Interesting velocity flip-flop

[DrCaveman]

Ive been having a ton of fun with a new accurate mold, it's this one

http://www.accuratemolds.com/bullet_detail.php?bullet=36-180F-D.png

The thing is like a long-seated wadcutter, almost, with just enough aerodynamics to shoot pretty well at 25-35 yds. Havent really tried it further since i am still no good at 50 yd iron sight off hand shooting. Working my way there.

My magnum load is doing great...it is a hammer. It's the 38 special loads that are proving interesting.

Im working on my own, using a fast shotgun powder that i like a lot, and have enough to keep shooting with. That is what determines my load choices, not the books. Ive thrown in the towel as far as ever having my "choice" of powder again. What i have is what i will shoot.

In the LCR (1 7/8" barrel) the light load goes 600 fps. Same load in 4" model 19 goes 570. The medium load goes 635 in LCR, and 625 in the model 19. The top load goes 700 fps in both guns.

Just wondering what this is telling me. Im sure im pushing +p levels with the top load, but wonder if i am past the "balance point" of the powder in the snubbie at my top end. Seems curious that the light load consistently shoots faster (several chrono tests have confirmed) in the short barrel. But then the m19 catches up as i increase charge. Makes me question the old notion that "all of the powder is burned in the first inch of barrel"

Fyi, the powder i am using has a speed very similar to bullseye, 700x, green dot, or unique, depending on the chart or cartridge load performance data you wish to reference

Any thoughts are quite welcome. Except those warning me against what i have done safely.

Thanks!

[coloraydo]

Just to throw out a couple of WAG's. Differences in: chamber dimensions, cylinder gap, bore dimensions. Also, if you might be using pure or close to pure lead, as the speed increases, boolit obturation could be resulting in the narrowing of speed differences.
Or......

[GREENCOUNTYPETE]

have you slugged the throats , and barrels

a tighter throat would result in more pressure before making the jump across the cylinder gap and into the barrel with a small volume of fast powder thsi could give you the speed that you wouldn't get with larger throats

the other thought is with the light load if they both had 1 7/8 barrels they might be much closer but that with a fast powder it is done burning by 2 or so inches but with the powder finished burning the bullet begins to slow in the longer barrel

I recall reading at one point that there was no benefit to a longer barrel in 45acp rifles as the common powders were completely done burning at about 12 inches

as you add more powder there is more gas to shove the bullet down the barrel

there is of course much difference between barrels that can be seen in these numbers the same round in several different makes of barrels do very different things http://www.ballisticsbytheinch.com/45auto.html

[shorty500M]

Stuff like that happens ALOT! most interesting case i personnally ever had was when testing 2 S&W M57's. All dimensions were very good and very similar except for the barrel length- one was a 4" and the other was 8-3/8". was working loads to duplicate the old POLICE LOAD and a full power load for hunting with 2 different bullets. powders ranged from fast thru medium to slow. depending on seemingly both powder and the exact bullet velocities did some very unpredictable things, yet both slugs shot good from both guns at all speeds.

[str8wal]

I recall reading at one point that there was no benefit to a longer barrel in 45acp rifles as the common powders were completely done burning at about 12 inches

I have a 16" 45 acp carbine and it runs around 60 - 70 fps slower than my 5" 1911, 4.8 grains of TG with a 230 so I can attest to this statement.

[44man]

I have a 16" 45 acp carbine and it runs around 60 - 70 fps slower than my 5" 1911, 4.8 grains of TG with a 230 so I can attest to this statement.
That is sure true, even a .22 rifle over 16" will be slower as push is gone.

[DrCaveman]

Wow, internal ballistics are pretty complicated if you look hard enough, i suppose. I messed around with imr4227 with a 200 grain slug in the snubbie a while back, and there was sure a mess of powder in the barrel and most likely coming out the muzzle. I wonder how a ladder test with unique or sr4756 would compare in my two guns. Maybe i will enter the 6" ruger into the mix for a third variable.

This sure bodes poorly for my 460 magnum (with 5" barrel) burning completely without anything but a fast-ish powder. (just like i was told many times)

Oh yeah, i am using air cooled 50/50 ww/pb. Might try using some of the water-dropped just for yet aother variable.

Fun fun 38 special!

[GREENCOUNTYPETE]

That is sure true, even a .22 rifle over 16" will be slower as push is gone.

this makes my heavy barrel 26 inch 22lr more pleasant to the ear than a shorter barrel , but oddly most 22s have a 18-21 inch barrel when 16 would likely get max velocity

Remington CBees from that 26 inch barrel are cap gun quiet , when I get a critter in my shed it is my go to tool as I have neighbors but with the door closed none are any the wiser

[str8wal]

I have a 16" 45 acp carbine and it runs around 60 - 70 fps slower than my 5" 1911, 4.8 grains of TG with a 230 so I can attest to this statement.


And as an aside, that same 45 acp load runs 30 fps slower through my 6" Bisley than my 5" 1911. I attribute that to the cylinder gap, even though there is nearly 3" more barrel length advantage to the revolver.