Why can't i reload exact cartridges?

[freddiej]

The inconsistency you are seeing with it being only 0.002" is as exact as you can get. the expansion and contraction of the copper sleeve the slug is made out of can vary between zero to 0.005" another manufacturing variable is multiple machines with multiple dies shaping the slugs. with the slight ogive inconsistencies I would say it was still a single die set making your slugs. use another set of calipers and see how the COAL is and if they only vary 0.002" to 0.005" then you have some of the best slugs made. 0.002" variation is very good. most of the 1000 count lots I was getting in Sierra MatchKings back in the late 1980's and 1990's were horrible. I would have to go in with five to ten friends and buy ten 1000 count lots and use a uniformity board to sort them for each of us to get the consistency you are seeing in yours. Sierra was using multiple machines to make the exact same slug. this meant more than one set of dies making slugs that went into one box. not good for uniformity. nowadays they only use one machine, one set of dies and the consistency is much better. my advice.. don't worry about 0.002" it's not going to hurt you or make any more than maybe 1 to 3 feet per second out the muzzle. that is if you get any variation in muzzle speed.

 

[dana bodnar]

As the Title suggests, I find it almost impossible to load cartridges that are all exact. I understand there are so many variables it is impossible, but something has been bothering me for years. Let me see if I can explain what I'm trying to say here, and it has to do with the measurement of a loaded round, namely, off the Ogive.

A few specifics, this caliber is 6,5 x 55 but applies to any. Bullet is 130gr the Nosler Accubond. My press is a Foerster Co-Ax, and the Die is RCBS Comp Micrometer Bullet Seater. I am using a Stoney Point Comparator (now Hornady LnL), with the 6.5 insert.

Here is what I'm looking for:

Many do measure exactly 2.530, however I always get a few off, mostly under, and I have learned when all adjustments are set, not to touch and play with adjustments, because that seems to make it worse. If one measures simply to the point of the bullet, you will have variances. But how can it vary measuring to the Ogive?

Ok, close enough, or is there some reason I just can't get 100% of my loads to measure exactly the same? I have not touched anything, how can the measurement possibly be different? This has had me stumped for years, as I have no logical explanation how the measurement can be different.

Bullets are not perfect if you start really miking them out you will find all kinds differences. I have found Berger to the best in uniformity. And then weigh them out on a triple beam and you will see all different weights.

 

[Bob Wright]

Looks like we need to define ogive.

In aerospace engineering we always have a datum line running through the arc (perpindicular to the arc form) to establish an exact gage line, on the drawing. Lets say it is measured from the base of the bullet to this gage line.The bullet mfr.s have to determine the tangent point of where that arc starts on the bearing of the bullet.
From there, we quailify a tool to pick up that gage line to mechanically measure the theoretically exact gage line to another surface on the cartridge "assembly". Forget CMM's for now (for us shop rats).
Regardless of how or what measuring tool you use, the variation in the bullet ogive, the seater die, the ogive gages we buy from a store are NOT going to coincide with the drawing gage line of the ogive. Add all those tolerances up, including not measuring in the correct spot, and you have variation, not including tension or compressed loads. So, get used to rework if you want to long seat and tweak in a second seating, or just create a tolerance you're willing to accept like +/- .001. Otherwise, ( I have the Hornady aluminum gages) design and custom make all hardened, precision made aerospace grade tooling, seater dies and gages that hit that bullet drawing gage line within .0002 or so, lol.....it's diminishing returns in a hurry. Not feasible for my budget.
The ogive tools we buy to measure jump or jam give us a reasonable repeatable number on our bullets only. If I measure your ogive with my tools, they would be startlingly different than the results you got on your equipment using the same bullets and brass you measured and had me check. They will not coincide.

 

[Bob Wright]

In aerospace engineering we always have a datum line running through the arc (perpindicular to the arc form) to establish an exact gage line, on the drawing. Lets say it is measured from the base of the bullet to this gage line.The bullet mfr.s have to determine the tangent point of where that arc starts on the bearing of the bullet.
From there, we quailify a tool to pick up that gage line to mechanically measure the theoretically exact gage line to another surface on the cartridge "assembly". Forget CMM's for now (for us shop rats).
Regardless of how or what measuring tool you use, the variation in the bullet ogive, the seater die, the ogive gages we buy from a store are NOT going to coincide with the drawing gage line of the ogive. Add all those tolerances up, including not measuring in the correct spot, and you have variation, not including tension or compressed loads. So, get used to rework if you want to long seat and tweak in a second seating, or just create a tolerance you're willing to accept like +/- .001. Otherwise, ( I have the Hornady aluminum gages) design and custom make all hardened, precision made aerospace grade tooling, seater dies and gages that hit that bullet drawing gage line within .0002 or so, lol.....it's diminishing returns in a hurry. Not feasible for my budget.
The ogive tools we buy to measure jump or jam give us a reasonable repeatable number on our bullets only. If I measure your ogive with my tools, they would be startlingly different than the results you got on your equipment using the same bullets and brass you measured and had me check. They will not coincide.

Here are the minimum three culprits of variation
A 7mm RM mag bullet marked for reference.
Notice where the seater tool hits on the bullet (RCBS seater)
Notice where the Hornady .28 gage hits way up closer to the bearing diameter.
All along the ogive there is variation in its form that is acceptable to quality control at Berger. We really only get a "reference measurement" that applies to our cartridge using our tools. It's important but not perfect for repeatability.
This contributes to bullet seating errors among a ton of everything else....

 

[Mikecr]

What folks are using ogive as a misnomer for is supposed land contact datum.
Many believe this would be a point measuring bore diameter but that is false.
The actual parameter changes with leade angle of the finished (and then worn) barrel.

I notice other folks thinking there is some kind of mass conspiracy preventing seating stems from contacting 'at the ogive', and as though this is a problem..
That is no more than lost as a nine-eyed dog.

 

[Zymurgist]

It is impossible to make anything exactly the same over and over again. There will always some variation from piece to piece. Likewise there will always be variation in measurements you take of those pieces. Start with checking how accurate the measurement system is. Measure the same cartridge a number of times to determine how repeatable it is. The measurements should be very much the same if your measurement system is good.

 

[jsthntn247]

What folks are using ogive as a misnomer for is supposed land contact datum.
Many believe this would be a point measuring bore diameter but that is false.
The actual parameter changes with leade angle of the finished (and then worn) barrel.

I notice other folks thinking there is some kind of mass conspiracy preventing seating stems from contacting 'at the ogive', and as though this is a problem..
That is no more than lost as a nine-eyed dog.

Could you have a smith take your Hornady ogive measure tool that clamps to your calipers and run your chamber reamer or a throating reamer in it? Now your tool would match the throat of your rifle and the measurements you took would be a true reading of where the bullet is to the throat in the chamber.

 

[Rich Coyle]

I think I like it.

 

[Bob Wright]

Could you have a smith take your Hornady ogive measure tool that clamps to your calipers and run your chamber reamer or a throating reamer in it? Now your tool would match the throat of your rifle and the measurements you took would be a true reading of where the bullet is to the throat in the chamber.

If you load for multiple styles of bullets you would need a set-up for each one.
I would say it would be wasted money. The off the shelf stuff, generic as they are, work well if used properly. Not perfection. Most of the other posters on this thread have mentioned it isn't that critical; money down the rabbit hole. I only get an average of .002 variation as it is with Redding dies and Hornady comparators. I only measure the first 5 then every 4 or 5 as I load. I'm more worried about powder weight repeatability.

 

[Bigaldepr]

Although you cannot eliminate variations completely, Nosler sells a seating plug for the RCBS made specifically to fit the Accubond LR ogive. They also have a video showing polishing the plug on a bullet to get the best seating.

 

[Mikecr]

Could you have a smith take your Hornady ogive measure tool that clamps to your calipers and run your chamber reamer or a throating reamer in it? Now your tool would match the throat of your rifle and the measurements you took would be a true reading of where the bullet is to the throat in the chamber.

The Hornady attachment doesn't have rifling, groove to bore, to be throated(like your barrel). I don't know if it would work or not as you intend here.

If you load for multiple styles of bullets you would need a set-up for each one.

I'm not understanding this notion. jsthntn247 was talking about matching barrel leade, (not normally established for any bullet 'style'), for measurement.

Matching CBTO to that tested as best can matter. Sometimes our best seating window is pretty narrow, like 8thou for one of my combinations, which is +/- 4thou.
What matters way less IMO is the tool chosen for the CBTO measure. I get by just fine with the Sinclair 'nut': https://brtshooterssupply.com.au/products/sinclair-comparator-nut-no-1.html
Same function but a step up in versatility (doing both CBTO and headspace) is Forster's Datum Dial kit:

Ultimately all that matters is recreating tested best CBTO, and any tool will work for this, provided ogive radius matches for every bullet. You can reach that match using a Bob Green Comparitor (BGC). http://greensrifles.com/New_Products.html

 

[XSIVSPD]

Not sure if it's been mentioned in the previous 5 pages or not, but even very good, expensive calipers are only typically rated as accurate to 0.0015" your measuring an inaccuracy of 0.002" while using a pair of calipers that are basically identical to the $15 harbor freight ones (rcbs re-branded). Just some food for thought there. If you want better accuracy you should be using a micrometer.

I'm not saying that you're not achieving good enough accuracy (either measuring or shooting) just that if you're worried about that small of a measurement you you use the correct instrument

 

[RockyMtnMT]

Not sure if it's been mentioned in the previous 5 pages or not, but even very good, expensive calipers are only typically rated as accurate to 0.0015" your measuring an inaccuracy of 0.002" while using a pair of calipers that are basically identical to the $15 harbor freight ones (rcbs re-branded). Just some food for thought there. If you want better accuracy you should be using a micrometer.

I'm not saying that you're not achieving good enough accuracy (either measuring or shooting) just that if you're worried about that small of a measurement you you use the correct instrument

Yes^^^^

The Mic I use for measuring bullets cost $250.

 

[bigngreen]

I believe it's worth the time to get things pretty much on the money with seating, I've played with my 6 Dasher at 1000 yards changing the seating depth .001 for each group and you could watch the group shapes change, coming in and out. For that rifle I seat with a Sinclair micrometer die that is set in .0005 increments.