Seating depth accuracy

[Lloyd90]

After making up a batch of ammo are they all the same size to 0.001" or is a variance "acceptable".

 

I've recently started using my new rock chucker. Enjoying it very much just wondering if I should be really striving or if everyone else also experiences some variance ?

[Dave-G]

0.010 is well good enough for my 25 grn 17REM V-MAX.

[Dougy]

See what the accuracy is like length wise of the bullets.

You will probably see were that 0.001 comes from.

You got your hole's sorted then Lloyd ;-)

Do you measure from bullet tip to base or from ogive to base of case ?

Edited October 5, 2016 by Dougy

[Lloyd90]

0.010 is well good enough for my 25 grn 17REM V-MAX.

So getting them to witching 0.01 rather than 0.001" isn't a big difference ?

See what the accuracy is like length wise of the bullets.

You will probably see were that 0.001 comes from.

You got your hole's sorted then Lloyd ;-)

Do you measure from bullet tip to base or from ogive to base of case ?

Yer mate luckily my bench isn't like Swiss cheese just yet!

[Vince Green]

Don't over think this, just shoot them. Extreme target shooters go to extreme lengths to get consistency. When you are trying to break an egg at 1000 yds we will talk about it, until then don't worry.

[wymberley]

As previously indicated, you're better off measuring at the ogive. With infinite patience you can get all rounds to the same COL but for consistency that assumes that all bullets are precisely the same length with no distortion and particularly at the tip. Measuring at the ogive will usually mean some variation in COL but this is of no consequence as the critical bit is consistency in the distance between the bullet ogive when chambered and the lands when fired. That said, VG above says it all.

[Lloyd90]

Don't over think this, just shoot them. Extreme target shooters go to extreme lengths to get consistency. When you are trying to break an egg at 1000 yds we will talk about it, until then don't worry.

Thank you all!

 

As I've not done it much before I was just unsure to what it is for everyone else.

[zx10mike]

disagree .... 5 tho can make the difference from .25 to .50 or to put it another way double accuracy.that said 1 tho is acceptable variation but max.if your dies are set up well and your measuring quality bullets base to ogive then 1 tho is max i would want.

[Dougy]

disagree .... 5 tho can make the difference from .25 to .50 or to put it another way double accuracy.that said 1 tho is acceptable variation but max.if your dies are set up well and your measuring quality bullets base to ogive then 1 tho is max i would want.

 

The only thing is with general run of the mill varmint bullets they will invariably be variations in their length even from measuring to the Ogive.

I don't disagree Mike that it makes a difference believe me I use bullet comparators to check run out, turn my necks, use bushing dies the lot so I don't doubt what you say, but for general Fox rounds how far do you want to go.

If your shooting rabbits at 400 -600 yards then yes go the extra length because then you will see a difference.

[Lloyd90]

First question , what's the O give ?

[Elevation]

A datam point on the bullet. Measuring using the ogive removes the 'tip variation' concern. You will be measuring from the head of the case to a fixed point on the curve of the bullet.

[Lloyd90]

Running before walking

What should I be looking to do first?

 

No good saying I'm doing it wrong but not offering any advice or guidance or what I should be doing is there ?

[Savhmr]

Bullets often measure several thou (or more) differently within the same batch due to the meplat (pointy bit) being deformed or slightly different between them, hence using COAL (cartridge overall length) will result in some variances. Using a bullet comparator you remove that inaccuracy as the measurement is taken from a reference on the curved bit of the bullet (ogive). Once your seating die is set, you'll find that your seating depth is pretty much within 1 thou for almost all loads unless you change it yourself, and it's just the COAL that varies a bit (and this wont affect accuracy much if at all).

 

Variances of seating depth will make a difference to grouping, and some barrels and bullet combinations can see groups opening up more rapidly than others for say a 5 or 10 thou difference, but at 100 yards, at 5 thou the differences will be minuscule (usually).

 

The reason for the groups changing with seating depth are related to something called barrel time. This is the time that the bullet is in the barrel from detonation of the round until it exist the muzzle. Why do groups open up if barrel time is changed? Simply due to the barrel harmonics effects. The barrel may look and feel rigid but if you could look sideways on at a barrel using an ultra slo-mo camera, it would whip in a sinusoidal fashion and where the muzzle ends up when the round exits as it whips around, can scatter the group.

 

This is why seating depth, or charge, or both can be altered to vary barrel time such that the bullet leaves on a barrel node (ie a point at which it comes to rest on-axis, therefore pointing where it needs to) within that harmonic motion.

 

The degree of opening up or tightening up varies with barrel contour (ie how rigid the barrel is) and its length for any given load, plus the rate of twist of the barrel, and how its bedded to the stock etc.

 

With 69gr TMKs in .223 I found two nodes on seating depth between 5 thou off the lands and 130 thou off. These were at 15 thou and 100 thou in my rifle. It's pretty common to find two nodes between lands and say 150 thou where you'll get optimum groups for any one charge. To give an idea, with this particular bullet how it was affected, the difference of 30 thou either way from 100 thou made 0.7 inches at 100 yds differences to the group (consistently) in either direction.

 

 

As Vince says though, it's very easy to over think things. Just shoot groups at 100 (and if you can at 200) yds, pick the load that gives acceptable hunting groups and leave it at that, If you can't get a group at 10 thou off, move back in 25 to 30 thou jumps for obvious opening up or tightening for any given charge and you'll find a node.

Edited October 5, 2016 by Savhmr

[Lloyd90]

Discussing a 0.001" tolerance without even knowing what you are measuring

I just measured from the base to the tip.

 

Again, thanks for the constructive advice lol!

 

Savhmr, thank you. That's actually helpful

Edited October 5, 2016 by Lloyd90

[zx10mike]

some harsh comments on a new guy learning ? we have all been there and i wager the guys with negative comments would not look so hot in the right company.lloyd 90 your learning and on a great ride to accuracy.ignore the negative bud and enjoy the learning bits.we are all still learning.have fun

 

The only thing is with general run of the mill varmint bullets they will invariably be variations in their length even from measuring to the Ogive.

I don't disagree Mike that it makes a difference believe me I use bullet comparators to check run out, turn my necks, use bushing dies the lot so I don't doubt what you say, but for general Fox rounds how far do you want to go.

If your shooting rabbits at 400 -600 yards then yes go the extra length because then you will see a difference.

totally agree bud

[Vince Green]

First question , what's the O give ?

The ogive is actually the curved bit, more technically its the radius of the curved bit. You can get a single ogive or a double ogive, (theoretically I suppose a triple ogive?) but your only real comparator is the size of the group.

 

That's most significantly affected by the choice of powder and the charge. That's where you start and only when you nail that can you even think about other variables. One thing at a time, chances are once you have the charge sorted out you will be happy with what you have

Edited October 6, 2016 by Vince Green

[Savhmr]

Just to add to what Vince has said. Sometimes you can get a decent group by just playing with the charge. Sometimes you may not because within the charge variables, you may not have the barrel time nailed for a specific type of bullet. However, you should be able to get minute of angle with most bullets (ie an inch and a bit at 100 yds) which is good enough for most. For vermin shooting such as crow at more extended ranges, you really have to be doing better than 1moa at 100 yds for precision. I aim for a minimum of 0.5moa, and this is where playing with seating depth really comes into its own.

 

You also have to be mindful of terminal ballistics and many start out wanting high MVs to retain as much down-range energy as possible, especially for things like fox control, and also to extend MPBR. Truth is, even at the lower end of the load scale, terminal ballistics for anything of 40gr upwards will be more than adequate for fox out to 300 yards (retaining over 300ft=lbs in .223) so accuracy is the key. Many really accurate loads I've found aren't at the higher end of the load scale but the lower to mid end for the bullets that I use with the exception of V-max bullets which seem to do better, the faster you push them.

 

Simple thing is to start at 10 thou out on seating, develop your tightest group, repeat several times with at least 6 shot groups to ensure consistency, and then decide whether you want or need to play with seating depth. With some bullet/barrel combinations, you have to, plain and simple. Some bullets such as SMK Palmas (large radius ogive) aren't very jump tolerant so you have no choice but to stick with close-to-lands and develop on load alone.

[wymberley]

The ogive is actually the curved bit, more technically its the radius of the curved bit. You can get a single ogive or a double ogive, (theoretically I suppose a triple ogive?) but your only real comparator is the size of the group.

 

That's most significantly affected by the choice of powder and the charge. That's where you start and only when you nail that can you even think about other variables. One thing at a time, chances are once you have the charge sorted out you will be happy with what you have

Tangent, secant or hybrid. Flippin' 'eck, it's getting complicated. Thank heaven for Savhmr above!

[Dougy]

So Lloydy now get that lot in your head and play, I am beginning to think now, for a chap that wasn't sure how big to make a hole,, you may now face a future of head aches.

[Lloyd90]

So Lloydy now get that lot in your head and play, I am beginning to think now, for a chap that wasn't sure how big to make a hole,, you may now face a future of head aches.

Shall I just sell my press now before it's too late ? 😂😂😂

With perseverance comes success

[Dougy]

Shall I just sell my press now before it's too late ?

With perseverance comes success

 

I am sure you will find sucksess somewhere

 

The more you look into reloading the more,,,,,,,, er,,,,,,, interesting / confusing (delete as appropriate) it becomes. I see it as all part of the hobby / sport its just like building an Airfix Kit. There are those that just stick them together, there are those that slap some paint on as well, and there are those that go to far far ends of the earth and paint on the rivets, build complete war sets the complete danglies. Then then there are those that have done it all, know it all, got bored with it all and go off and play with something else. We are all different

You enjoy your reloading and be careful

[Bewsher500]

stop measuring OAL until you have found an actual charge level that shows promise

ALL your load development should be done with at least a calibre depth of the shank (straight bit!)of the bullet in the neck of the cartridge

 

You don't have a custom throat length, you have a factory rifle I am guessing. They are cut long pretty much all the time to take ALL factory ammo

Also this isn't benchrest target loading clearly

 

determine what accuracy you are looking for.

usually most people are very happy with close to touching or touching holes at 100m

if you want to shoot groups that are measured as a fraction of the calibre sized hole and start with 0.1xx MOA...I suspect you are a long way off that

 

 

keep it simple

load a range of charge levels across the powder manufacturers data for the bullet you are using or the closest one to it

lets say its between 25-30gr (no idea what round you are loading btw thats just an example)

 

your lower end you have no interest in looking for an accuracy point, thats the powder makers insurance policy

you only want to exclude any chance of pressure signs in your rifle

 

If I were doing it

1x 25gr

1x 25.5gr

1x 26gr

3 x 26.5

3x 27gr

3x 27.5gr

3x 28gr

3x 28.5gr

3x 29gr

3x 29.5gr

3x 30gr (although I would expect to pull these having found at least one, ideally two points in that range that show significantly more accuracy that the rest)

 

you can run groups of 5 rounds for every 0.2gr of powder across the whole range if you want, waste of powder, bullets and time if you ask me and wont help you

Obviosly stop if you see any pressure signs at any point, stiff bolt, overly flattened primers, marked case head etc etc

 

lets say the two in bold show the smallest group size (yes you could shoot 5 or 10 or 20 to get the true average.....but if you can't shoot a triangle and see which one is smaller then the problem is not with the reloading...its development)

 

choose the one that is at the velocity level you want or the better group size

 

use smaller charge levels either side in 0.2gr increments

do any of those show smaller groups?

Great. NOW start ******* around with seating depth to fine tune your best charge level.

 

unless you have good brass prep (trim to length, fresh non work hardened brass, sized well, ) you will have inconsistent neck tension which is infinitely worse for its effect on accuracy

you can weigh to the 100th of a grain, measure OAL to the 1/1000th of inch (which is pointless by the way as NO bullets have tolerances at that level)...but if you dont have consistent neck tension you are still going to lose accuracy.

[Walker570]

For over 40yrs I have loaded my rifle ammo and set the bullet just off the lands by a smidgen. NO, you can't buy a measuring tool for that. I mark up a bullet with black marker pen, insert and then ease back until no marks appear on the bullet. In over 40yrs it has not failed me along with not always striving to get the bullet to go another 100fps faster, often my loads are well below max but group nicely to an inch or less at a 100. Certainly adequate to stalk/ambush and shoot deer/boar and foxes.

 

In no way do I decry those who wish to measure ogives etc etc., if that gives satisfaction and enjoyment away you go.

[steve_b_wales]

For over 40yrs I have loaded my rifle ammo and set the bullet just off the lands by a smidgen. NO, you can't buy a measuring tool for that. I mark up a bullet with black marker pen, insert and then ease back until no marks appear on the bullet. In over 40yrs it has not failed me along with not always striving to get the bullet to go another 100fps faster, often my loads are well below max but group nicely to an inch or less at a 100. Certainly adequate to stalk/ambush and shoot deer/boar and foxes.

 

In no way do I decry those who wish to measure ogives etc etc., if that gives satisfaction and enjoyment away you go.

What about a Hornady OAL gauge? I've got one and have checked every rifle that I've bought.

[Walker570]

A black marker from WH Smiths is cheaper