doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com OT-shotshell velocity

Have been "rollin' my own" in an attempt to get some low pressure loads for my "elderly" classic sxs's. Use a modern sxs test gun and a chrony chrongraph. Using virgin components. Have read Ken Olerer's comments on chronographing shotshells. Have found using well established "recipes", that here at sea-level the recommended low velocity(probably also low pressure) seem to read consistenly 150-250 fps over book values. No pressure signs,etc. Any thoughts? Thanks, Dr. BILL

If you're loads are below the speed of sound, it's very easy to chronograph the shock wave.

Thanks for the thought, however supposed 1100 FPS loads are reading 1250-1300 FPS???? Weird! BILL

Do you have the switch set for Canadian?

Bill, I am not familiar witht he book you cited, so at the risk of preaching to the choir.....

Does the data book spec the distance from the muzzle the readings were taken, so as to duplicate with your set-up?

As an example I think I recall in the transition between two of the Lyman's manuals they went from 15' to 3' from the muzzle.....English specs are even further out?

Are you using a light card over the shot that might be blowing through ahead of the shot?

I ran a hypothetical ounce of #7 at "1100fps" (3ft from muzzle as per SAMMI?)...reportedly leaves the muzzle at 1150 fps and is down to 950 at 10yds.

While our chronys are not he same type of instrument used for the actual tests, I usually get very similar readings to the load data.

It would also not be unheard of for the data to be off, can you cross reference to a same or similar load from another source?

Best,
Mark

775
FYI
Engish shotshell specs are most often taken at the muzzel, where US shotshell specs are 3' from the muzzel, so English shells publish higher speeds for basically the same shell as US manufactures.

After years of chronographing pistol/rifle loads I have sortta settled on about 12-13 feet. I've even taken to measuring the crimp depth and use 0.055" as per the Hogdon book. The components are also straight out of their load "recipies"???? Really appreciate the thoughts. Best, BILL

It's best to chronograph on overcast days. When I've gotten spurious high velocities, it's either been light conditions or placement of the chronograph too close to the muzzle. for shotshell measurements I like a distance of about 4 to 6 feet from muzzle to front screen.

Sam

Subgauge, thought CIP was 2.5 METERS from muzzle?

Not sure where I saw that.....and yup, could be wrong!

Also, does the British proof house have velocity testing standards at all....if they do, are they different than CIP? Would think they are mostly concerned with pressures?

Bill, it is wise of you to consider your crimp depths in the equation, it can make some difference.


Best,
Mark

Subgauge,
No body measures velocities actually at the muzzle. The first measuring point (either by a sky-screen or induction method or whatever) can be close to the muzzle but the second has to be some distance away (often around 3’ to 6’) thus the as velocity quoted is taken to be at the mid point of the stop & start screens.

I recently asked representatives of ‘Hull Cartridge Company’ here in the UK how they measure their velocities. They said for in-house testing the first point is just in front of the muzzle & the second one is 2 meters beyond that. This means their velocities would be at around 3’-6” from the muzzle.

From memory - ‘Clay & Game Reloaders’ in the UK used ‘Gamebore’ to test some or all of the loads quoted in the C&GR reloading manual. The muzzle velocities are noted as at Vo 2.5m so I assume that Gamebore must measure their own cartidges at the same point.

You will also see ‘observed velocities’ quoted in British literature – this is the average velocity over the first 20 yards.

The proof houses now have to comply with CIP regulations & test procedures.

Regards
Russell