Seating depth test. Thoughts on where to tune?

[Nik S]

This is an update on a previous thread: here.

Looking to tune this seating depth test. Could use some insight on best practice.

Shooting:
6.5 Creedmoor
20" barrel
IMR 4451, 40.4 gr
Federal large rifle primers
Lapua 139 Scenar-L
The target crosses are 2"x2"
4 shot groups
No chrono

Following a previous load test, I went with 40.4 gr IMR 4451 and then experimented with seating depth in .01 increments between 2.70 and 2.79 COAL. Results look better results overall. I think we're narrowing down, but not quite there yet.

2.74 and 2.75 look remarkably similar. Should I be experimenting in .003 increments between those?

2.77 looks quite tight, but I'm a little concerned with the spreads of 2.76 and 2.78 around it. Would this be considered an "unforgiving" node to stay away from?

 

[FUNCTIONAL]

Those groups look way too big overall even in the better ones. I would look to change the charge weight, maybe even the powder first with the bullet .02 off the lands. You really should see if you could hookup with someone who has a chrono, can be done without it but it's more testing.

To answer your general question I've recently been seeing there is a range with bullet seating depth that will give good accuracy. It's own type of node. Saw it for sure in my last workup with RDFs that between .1 off and .12 (yes those jumps are correct) off it shot the same. I picked .1 to off so as lands erode and jump gets bigger ill still have a tolerant bullet jump. I've read some bench rest guys have been mapping this also. They go in .005 increments but I feel .01 increments are fine. My "wide" seating depth test I do in .02 increments from on the lands to .140 off.

 

[CK1.0]

I can see you're shooting a 20" barreled 6.5CM, and I'm no Sherlock Holmes here, but I'm going to bet it doesn't weigh 23lbs and have a sick 6oz trigger too?

If you're fairly new to this and also shooting a light rifle with a heavy trigger, then making calls based off group sizes isn't going to work quite as easily as some guys make it look. No douche-baggery meant here, but it just kind of looks like you can do better than that as far as the overall groupings are concerned before getting into specifics over which load is working better, and I feel like once you've got it figured out a little more there should be no reason why at least a couple holes aren't touching in each and every group regardless of what the load is doing, ya know?

IMHO if you're using a bipod/rear-bag now, I'd switch to bagging the front and the rear, or seeing if you can get it into a full-on rest rig (just try to remove the shooter from the equation as much as you can). Try to get the rifle super stable . as stable as you can manage, and then shoot some groups, my guess is they'll look a lot different.

 

[BuildingConceptsllc]

I've had a good friend who is experienced at reloading helping me develop loads because I'm really just not there yet doing it on my own. I would be waiting too much ammo and time without his help. Those really aren't the kind of groups that we would be trying to tune. I would consider what the poster above said, and make sure that all you are seeing in your groups is the gun and ammo. Then I'd get a chrono, and figure out my powder and powder charge. Once you have groups that are tight, and are all generally tight, then you can start looking at seating depth. There's Many others here with more experience than I have at this, but that's my 2 cents.

 

[Cfshooter]

This is an update on a previous thread: here.

Looking to tune this seating depth test. Could use some insight on best practice.

Shooting:
6.5 Creedmoor
20" barrel
IMR 4451, 40.4 gr
Federal large rifle primers
Lapua 139 Scenar-L
The target crosses are 2"x2"
4 shot groups
No chrono

Following a previous load test, I went with 40.4 gr IMR 4451 and then experimented with seating depth in .01 increments between 2.70 and 2.79 COAL. Results look better results overall. I think we're narrowing down, but not quite there yet.

2.74 and 2.75 look remarkably similar. Should I be experimenting in .003 increments between those?

2.77 looks quite tight, but I'm a little concerned with the spreads of 2.76 and 2.78 around it. Would this be considered an "unforgiving" node to stay away from?

I would say pick the smallest 2 groups and do .003 increments towards the smallest group next to them.

 

[Nik S]

This is all pretty sage.
Yes, rifle is a pretty light CTR and 10x scope. Works fine for hitting steel, but for exacting aim in isolating gun and ammo, I do find more magnification to be a bit easier. There is definitely a component of shooter in this equation.

 

[CK1.0]

This is all pretty sage.
Yes, rifle is a pretty light CTR and 10x scope. Works fine for hitting steel, but for exacting aim in isolating gun and ammo, I do find more magnification to be a bit easier. There is definitely a component of shooter in this equation.

Yep, a light gun can make shooting groups a PIA sometimes and makes it hard to remove the shooter's influence.

I should have suggested earlier (but forgot): a super easy and quick way to help you stabilize the rifle for groups would be just to throw a sandbag right over the top of the scope... that way you can add a bunch of temporary weight to the gun without touching/disturbing the barrel.

 

[Nik S]

I should have suggested earlier (but forgot): a super easy and quick way to help you stabilize the rifle for groups would be just to throw a sandbag right over the top of the scope...

Now that, I will definitely try. Very nice, thanks!