Want to duplicate a home-made copy of my Sinclair Intnl., bullet comparator,

[jjrothWA]

for measuring the 8mm Mauser cartridge.

I thinking, that after viewing the SAMMI chamber drawings for the .233, 7mm Mauser & Rem Mag., & Cal.30 & .308 Win. for identifying the "land" diameter, then measuring the ID's of the "HEX" comparator.

I believe that using a standard brass/bronze threaded nut, and drill thru a flat using either of the following:

5/16" [0.3125"]
or 8.0 mm [0.315"]
or 8.2 mm [0.3228"]

The last two drill will have to be purchase at a Tooling supplier store.

What diameter would the "brethern here" recommend

I'm reloading for a WWII check 8mm rifle.

Thanks.

[Parashooter]

"We have been making these hex style bullet comparators for over 20 years, and believe we make the most accurate tools available. The holes in the Sinclair Bullet Comparators are cut with throating reamers to accurately duplicate the actual throat of a rifle." https://www.sinclairintl.com/reloadi...prod83792.aspx

If Sinclair's copy is accurate, the holes are taper-reamed, not simply drilled straight. That could make a significant difference in where they come to rest on the ogive.

[jjrothWA]

Follow-up:

Located an old Clymer catalog. and they make their "throater" reammer " bullet diameter and 0.001 / 0.002: addtional clearance.

Looked at Hornady website and they use the same comparator insert for the .30 calibers and 8mm diameter, spoke with a tech and they just using it a a "reference point for length of case head to a known reference point.

So I will use a pilot drill bit to set up the brass nut I have for perpendicularity of a flat , drill thru and open bore up with a new 5/16" bit and go with that!

[fguffey]

jjrothWA

Want to duplicate a home-made copy of my Sinclair Intnl., bullet comparator,

There is nothing I can say that would get you to consider a different method and or technique.

So I will use a pilot drill bit to set up the brass nut I have for perpendicularity of a flat , drill thru and open bore up with a new 5/16" bit and go with that!

If 5/16" is .3125" you can forget using the hole to measure the .308" bullet because the diameter of the 308 bullet is .308"

and then you spoke to a tech. person.

spoke with a tech and they just using it as a "reference point for length of case head to a known reference point.

I have given up on reloaders using standards and transfers; it would be nice if Hornady could make it possible to 'Zero' the comparator or train their tech personal to zero the gage. Reloaders have always assumed the tool was accurate but could never get the gage to match SAAMI specifications; the problem is caused by Sinclair/Hornady's insistence on using bullet friendly radiuses.

I use 'the datum', the datum does not have soft, rounded or beveled edges. And then there is the exception: The L.E. Wilson case gage is a datum based tool with a radius on the datum. "How do they do that?" They have been making the L.E. Wilson case gage for over 80 years and for most of those years reloaders have called the case gage a 'drop-in gage'.

And while you are making copies of tools for measuring cases think of the gage that measures the length of the case from the datum/shoulder to the case head. For years and years reloaders thought the datum was a line and then one day someone informed them the datum was not a line, he informed them it was a round hole/circle. He informed reloaders the round hole/datum for the 30/06 was .375" in diameter.

He then assumed reloaders had shop skills and assumed reloaders could drill a 3/8" hole; instead they went to the hardware store and purchased bushings with 3/8" hole through them. It was about that time they could not get SAAMI and their dial calipers to agree because the bushings had a radius at the opening of the hole through the bushing.

F. Guffey