After experiencing a number of problems relating to my 6.5x47 blowing the back off the primers I decided enough was enough and it was time for a bit of Research & Development.
Having looked at a number of possible causes and taking on the advice of the members here, I popped down to Brock & Norris to see what could be done.
Mike is an expert in the field of all things that go bang and no doubt he would be able to find a solution.
So both I and Dan534 (who is also getting a 6.5x47 in the same Accuracy International AE platform)
packed are kit and headed off to Shropshire.
Once we arrived I explained the issues in more detail with Mike and after inspecting and stripping the gun a number of possibility's were ruled out.
It appeared the firing pin was fully intact, fully functional and not to long - so that was not hitting the primers to hard.
The internals of the rifle were as they should be so all OK there.
The most likely cause of the primers was overpressure, now although my original load - 38.5gr RL 15, 123gr Senar & CCI 450 small rifle magnum primer, works well in some rifles it isn't always going to be the case in every rifle. Each rifle is unique and individual and although the barrel might be cut with the same tools that make many others guns. Each one will have its own accuracy nodes and perform ever so slightly differently from the next.
Mike then measured the barrel length, checked the seating depth and other gun measurements. He then started the full process of case prep, carefully checking each individual case, resizing, measuring and double checking to ensure uniformity through out.
After batching up all the cases, Mike ran a number of known accuracy nodes with different powders through "Quick Load V 3.4" to get the starting points for the test loads.
First up was Vit N150, according to Quick load the place to start was 38.5gr, so following on from this the first 5 rounds were reloaded, measured and double checked. This process was then repeated for IMR @ 40.7gr, H4350 @ 40.7gr & RL15 @ 37.1gr.
According to "Quick Load" the powders should be producing the following:-
Vit N150 = 2831fps
IMR = 2868fps
H 4350 = 2862fps
RL15 = 2886fps
All the test rounds were seated at 2.102 to the ogive.
With all bullets being 123gr Lapua Senars.
Primers being CCI 450s.
After the heading down to the range (measured at 98m) with the test ammo, the gun was set up along with the chrono.
The Met data was recorded:-
Temp = 23.4 C
Station Pressure = 1012mb
Humidity 67.4 %
Once set up and we then fired off each group in order, the results are as follows:-
IMR was ruled out strait away.
1. 2917 fps
2. 2918 fps
3. 2931 fps
4. 2942 fps
5. 2941 fps
Average 2929 fps
Extreme spread 24 fps
H4350 seemed ok - although a adjustment of seating depth + or - could tighten up the group.
1. 2907 fps
2. 2901 fps
3. 2884 fps
4. 2895 fps
5. 2898 fps
Average 2897 fps
Extreme spread 23 fps
Vit N150 groups could be made tighter with + or - of powder. Adjusting seating depth would also improve.
1. 2986 fps
2. 3014 fps
3. 2996 fps
4. 2994 fps
5. 3004 fps
Average 2998 fps
Extreme spread 28 fps
RL 15 group also good but adjusting seating depth and powder would also assist.
1. 2915 fps
2. 2919 fps
3. 2911 fps
4. 2920 fps
5. 2933 fps
Average 2919 fps
Extreme spread 18 fps
The results were interesting, they showed a number of different things, primarily that my barrel was tight in comparison to not only "Quick Loads" virtual barrel. But also tight compared to a good friend of mine who has a very similar gun, all be it the AW version in 6.5X47.
The reason for the overpressure could be put down to my original load of 38.5gr RL15 being to hot (to much powder at to higher burn rate) for my gun - resulting in the blown primers. Also of note, the more powder in a case does not always mean more fps, but does on occasion mean overpressure.
One key difference on all the powders I tested was that none of them showed any pressure signs and the primers were not damaged.
There are, as one would expect differences between Quick loads predictions and the real world data collected:-
Quick Load - Vit N150 = 2831 fps
Real world - Vit N150 = 2998 fps
167 fps difference.
Quick load - IMR = 2868 fps
Real world - IMR = 2929 fps
61 fps difference.
Quick Load - H 4350 = 2862 fps
Real World - H 4350 = 2897 fps
35 fps difference.
Quick Load - RL15 = 2886 fps
Real World - RL15 = 2919 fps
33 fps difference.
Moving forward I intend to play around with the RL 15 powder, I will look to possibly increase 0.2gr increments and adjust seating depth to get the best I can from this impressive little round.
I hope this has been of interest.