OzFclass

Back in May/June I posted regarding pressure problems with a 260. After a lot of searching I found I had 3 # of 2209, and one was significantly faster than the others. Having now used all the problem (?) batch, all was well for a while, but here we go again. 3 primers blanked from 3 firings.
But at some unholy hour of the morning (like about 0400) I had a flash of inspiration. Maybe the case length was the problem.

At a more reasonable hour, out with the calipers and guess what. Cases were about .002in OVER spec.

Out with the Wilson trimmer, and cases are now .003 UNDER size. Loaded 5. off to the range and NO PRESSURE PROBLEM.

Loaded enough for Sat competition, fired every one without any pressure problems. Admittedly, temps were low, about 17c but I now feel much more confident that the problem has been solved.

As a guess, as I have no means of checking chamber specs, I suspect that the chamber was at the minimum length and coupled with overlength cases, as the bolt closed, the case was crimped onto the projectile, and pressure went up.

Anyway, I will keep a close watch on things as temps rise, and will post again if anything developes.

Cheers
Maurice

G'Day Maurice,
if you're happy to have found a max case length, I'd be trimming to beat least 0.010" (10thou) shorter and I always check my cases for length prior to any big match to avoid issues such as this.

I know of H322 being fast and slow batches of powder and since it came from the same factory as 2209 I'd always buy a large amount and check my loads for each new batch and adjust if necessary.

The flip side is I've never noticed this with 2208 in my Remmy 223 or BM2 in my 6ppc BAT, but the loads are either just below max or used in BR actions that can handle the pressure variations. Either way, I've never had a problem.

Hope this helps.

Cheerio Ned

Hi MGS
Get your self a overall chamber length plug from Sinclair’s you will be able to measure your max length it is reusable also very handy to avoid that type of problem.

http://www.sinclairintl.com/cgi-bin/cat ... type=store

Cheers
RB

MGS wrote:Back in May/June I posted regarding pressure problems with a 260. After a lot of searching I found I had 3 # of 2209, and one was significantly faster than the others. Having now used all the problem (?) batch, all was well for a while, but here we go again. 3 primers blanked from 3 firings.
But at some unholy hour of the morning (like about 0400) I had a flash of inspiration. Maybe the case length was the problem.

At a more reasonable hour, out with the calipers and guess what. Cases were about .002in OVER spec.

Out with the Wilson trimmer, and cases are now .003 UNDER size. Loaded 5. off to the range and NO PRESSURE PROBLEM.

Loaded enough for Sat competition, fired every one without any pressure problems. Admittedly, temps were low, about 17c but I now feel much more confident that the problem has been solved.

As a guess, as I have no means of checking chamber specs, I suspect that the chamber was at the minimum length and coupled with overlength cases, as the bolt closed, the case was crimped onto the projectile, and pressure went up.

Anyway, I will keep a close watch on things as temps rise, and will post again if anything developes.

Cheers
Maurice

Maurice,
Your precision-made chamber is certainly not too short. Dimensions given by SAAMI and CIP are MINIMAL for the chamber and MAXIMAL for the cartridge.
If you closely look at a chart giving together the crtidge and chamber dimensions, you will notice the differences.
I always took great care on case lenghts, and, instead as measuring them or gauging them, I preferred to have a simple made case trimmer permanently set for a given calibre, and passed the cases in a each relos, be they in need of trimming or not. case lenght. The case trimmer was then used as a gauge, and cases never varied in lenght from reload to reload.
This also allowed to discard immediately any case in a batch having shown an abnormal elongation during the precedent firing....

FWIW
R.G.C

Robert Chombart said

I always took great care on case lenghts, and, instead as measuring them or gauging them, I preferred to have a simple made case trimmer permanently set for a given calibre, and passed the cases in a each relos, be they in need of trimming or not. case lenght. The case trimmer was then used as a gauge, and cases never varied in lenght from reload to reload.

Top advice Robert

Ben...

I always took great care on case lenghts, and, instead as measuring them or gauging them, I preferred to have a simple made case trimmer permanently set for a given calibre, and passed the cases in a each relos, be they in need of trimming or not. case lenght. The case trimmer was then used as a gauge, and cases never varied in lenght from reload to reload.
This also allowed to discard immediately any case in a batch having shown an abnormal elongation during the precedent firing....

Good idea Robert.

I will do the same.

Thanks

Maurice