoot 3 shot groups with a small barrel like that. Its for hunting- 2 shots will tell the tale and it wont get smaller with another shot. And with barrel heating that 3rd shot could go anywhere giving you a false negative on a load.

 

[Willie]

I would suggest shooting over a quality chronograph. The target and your velocities will give a better view of how consistent your loads are. I use a modified Berger test, from .010 off to compressed. It takes a while, but I let the barrel cool between shots.

 

[Pvt.Donut]

Berger test is a good starting point. Depending on your magazines I've also loaded to mag length, then seated deeper in 0.020" increments similar to the Berger test.

 

[dcali]

I agree the test was pretty narrow and I was limited on time and needed to start somewhere. Isn't the Berger test for VLD's? Do you think this would work for non VLD's? When I was measuring to the lands, using the Alex Wheeler's approach and the Hornady gauge using a modified case that I made from my fired cases, the 120 NBT does not leave enough bearing surface to start at the lands

I don't think there is anything special about VLDs - Berger's suggestions are just basic reloading practice, in spite of their focus on VLDs. I think VLDs got a reputation for being finicky for reasons other than actually being finicky, but that's another topic.

Also, don't read anything into the shape of 3 shot groups. They're probably random.

I've found that seating depth windows can be much smaller than Berger says, but the general method is sound. .003" is a pretty tight step in seating depth. I usually start .005" into the lands and then back off in 10 or 15 thousandth increments. (If the load is to be used for hunting, skip the jammed load). Then, once you get a good feel for where the loads shoot well, THEN fine tune it with .005" steps. That ought to get you in the right spot. I would also shoot 4 shot groups rather than three, and 5 shots for the final tuning. (You may have to do this slowly, as heat *could* screw things up).The fine tuning may or may not help with a factory rifle. I would stop if you can get consistent 5/8" groups of 5 shots, and I wouldn't be surprised if you don't get there at all. The rifle's only so good - a consistent 3/4 MOA may be all it's good for, and possibly not even that.

 

[RGRobinett]

"Also, don't read anything into the shape of 3 shot groups. They're probably random." (damoncali, above)

Especially with such a small sample, and relatively equal group sizes. That said, I have a Tikka T-3, 300WSM, which consistently stays under .625" for 5-shot groups. I did pillar-bed and install a Harrels' muzzle-brake.
Though not great precision, for a factory riflle, intended for hunting, and featuring a light barrel, it's decently solid performance. The BIG key - the first shot - cold/clean barrel - is always right in the "group". RG