After years and years, I finally got into .300 BO.

I built a .300 BO with a 7.5" barrel. I intend to shoot it solely suppressed with subs.

I finally shot it today with some hand loads. 208 gr AMAX's, with 12.0gr of CFE Black, which according to the Sierra App I have should be 1080 fps.

Tested my first 5 rounds today, and they're stable, and quiet as hell! Only thing is they don't cycle 100% reliably. Obviously there is not enough gas getting back to the action to push the BCG back.

Now my question is; am I really getting 1080fps? If the app doesn't know what barrel length I'm using it wouldn't know the true velocity, and I dont have access to a Chrono.

Does anyone know from experience what kinda speeds I'm actually getting? Can I afford to up my powder, or do I need to turn my attention toward the gun?

Thanks!

You really need a chronograph to test your loads. I used 12 gr cfe black on 190 gr sns plated bullets out of my 10.5" and was getting 1050 fps. Seating depth plays a part in the pressures and speeds you get also. Best to confirm on your own equipment. A reloaders must have.

For subsonic velocities you can build a chrono with a vise, level, some paper, 1x1 strips, a laser, careful measuring, and a calculator.

Place gun in vise.  Ensure bore is level to ground and lock in place (cleaning rod down the muzzle, very small bit sticking out, and a bubble level).

Easiest for math to measure in meters.  Place target 10m in front of muzzle.  Laser down the muzzle, mark point on paper. Fire a shot.  Measure vertical distance from marked point to center of bullet hole.

9.8m/sec/sec on the drop, plug-n-chug on a calculator to figure out drop time.  This gives time for bullet to travel 10m.  More plug-n-chug to get meters/sec.  More plug-n-chug to get feet/sec.


Did this in the late 80s when I skipped three weeks of high school fizzicks class to shoot skeet, small bore rifle, go fishing and get some diving in.  Had to make up the work I missed when we were covering gravity.  Did it with a single shot 22 and 22 shorts, compared my results to a real chrono and was 5fps off....

Until you run them across a chronograph you are guessing..

I'll start looking through the 71 pages, lol

buying a chronograph will be easier

Magnetospeed Sporter is very simple and one of easiest to set up.  Mostly inexpensive too and harder to shoot/destroy.

If you use reading glasses, secure a set to the container you keep this with.  The device was absolutely useless to me when I forgot my glasses almost every time.

It did work very well to help diagnose the issue I was having.

I didn't know I needed a chrony until I bought this one, now I won't be without one. (Labradar now)