From folks who should know

https://www.hodgdonreloading.com/re...eled-rifle-require-different-reload-data

DOES MY SHORTER BARRELED RIFLE REQUIRE DIFFERENT RELOAD DATA?
We often get this question. In asking, the customer is unsure if the different barrel length will necessitate a loading data change in the powder chosen. Let’s preface the answer with a quick guide on testing data.

All our data is tested for Pressure and Velocity with instrumented equipment as established by the Sporting Arms and Ammunition Manufacturers Institute (SAAMI). The dimensions of the test equipment are established by SAAMI, both internal (such as chamber) and external such as barrel length. The barrel length is set based upon most popular usage. Rifle calibers are set at 24 inch barrels. Handgun calibers are set based upon the most common use at the time, i.e. a 45 Auto barrel is based upon the barrel length of a 1911, and a 38 Special barrel based upon a standard police issue revolver.

The first thing to remember is that the chamber dimension does not change based upon application. A 223 Remington chamber is the same whether the gun it is in is a handgun or a rifle. The chamber dimension determines the pressure. So, the pressure is the same when fired in that chamber in a rifle or a handgun. The barrel length has no impact on the chamber pressure and hence the reloading data (powder charge and pressure).

The length of the barrel will change the actual velocity you observe. In general as the barrel gets shorter than standard the velocity will lower, and as the barrel gets longer than standard the velocity will increase. This does not change the reload data (powder charge and pressure), just the velocity.

Please note that there is no magic number for how much velocity is lost or gained by changing barrel length. This is because cartridges go from big to small and use varying amounts of different burn speed propellants. The only way to know for sure what the effect is with your different barrel length is to shoot over a chronograph.

So, the quick answer to the question is that the different barrel length will not change the reload data but it will impact the velocity you get.

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