Low Velocity Blackhawk

[Durango Dave]

I like to handload both extremes for my Blackhawk. By that I mean I handload cowboy loads at 700 feet per second and I also load some powerful 357 magnums for the same gun.

For some reason this gun shoots lower velocities than what the handload books say it should, and slower than my other guns.
For example I have a Service Six with a 4 inch barrel that shoots 743 feet per second
My Blackhawk with 4 5/8 inch barrel shot 646 feet per second with the same handloads. Handloaded on the same day then chronographed on the same day.
I wonder why. The cylinder gap on my Blackhawk is .009", not too bad.

Now I'm looking for a powerful 357 handload. I can't get much more than 1200 feet per second.

Here's some of my 357 handloads (or at least the ones I chronographed)
All these are with 158 grain bullets. I have found out that the plated bullets shoot lower velocities than jacketed.

 

[PRichardson87]

Difference in rifling?

 

[contender]

I never get too hung up on velocity as THE main thing in my ammo. Yes,, I chrono my stuff,, and I use the chrono as just another tool in the bigger picture. As long as my loads are safe, & perform the duties I ask of them, I'm fine. Trying to figure out why the exact same ammo performs differently in different guns boils down to various mechanical differences in each firearm. And when you try & compare different components against each other,, you just added another variable.

I never try & "get the most powerful" ammo,, but I do try & get the most accurate ammo. Power doesn't always mean the best. If a gun, a caliber, or whatever isn't capable of doing the job,, I move to a bigger (or smaller) caliber.

Accuracy trumps everything. Bullet performance is critical,, especially if hunting. I let my guns tell me what they like,, and never worry about why one load does one thing in a gun & acts differently in another gun.

 

[Durango Dave]

I never get too hung up on velocity as THE main thing in my ammo.

True but when I get drastically lower speeds I wonder if something is wrong.
I use maximum charge and barely get 1200 feet per second when I'm told to expect 1300, 1400 or 1500 feet per second.

 

[Enigma]

Differences in barrel/cylinder gap can cause velocity differences, and sometimes barrels and just 'slower' than others for some unknown reason(s).

 

[Hankus]

What was the length of the reference barrel?

 

[308 Scout]

I think the .009" cylinder gap would be the culprit. What's the gap on your Service Six?

 

[contender]

When the publishers of the loading manuals build their ammo & test it,, their results are for their equipment. Either a universal receiver or a firearm. Then they build the ammo using listed powders, listed primers, and a specific bullet. And most often, in a very controlled environment, usually an indoor test facility, where the temperature is controlled, and all the conditions are almost identical.
When a handloader uses their gun, there's a variable. (Often a big variable.)
When a handloader changes a bullet, there's a variable.
When a handloader changes a primer, there's a variable.
When a handloader changes the bullet seating depth, there's a variable.
When the conditions are different, there's a variable.
Using different lots of powder & primers is another variable.

My point is,, there can be a lot of variables. ALL can come into play when we are loading our own ammo. That's why we always start a load below listed maximums & work up.

And by your own numbers in the OP,, your barrel gap is .009. That alone can reduce the velocities when compared to a gun with a .002 gap. And if the loading charts you are using were built with a universal receiver,, that .002 gap is gone, which allows for higher velocities.

And if your gun is at it's most accurate with the max charge listed,, fine. But as I've mentioned before,, performance is not measured in velocity alone.

Long, long ago,, a wise handloader once taught me something. He said; "My 1963 Chevy Impalla with the 409, and twin 4-barrel carb's will easily run 130 mph. But if I were to run it like that all the time it won't last very long. I get a lot better performance if I run it at a lower speed & only get into it occasionally. The same thing goes with ammo. Loads it to perform, not to go top end."

And I later equated it to gas mileage. You get the best gas mileage at one speed,, but you can always go faster or slower, but you won't get the best performance.

 

[vlavalle]

I like to handload both extremes for my Blackhawk. By that I mean I handload cowboy loads at 700 feet per second and I also load some powerful 357 magnums for the same gun.

For some reason this gun shoots lower velocities than what the handload books say it should, and slower than my other guns.
For example I have a Service Six with a 4 inch barrel that shoots 743 feet per second
My Blackhawk with 4 5/8 inch barrel shot 646 feet per second with the same handloads. Handloaded on the same day then chronographed on the same day.
I wonder why. The cylinder gap on my Blackhawk is .009", not too bad.

Now I'm looking for a powerful 357 handload. I can't get much more than 1200 feet per second.

Here's some of my 357 handloads (or at least the ones I chronographed)
All these are with 158 grain bullets. I have found out that the plated bullets shoot lower velocities than jacketed.

View attachment 39653

Many factors affect the final FPS of any given ammo, and on a revolver these are: (1) the barrel length. which you gave us for both guns, (2) the gap between the cylinder and the barrel, and (3) the gap between the cylinder and the firing pin. Of course, the ammo can have variances as well.

If you look inline and find MV for a given round, sometimes the ammo manufacturer will give the resultant ballistics for several different guns (Buffalo Bore provides this sometimes), all shooting the same ammo, and these do vary sometimes.

In the case you described here, the longer barreled gun had a slower MV, so IF all your reloads are exactly the same, which includes crimping pressure, then it seems like the former gun has tighter tolerances than the Blackhawk, which I find find very surprising. I would to suggest that in order to rule out your reloading at a possible culprit, do this testing between the to revolvers with pre manufactured ammo, and run at least 12 rounds thru each gun. If the results you get after this test are similar, then it seems that the difference is simply with the two gun designs.

 

[David Lee Valdina]

Where the bullet speed is measured may factor in as well. And do try another chrono as the readings may not be the same. And maybe get some factory ammo with published data and run it through your rig and contrast the results.