Using faster powders for short barrel loads.

[arakboss]

I have heard people say that 223/5.56 rounds are not "viable" in a 7.5" barrel.

These guys were getting 2300ish fps with 55gr 223 out of a 7.5" barrel. That doesn't seem awful to me. It would beat any 22 mag load, for energy, that I have seen.

View: https://youtu.be/v-7K8Fjx5DA?feature=shared



I am wondering if the velocity could be raised a bit by using a faster than normal powder or if the barrel length will limit speed regardless of the powder used?

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[eb in oregon]

I sort of doubt trying a different powder will gain much. A 7 1/2 inch barrel is just to short to gain the full potential of the cartridge. And realistically speaking another 100 fps or so isn't worth the effort in my opinion.

 

[lucusloc]

You also have to be careful of pressure. Faster powders increase pressure in the chamber, so even though you are relieving that pressure faster it may not be enough if the initial spike is too high. At the end of the day you can only do so much with 55k psi in 7.5 inches.

 

[Alpine]

The speed of powder that works in a given cartridge has more to do with expansion ratio… in the example of a straight cased pistol the bullet doesn't have to travel very far to double or triple the size of the original chamber which reduces pressure very quickly. Obviously rifle cartridges are another story.

For short barrels, powders with faster burn rates give up less velocity. Decreasing the weight of the bullet is another way to increase the expansion ratio as the bullet moves more quickly down the bore.

But unless you came out with a new bullet that is lighter than any others on the market you're going to have to use powders with similar burn rates listed in reloading manuals (for safeties sake).

 

[bcp]

I seem to recall an article from long ago that tested this. IIRC, the powders that gave the most velocity in standard length barrels also gave the most velocity in short barrels.

Muzzle flash and blast wasn't tested. There may be more difference in powders here.

Bruce

 

[Certaindeaf]

If the gun operates with nato ball / factory loads it'll likely not function reliably and or beat itself to death.
You pretty much want a given gun to be built around common factory loads barring special circumstances/ needs.

 

[rgold1963]

At the end of the day you can only do so much with 55k psi in 7.5 inches.

Interestingly enough, that happens to be the exact test specs from Trojan.

 

[lucusloc]

Interestingly enough, that happens to be the exact test specs from Trojan.

Man, if they are testing to that pressure they really want to keep the swimmers out of the pool.

 

[P7M13]

@arakboss, download Gordon's Reloading Tool and check for yourself.
For the most part, you are limited on powder speed by case design, caliber, and mass of the bullet.
The initial pressure spike following primer ignition is where things could go south quickly.
Hence, you might be able to go with a slightly faster powder, but I'd wager not much faster.

 

[DizzyJ]

You also have to be careful of pressure. Faster powders increase pressure in the chamber, so even though you are relieving that pressure faster it may not be enough if the initial spike is too high. At the end of the day you can only do so much with 55k psi in 7.5 inches.

This right here.