Determining case length for straight wall cartridges

[DeanWinchester]

Anyone have any tips for determining the max overall length of a straighwall case chamber?

The 45 colt handi rifle I'm soon to be the owner of is rumored to have a rather lengthy chamber if you can believe what you read on the interwebz. In an effort to get the boolit out as far as I can and properly engage the rifling, I would like to get the case as long as I can. Most likely I'll have to use 454 Casull cases, then I plan to use a Lee .454 case length gauge/trimmer and shorten it to custom length for this particular rifle. It being a single shot and not prone to massive consumption, I don't mind trimming every time to maintain that length. I doubt the case will stretch that much anyway as the Casull case is built like a tank. Add that to running what will likely be subsonic loadings of heavy for caliber boolits and I probably won't have to trim very often.

Short of just trial and error; Slowly trimming a case until it just fits, how do you guys accomplish this? I wouldn't mind sitting down and slowly creeping up on the length, I just figure some of you BPCR shooters might have a neat trick for determining it.

Thanks!!

[country gent]

A chamver cast can be made to get a close idea of chamber throat and leade. Some uned to make a slug of brass or soft leaded steel at a few thousandthe under chamber dia then insert this to stop and measure. With the break opens this would be easy enough with the depth rod on your calipers. Measure from back of barrel and add thickness of slug used. Keep in mind that you do need a little clearence to allow case mouth to open and release bullet on firing.

[DeanWinchester]

Right, too long and pressures will spike. Wonder what an acceptable amount of clearance would be. .005 or so?

[country gent]

I would go .005- .010 below chamber length.

[country gent]

After thinking some on this. Trim a case 1/8" short and deburr. Turn up a slug with a stem thats a snug fit in this case with a end thats just under chamber dia. This can then be chambered and measured easily with calipers. A 45 colt case trimmed 1/8" short with a cut to make it act as a collet and the stemmed pin will give a very accurate measurement for you.