Thread: Pressure Signs in the 6.5x47

Although there is much to like about the 6.5x47, one aspect does concern me. Cases anecdotally do not show the same evidence of peak pressure that one might see in other designs - particularly large rifle primer designs. Although the similar newer small rifle Creedmore cases may have the same characteristic (as may other similar designs; PPCs, Grendel and the like), I'd like to limit my attention to just the design in the title: the 6.5x47L with Lapua brass.

Published guidelines for load development typically describe loading up incrementally until evidence of peak pressure is noted in causing changes in the case dimensions and/or primer. The symptoms usually referred to are a marked and measurable expansion of the case head just above the extraction groove that necessarily mean primer pockets are stretching, or perhaps stiff extraction. At this point the guideline is usually to back off 1-2 grains and call max load. So far so good.

When I've taken this approach and cross-checked my loads and muzzle velocities against QuickLOAD and also with Pressure Trace equipment, the estimated peak pressure at which the above symptoms have first been observed in large rifle pocket brass has been around 64-66kPSI. Clearly there is variation around the temper of the brass, so only a rough figure.

I'm finding an ever-growing number of reports online saying that 6.5x47 Lapua brass does not seem to show the same developing pattern of signs of increasing pressure as described here: https://www.primalrights.com/library...nding-pressure
or at least if it does the progression is much compressed. Onset of the above indications with bolt lift or pocket expansion may only appear above 70kPSI.

This may seem at first glance to be a good thing; a case designed and manufactured to allow for higher pressure and resulting muzzle velocities, and that holds up at these levels over multiple reloads. The concern is that the ultimate failure point may be at much the same peak pressures as most other case designs, and whereas with these other designs, you as the reloader may be 4-5 grains of powder away from catastrophic case failure when sticky bolt lift is first noted, in the 6.5x47 the margin might be only 1-2 grains. I'm speculating here of course. I've not loaded a 6.5x47 to failure. In fact I've not seen sticky bolt lift or pocket expansion because of my conservative loading brought about by concern over the uncertainty of the above. Maybe the ultimate failure point is also raised proportionally?

But I am interested in hearing from shooters of the 6.5x47 who have seen pressure signs in their rifles.

Could I trouble you please to either reply here, or PM me if you don't want your experiences aired publicly, and let me know what signs of pressure you have seen in this chambering? I would like to put your load details through QuickLOAD to see what the predicted peak pressure comes out as. For this I would need to know the powder that was used and the quantity, the particular bullet, and the cartridge-overall-length, and ideally your crown-to-bolt-face barrel length and muzzle velocity as a first pass way of checking the simulation results. Rifle action type would be helpful if it is thought that it contributed in some way to the symptoms such as a propensity for extractor marks, primer cratering etc.

It may be that the traditional methods of load development are not well suited to the 6.5x47 without resulting in top loads of questionable safety.