Reloading Data / Barrel Lengths

Rgrabowski

Rgrabowski

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Hi,

Just picked up a Lee turret kit and just made an order for components, very exited!! Anyway... I had a question.. All the reloading data i see, Min\Max, but at what barrel length?? For example, im going to start with a load for my 10mm GP100 with a 4.2 barrel, when I take the same load to my PCC with 18.6 barrel.. What to do? will the longer barrel cause more pressure? will the revolver let gas escape and skew the data? Any tips on info on this would be great!!

Thanks,
Ryan
 
If the twist rates INSIDE the barrels are the same, or similar. All will be well.

You will likely see an extra 150+fps out of the longer barrel.

I have a Spanish Destroyer carbine, mini 93 Mauser bolt action with REAR locking lugs. It was originally chambered for the 9mmBergman round. I set it back for the 9x19 which has a shorter case but an identical taper. I didn't even have to rechamber it. Luckily the sights were at top dead center when the barrel was rethreaded and tightened up. My rifle was one of the last made and many were originally chambered in 9mm Parabellum (9x19)

I use the same loads in it that I shoot through my P35, P38 and Shadow 1. Each of the pistols have slightly different velocity averages but not enough to make any real difference. The Destroyer on the other hand, with it's 19+inch barrel and slightly slower twist rate gives an extra 170fps more velocity on average.

If I were only loading for the Destroyer and not the three pistols, I would likely load hotter. Both the P35 and the P38 can and do have issues with the extractors/spring and plunger following the extracted case. Try finding any of those components in Canada.

I don't have a PCC so I can't give you a definitive answer to your query. But the above examples should be reasonably representative.

Just remember, load for your pistol. The PCC should be able to handle stouter loads but as I've found out from experience, no matter how careful you are, mix ups can and do occur. This may not cause a blow up but it could cause cracks in your frame.

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The longer the barrel (other things the same) the greater the velocity.

peak pressure is in the first couple of inches, so barrel length has no impact.

Twist has no impact on pressure.

The big issue is bore diameter and throat depth. In revolvers, cylinder gap is an issue. Some pressure is lost through the gap. A gun with a larger gap will develop less pressure and velocity.

The loading manual might be based on a test rig rather than an actual revolver, so their data for a 6" barrel could show somewhat higher velocity than you can get in your 6" revolver.
 
Thanks guys, I do know a longer barrel = more Vel. I understand making a load from data on my revolver will be straight forward. If I started with my PCC with 18.6, I couldnt use the load data as my Vel. would be greater then the data because of my barrel length. How would I walk up the load having my Vel. already increased from barrel length? I guess start at the min powder grain charge, how would I know when to stop? or maybe it would be best to make a load for the handgun and just keep it for both? Thanks!!!
 
Use the same load data for both guns and develop one load that works in both of them. Extra velocity from the carbine barrel is unlikely to be a problem. In general, whichever powder gives the highest velocity in the short barrel will also give the highest velocity in the long barrel and slower burning powders will have a greater increase in velocity in going from short to long barrel compared to faster burning powders.

Rifle load data for pistol cartridges typically uses the same ranges of powder charges, just with higher published velocities from a longer test barrel. See, for example, Hodgdon data for .44 Magnum.
 
In my experience a revolver will definitely shoot a lower velocity with the same load than a semi with similar barrel length. I've read some on the Coonan oversized 1911's that shoot .38spcl/.357mag and people report higher velocities than the same loads in revolver.

For an extreme example I had one of the Redhawk's dual-chambered in .45ACP and .45LC and a load that shot a bit over 800fps with 230gr in my 4.2" 1911 only chronied ~675fps in the revolver; a 15% drop. When I tried bumping the load up for the revolver, the cases started sticking. So it appeared I was exceeding normal pressure while having poor velocity due to the jump (it is a .45LC chamber afterall) and cylinder gap. I would be surprised if the drop was as large with a purpose-built 10mm cylinder as you wont have such a huge jump or so much empty space to fill with gas.

I've had some friends be surprised by how little velocity they gain going from 4.2-5" pistols to 18.6" carbines, at least with 9mm. They were expecting a huge jump in velocity but saw quite a small gain from an almost quadrupled barrel length. 10mm has a significantly larger case capacity over 9mm though so it may be a larger increase.

You do sometimes find carbine/rifle loads for pistol cartridges that use slightly different powders. I have a really nice load for .44 mag rifle that uses SR-4759 which is generally a rifle powder. I can't find that powder used for pistol loads anywhere and haven't tried it myself to see if it just throws unburnt powder or something.
 
LUTNIT said:
For an extreme example I had one of the Redhawk's dual-chambered in .45ACP and .45LC and a load that shot a bit over 800fps with 230gr in my 4.2" 1911 only chronied ~675fps in the revolver; a 15% drop. When I tried bumping the load up for the revolver, the cases started sticking. So it appeared I was exceeding normal pressure while having poor velocity due to the jump (it is a .45LC chamber afterall) and cylinder gap. I would be surprised if the drop was as large with a purpose-built 10mm cylinder as you wont have such a huge jump or so much empty space to fill with gas.

I've had some friends be surprised by how little velocity they gain going from 4.2-5" pistols to 18.6" carbines, at least with 9mm. They were expecting a huge jump in velocity but saw quite a small gain from an almost quadrupled barrel length.
Click to expand...

That is similar in principle to rimfire velocities, the highest speeds come from a short barrel, 19" IIRC. Any longer the barrel, and the bullet is actually slowing down because smaller powder charge doesn't create enough gas volume as the available space increases and is the force of the expanding gas is overcome by the friction from the barrel.

Some rimfire rounds are specifically designed to get higher velocities from longer barrels, I believe some CCI rounds are like this.
 
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