chrono data contradicts load data...bigtime

[Texas Solo]

I just chronographed some new .308 loads using Hornady 168 BTHP Match and 44.0gr Varget. They grouped very well at .390". But I'm a bit concerned with the velocity/pressure. 5 shot string averaged 2901, with a 50ES. According to Hodgdon data, I should be at 2731 with a max load of 46.0, (using a Sierra MK) ???? I chose the middle of the road 44.0 because 1) I'm using LC brass, and 2) because the Hornady bullet seats deeper into the case when loading to the lands.
I can't see any pressure signs, no sticky bolt, easy extraction.
Which is more likely.....
1) data is off
2) my chrono is off (Chrony)
3) I'm actually over pressure and don't know it
FWIW....43.5gr Varget shot like a shotgun, 43.7 slightly better, 44.0 is GOLDEN, 44.3 slightly worse.
Rifle is a DSG #11VT .308

Can anybody run some ballistics for me and make an educated guess as to what's going on?

[stangfish]

Hey solo. I find 44 gr varget LC 07 Brass is golden with most 168's in a factory chamber that I have seen. Addressing #1 What was the COAL out of your book? #2 only one way to find out. And #3 Non VLD in the lands often accompanies higher pressures from my experience.

How are your primer pockets. I often found loose primer pockets after crunching powder and jamming combined.

[BillPa]

Can anybody run some ballistics for me and make an educated guess as to what's going on?

Bullet Type = .308 168 GR BTHP HORNADY Bullet Weight = 168.0 grains
Bullet Diameter = 0.308 in Bullet Length = 1.230 in
Bullet BC = 0.45 Sectional Density = 0.253
Case Type = 308 Winchester Case Length = 2.015 in
Full Case Capacity = 53.458 grains water Est. Overall Cartridge Length = 2.810 in
Net Case Capacity = 45.278 grains water Bullet Seating Depth = 0.435 in
Rifle Type = Barrel Length = 24.0 in
Effective Barrel Length = 22.42 in Barrel/Case Volume Ratio = 10.2
Cartridge Temperature = 70.0 °F
__________________________________________________ ________________________________

Powder: VARGET
Calculated Powder Charge = 40.1 grains
Load Density = 88.6%
Charge/Bullet Weight Ratio = 0.239
Estimated Muzzle Velocity = 2434 ft/sec
Estimated Chamber Pressure = 44929 CUP
__________________________________________________ ________________________________

WARNING: For starting loads reduce calculated powder charge by at least 10%.
Load Table
-------------------------------------------------------------------------------------
Load Charge Charge- Muzzle Chamber
Density Weight to-Bullet Velocity Pressure Notes
(%) (grains) Wt. Ratio (ft/sec) (CUP)
-------------------------------------------------------------------------------------
75 34.0 0.202 2064 31260 OK
80 36.2 0.215 2197 36190 OK
85 38.5 0.229 2337 41344 OK
90 40.8 0.243 2477 46498 OK
95 43.0 0.256 2610 51428 High Pressure
100 45.3 0.27 2750 56582 High Pressure


Bill

[Texas Solo]

Hey solo. I find 44 gr varget LC 07 Brass is golden with most 168's in a factory chamber that I have seen. Addressing #1 What was the COAL out of your book? #2 only one way to find out. And #3 Non VLD in the lands often accompanies higher pressures from my experience.

How are your primer pockets. I often found loose primer pockets after crunching powder and jamming combined.

Well, it's comforting to see the load is popular. In theory, it should not be over pressure. But the chrono readings say maybe so.

1) COAL from all the books say 2.800, as does Hodgdon site and SAAMI. But that's all relative to the bullet you're shooting. I'm under that spec, and maybe .001 > .002 off the lands. (weird ogive on this bullet)
2) already thought of that, but none of my cheap redneck friends have a chrono to compare....they barrow mine
3)I'm not actually "in" the lands, but just kissing them, or maybe .001 > .002 jump, best I can measure with an OAL gauge and comparator.

No idea on the primer pockets. I got 500 rds. of LC prepped to load and haven't tried to reload those I just shot.
But they should (?) be OK. I'm not crunching powder or jamming. The load volume is just short of the shoulder.

Maybe I'm being overly cautious (if there is such a thing). It's just that the 2900fps doesn't seem correct at 2.0gr UNDER the max, which yields 2750fps. With no signs anywhere of over pressure, I'm beginning to think my chrono is toast.

And on a brighter note, I popped 3 coyotes this AM with my AR :)

[sharpshooter]

Pay no attention to the data, it was gathered with a different rifle and different lot of powder and a different bullet. If it works, don't argue with success.

[Texas Solo]

BillPa...thanks for the data. Not sure what to believe now.

That data shows very comparable with Hodgdons data in terms of load volume/velocity, but they differ greatly in pressure.Your data shows 41,200CUP attained at 38.5gr, where as Hodgdon's data doesn't reach that pressure until 42.0gr
They show a max 50,600 CUP @ 46.0gr, your data shows 51,400 @ 43.0gr.

My head is spinning. To much thinking.

[missed]

I bullet drop them to verify speeds. But yeah seems fast. For some reason it must have been a weird day but my ballistic program is showing that my 168g SMK 308 loads are at 2917, must have had the magic weather that day.

[Texas Solo]

I bullet drop them to verify speeds. But yeah seems fast. For some reason it must have been a weird day but my ballistic program is showing that my 168g SMK 308 loads are at 2917, must have had the magic weather that day.

Explain the "bullet drop" thing. Never heard of it.
Your ballistic program says 2917, but what does it chrono? Powder type & charge?

[darkker]

In theory, it should not be over pressure'

Unless you use your pressure trace, don't read chicken bones.... Brass tensile strength is typically around 70,000psi, you when you get difficult extraction; guess where your pressures are?!!
There was a member here I donated a 25-call barrel & bullets to, when he bought a PT from Rocky Raab. Was supposed to get some data from him as intellectual curiosity, but waiting for the miracle never gets us anywhere; so it was time to call that a lostt cause and buy my own equipment, and hope karma evens us in the end.

[missed]

Shoot at one distance, back up to a further distance shoot using same elevation measure the distance between the two impacts. Put yardage distance difference and impact elevation difference in the Strelok calculator and it will get you the speed. My 168 grain 308 42.5 grains Varget should have been like 2600~ fps.

[Texas Solo]

My 168 grain 308 42.5 grains Varget should have been like 2600~ fps.

So the Strelok calculator said 2600, your ballistic program said 2915, but where does it chrono at 42.5? I'm at 2901 with 44.0 Varget

[Wildboarem]

Your chrony may not be toast. You could have a fast barrel. My barrel shoots 100 fps + then published and unpublished loads. It just shoots fast.

I have a chrony and don't always trust it. I verify by shooting at longer range. The longer the better. For you a 168 bthp moving at 2900 @ 1000ft DA will drop 11.8" at 300 yds and 50.3" at 500. I usually reverse the calculation by shooting at distance and with ballistic calculator dialing in the appropriate dope. If it hits, your velocity is verified if it doesn't adjust and reverse calculate to figure your speed.

[missed]

Sorry I'm tired tonight...

The load charts suggest 2600fps

Last time I was out with those loads the bullet drop calculator in Strelok showed that it was moving 2917 from the data I put in from the measured drop from 100 to 400.

[Wildboarem]

Drop at distance doesn't lie, in fact it's the only thing that matters. It's always nice to have a fast barrel, as long as its accurate also.

[stangfish]

Drop at distance doesn't lie, in fact it's the only thing that matters. It's always nice to have a fast barrel, as long as its accurate also.

This is so true...as long as you know the B.C.