308 168BTHP 3200-3300FPS?!

[donshaw]

I reloaded some ammo and I shot it today through my chrony and i was getting 3100fps to 3400fps?????

I figured that it had to be wrong so i had my buddy shoot his 16in ar-15 through it and he was getting 3200-3400fps no factory bulk ammo.

The chrony was 8-10 ft away

308 loads:
42.5gr IMR 4895
LC match brass
Remington Magnum primers
sierra match king 168gr bthp

Is this ok?

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

And 2.81 length

 

[RobG]

Re: 308 168BTHP 3200-3300FPS?!

Time for a new chrono.

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

That's what I fig but it's brand new AND the 223 that was shot through it was at accurate fps??

 

[Wylie Custom]

Re: 308 168BTHP 3200-3300FPS?!

I borrowed a chrono like yours and it gave me really high speeds also. I now use a CED M2 and speeds are what they should be.

 

[Trmorris21]

Re: 308 168BTHP 3200-3300FPS?!

If it's new, I would send it back and let them test it or replace.

 

[tacgnut]

Re: 308 168BTHP 3200-3300FPS?!

Not sure it makes any difference, but I normally place my chrony 10-15' from muzzle.

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

It read slower @ 8ft??

And the ar that we shot through it read correct??

This is the first time I had it out

It's a chrony f-1

 

[bohem]

Re: 308 168BTHP 3200-3300FPS?!

It's possible you were getting muzzle blast from the 308 over the sensors and the 223 wasn't getting it there. Push the chrono out to about 15' and try again, see if the numbers look more reasonable.

168BTHP @ 3100 = Hot 30-06 load

From a 308 gas gun with only 42.x gr of powder under it I don't believe those speeds.

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

The rifle I'm shooting is a savage 10fp


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">It's possible you were getting muzzle blast from the 308 over the sensors and the 223 wasn't getting it there. Push the chrono out to about 15' and try again, see if the numbers look more reasonable.

168BTHP @ 3100 = Hot 30-06 load

From a 308 gas gun with only 42.x gr of powder under it I don't believe those speeds. </div></div>

 

[fastex500]

Re: 308 168BTHP 3200-3300FPS?!

I've pushed that same load out of a 24" savage 1-10 barrel and got 2560 fps on a 50F day at 200 ft asl.

I'd say something interfering with Chrono (I have an F1 also).

Was it indoors or outside? Did you use the diffusers or just rods? Also as bohem said, try pushing it out. I do a minimum of 10ft. And measure at least 10 rounds.

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

Outside

Diffusers were on

 

[fastex500]

Re: 308 168BTHP 3200-3300FPS?!

I'll get a weird reading here and there, but never consistently out of range..... may be a faulty chrono. Call them Tuesday and see what they say.... or take some known velocity ammo and try again with the chrono 10-15ft away. Maybe the planets were out of alignment ;-)

 

[donshaw]

Re: 308 168BTHP 3200-3300FPS?!

Ok..... I just hope the customer service is good

 

[bohem]

Re: 308 168BTHP 3200-3300FPS?!

Missed the part where it's a bolt gun. Still, I suspect muzzle blast issue if you're getting reasonable numbers from the 223 and not the 308.

 

[tomt53]

Re: 308 168BTHP 3200-3300FPS?!

As the others have said, try moving the cono futher out.
Here are some predictions:
.308 Win
186 SMK
42.5 gr IMR4895
47,740 psi
2620 fps
94.4% Case filling ratio

Now to get to what the cono is telling you
51 gr IMR 4895
<span style="font-weight: bold">86880 psi</span>
3100 fps
<span style="font-weight: bold">113.3%</span> Case filling ratio

I don't use IMR 4895, but I doubt you can get 51 grs of powder in a .308 case.

If it is still giving false readings send it back for calibation.

Good luck Tom

 

[biggin69]

Re: 308 168BTHP 3200-3300FPS?!

For what its worth, I always take a 22 pistol with me when I chrono rounds. I fire a string of 8 to 10 rounds through just to make sure its working before I start firing my rifle rounds.

 

[Scaup58]

Re: 308 168BTHP 3200-3300FPS?!

You didn't say bullet weight for the AR15 but assuming 55gr., those numbers are high also for a 16" barrel. I get 3000 - 3150 with 55 Amax's from my 16. I have a Beta master chrony and it's worked well for 6 yrs. Chrony was good to deal with when I shot it a couple of years ago, I'm sure they'll make it right.

 

[steve123]

Re: 308 168BTHP 3200-3300FPS?!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: donshaw</div><div class="ubbcode-body">I reloaded some ammo and I shot it today through my chrony and i was getting 3100fps to 3400fps?????

I figured that it had to be wrong so i had my buddy shoot his 16in ar-15 through it and he was getting 3200-3400fps no factory bulk ammo.

The chrony was 8-10 ft away

308 loads:
42.5gr IMR 4895
LC match brass
Remington Magnum primers
sierra match king 168gr bthp

Is this ok?
</div></div>

Those Chrony's are a waist of time and money! I've learned the hard way!

I wish I had bought a Oehler 35P eons ago!

Google ladder test or OCW to find a good load for the rifle. Then determine velocity from a Ballistic program, correct yardage, LitZ BC's and Density altitude.

 

[former naval person]

Re: 308 168BTHP 3200-3300FPS?!

Check and make sure the hinge opens flat. If not, the screens are closer together, making the readings high. Also will cause a variance depending upon the height of the placement of the bullet in the window. Such a short "beam" to shoot through makes it very sensitive to the angle changes. JMHO