Question about coal

[JeepHammer]

JeepHammer, if you're a stickler for COAL, do you raise your bullet seater stem .0001" for every 2 or 3 rounds fired so bullet jump distance stays in that tolerance? Or is is every 20 or 30 rounds that the stem's moved up .0010"?

No Bart, I'm not an idiot.
Since I know the difference between actual freebore and some set of drawings somewhere for the 'Perfect' SAAMI chamber,

I measure my shortest freebore I current own for the caliber I'm loading,
And I make my rounds as close to that shortest chamber as I can.

That allows me to shoot the rounds in ANYTHING I own in the same caliber, some have a little more freebore than others,
But I don't run around and load for each and every ammo burner I have specifically.

That's why I CLOSE UP FREEBORE so the chamber lasts longer with rounds that will fit in the magazine...

-----

And the claim the freebore changes 0.001" for every 10 rounds is RIDICULOUS!
That would have to be the SOFTEST barrel material in history, made from Japanese beer cans!

Freebore, just like rifling, will compact the metal layers (work harden) a little quicker when you first break in the barrel,

But you first said it would compress or erode 0.001" every round,
Now you say 0.001" every 10 rounds...

That's 0.010" in 100 rounds,
0.100" in 1,000 rounds.

I've not seen that much compression in .300 mag chambers, and I've got a BUNCH more than a 1,000 rounds through them!

My current favorite .308 has more than 5,000 rounds through it, and the freebore has increased just under 0.010"...
Still ROUND, just increased, not 'Eroded' sideways...

Don't confuse erosion and freebore with 'Bullet Jump' (what ever that is) and you won't have these issues...

 

[Bart B.]

JeepHammer, you must not be familiar with the 1000-yard accuracy levels 7.62 NATO Garands got shooting Sierra 190's from their 1:12 twist barrels.

Nor the accuracy Win. 70 match rifles produced with their 1:12 twist barrels shooting 197 or 200 grain Western Cartridge Company match bullets at 1000 yards.

And you're misquoting me; again.

Just did a test with a new Hart barrel chambered for .308 Win. Sierra's 168's contact point with the rifling was at a diameter of.3035" to .3045" on the bullet's ogive. The middle part of the throat angling from the barrel's .3078" groove diameter down to .2990" bore diameter. Bore diameter on the bullet's ogive was several thousandths forward of the rifling contact and didn't touch anything.

 

[Unclenick]

The Burger information is almost identical to Sierra.
They recommend you keep freebore down to around 0.040" or under,…

You misread the Berger information:

What has been discovered is that {secant ogive} VLD bullets shoot best when loaded to a COAL that puts the bullet in a “sweet spot”. This sweet spot is a band .030 to .040 wide and is located anywhere between jamming the bullets into the lands and .150 jump off the lands.

So they adjust in 0.040" steps, starting jammed into the lands for target shooters and starting 0.010" off the lands for hunters (due to fast feed requirements for follow-up shots). There you see jump defined a bit obliquely. It's a term that came from benchrest shooting, and refers to how far the bullet must travel from its position in a full seated forward cartridge case to touch the throat. This was for secant ogive bullets. Tangent ogive bullets are much more forgiving, which is why Berger came out with their hybrid ogive that starts as a tangent ogive, for less seating depth sensitivity, the changes to a secant ogive for lower drag once the tangent ogive has narrow below throat diameter.

The long VLD's usually can reach a throat, but there are, as you point out, some very long freebore chambers, like the Weatherby designs (SAMMI drawing has the 300 Weatherby freebore at 0.308-0.328"), and some Remington barrels these days seem to be beyond SAAMI standard length. The SAAMI standard for .308 has the freebore 0.090-0.105" long. Match reamers for M852 (168 grain SMK bullet) have a shorter 0.075" freebore, and 7.62 NATO runs a longer 0.150" freebore (these are Clymer's dimensions). So the bottom line is that your bullet choice affects flexibility in this regard.

As far as throat wear goes, it depends how you measure it. Bart seems to be using bullet contact with the lands. The M1 Garand and M14 throat wear gauges don't measure that directly. Instead they are a tapered rod with graduations that stops against the inside corner of the throat taper onto the lands in the rifling. So the taper depends on that point widening by 0.001" for to register as a 0.001" throat wear. That does take more wear before it occurs.

 

[Bart B.]

Regarding Unclenick's throat erosion gauge for measuring throat wear.

They're tapered from .3100" down to .3000" over a 1 inch long section of the gauge head; taper is .0010" per .100" of gauge head length and their scale increments in .100" spacing. My new .308 Win barrel mentioned earlier reads "0" at the receiver's reference point when it's against the rifling's contact point. On that barrel with 2000 rounds through it an extra .060" of bullet jump for a given COAL with Sierra's 168's, it reads "4" which is ,400" inch deeper in the barrel than the new one showed. Compare that to the .060" difference in COAL's in each with the same 168-gr. bullet seated against their lands.

All of which means the angle on a bullet's contact point with the throat will vary with that of the throat angle.

 

[JeepHammer]

Unclenick,

I get the throat erosion gauges, worked with them for many years...

What I have an 'Issue' with is Bart's instance that 'Freebore' is a set dimension,
Completely Dependant on SAAMI specification, carved in stone.

ANY changes from SAAMI is 'EROSION' or it's UNDERSIZE to SAAMI.

I wasn't going to let this cat out of the bag, I was going to let Bart dig the hole deeper first...

------

In BENCH RIFLE chambering, and in the Marine Corps,
FREEBORE is the distance the bullet travels before it hits the throat.

PERIOD.

Freebore can INCREASE as he chamber 'Erodes' or simply compress.

Freebore can be closed up by seating the bullet long,

Freebore can change, without any changes to the chamber/throat,
By using a different profile the freebore changes.
(Oglive isn't EXACTLY the correct term, but it will do for this particular situation)

Blunt bullets will simply hit the throat before longer tapered bullets will,
And that is 'Freebore',
Where the bullet is CONTROLLED by the cartridge case mouth.

Now, 'BULLET JUMP' is shortened from 'Bullet SIDEWAYS Jump' when the bullet is no longer being controlled by the case,
And moves sideways hitting the throat at an angle becasue of EXCESSIVE freebore.

--------

When Marine hand built rifles are issued to field troops,
Usually Scout/Snipers,
That man is issued a erosion gauge for that particular rifle.

As erosion increases,
The HAND BUILT ROUNDS for that particular rifle can be increased in length to compensate for the increasing freebore.

It's HARD to get a rifle in from the mountains of Afghanistan, Iraq, or what ever crap hole he's stationed in, to correct the chamber,
So the mounting goes to him.

When the erosion reaches a point where the rounds are getting too long for the MAGAZINE,
The rifle is recalled, and he gets a new rifle,
(Or the barrel is replaced by a qualified tech, and a new throat erosion gauge specifically for that rifle is issued.

Combat rounds MUST be crimped into place, the bullets and primers sealed, ect.

Since these are NOT paper punchers on nice weather days that never get banged around,

The bullet MUST stay positioned in the case, and a crimp required,

And since they will be dragged out in all weather, amphibious landings, fording rivers, ect.
The bullet/primer MUST be sealed.
So the rounds simply can't be made long with no crimp and let the chamber set freebore to zero...

The chamber FREEBORE is cut short, with a tolerance of -0.002",
The rounds are cut short,
So as erosion happens, or the NORMAL process of compaction happens,
The freebore gauge lets Quantico build ammo that FITS THE FREEBORE and the rifle stays accurate...

Now, these aren't paper punchers,
No paper puncher ever had a company of hostiles dumping hundreds of rounds on a paper punchers shooting position...

So I'm SURE the paper puncher will say...
"We do things differently, We are more accurate",
Um, comparing apples to mortars with a seriously inflated sense of self importance in those general statements...

And ANY SCOUT/SNIPER will run with the cream of the crop paper puncher...
They wouldn't be Scout/Sniper if they couldn't shoot as well as any of the top civilian shooters.

If they can't run with the TOP civilian shooters in accuracy at 1,000 yards, they don't graduate Scout/Sniper.
Marine Snipers are simply the best all around marksmen in the world, and they prove it regularly...

Paper punchers wouldn't have a clue what to do with a SPRINTING target at 1,000 yards,
Marines knock them down on a regular basis,
All the while having people drop mortars, lob in RPGs, people dumping rounds at them...

You want 'Competitive Pressure' there it is!
It's not a win, second, third place,
It's live/die...

------

The other end of the spectrum is the bench rifle shooters.

No general paper puncher will ever run with the bench rifle guys.
While general rifle guys talk about a 'Sub MOA' or 'Raggged Hole' groups,

Bench rifle guys punch ONE hole, you just watch it close to make sure it gets a little darker and a little more 'Fuzzy' during the next 4 to 10 bullets going through that same hole... depending on 5 or 10 round groups...

Bench rifle guys ALL cut the case in a separate process from the throat/freebore,
The term 'Freebore' is any distance from case mouth to throat since the bullet always rests on the throat.

------

Having someone try to force his particular 'Sport' rules,
Or his particular set of 'Standards/Terminology' down my throat is exhausting at the very least.

While trying to explain to someone how to measure their particular chamber 'Freebore' (as compared to SAAMI or Wylde 'Ideal' specifications),

While using the BULLETS THEY SHOOT,
Not a particular 'Match' bullet this or that competition body uses is frustrating,
And I also don't need the little snipes/attitude.

I didn't come here for someone to try and cram a solidly locked in set of standards down my throat, then belittle me when they can't seem to grasp the guy having 'ISSUES' probably isn't running the caliber/ammunition or even the chamber he is talking about...

IT'S NOT ABOUT WHAT BART DOES/HAS/THINKS, It's not about BART at all.

It's about what THEY HAVE RIGHT NOW,
WITH THE BULLET THEY ARE SHOOTING...
And trying to help them get running a little better, if possible.

I DON'T PAY ATTENTION TO SOMEONE THAT THINKS THERE IS ONLY ONE WAY TO SKIN A CAT...

And as several people pointed out,
Roy Weatherby uses LONG freebore in his chambers,
So do some others...
You can't argue with success, but you can debate WHY it works in some rifles/calibers, and doesn't work so well in others...

DEBATE isn't cramming 'SAAMI' down everyone's throats at every opportunity and trying to make someone with a different idea feel stupid...

Match shooters use ZERO freebore when they can get away with it,
Other use shortened freebore, like Wylde,
And again, it's hard to argue with success.

-----

Classifying normal compaction (Concentric) as 'Erosion' is also misleading.

Again, if the throat is concentric,

Which I tried to give a way for the 'average guy' to test for with nothing more than a case, bullet, drill bit and small tap (about $5) that ANYONE can do,

And that throat is NOT Eroding on one side more than the other, or eroding away at a specific spot,
Then it's just increasing FREEBORE,
Not RUINING the chamber...

No reason to scrap the barrel or do major surgery to reduce the freebore as long as the rounds you build fit into the magazine and feed well...

Not everyone is running a 'Match' rifle, changes barrels or does major surgery/rechamber,
And they simply don't have to...

The same barrel for YEARS AND YEARS is fine,
As long as you are aware of what it's doing...

 

[T. O'Heir]

2.570" is too short for a 165. Should be 2.750". However, 2 thou difference OAL isn't unusual. Forget about it. Copy paper is about 0.004 inches thick.
"....0015" is nothing..." Right. 1.5 thou is virtually nothing. It's 15/10,000ths.

 

[Wendyj]

That was typo on my old eyes. 2.750 is what I was tring to type and they were all very close. Being new I assumed that once one finally came out at 2.750 they all would. Proved that wrong just measuring factory which varied from cartridge to cartridge itself. Still just hanging with the 2.750 as manual states 2.80 as max. Loaded a few more earlier today and still getting average from 2.748 to 2.750. Seems like I've done more math since Saturday than since I got out of school. I'm hooked for sure though. My reloaded groups with 3 different powder charges put my factory high dollar ammo to shame. I really want to try some hpbt bullets but can't find any. Varget powder is all but history here as that's what most people have suggested for me. The Hodgdon Benchmark at 40 grains and Nosler 165 bt did good this weekend. Going to 600 yard range in two weeks and going to see what they really do. Not at 600 but really want to see the 200 yard groups. Maybe ring a gong at 600 or so just for the heck of it. I shot for recreation but am an avid hunter and am hoping to book a hunt for axis deer at Y/O ranch in Texas this fall. Brochure claims stalk and hunt with extreme shots being max 300 yards. I've taken a few here in Ga that far but it's only because I hunt a lot of power line right of ways.

 

[Metal god]

tag , with the pop corn ready

 

[Bart B.]

In the Marines, building sniper and match rounds, The first thing we did was weigh every bullet, Then start measuring...

The 'Average' box of 168 Match King hollow points, 100 in a box, Half the box was under/over wight by about 1/2 grain, Then we started throwing the proper weight bullets (+/- 1/10 grain) into the calipers for length/diameter.

If you do all that but don't sequentially serial number each round to HOCL's that match the individual rifle's throat erosion rate so the rifle they're shot in proper sequence, they all will not have the same bullet jump distance for the life of the barrel, so isn't all that a waste of time?

Exactly how much accuracy change does each of those bullet measurements cause?

Wouldn't you need ammo that had a muzzle velocity spread of less than 5 fps to tell the difference in one grain of bullet weight?

Unless you spin the bullets (a Juenke bullet spinner or a current metered Dremel Moto Tool with a collet to hold them) to sort the perfectly balanced ones from the others, a 1% spread of all the bullet's BC's caused by unbalance will easily mask a 3 grain spread in bullet weight as well as .005" spread in length.