40 S&W load over book velocity?

[Andy0313]

After shooting today I am looking for someone who can verify my measured velocity vs the loading manual.

Im getting started in shooting USPSA so I'm trying to build a load for production. I was using a 155 plated bullet that matched my carry round but I decided (after reading a lot on this forum) to build up a 180 grain minor load. I loaded 150 rounds at the minimum load shown in the Lee modern reloading second edition manual. The load is:

BBI 180 grain coated bullet

5.2 grain unique

Winchester small pistol primer

Mixed twice fired brass

1.125" cartridge length

The book says this load is 919 FPS. My first 5 rounds averaged 1013 FPS over my Shooting Chrony. Pistol was a Glock 35 3rd Gen with stock barrel. Temperature was around 90, altitude of 2000ft and the rounds were stored out of the sun. Sky screens were used and the sun was overhead, not at a sharp angle (around 10am). I was very surprised that my minor load was a 180 PF!?! SD was 12 for the 5 shot string, rounds were very accurate and the brass showed no primer flattening, bulges, hard ejection or other signs of pressure. According the the lee manual this velocity is over the max load listed.

I figured it was a bad reading on the chronograph and decided to keep shooting drills. I saved the last 5 rounds and shot them over the chrono again after checking the 10ft muzzle to chrono distance. Temperature was now 104 (29 Palms sucks) and the shots averaged 999 FPS. Still well over what it should have been. Now, why is this load fast?

1- BBI sent me 165 grain bullets: nope, 5 rounds averaged 181.4 grains.

2- my Powder measure is off: nope, checked 10 throws on my digital and balance beam scales, 5.2 grains

3- the lee data is from a 4 inch barrel. Possible, I can't find test barrel length listed. 96 FPS from an extra inch of barrel?

4- the data is for cast lead, the polymer coating gives extra speed due to reduced friction. Possible, but 96 FPS?

I'm guessing it's a combination of 3 and 4, but can anyone verify the velocity from this load? It's very accurate but hot for production. I'm debating going below the starting load to try and get an advantage on split times, but I might just try this in two weeks at the nearest club match.

[superdude]

- A longer barrel will produce a little more speed, about 50 fps per inch.

- Glock barrels can be a little faster than a conventionally rifled barrel.

- Some barrels are faster/slower than others.

- Different lot numbers of powder will produce different velocities.

- Not all chronographs are calibrated the same.

- Temperature can make a difference for some powders.

In my experience, the coated bullets are just a little slower than plain cast lead bullets - in side-by-side testing.

[LilBunniFuFu]

Super dude pretty much hit it on the head. That's why we always start low and work up with a chrono.

[Hi-Power Jack]

Might also be getting some bullet set back ... Try pressing the bullet hard

against your reloading bench and see if the bullet becomes shorter ...

[Glockinator]

No one has mentioned the most obvious.Every lot of powder varies from lot to lot.

[Andy0313]

Thanks for the replies. I've been reloading rifle and pistol for 20 years and I've never seen a load that is 10% above the posted velocity. Usually it's the opposite.

Hi-power jack, I did check for setback when I loaded the rounds. No movement there. Plus, that would have made one round or two increase pressure. But the SD and extreme spread on these rounds were very small, showing consistent pressures.

FuFu, this is the starting load. Which equals full power factory ammo? Glad I did start low!

Glockinator, this same lot in my SAA 44 specials shoots well below the book velocity.

I'm thinking a combination of factors just combined to surprise me. I hadn't thought about the polygonal rifling adding a bit as well. I guess I'm going to drop a few 10ths and try some more. There are worse things I could be doing with my time than load development

[superdude]

No one has mentioned the most obvious.Every lot of powder varies from lot to lot.

See post #2.

[noylj]

If you compare alarge group of manuals from different companies, you'll see quite a difference in the velocity and charge weights that produced that velocity--and they all produce close to the SAAMI max pressures.

I know, when I first started loading in the '70s, that TWICE I found the starting load was at least MAX in my gun with my lot numbers of components. That is why I don't just start at the starting load, I look for the lowest starting load in my various manuals.

Your chamber is different, your lot numbers are different, in fact, your cases and primers are probably different makes entirely from those used in any given loading manual.

There have ALWAYS been fast and slow barrels, and they aren't fast or slow due to the pressure generated. Some day someone will discover the cause, but for at least 150 years, it has been "magic."

[PKT1106]

Never mind, read the rest.

Edited May 31, 2015 by PKT1106

[LilBunniFuFu]

FuFu, this is the starting load. Which equals full power factory ammo? Glad I did start low!

Hell, I'm glad for you.

[peterthefish]

I've seen cast 180 GR 40 bullets in TC and RNFP profiles, with and without lube grooves. As your Lee manual doesn't have a cast TC bullet with no lube groove, you're not matching the book load (coating aside). Looking at my lee manual I believe they stole (sorry, compiled) that load data from the manufacturers load data as it matches the VV published data.

If the book uses a shorter bullet and you load to the same OAL, you're reducing the volume and thus increasing pressures, and as a result, velocity.