Hornady cbto length difference

[hughes.s]

I have discovered a cbto length change of .031 between the last bullet of a previous batch and a new box of 55g spsx, using the rifle formed split neck case method, measured using a Hornady comparator.The only thing I can find is the last batch bullet is .006 shorter at .357 using the comparator than the new box which are constant at.363, any thoughts?.

 

 

 

Hughes.s

 

[jcampbellsmith]

Welcome to Hornady manufacturing tolerances. Regards JCS

[The Gun Pimp]

As I've mentioned before on this forum, I was once privileged to visit a bullet-making factory.

 

The final process the bullet goes through on its way from a copper disc to what we shoot involves a tungsten forming die. "How long do you think these dies last?" asks our guide.

 

Various guesses are proffered - 6 months? Six weeks? One week? "Nope - one eight hour shift!"

 

Now, there were half a dozen machines spitting bullets into a large tub. They are then boxed - or loaded into ammo. Clearly, there will be discrepancies between bullets swaged at the start of the shift to the end of the shift.

 

That's why benchresters use custom hand-made bullets to shoot consistent small groups.

[gbal]

+1 on Vince's point about manufacturing...

 

Bullets vary in 'length'-one reason why 'Cartridge Overall Length"-COAL- is often misleading,,apart from telling you whether they will fit your magazine.

Think of just cutting off the plastic tip-makes no difference to the bullet seating,but does dramatically alter "COAL". The pointed bit of the bullet sitting in the middle of the bore has little effect on bullet seating consistency,though even if it's a bit of low tolerance plastic,it can improve BC,so long as it isn't bashed up.

 

"Bullet base to ogive" does,and that's what matters,and "base to ogive" should be given when talking about 'seating depth"...(unless the bullets are all the same length...across production runs,which as we've seen , is unlikely!)

Fortunately good bullet makes-and not just custom-are much more uniform in their ogives,which obviously does matter. It may contribute to the cost (eg Bergers).

 

gbal

[onehole]

Yep,,,,Hornady can be pick and mix in a box sometimes as well,,,,,,,,!...............Sometimes you get lucky,,,,found 700 105Amax the other day and same lot same measurements everywhere,,,yeeeeha.

Inconsistency can really mess with load development especially if your experimenting with varying off land loads then heaven help you. I,ve resorted to measuring each and every Hornady head that comes my way and batch and label into "my own lots" doesn,t actually take long to do this and the benefits really do show,,,,not had any "flyers" in my groups for a long time now ,,,,good luck hughes.s,,,,,O

[hughes.s]

Thanks to all for the replies,

 

Hughes.s

[Andrew]

I load entirely by depth, seating my initial loads with a bullet to the base of the neck and letting the dies to the work with regards to alignment. It may be 'old fashion' but I have found this technique to be so successful that I have stopped measuring the distance from the ogive to the lands entirely. Considering the aforementioned variances in bullet dimensions coming from the factory, concentrating on a uniformity of pull weight and combustion chamber volume seemed a good alternative. Both affect burn rate of the individual cartridge which influence pressure and velocity uniformity. In your average rifle chamber these factors are of much higher importance than distance from the lands, ballistically speaking. JMHO~Andrew

[gbal]

Andrew,an interesting alternative method.If the ogive is reliable the same distance from the bullet base,sounds like base to ogive constant depth will produce the same ammunition as seating to your constant base depth...?

 

....actually,I mean your base to ogive measurement will be constant,which is what the alternate achieves too? Agree of course COAL is unreliable.

g

[Andrew]

It should if the ogive is reliable. I measure a sample of bullets to get an average length, measure the length of my trimmed cases, and proceed to my desired seating depth. After that I don't mess with it, leaving the die set. I have found that deep seating (with a crimp) gives me more consistent MV and SD. The use of "seating depth" to indicate the amount of bullet stuck into the case is an old way; my original RCBS Micrometer seater made constant reference to seating depth, instead of "OAL" and a list of suggested 'seating depths' were with it -all in decimal parts of an inch. Considering the variances in throating on most commercial rifles, controlling the neck tension and powder volume/combustion chamber is far more reliable than seating out to .010" (or which ever) distance off of the lands. I know my CZ Hornet would have a 35 grain V-Max hanging on my the very edge of the bullet base if I was .015" from the lands. To counter this I concentrate on a good grip of the neck on a concentrically seated bullet. Shoots one hole groups despite having that long jump to the lands.~Andrew

[triggersqueezer]

guys going through a batch of sierra's 6mm i found my bto longest was 0.6800 and shortes to be 0.6730 giving a possible 7 tho difference but i would say a more common 4-5 tho difference .in your experience how much would you expect this to show in groups at say 100 and 200 ?

[hughes.s]

Hello mi duk,

I"am not that good enough to see a difference at those ranges even if I were looking for it, the reason it came to light my other friend came to dinner and I was showing him some groups, one was particularly good and I noticed the recorded cbto and thought that cant be right!.(I have found this to correct for that base to ogive bullet) Thats when I started checking against what I thought was the control bullet, what got me twitching was I did not want to load ( a different btog) to my used and tested cbto if it then put me into a jam instead of a jump, it seems the more technical I try to be the more I worry. I loaded hundreds of 55g spsx"s for my styer scout using oal, but it did have a long throat.

Any way how are you?.

 

Hughes.s

 

(some times a 50yd swimming stifcate and a cycling proficiency stifcate aint enough)

[triggersqueezer]

i'm all good buddy.you have touched on a subject i'm only just starting to play around with in my never ending quest lol.

[hughes.s]

Sir, Step away from the vernier, sir

[onehole]

guys going through a batch of sierra's 6mm i found my bto longest was 0.6800 and shortes to be 0.6730 giving a possible 7 tho difference but i would say a more common 4-5 tho difference .in your experience how much would you expect this to show in groups at say 100 and 200 ?

I would only guess but if your loading at least 10-15 thou off lands then maybe nothing too much will show up.its only when you load closer ie 5 thou or less to lands then you could very well be just off, ,touching or in and this may well show up and cause some loose grouping. You don't say how these different measurements are spread but what I found with Hornady is that you could get up to three clearly different BTO in a box or boxes in a particular LOT . So in a box of 100 you would get 25 at say .669 BTO then 30 at.705 and 45 at .708,,,,,,,and if wanting to load close to lands then this would clearly cause a problem and it does! Worst spread ive seen is 14 thou!,,,,,,,O

 

I have edited BTO figures I made error in original post,,,,these are actual readings from one lot of 105 6mmAmax.,,,O

[triggersqueezer]

i went through them last night again it was a box of 500 3 were 6720 10 were 6730 10 were 6740 100 were 6750 50 were 6760 50 were 6770 the majority were 6780 with30 being 6795 .i'm jamming my bullets and they shoot well.only picked up a modified case yesterday to start measuring ,all loads were developed seating till the bolt would close and backing off ten thou.the 105 amax just drill nice groups but the 107 will shoot stunning groups but when tested a flyer might appear still not to shaby say open up to .50 .that is what started me off measuring.if i shot 4 that measured 6780 and 1 that was 6730 would a 5 tho difference show that much?

[triggersqueezer]

Sir, Step away from the vernier, sir

i do have a habbit of looking for problems that aren't there on rainy days

[gbal]

ts,we all have that tendency-the problems are more likely to show on nice windless sunny days,when conditions allow the rifle/shooters full potential,and small variation factors don't get swamped by poor weather etc conditions.

Rainy days can be used to reduce the (potential) problems.

Bullets are ever likely to vary in OAL -most are not made like the best Havana cigars used to be-individually rolled on the inside thigh of a young Cuban maid,and cosseted in an individual aluminium case,lined by silk.Nothing like-if you can,have a look at the youtube video of the process Vince(GP) describes.

Tolerance may well be over 5 thou for the same box...but it varies.The rainy day therapy for the conscientious-'anal' is inappropriate here-is to measure and batch your bullets,as eg onehole suggests.

Then that's oneless variable to think about.

It is quite likely that different rifles have somewhat variable tolerances for bullets-they often have design differences in freebore etc.Trial and error will tell your rifles idiosyncracies,if any. Of course,bullets will vary in their manufacturing tolerances-you'd expect custom to be more uniform,maybe Bergers-and the latter's "hybrids' are designed to be more seating depth tolerant,which might help in theory.For what it's worth,the first nine digits above the bar code on a Sierra box is the batch number,made at the same time/materials -so that should help....a bit.

The most crucial/sensitive situation will probably be where you want to seat touching the lands,or close-ie you don't want a 10+ thou jump-that's what your worst bullets might end up as,unsorted.

Of course,much of this OAL variation mattters but little,if you seat using ogive measures.A few extra thou of pointy plastic tip in the space of the centre of the bore line is not likely to be a big issue.And,glory be thanked,most good bullets are actually more consistent in base to ogive length anyhow.

I'm pretty sure that many 100y Bench Rest shooters did not sort bullets,and still shoot pretty small 'groups'-if one hole can be a group.For varmint ranges,I doubt that meplet trimming has been shown to be a 'must do' procedure (1000y maybe?)

Of course,(alas?),you don't need yet another bit of gizmo gear,your good comparator will do it all.If it's set in wet for the day,you can check primer seating depth uniformity too-close calipers,hold primed case on the other end,gently ease out calipers,take reading.Don't fret about it,though-unless if you're getting light strikes/slam fires.

 

So,"batch and match"-can't do any harm,gives that warm glow of peace of mind,job well done, and keeps you dry.

 

have fun

gbal

[triggersqueezer]

gbal i think your right its just piece of mind and gets me away from the wifes violin practice.i was trimming meplats last year when it dawned on me that i was wasting my time untill i learn to read the wind better.this year is all about wind wind wind for me.

[pork chop]

i went through them last night again it was a box of 500 3 were 6720 10 were 6730 10 were 6740 100 were 6750 50 were 6760 50 were 6770 the majority were 6780 with30 being 6795 .i'm jamming my bullets and they shoot well.only picked up a modified case yesterday to start measuring ,all loads were developed seating till the bolt would close and backing off ten thou.the 105 amax just drill nice groups but the 107 will shoot stunning groups but when tested a flyer might appear still not to shaby say open up to .50 .that is what started me off measuring.if i shot 4 that measured 6780 and 1 that was 6730 would a 5 tho difference show that much?

 

you need to get out more

[hughes.s]

Thanks Pork Chop,

An observation I was about to post.

Just scrolled down to check something saw you post, result?

 

 

I hours worth of composing, spell checking, paragraphing, that I have now deleted. But I have gained something thanks to previous views that I did not know on Friday.

Will there ever be a time when shooters are satisfied/happy. Hey ho, upwards and onwards?.

Hughes.s

[Andrew]

i do have a habbit of looking for problems that aren't there on rainy days

 

As you get older you'll get by that.~Andrew