Seating depth, where to start ?

[DLT]

I have done a small load development with a well worn 6 creedmoor that shoots well and great s.d. Across all the charges but my groups open up from the initial charge. I’m trying to run a 75vmax in a saami chamber so getting to the lands is not possible and where I shot groups was hornadys recommended length so there is little case neck holding the bullet in there. Obviously I’m going to start pushing the bullet into the case but how much would you guys say jump at a time ? I have seen anywhere from .003 to .006 to doing the Berger seating depth test.

I’ll add this is a factory rifle if it matters what you would do

 

[243winxb]

Seat full dianeter of bullet base/shank @ case neck/shoulder junction.

Buy Redding Type S fl sizing bushing die. Set bushing to size only 1/2 of the necks. .002" Neck tension.

Adjust powder for accuracy.

 

[L.Sherm]

I shoot alot of Bergers in 6mm, 6,5. 7mm and 30 cal and all are tested .003 at a time but also at 665- 700 yards, you will see how that small will change things

 

[Jet]

Hornady bullets tend to like a lot of jump. Factory rifle with a throat that is already eroded likely wont respond to small adjustments. Start your seating depth at magazine length and work into the case at .010" intervals. Once you find a sweet spot go to .003" around it to fine tune.

Time to order a new barrel.

 

[Skunce]

You might try a flat base bullet like the Berger 80 or 88 grain to help reaching the lands. The 87 Vmax would get you a little more bullet shank in the neck also. I usually start my seat depth test at touching the lands and work out in .003" steps.

 

[DLT]

Hornady bullets tend to like a lot of jump. Factory rifle with a throat that is already eroded likely wont respond to small adjustments. Start your seating depth at magazine length and work into the case at .010" intervals. Once you find a sweet spot go to .003" around it to fine tune.

Time to order a new barrel.

Thank you Jet. I will try that tomorrow and I know it, I retired it from playing at distance, stuck a varmint bullet in there and it shot surprisingly well a couple or 3 different days so it made me hold off tearing it apart. That bullet like I have it seated now is a long way from not fitting into the magazine. I’ll start going in .010 from where it is now.

 

[PatMiles]

...

 

[Ringostar]

Vmax and old Amax shoot well with bigger jump. Don’t be scared to try that.

 

[DLT]

Also if I’m getting great chrono numbers with what I’m loading which I am. If I were to move to a different bullet around same weight class would/could that upset the es/sd leaving the power and primer of choice alone ? All things I’m hoping to learn with my new chrono

 

[FeMan]

Tuning for accuracy and tuning for low SD are independent exercises. Low SDs without accuracy have no real value. So I would work toward the accuracy you are after. Once you are satisfied with the results, check your velocity numbers. If you are not satisfied you can tweak things to try and improve them, but most of the time the changes decrease the tune and decrease accuracy. I personally have never been able to find a predictable correlation between accuracy and low SDs and many of my best loads have SDs around 10 or even higher.

 

[DLT]

Tuning for accuracy and tuning for low SD are independent exercises. Low SDs without accuracy have no real value. So I would work toward the accuracy you are after. Once you are satisfied with the results, check your velocity numbers. If you are not satisfied you can tweak things to try and improve them, but most of the time the changes decrease the tune and decrease accuracy. I personally have never been ever to find a predictable correlation between accuracy and low SDs and many of my best loads have SDs around 10 or even higher.

Thank you. Numbers wasn’t my goal they just happened to be great with the load I tried

 

[L.Sherm]

Why the 75 vmax in a saami chamber, what is intended use?

 

[DLT]

Why the 75 vmax in a saami chamber, what is intended use?

Because I have a 6xc and feeding them both for the same thing seemed pointless to me. I just stuck a 75 in there for varmints seeing if it would shoot them mentioned in post 6.

 

[Bill Norris]

Tuning for accuracy and tuning for low SD are independent exercises. Low SDs without accuracy have no real value. So I would work toward the accuracy you are after. Once you are satisfied with the results, check your velocity numbers. If you are not satisfied you can tweak things to try and improve them, but most of the time the changes decrease the tune and decrease accuracy. I personally have never been ever to find a predictable correlation between accuracy and low SDs and many of my best loads have SDs around 10 or even higher.

Agree 100%. Low S Ds do not always give the best accuracy.

 

[J.D.Erwin]

I would start at 40 ths jump so I have only one way to keep moving my bullet build a seating ladder starting at 40 and making 3 ths increments like 40,37,34,31 ans so on I use three shot groups pck the group you like the best and find tune that load out to your max distance let the target tell you what your barrel likes. A good tune will include your cold bore shot and group at distance.

 

[slickshot223]

Shot a lot of AR rifles over the years with various bullets, have always seated the bullets to magazine length!!
Am not a fanatic about group size as long they shoot 3/4" or under! Early years I would spend time and money to see the tiny groups, as the years past, not so important!! Just some thoughts!!

 

[barefooter56]

I have done a small load development with a well worn 6 creedmoor that shoots well and great s.d. Across all the charges but my groups open up from the initial charge. I’m trying to run a 75vmax in a saami chamber so getting to the lands is not possible and where I shot groups was hornadys recommended length so there is little case neck holding the bullet in there. Obviously I’m going to start pushing the bullet into the case but how much would you guys say jump at a time ? I have seen anywhere from .003 to .006 to doing the Berger seating depth test.

I’ll add this is a factory rifle if it matters what you would do

Try this:
BERGER tangent ogive bullets like the FB and BT TARGET along with SOME OTM bullets are usually very tolerant of jump. We suggest that if you are doing any bullet seating depth testing that you start with the bullet TOUCHING THE LANDS. Then work BACK INTO THE CARTRIDGE CASE in .005 or .010 increments using the starting powder charge listed for the bullet/ powder/ cartridge combination you are loading.

 

[DLT]

Try this:
BERGER tangent ogive bullets like the FB and BT TARGET along with SOME OTM bullets are usually very tolerant of jump. We suggest that if you are doing any bullet seating depth testing that you start with the bullet TOUCHING THE LANDS. Then work BACK INTO THE CARTRIDGE CASE in .005 or .010 increments using the starting powder charge listed for the bullet/ powder/ cartridge combination you are loading.

Thanks I’m just not able to reach them with the 75vmax. Will try it again with different bullet

 

[barefooter56]

Thanks I’m just not able to reach them with the 75vmax. Will try it again with different bullet

Hey! TANGENT OGIVE BULLETS like yours are usually very tolerant of jump. Try working the load up slowly checking for pressure signs and accuracy with the bullet seated to magazine length first ! You MAY find something there!

 

[misser]

it you are going to use a magazine ,make them that long ,then shorten them till you find a happier place. if you don't find it different powder or different amount of powder. or threaded muzzle? install a tuner