Velocity Drop

[Sasquatch-1]

For lack of a better place I post this here. No real questions, just to generate discussion.

Met a friend at the range yesterday and he brought his chronograph with him. I brought my Redhawk (7.5") and Super Redhawk (9.5") both in .44 mag. I brought three different loads with me. First was a 252 grn. gas checked semi-wadcutter with 7.5 grns. of Unique. Second was a 252 grn jacked soft point (made from 40 S & W brass) same powder charge. Third was a 240 grn JSP (40 S&W) with 23 grns. of W296.


Starting with the light loads. We fired 5 rounds of each through both guns and found a velocity drop off of 75 to 100 fps with the jacketed bullets. The 9.5" with the Unique powder climbed 50 to 100 FPS over the 7.5" barrel.

Now the real conundrum came with the 296. The rounds fired through the 7.5" barrel were 100 fps FASTER then those fired through the 9.5" barrel.

I do not know the brand of the chronograph. We also had to take a black magic marker and color over the exposed portion of the slug with the 296 to get the chronograph to read correctly.

Dave, sorry if these numbers are not exactly right. Going by memory and we all know how that gets once you can get senior discounts at restaurants.:veryconfu

[Teddy (punchie)]

basically your saying one load with a jacketed bullet was faster through the 9.5" barrel and slower through 7.5"

Opposite be said for a cast boolite load.

I have no idea?? Make no sense.

[IllinoisCoyoteHunter]

As for the jacketed being slower than the lead, I would assume the lead is creating a better seal in the bore and letting less gas blow by. As for the higher velocity with the shorter barrel....did you maybe put the unique loads in the 9.5" barrel and the 296 loads in the 7.5"?

[Sasquatch-1]

The cast bullets were gas checked. My jacketed bullets consistently have full rifling marks on the rim so I am guessing the seal was similar.

The test with 296 was definitely 296 through both guns. That and the fact that the Unique loads were a thousand fps slower.

One explanation that was proffered was the fact that 296 is a high pressure load and was producing all it pressure in the breech end of the barrel where the Unique was taking longer to burn thus creating the final push at the end of the barrel. This explanation was offered by someone else at the range.

Another explanation was that the brass jacket created more drag in the barrel then the lubed cast bullet.


As for the jacketed being slower than the lead, I would assume the lead is creating a better seal in the bore and letting less gas blow by. As for the higher velocity with the shorter barrel....did you maybe put the unique loads in the 9.5" barrel and the 296 loads in the 7.5"?

[Smokin7mm]

The cast bullets were gas checked. My jacketed bullets consistently have full rifling marks on the rim so I am guessing the seal was similar.

The test with 296 was definitely 296 through both guns. That and the fact that the Unique loads were a thousand fps slower.

One explanation that was proffered was the fact that 296 is a high pressure load and was producing all it pressure in the breech end of the barrel where the Unique was taking longer to burn thus creating the final push at the end of the barrel. This explanation was offered by someone else at the range.

Another explanation was that the brass jacket created more drag in the barrel then the lubed cast bullet.

296 is a slower burning powder than Unique so I think you have your pressure statement backwords. I can say that for a given load a cast bullet will produce higher velocity due to the increased drag of a jacketed bullet. As for why the 7.5 inch barrel produced higher velocity than the 9.5 inch barrel it could be alot of factors including, cylinder chamber dimensions, throat, bore/groove diameter fit to the bullet used. Try slugging both guns in the cylinder and bore and see what measurement you get.

Bret

[Ola]

Smokin7mm got it. Differences in the guns is the most likely explanation.

[tjones]

These data are not unusual at all. It's well documented in early Stoegers or Gun Digest articles. So many factors play a part in the final velocity. -tj