6.5 Grendel Bullet Dimensions

[EigerWand]

Comparative figures for 3 common bullets.
Please add more if you've got them.

Nosler 120gr Ballistic tip 26120: Base to tip 1.127"; Base to 0.26 ogive 0.701"
Hornady 123gr ELD-M 26176: Base to tip 1.141"; Base to 0.26 ogive 0.666"
Sierra Pro Hunter 120gr 1720: Base to tip 1.083"; Base to 0.26 ogive 0.601"

The base to tip length is used to calculate stability relative to twist and velocity.
The ogive of course tells you where you want to seat them if you're seating relative to the lands.
Brian Litz gives these dimensions for many bullets but weights suitable for the Grendel are a bit below his range of interest, which is heavy for calibre bullets from full size cartridges.

3 bullet dimensions copy 5.jpeg

[Lemonaid]

JBM has a lot(most all) of bullet lengths listed. I don't know if there is a site that list base to ogive but perhaps someone else knows.

https://www.jbmballistics.com/ballistics/lengths/lengths.shtml

[Klem]

Base-to-ogive all depends on the inside diameter of the measuring device. Like their headspace attachments the Hornady ogive device is not machined with enough precision that we can confidently compare across devices. Great for the individual loader but not so good for comparing with other loaders.

Don't get me wrong - base-to-ogive instead of base-to-tip makes perfect sense but if you are going to compare across shooters their attachment ID's must be exactly the same.

[JASmith]

[Klem]

Sure, if we also list the ID of our measuring inserts, to make sure we are comparing apples with apples.

Mine is 0.2070" from the older Stoney Point set.

[AK_Reloader]

An optical comparator tells no lies...& is repeatable.

[Mad Charlie]

An optical comparator tells no lies...& is repeatable.

Which one would you recommend for finding length from base to ogive?

[Klem]

Which one would you recommend for finding length from base to ogive?

I don't think it's a serious reocmmendation - they cost an arm and a leg.

[Mad Charlie]

I don't think it's a serious reocmmendation - they cost an arm and a leg.

No kidding. anything usable does anyway, there are some hand held types out there, but I consider them useless for most things.

But this gentleman presents as knowing all about it, so I wanted to see how he goes about it. I am sure he has some new things for us to learn.

I did serve my apprenticeship in a mold making shop starting back in '75 and carved on various kinds of metals since then. Been retired for a while now.

Deciding just where on the bullet we start to measure to determine the beginning of the ogive has to be specified, and to how many places? Sometimes .001 might as well be a foot.

[JASmith]

One could create a bullet insert for the Stoney/Hornady tool that has the same angle as the Grendel throat. The opening wants to start at the expected max bullet diameter and be long enough to catch the smallest bullet diameter.

That would give the base to contact point as long as the angle is the same as that in the rifle.

That could be a straightforward DIY for one who has access to a lathe and a Grendel reamer.

[jasper2408]

One could create a bullet insert for the Stoney/Hornady tool that has the same angle as the Grendel throat. The opening wants to start at the expected max bullet diameter and be long enough to catch the smallest bullet diameter.

That would give the base to contact point as long as the angle is the same as that in the rifle.

That could be a straightforward DIY for one who has access to a lathe and a Grendel reamer.

Short Action Customs has a different design on their comparator inserts. They explain their design toward the bottom of the page.

https://www.shortactioncustoms.com/modular-headspace-comparator-inserts-1

This is the short insert holder. They also make a longer version.

https://www.shortactioncustoms.com/modular-headspace-comparator-body

[Klem]

The spirit of the exercise is to measure bullet length to a more reliable part of the bullet. This is driven by the variability of tips relative to the rest of a bullet's shape.

If it is something related to tips only then presumably the closest to the tip but not the tip itself will be the most usable/informative metric. The unique shape of the calibre's chamber should be a non-issue - we are comparing OAL's only. The issue is standardizing the ID of the measuring device or in other words the 'datum diameter' (similar to a calibre's datum line).

[EigerWand]

Hi, these are the boxes, just for fun.

Bullet boxes 81kb.jpeg

Bullet box end info 76kb.jpg

[EigerWand]

Thanks heaps for the link to the JBM site !
That's what I was hoping for when I put these up - a good place to look up.

120 NBT EW 1.127" JBM 1.220" OK I suppose that's fairly close considering I only measured one bullet out of the box
123 ELD-M EW 1.141" JBM 1.236" WTF ? So I went back and remeasured a few bullets and looked sat my own notes and I had copied / typed it wrong. My length is actually 1.241"
120 Pro Hunter EW 1.083"; JBM 1.079 (Litz 1.093) OK that's alright too.

So, I measured about 0.005" longer than what's in JBM.

[EigerWand]

Measuring equipment

I used a hornady comparator insert which I think is really intended for measuring cartridge base to ogive.
I've also got one of those hex nut measurers (Sinclair I think) but didn't use it for this as its a bit more fiddly to hold in place.

I understand the "ogive" to be measured at the nominal diameter of the bullet, where the bullet sides change from being cylindrical to curving / tapering in towards the tip. In this case it would be either 6.5mm or 0.264"
I bought one labelled .26 and, as Klem points out, it's fine for me to compare my own loads with my own.
But I've also had doubts about just what the internal diameter really is.
The opening on that and the nut device look as if they are chamfered so is it the hole or the outer surface that's meant to be 0.26 ? You can't measure a round hole with square calipers ...
The idea of 0.26" suggests they weren't really trying to measure to the diameter of commercial bullets.

Here's my setup:
Bullet measuring gear 84kb.jpg

Also, for my own personal use, I've recorded the setting on my Redding micrometer bullet seating die.
DO NOT USE THESE SETTINGS UNLESS YOU CHECK THEM YOURSELF WITH YOUR GEAR AND RIFLE.
I started with the NBT which I'd seated to the max length I could eject unfired. OAL to tip is 2.234" CBTO was 1.704" This seems to be at least 0.090" from the lands in my rifle as best I could measure.
Then I made a new load with the ELD-M to the same OAL to tip. In this case CBTO was 1.644" ie 0.056" shorter because the tip is so long and pointy.
With the Sierra Pro Hunter, which I havent tested yet, the tip is much fatter and stumpier, so I matched the CBTO of the NBT because I knew that was still well off the lands. Now the OAL to tip is only 2.187". I've got this idea I'll try increasing the OAL out a bit in future to increase the space for powder ....

So, as people point out above, I don't know what the diameter of the seating cone is or even where it really is inside the die.
But I need to adjust the setting whenever I change bullets and I've recorded these below just for interest.
I check the loaded rounds for CBTO and OAL as well to make sure I haven't made a mistake or the micrometer hasn't got out of adjustment (the dial can be reset too).
Nosler 120gr Ballistic tip 26120: Base to tip 1.127; Base to 0.26 ogive 0.701; Loaded round CBTO 1.704 OAL tip 2.234; Redding seater micrometer 0.181
Hornady 123gr ELD-M 26176: Base to tip 1.241; Base to 0.26 ogive 0.666; Loaded round CBTO 1.644 OAL tip 2.235; Redding seater micrometer 0.140
Sierra Pro Hunter 120gr 1720: Base to tip 1.083; Base to 0.26 ogive 0.601; Loaded round CBTO 1.701 OAL tip 2.187; Redding seater micrometer 0.165