Seating Depth Accuracy?

[jstanton]

As I slowly but surely make my way through the load development process I find myself agonizing over accuracy and precision, just my nature, but I also find myself wondering am I over analysing too much? And am I expecting too much from the equipment I am using?

When it comes to seating depths what is the allowable tolerance on the measured COAL?

Using my lock n load gauge, comparator set and Hornady digital caliper I measured the chamber COAL in my 7mm Rem Mag at 3.736" with a 7mm Berger 180gr VLD hunting bullets. I did this 3 times and got the same number each time. Then using a standard RCBS seating die I made up a dummy round progressively seating the bullet deeper and measuring until I reached 3.716" or .020" off the lands which is where I want to start for my load development. I then set the jam nut and began seating bullets into my prepped and charged cases.

As I measured each loaded round I found that I was averaging 3.715" +/- .001" not the 3.716" I was after. Now I understand this could be the accuracy tolerance of the caliper or the repeatability of the die and seating stem, which is a whole nother issue as I am using the standard stem with the VLD bullet but I didn't want to go through the whole process of ordering a custom stem for these dies and VLD bullets when I can already see I will soon upgrade these for a set of Redding dies. Plus I am only seeing a very faint ring approximately .260" off the meplat.

So is this an acceptable tolerance for seating depth and would you still classify this as .020" off the lands? These first rounds will be used for a ladder test so I am not too worried about this right now but the next step for me is tuning seating depth where I may be adjusting it as little as .002" and with a +/- tolerance of .001" this may be a bit if a problem.

Just looking for guidance and experience!

Thank You,
Jacob

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[jstanton]

Here are my recorded COAL for each charge weight consisting of 5 loaded rounds per charge.

I am going to do a 2 string ladder test and separately, out of curiosity, shoot 3 shot groups with each charge weight and compare the data to see if I find corresponding accuracy nodes.

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[sierracharlie338]

The ring you are referring to I get with my RCBS dies as well as the variance in depth.

I can tell you from experience the VLD seating stem is worth the money a million times. Once you set it you can run through 100 rounds and it will be the same as your first round.

I generally don’t waste rounds with that little of a change in seating depth. I’ll do some thing like .020 off the 30 then 40 until I find what I’m looking for. From there the smallest I’ll get will be about .005 increments just for giggles.


Sierracharlie out…

[jstanton]

The ring you are referring to I get with my RCBS dies as well as the variance in depth.

I can tell you from experience the VLD seating stem is worth the money a million times. Once you set it you can run through 100 rounds and it will be the same as your first round.

I generally don’t waste rounds with that little of a change in seating depth. I’ll do some thing like .020 off the 30 then 40 until I find what I’m looking for. From there the smallest I’ll get will be about .005 increments just for giggles.


Sierracharlie out…

So do you think the variance is from using the standard seating stem with the VLD bullet?

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[Mike D]

As I slowly but surely make my way through the load development process I find myself agonizing over accuracy and precision, just my nature, but I also find myself wondering am I over analysing too much? And am I expecting too much from the equipment I am using?

When it comes to seating depths what is the allowable tolerance on the measured COAL?

Using my lock n load gauge, comparator set and Hornady digital caliper I measured the chamber COAL in my 7mm Rem Mag at 3.736" with a 7mm Berger 180gr VLD hunting bullets. I did this 3 times and got the same number each time. Then using a standard RCBS seating die I made up a dummy round progressively seating the bullet deeper and measuring until I reached 3.716" or .020" off the lands which is where I want to start for my load development. I then set the jam nut and began seating bullets into my prepped and charged cases.

As I measured each loaded round I found that I was averaging 3.715" +/- .001" not the 3.716" I was after. Now I understand this could be the accuracy tolerance of the caliper or the repeatability of the die and seating stem, which is a whole nother issue as I am using the standard stem with the VLD bullet but I didn't want to go through the whole process of ordering a custom stem for these dies and VLD bullets when I can already see I will soon upgrade these for a set of Redding dies. Plus I am only seeing a very faint ring approximately .260" off the meplat.

So is this an acceptable tolerance for seating depth and would you still classify this as .020" off the lands? These first rounds will be used for a ladder test so I am not too worried about this right now but the next step for me is tuning seating depth where I may be adjusting it as little as .002" and with a +/- tolerance of .001" this may be a bit if a problem.

Just looking for guidance and experience!

Thank You,
Jacob

Sent from my SAMSUNG-SM-G935A using Tapatalk

You are talking about .001” variance. Your gun isn’t going to know the difference.

The variance is most likely in the bullet itself. Very few are perfectly straight at the tip.

If you were to get a comparator and measure using that you would see virtually no variance.


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[bboswell]

When Berger suggest testing seating in 0.030” increments I’m not loosing sleep over +/- 0.001 variance.

[Livin'2hunt]

Length sort your bullets.

That will cure a lot of the ills you are experiencing. You will need a length sorting tool but it is worth its weight in gold if you are extremely particular (and, you are). The differences in bullet lengths as measured to the ogive can vary widely depending on manufacturer. Some far more than others.

In a 500 count box of SMKs, I can expect a extreme spread of usually, no more than 3.5 thousandths. 98% of those being within 2 thousandths. Hornady....not so much. It's not uncommon to see 7 or 8 thousandths ES in a box of 100. I dont shoot Berger but the ones I have checked have been of high quality.

It's also helpful when you find a 168 grain pill in a box of 178s. Thank you Hornady. Length sorting will make your loads more accurate, especially at long range.

Going to the Redding dies will be a life altering experience. If that is what a drug induced euphoria is like, I know why people become addicted. I highly recommend them. Your inconsistency will plummet to nearly immeasurable numbers.

.

[kmon]

.001 isn't enough to worry about IMO. Like said above though if using VLD type bullets get that seating stem otherwise you most likely are seating off the tip of the bullet and that is not as consistent as the ogive.

[cattlelackranch]

If your not using the right seating stem your more than likely introducing a lot of runout. That's going to cause you more accuracy issues than seating depth. That and pulling an expander ball through your necks

[sierracharlie338]

So do you think the variance is from using the standard seating stem with the VLD bullet?

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Most definitely because it’s not seating on the stem the same way everytime. As mentioned above that will create a lot of runout which affects accuracy.


Sierracharlie out…

[jstanton]

You are talking about .001” variance. Your gun isn’t going to know the difference.

The variance is most likely in the bullet itself. Very few are perfectly straight at the tip.

If you were to get a comparator and measure using that you would see virtually no variance.


Sent from my iPhone using Tapatalk Pro

I did use a comparator and tried to apply even pressure every time I measured a round but I would still get the +/-.001" variance listed above.

[sierracharlie338]

And again .001 is not gonna be measurable by you, the gun or the groups you print on paper. Making work for yourself buddy!

[jstanton]

When Berger suggest testing seating in 0.030” increments I’m not loosing sleep over +/- 0.001 variance.

I thought the .030" increments were for finding the "sweet spot" at which point you would make .002" to .005" adjustments to fine tune or tweak the load?

[jstanton]

And again .001 is not gonna be measurable by you, the gun or the groups you print on paper. Making work for yourself buddy!

In the back of my mind I know that I am probably obsessing over this and it wont make a hill of beans difference but I guess I was expecting the exact same dimension every time which again may be asking too much for this setup and the .001" variance may be totally acceptable.

[sierracharlie338]

In the back of my mind I know that I am probably obsessing over this and it wont make a hill of beans difference but I guess I was expecting the exact same dimension every time which again may be asking too much for this setup and the .001" variance may be totally acceptable.

Haha I feel your pain. I went through the exact same thought process when I started but once I had someone help me through some of that kind of stuff life has been easier!