[69khz]

I'm slugging bores & my calipers don't give me readings like .318, .323 etc..

It gives me 4 digits, 2 normal size ones & 2 small ones labeled as inches,

so, if my slug measures up as .3115 would that be a .311 bullet or??

This confuses me.. sorry, but my old brain don't remember math like this

 

[tm45]

Your .323” is the 8 mm (8x57) Mauser bullet diameter.
.323" / .03937 = 8.2042 mm (They rounded the 8.2 number to get the 8 mm. IIRC?)
(.318” is the pre 1905 bullet.)
Corresponds to the bore diameter measuing to the deepest part of the grooves. (across the bore.)

Your .311xx etc, is the measurement across the bore, face of the lands (lans?) one side of the bore to the other.

7.90 mm x .03937 = .311023”
7.91 mm x .03937 = .31142”
7.93 mm x .03937 = .31220”
etc.
You can also find conversion formulas on line, or in typical dictionary.
If you are talking about early K98k, this ‘may’ be able to give you a rough idea of bore wear? (I never see anybody write about this though.)

I figure that a K98k bore with anything less than .315- .316, is fairly good. Have read numerous info about accuracy may start to deteriorate after something like .0025” plus of wear. Not necessarily always true. Some worn barrels can still be quite accurate. (Depends some on if the wear is even all around.)

Once measured a Czech VZ-33 bore at .310”. That is very ‘tight’ to me!
If I measure an RC bore at .311 - .312” , or close to that, I tend to think of it as ‘pretty pristine’.
I don’t know what rifle you are dealing with. Just guessing. HTH, Tm

 

[69khz]

My caliper gives me readings in 4 digit decimals.

For 7.92 I am getting 0.3115 which was the size of my slug.

What I want to figure out is how to translate that 0.3115 into a 3 digit bullet size

I'm slugging all my bores, but this particular example is from a Gew 88 without the S marking.
I'm going to assume it's .318 but still, I need to figure out how to read these

 

[69khz]

Did a slug from another gew88, this one with the S mark & it comes out as 0.3160 which is 8.03mm

 

[DocAV]

Significant digits and decimals

Your caliper is set up to give you a reading to four significant decimals ( correct to 1/10,000 of an inch)
As this level of accuracy is only required by engineers in tool setting and tolerance determination, you can simply go to "3 digits or decimals of significance," so your .3115 becomes, by rounding up, .312 (Rounding rule is, if it is 4 or less, go to 0, if it is 5 or more, go up to 10.); so, also, .3160 becomes simply .316.

As to the importance of this level of accuracy in casting lead bullets or Bore slugging...very little importance whatsoever in a practical sense, unless your Barrel wear is such that accuracy is compromised unless you use oversized cast bullets to "Take up the slack"

Dimensions Land to land (ie, original BORE dimension) give an idea of the amount of barrel wear...the germans, czechs and Turks stamped the Factory Bore dimension on the barrel shoulder/shank to indicate to the Field Armourer the original factory bore diameter, so that wear could be gauges and barrels replaced as necessary...the Swedes did the same on their Butt discs of their M96 and M38 rifles, and Ag42 as well.

Groove dimensions can be variable for a number of reasons...one is that in many rifle designs, the Groove dimensions are notable larger than actual projectile diameters, by design, and not by wear ( see the original Mannlicher 8x50R M90 and 95 Rifles...Bullet .323, groove .329) The French had the same combination of .323-326 Bullet, but .325-327 grooves. And we won't go into the J/JS German controversy...

The other reason for wide diameter grooves is plain flame erosion, combined with corrosive and erosive (powdered glass) Primers, improper cleaning (or none at all), over a long period of time ( so-called" Sewer Pipes") a common feature of Ex-China Mausers and Arisakas.

Whilst the best Bullet to Bore corrispondence is a laudable goal, with cast bullet shooting, it is only necessary to have the bullet soft enough to Upset properly in the existing rifling (with or without gas check) and that the Bullet diameter is not "undersized" (less than groove diameter) nor so "oversized" that it swells the case neck and prevents cartridge seating in the chamber (Have had this happen with a Chinese Vz24 with a bore such that only .330 cast (ex Steyr Mould) would take the "rifling", but they had difficulty chambering, as the oversized neck would scrape into the chamber. One reason for "Wall hanging (or Film Gunning)" this particular rifle.

Regards, Doc AV
AV Ballistics.

 

[69khz]

Thanks Doc, but now I'm more confused than ever, lol

I'm not confused by the info you provided, which did help me figure it out, but I'm confused to as why I have a .312 & .316 bore sizes for a rifle that was supposedly originally configured at .318 (Gew 88)

I think my caliper is malfunctioning.

Thanks for taking the time out to help.

 

[tm45]

.323 bullet uses barrel that is about .312 across faces of the lands.
.323 -.312 = .011” approx. (or means grooves are about .0055 ‘deep’ on EACH side of the barrel.)

If you apply same logic to .318 bullet, I would expect:
.318 - .011 = .307” across the faces of the lands.

IF you say your barrel measures .312 or .316 across faces of the lands right? I would think that your barrels have been reworked.
I’m assuming - (You are not getting that measurement from valley of barrel groove to valley of groove right?)
Are you aware that many pre 1905 rifles were reworked (re-bored) to accept the
LARGER .323 bullet?

If you are getting .312 across, (barrel) groove valley to groove valley, then that thing was not designed for a 8 mm bullet. No way a .323 bullet wants to get stuffed down a .312 barrel. Kind of thing that could really mess up your day!!!
I'm talking about barrel measurements, not a slug.

 

[69khz]

I just stuck the id end of caliper in muzzle & got .312

My measurements in above posts were for the slugs, I assume for the lands as I measured from one side of slug to the other. I didn't get much of a valley that I could see clearly.

I slugged with 00 buckshot

 

[tm45]

I’ve never ‘slugged’ a barrel. Have read of others doing it.

Have a feeling your caliper is OK. Have you got anything to check it with? A set of feeler gauges, or sparkplug gapping tool? Something like that. (some of these items are not terribly accurate.)

Do you have any Mauser 8mm ammo? My Yugo 8 mm bullets will measure just about .322 (maybe .3215 to .322), just at the point where they protrude from the cartridge case. (The .323 part is inside the lip of the case.)
(‘50’s and ‘70’s Yugo measure equal for me.)

(For standard K98k rifles), if you remove the bolt and carefully slip an 8 mm round into the chamber part way by hand, if the chamber is well cleaned, when you release the round, it should gravity feed all the way into the chamber easily. (With barrel pointed downward.)
Actually may make a light clunk or thump as it drops into the chamber. Tip the barrel up, and the round should drop out, may need to tap it a couple times. Assuming that your barrel(s) have been reworked for the larger round.
I don’t think it would act this way at all in chamber that has original cut for the older .318 bullet. Guessing some here.

Should also note here that I’ve read conflicting opinions about the wisdom of shooting .323 ammo in older rifles, (pre 1905) even if the rifle has had the chamber reamed etc.
Something you should ask more about, if you intend on firing them.
DocAV can probably tell you, or maybe try asking on the appropriate rifle forum?

 

[CandRNut]

If the rounding is too confusing, then just drop or disregard the last digit.

0.3115 becomes 0.311
0.5353 becomes 0.535

This isn't the best advice, but it should remove the confusion.

While we're on the topic of rounding, a "5" only rounds up on even numbers and rounds down on odd numbers. We were never taught this in high school for some reason--picked it up later in college.

 

[jimlay]

Before you rely on your caliper, you should check its accuracy. For a "quickie", grab a new 1/4" drill bit and examine the shank of it... smooth and un-marred? Okay, measure that and you should be seeing .2500 on your caliper. Try other sizes too. Set your caliper to "zero" and read the dial; does it SAY "0"?

Here is a link to a free conversion utility. It is nice because it has zillions of possibilities for converting measurements between units and systems. The Versaverter. Download and install on your desktop. As I said, FREE.

http://www.pawprint.net/vv/