MV decreases as charge goes up

Rover31

Rover31

Jedi Master
Full Member
Minuteman
Oct 27, 2007
981
376
Mos Eisley
#1
Been testing out my .308 for OCW. Did a ladder for fun last week and an OCW today.
Very happy with the results but... my MV went down on my last 5 rounds I tested.
started at 43g and went up in .5 increments to 45g. All loads the same cept for charge weight. Primers were only slightly flatter no pressure signs to note.
The 45g lost 100 fps across the board.
Found that interesting, just a byproduct of the gun not liking the load?

FYI
.308
Win brass neck sized all 1X fired
CCI LR primer
175SMK
ogive loaded.. cant remember length have to get back on that
Varget powder
Savage 24 inch barrel caressed by Benchmark!
 
#2
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rover31</div><div class="ubbcode-body">Been testing out my .308 for OCW. Did a ladder for fun last week and an OCW today.
Very happy with the results but... my MV went down on my last 5 rounds I tested.
started at 43g and went up in .5 increments to 45g. All loads the same cept for charge weight. Primers were only slightly flatter no pressure signs to note.
The 45g lost 100 fps across the board.
Found that interesting, just a byproduct of the gun not liking the load?

FYI
.308
Win brass neck sized all 1X fired
CCI LR primer
175SMK
ogive loaded.. cant remember length have to get back on that
Varget powder
Savage 24 inch barrel caressed by Benchmark! </div></div>

Sometimes you reach a peak and you're just spinning your wheels.

Other times, your barrel gets hot, opens up and you'll see MV decrease.

Can't say for sure.

Chris
 
#4
Re: MV decreases as charge goes up

I had that happen to me in a gun with 155 Scenars and H4895. Fortunately it was very accurate around the point where I stopped getting MV increases so I just ran with that and didn't worry about it further.
 
#6
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Falar</div><div class="ubbcode-body">What brand chrono? SHooting in the shade? Intermittent clouds? </div></div>

Would the conditions your talking about make 100fps difference?
 
#7
Re: MV decreases as charge goes up

Sunny blue sky day no clouds.
Chrony Master Beta
The thought that the barrel heated up had me going but that was after total of 25-30 shots over the course of an hour... maybe but kinda thinking not, it was about 55f very minor 2-3mph breeze.

hmmm...
 
#8
Re: MV decreases as charge goes up

forgot to mention the 44.5 load very very nice group! and 2900fps.
so yeah I could just be spinning my wheels. Had to complete the test though ya know!
 
#9
Re: MV decreases as charge goes up

I've had it happen before during load work ups. IIRC, MV went flat or dropped off just a hair. But then it started to increase again as the powder charge kept increasing.
 
#10
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rarebreed93</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Falar</div><div class="ubbcode-body">What brand chrono? SHooting in the shade? Intermittent clouds? </div></div>

Would the conditions your talking about make 100fps difference? </div></div>

I've had a cloud cover the sun and put my chrono in the shade alter the readings by several hundred fps. It was a shooting crony too, the shittiest of all chronos.
 
#11
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Falar</div><div class="ubbcode-body">
Rarebreed93 said:
It was a shooting crony too, the shittiest of all chronos. </div></div>

yeah yeah I know.
I get Err1 or Err2 about 25-30% of the time
someday when I'm rich I'm gonna...
Click to expand...
 
#12
Re: MV decreases as charge goes up

I don't remember which issue it was in, but a few years ago I read a very interesting article in either Rifle or Handloader magazine. They were writing an article on pressure signs. They put a pressure guage on a rifle and worked up to a max, or slightly over max, charge while looking for the traditional signs of pressure- flattened primers, sticky bolt lift, etc. They saw that they reached max pressure before any noticeable signs of pressure. The load at or near max also showed a decrease in velocity.
This was the same issue- I think, where they found that a very light charge of powder in a handgun can cause overpressure. They had noticed extremely different points of impact between 2 shooters shooting the same pistol, same load, same everything except how they help the pistol. One shooter pointed the barrel up before settling on target. The other shooter would tend to lower the barrel and come up on target. They figured out that the shooter who lowered his barrel allowed the light charge of powder to fall away from the primer and almost detonate. They confirmed the pressure was over max- with a light load far under a max charge of powder.
The conclusion of their article was to use a chronograph and the published velocity to watch for pressure instead of flattened primers or a sticky bolt. Most of us will never have access to a pressure gauge, but the chronograph will tend to show a loss of velocity when overpressure after a climb through the listed target velocity.
They also noted that accuracy was usually best just under ot at a max powder charge. In the past the best velocity was usually further under the max charge. I think I remember their reason as the bullets have changed even in the last 10 or 15 years as have powders.

I apologize for the lack of cites, but this is a fairly accurate paraphrase of the article.

Jim
 
#13
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rover31</div><div class="ubbcode-body">forgot to mention the 44.5 load very very nice group! and 2900fps.
so yeah I could just be spinning my wheels. Had to complete the test though ya know! </div></div>
Rover,

Did I read that right? 44.5 grains Varget and 2900 FPS from a 308 Winchester, w/175 Gr SMK??????

Since Hodgdon lists max load as 45 grains and only 2690 FPS, I would think you might be WELL OVER max if your chrono is reading anywhere near right....

Just to frame it for you, 300 Rem SAUM 56.5 grains Varget 168 gr SMK 2955 FPS. And your running a case that holds nearly 20 grains less powder, and a bullet 7 grains heavier.....and only going 55 fps slower.......

"Farewell and adieu to you fair Spanish ladies,
Farewell and adieu to you ladies of Spain;
For we've received orders to sail back to Boston,
And so nevermore shall we see you again. "
 
#14
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rover31</div><div class="ubbcode-body">forgot to mention the <span style="color: #FF0000">44.5 load</span> very very nice group! and <span style="color: #FF0000">2900fps</span>.
so yeah I could just be spinning my wheels. Had to complete the test though ya know! </div></div>

Uh, I doubt it.

Time for a new chrono.
 
#15
Re: MV decreases as charge goes up

Thats what i was thinking too...

Anyone shooting a 175smk, at 155 Scenar like speeds, in a .308win is either

A) Suffering from a chrony error / or busted chrony
B) Talking shit

Option a) sounds like the culprit... and this is not suprising as it is rather easy to set up a chrony the wrong way.
 
#16
Re: MV decreases as charge goes up

Cloud cover will have an effect on readings. I have shot on sunny days and cloudy days. The cloud cover usually is about 100 to 200 fps slower. This is using a CED m2. This is shooting in a control environment to the outside target. Adding more powder is adding more pressure. You are adding more fuel, You will get more fire.
Shooting a string of shots. I have shot a 20 shot string over a chrono to determine the SDS in 3 to four minutes. This shows me when at a match the load will hold up. With this you will still maintain fps.
 
#17
Re: MV decreases as charge goes up

It is
My first chrono and not a good one at that.
So I would agree with the doubters, just reporting the data I see.
As to being overloaded it's not showing any pressure signs.
 
#19
Re: MV decreases as charge goes up

Both pressure signs and conventional wisdom suggest against excessive charge.

How far away is the chrono? Unless it's at least 8-10ft away, 15ft is better, you're probably not getting valid readings.

Greg
 
#20
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">
How far away is the chrono? Unless it's at least 8-10ft away, 15ft is better, you're probably not getting valid readings.

Greg </div></div>

Right about 10-12 feet
 
#21
Re: MV decreases as charge goes up

Sir, there is no way in hell you are getting a real muzzle velocity of 2900 fps out of 175 SMKs over 44.5 gr. of Varget and I seriously doubt your velocity is actually going down as the charge increases. Do more testing with a couple of different chronos on a good clear day and I suspect all the MYSTERY will evaporate.
 
#22
Re: MV decreases as charge goes up

I shot the 178gr AMAX today with 45g Varget out of a 24" and recorded it at 2700. To get 2900 with the 175 SMK is unusual to say the least in a 24" and especially with no pressure signs.

Either you've loaded a lot more powder than you think (but suspect you would see pressure signs) or you weren't shooting a 175 SMK or your chrony wasn't set up correctly (sounds possible since you mention 25-30% error rate)?

If you are certain on your load being accurate, the bullet being a 175 and the chrono being gtg you bet we want to see and hear more on this.
 
#24
Re: MV decreases as charge goes up

I agree with several of the other guys. Bad chrony. 45 grains of Varget behind a 175 SMK is well beyond the manual but I doubt it would drop velocity OR get to 2900 fps. My Remington 5R load with that bullet is 42.5 gr @2600 fps and that's a fairly warm load.

Oehler was making a special run of 35P chronographs over the last few months. You might want to pick one up. I did. And my Gamma Chrony is for sale...CHEAP!

-David
Edgewood, NM
 
#25
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rover31</div><div class="ubbcode-body">forgot to mention the <span style="font-weight: bold">44.5 load very very nice group! and 2900fps</span>.
so yeah I could just be spinning my wheels. Had to complete the test though ya know! </div></div>

Something's not right. Your velocity is way too high for that charge weight with 175's.

Double check your chrono and your SCALE.

Also, when you are at are near max, sometimes you don't get increased velocity but accuracy starts to go away, then pressure really spikes and pierced primers result.
 
#26
Re: MV decreases as charge goes up

One of the easiest ways to verify MV is get a good 100 yard zero and with that zero shoot a 300 yard group. The bullet drop is easy to compare to a ballistic chart.

Good Luck
 
#28
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pepperbelly</div><div class="ubbcode-body">Do you have any other bullets like 155gr Scenars that you may have accidently loaded instead if a 175gr SMK?

Jim
</div></div>

Nope none at all. Have A-Max and some round nose so no mix up.
Chalk it up to a bad Chrono.

Still the ques is about a loss of MV at max load. Just wondering if others have seen that.
Honestly I don't care what the MV is. It was just curious to me to see it rise about with each charge increase and then drop 100fps with the last test group.
 
#29
Re: MV decreases as charge goes up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rover31</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pepperbelly</div><div class="ubbcode-body">Do you have any other bullets like 155gr Scenars that you may have accidently loaded instead if a 175gr SMK?

Jim
</div></div>

Nope none at all. Have A-Max and some round nose so no mix up.
Chalk it up to a bad Chrono.

Still the ques is about a loss of MV at max load. Just wondering if others have seen that.
Honestly I don't care what the MV is. It was just curious to me to see it rise about with each charge increase and then drop 100fps with the last test group. </div></div>

That may also be due to the chronograph. Until you verify the test loads on a new chronograph all of your results are suspect.
I would be happier about the small group than worrying about the MV.


Jim
 
#30
Re: MV decreases as charge goes up

totally agree about the crap chrono.
But what about taking the data for what it is worth...
consistent MV from one load and an appropriate rise in MV with an increased charge? wouldn't that be worth something?
We all know that every chrono is going to be a little different but as long as the data is consistent we can use the data to some extent. We all have to take into account Temp, sun, clouds, altitude time of the month etc. now I just have to take into account my chrono is super optimistic!

Now about the group size yeah I am very happy!
 
#31
Re: MV decreases as charge goes up

I shoot 45gr of Varget in LC-90 cases with 175gr SMKs in my 24" 1:12 AR-10 upper (Sabreco). My MV is around 2760 fps for reference.
 
#32
Re: MV decreases as charge goes up

I get nice 20-30 fps increase in .3 gr. increments up to 45.4 gr. of RE15 behind 175 SMK's. Beyond that, the MV really flattens and the ES jumps up. In laymen's terms, you can only push on the gas pedal so hard, but that doesn't mean it will go faster or is safe. I'm getting 2678 fps with 45.4 gr. of RE15 behind a 175 SMK in Win. brass and Fed. 210M primers out of a 26" pipe, with ES in the single digits. 46.0 gr. only yielded 9 more FPS with an ES of 31. It told me I had reached the limit.
 
#34
Re: MV decreases as charge goes up

I had a shootin chrony alpha master as I recall before purchasing an Oehler. I had EXACTLY the same problems with it. Did everything I could to set it up perfectly and still got readings 200 fps faster thsn they should have been. I never could get that thing to read regardless of the conditions outside. My advice is to find another chrony. You'll be pissing in the wind until you do.

Jay
 
You must log in or register to reply here.

Similar threads

B
New Shooter - 6.5 Creedmoor Load Development
Replies
7
Views
619
VikingSinEater
V
bushman77
Copper Creek Cartridge Co load pack
Replies
4
Views
333
Patrick1956
P
N
First Timer Help! LR Hunting 308 Handloads
Replies
44
Views
2K
JerkyFreak
JerkyFreak
padom
20" Green Mountain AR15 Fluted 416SS 1-8 Testing
Replies
16
Views
1K
NHPiper
NHPiper
Zigjib
Powder giving slower MV
Replies
5
Views
408
secondofangle2
secondofangle2
Top Bottom
Back
Home
Forums
Merch
Alerts