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Miseryguts

CBTO measuring not going too well!

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Hi, as a newcomer to Centrefire rifle reloading, having got a reasonably(for me anyway) accurate load worked up, thought to try tweaking jump(free travel) to see if I could improve it. I use two bullets -Amax 52gr and Sierra FMJBT 55gr in 223 calibre.

Using the Hornady OAL gauge, modified cartridge and their comparator I set off......

A max gave reasonably constant CBTO of 1.877 to 1.880 touching the lands (1.8785 +/- 1.5), COAL 2.277 - two sets of readings on different days

Sierra is all over the place - I have 1 set 1.941 to 1.946, then another 2 sets 1.966 to 1.969 (1.967.5 +/- 1.5), COAL 2.330 - all on different days

Probably the 2 sets of results is the truth, but what I do not understand is why the CBTO for an Amax bullet touching the lands is different (by around 100thou) to the Serra bullet when measuring to the Ogive? Surely they should be the same? Or am I being stupid?(it has been known)

Both bullets mike at 0.224, and I am using the same bullet(s) for each set of readings, and each set is 5 tries

 

When I measure CBTO on the cartridges I have loaded, all to 2.230 +/- 1 COAL, I get Amax 1.8425 +/-1.5 over 20 cartridges and Sierra 1.873 +/- 2 again over 20 cartridges. This I can understand, its due to the bullet shape from the ogive to the tip.

 

Any Thoughts??

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The problem in measuring using the Hornady gauge is that you have to do it by feel. Different bullets have a different angle at the ogive which gives a different feel and often results in you feeling resistance either before there is actual contact or with a good jam into the rifling.

 

What I tend to do is push very hard so I'm not measuring to the point where I think there's contact but to the point where it is definitely jammed into the rifling as much as is possible with the pressure from my thumb. This has given me far more consistent measurements to work from.

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The problem in measuring using the Hornady gauge is that you have to do it by feel. Different bullets have a different angle at the ogive which gives a different feel and often results in you feeling resistance either before there is actual contact or with a good jam into the rifling.

 

What I tend to do is push very hard so I'm not measuring to the point where I think there's contact but to the point where it is definitely jammed into the rifling as much as is possible with the pressure from my thumb. This has given me far more consistent measurements to work from.

OK that has improved consistency for a given bullet, but the difference between the two is still large

Now have Amax CBTO at lands 1.896 +/-0.5, Sierra 1.980+/-0.5 that still leaves 84 thou difference - looking at the bullets under a magnifying glass, the Sierra has a more bulbous shape to the last portion of the bullet, whereas the Amax looks almost like a straight line and the ogive has been clearly marked by the comparator, whereas the Sierra has no marks to signify the ogive. So it would appear that the problem lies in the comparator not finding the true ogive of the sierra bullet. It looks like I will not be loading any more Sierra when I have shot this lot, as I am nervous of playing with COAL when I do not know the free travel for sure

Thanks for the input

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Measure and batch the bullets themselves with the comparator (bullet base to ogive). if there is a large range, you'll never get consistent cartridge BTO results. Secondly, check everything in your press and die set up. Finally check the bullet tips don't 'bottom out' in the seater die stem. If that happens, COALs are all over the place.

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Sorry to hijack...I think my Lee Dead Length bullet seating die does bottom out on the tips of my 140gr 6.5 CM bullets - can anyone recommend a good Seating Die that will address the problems Laurie mentioned and seat reliably using the O-Give? (Ideally one with a micrometer built in, as it's a pain constantly tweaking and remeasuring without!).

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Redding do a nice one with a VLD micrometer seater designed for long pointy bullets.

Talk to Mark at 1967spud I got mine from him.

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Sorry to hijack...I think my Lee Dead Length bullet seating die does bottom out on the tips of my 140gr 6.5 CM bullets - can anyone recommend a good Seating Die that will address the problems Laurie mentioned and seat reliably using the O-Give? (Ideally one with a micrometer built in, as it's a pain constantly tweaking and remeasuring without!).

 

 

Look at the Forster 'Ultra' seater with micrometer top too. Die manufacturers are belatedly waking up to this issue, especially with the proliferation of acetate tipped bullets that makes the problem even more acute. (It's 'interesting' that Hornady dies wouldn't cope with 6.5 and 7mm AMax and VMax designs for years, and for all I know maybe these bullets in other calibres too despite one company making both tools and bullets! I don't know if it's 'sorted' now - probably, but I'd always check especially with cartridges in these two calibres.) Forster has been the one manufacturer whose seater dies that I've bought in recent years that accept everything - can't comment on Redding as I've not bought a new set of this make for several years now.

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If you are using Hornady dies they make additional seating stems for the A-Max and ELD bullets and they also make a micrometer adjustable seating stem to upgrade the standard seating die

 

 

https://www.hornady.com/reloading/dies/individual-dies-and-accessories/#!/

 

 

The latter isn't new - I bought a Hornady micrometer adjuster maybe 15 years ago and still have it in one of my many Hornady die sets. The new seating stems are though and my complaint is that Hornady made and sold AMax bullets that didn't match its own dies for years and years and years. As we know, the AMax is now an obsolete withdrawn design.

 

Just last year I took the 162gn 0.284" Amax and tried it in around 6 makes of 7mm seater die, most of the market but less Redding. The only ones that accepted the bullet properly were my Forster models.

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with regard to measuring seating to ogive I have found big differences with the hornady case etc, finally tried using a sharpie marker pen to blacken the cases neck area and give it a good shove up the bore withe a bit of twisting too - eventually got a rim mark on the black part and was then happy that the case was going all the way into the chamber to the correct depth ,also ram the chamfer tool around the outside of the hornady dummy case just to make sure there wasnt any burrs stopping the case from fully seating in the chamber . hope this helps

 

cheers Richie

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Miseryguts,,,,Hi,,,,First off,,,,try to get one of your fired cases threaded and you will get a much more accurate BTO for your rifles unique chamber..[.I could do this for you if you cant find anyone local,,,,,PM me to arrange post etc] The reason that you are getting such a huge difference in BTO with these two bullets is a combination of bullet shape and possible small difference in actual bullet diameters and also the comparator bushing if its anything like mine will be machined around appx .213 and its this measurement that is touching your bullet.As you have noticed bullet shapes are different so the .213 of your comparator will be contacting at different places on each bullet.ie the .213 bushing will contact either higher or lower on the bullet for different shapes..

I have just compared 50 Vmax to 50 Blitzking in my .223,,,,,,,BTO difference is 60 thou and quite understandable looking at the bullet shapes. Remember this ogive you are measuring is ONLY a point of reference and NOT the part of the ogive that is actually touching the lands[usually at .218] in your rifle.What your doing is just fine and you are truly finding out where each bullet is actually touching,,,don't worry.,,,.....O

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Hi All

just read my instructions on the hornady OAL gauge and it does say to deburr the case inside and out. I am using redding dies for the 308 and have checked the contact point of the seating die on lapua-l ,lapua std ,a-max, berger fullbore and sierra tmk all of these in 155 gr and the contact point is all different from one make to another but at least it doesnt bottom out even with the very long TMK's . done this by taking the seating bush out of the die and push a bullet up into the die and give it a twist or two this marks the bullet contact point . Regarding bottoming out - if your bullet does bottom out and you can drill or put seating part in a lathe then its possible to put a drill through the seating die @ 3 mm or base of plastic diameter this would allow the tip to travel further into the die and not bottom out .Make sure everthing is square and a pedestal drill would be advantageous . Would save buying a new die set

 

Cheers Richie

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