Barrel lenght vs burn rate

[krkdvm]

Most of the reloading manuals test their loads in 24" to 26" barrels.  They list velocity out of the test gun using a certian powder.  In rifles with shorter barrels, specifically Ruger mk II ultralight in 204 with 20" barrel, would a slightly faster burning powder be more efficient than say Varget that I currently use?  I lose about 45ft/second per inch of barrel lenght when using 26.6g varget as compared to "expected" velocity.  That will occure reguarless of powder.  Open for thoughts.

[Chris]

The velocities quoted in reloading manuals have to be taken with an oversize dose of salt. I gave up believing their relevant accuracy many years ago.
Pressure figures are a better indicator to follow. I don't have any experience reloading the .204 Ruger. But, quicker burning powders often raise pressures.. and may not produce
higher and consistent velicities... even from shorter barrels. They just raise pressure, and there is a limit to how much pressure can be accomodated without problems (SAAMI max pressure is not something you want to exceed).

You might look at various loading manuals... establish where Varget fits into the burning rate of other powders that show equivilent velocity figures... and then pick a "slightly" faster burning powder within that range and start working up a load. And, carefully watch pressure signs. It's a matter of experimentation, and there's no guarantee that faster burning powders will produce better results. You seemed to indicate that you have a chrono.... that's good! Chrono the loads you develop and look for Extreme Spread. Anything much beyond 30 -40 fps per load is an indication (and just that, an indication, not concrete proof) that that the powder is not the best choice and is not giving a consistent burn. I'd rather have a 10-15 ES load than an extra 100 fps velocity.
Chris Christian
(sticky extraction, flattened primers, etc.)

[Jim Fleming]

tagged to subscribe, please ignore this post

[krkdvm]

Chris,

The load chronyed with ES of 87ft/sec and SD 0f 33.  I am more of a novice than pro at reloading.  As soon as I can I am going to rework my 204 load with Varget.  Of the two manuals and bullet manufactures web sites I referenced. Seems as if around 28g is max charge.  I loaded them to 27.0 grains and went with most accurate load to that point.  I shall start at 27 and work my way .2g at a time to 28g or until pressures look excessive. If I find more accuracy above the current 26.6 then I will chrony 20 rounds and see if they are more consistant.  If load is still "spread out" I will try different powder. ??

The chrony is something that is most often overlooked when reloading.  It provides so of the most valuable info in my opinion.

Thanks.  Kenneth

[Chris]

Keith,
How are you measuring your powder charge? 87 fps extreme spread is excessive. It could indicate an incomplete burn (and maybe the need for an increased powder charge, or a slightly faster powder like BL-2)... or it could indicate an inconsistent powder charge drop. When I'm loading "precison rounds" I scale weight each powder charge and get less than 15 ES.

Another possibility... are you using mixed head stamp brass? Different manufacture's cases can (and often do) have different internal volumes that will result in a different burn for even the same scaled weighed powder charge.

An excessive ES doesn't necessarily mean poor accuracy. What kind of groups are you getting with your current loads?
Chris Christian

[krkdvm]

Chris,

     I throw powder with an RCBS to under desired load then trickle to load.  Use a 5-0-5 RCBS balance scale.  Am using new Hornady brass and federal sm rifle match primers with 40g Nosler Balistic tip bullets.  Groups have been an inch max but not the small groups of other calibers I use. As stated before I am goting to try more powder to see if I can get smaller groups.

    You bring up an interresting thought.  How can you determine in complete combustion of a given load.  Is that possibily indicated in the large variation in velocity?

Kenneth

[Chris]

A large ES is an indication of an incomplete in the barrel burn (or too slow a powder for the bullet weight)... especially since you are weighing charges and using one brass head stamp. Another indication is black soot on the case, or the neck.
Chris Christian