Depends on the casing used. 

  Joe.

I've tried compressing and not compressing.  In the .38-55, with Starline brass the cases will stretch in my CPA rifle.  The finer the powder the greater the stretch I see it seems.  When I Switched to Goex FFFg Express, I started separating cases with or without compression.   

Fg powder seems to get rid of the stretching but you lose a fair bit of accuracy.  Interestingly though, my most accurate 200m rifle at this time uses Fg in a .38-50 Rem-Hep with a breech seated bore diameter PP bullet.  The extra case capacity gives me 59gr of Fg, no case stretching, an excellent accuracy.

In my .38-55 C. Sharps I also shoot a breech seated PP bullet but get no stretching regardless of powder, or compression used. 

There is one big difference between the chambers on my CPA and my CSA.   The CPA has a taper from case mouth to rifling, no 45 degree step at the case mouth.  My C. Sharps has a 45 degree step at the case mouth.  I wonder if this limits stretching?   

A few here have posted of using thick wall brass and wads to eliminate air space between bullet and powder.  Steve Garbe wrote of this technique in the BPCN a few years ago.  I have yet to try this.  He recommended shooting with a small amount of compression when breech seating.  If you like I can give you the issue number of the magazine article.

Chris.

Hank, SPG's article on breech seating with black powder was in the Summer 2008 edition of the Black Powder Cartridge News.  It's a good article, as are almost all of the ones he writes.  I'd recommend all of his magazine articles to anyone interested in maximal accuracy with black powder rifles.

Chris.

I had a case stretching problem in a 40-70SS until I quite using a 0.060 poly wad.  The brass was sparkling
new BA stretched brass.

I'm going to be working on my 38-55 brass today, so will chime back in if I am getting stretching.

Keep on hav'n fun!
MikeT

Hi Bob,

How much case capacity do you loose with the RMC everlasting brass?

Thanks,

Chris.

Thanks Bob.

Chris.

I too am using RMC cases in my Ballard No. 3 .25-25 Stevens.  Due to it being a cast action, I only use Holy black...Swiss 3FG.   I was shooting fixed and attempting to reduce charge for accuracy experiments..filled excess space with COW..cases began stretching..some nearly .100 longer & had 1 seperation.  With only veg. fiber wads, and/or grease cookies there is no stretching.  I believe the fine tool marks left inside case by the lathe turning were grabbing onto the COW.   I plan on trying B.S. this season, as well as trying some Goex Olde E.