Python observation

[brutus51]

Took my new 6" Python along with my old 6" to the range the other day.
I was shooting .358 dia. 158gr Missouri bullet lead SWC's on top of 4.0gr. of HP-38.
Results from Labradar.

New revolver yielded:
Stats - Average 856.3 fps
Stats - Highest 884.52 fps
Stats - Lowest 825.94 fps
Stats - Ext. Spread 58.58 fps
Stats - Std. Dev 17.88 fps

While the 1978 version yielded:
Stats - Average 751.03 fps
Stats - Highest 768.65 fps
Stats - Lowest 729.89 fps
Stats - Ext. Spread 38.76 fps
Stats - Std. Dev 14.39 fps.

Old Python is more accurate but after being shot for 45 years she has developed a 2lb. trigger pull.
Any clues as to why the velocities are so different?

 

[GeoDudeFlorida]

Took my new 6" Python along with my old 6" to the range the other day.[...]
Any clues as to why the velocities are so different?

Tighter throats?

 

[brutus51]

Could be, have to measure them when I get a chance.

 

[Slamfire]

Took my new 6" Python along with my old 6" to the range the other day.
I was shooting .358 dia. 158gr Missouri bullet lead SWC's on top of 4.0gr. of HP-38.
Results from Labradar.

New revolver yielded:
Stats - Average 856.3 fps
Stats - Highest 884.52 fps
Stats - Lowest 825.94 fps
Stats - Ext. Spread 58.58 fps
Stats - Std. Dev 17.88 fps

While the 1978 version yielded:
Stats - Average 751.03 fps
Stats - Highest 768.65 fps
Stats - Lowest 729.89 fps
Stats - Ext. Spread 38.76 fps
Stats - Std. Dev 14.39 fps.

Old Python is more accurate but after being shot for 45 years she has developed a 2lb. trigger pull.
Any clues as to why the velocities are so different?

Something like that is very hard to determine. Lots of different factors, forcing cone angle, surface finish in barrel, internal barrel dimensions. ETC. Or maybe the 1978 version is getting old, and like us geezers, is slowing down!



Incidentally, based on my chronograph testing of factory 38 Special, I picked 760 fps with a 158 grain lead, as a "factory" equivalent load. I see your 1978 pistol is right there, plus or minus, with your load.

 

[tightgroup tiger]

The riflings are the same between the two. 1/14".
New one must have a looser bullet to barrel fit allowing it to have a fast barrel so to speak.
Didn't the original Pythons have a progressive rifling? I wonder if the new one does.
Just speculating on what could be different between the two.

 

[EricBu]

Tighter modern manufacturing tolerances would be my guess. I bet the older one has a wider cylinder gap. That or throat/bore wear, or even the bore on the old one came from the factory slightly larger.

Thanks for sharing, that's an interesting comparison, and I've not heard any feedback elsewhere on a direct comparison like that, neat to know!

 

[jmorris]

Any clues as to why the velocities are so different?

What is the gap between the cylinder and the barrel, in thousandths of an inch, both the new and old one?

Now where did you put those feeler gauges…

 

[LaneP]

b/c gap is probably the largest single influence. If you have feeler gauges, see how they compare.

My old 6-inch barrel Ruger Security Six made in 1982 has a .005" b/c gap and shoots faster than my much newer 7-inch barrel 686 with its .009" gap.

20.5 gr H110 under a Remington 125 gr JHP produces 1622 fps in the 686 but hits 1658 fps in the Security Six....with 1-inch shorter barrel no less.

 

[GeoDudeFlorida]

b/c gap is probably the largest single influence. If you have feeler gauges, see how they compare.

My old 6-inch barrel Ruger Security Six made in 1982 has a .005" b/c gap and shoots faster than my much newer 7-inch barrel 686 with its .009" gap.

20.5 gr H110 under a Remington 125 gr JHP produces 1622 fps in the 686 but hits 1658 fps in the Security Six....with 1-inch shorter barrel no less.

That load in the 686 must be a real light show at dusk.