223 Load Tests and an unwanted surprise!

[VarmLR]

69grain TMK Load Assessment

Finally got round to switching powders for the 69 TMKs having had excellent results with RS50 and the 77TMKs.  I was aiming to replicate an accuracy node that I had using N140 of 23.6gr for 2830fps.

Whilst the chrono was out, I also did some further tests on the 60gr Vmax/N133 OCW results which suggested a good node lay between 23.8 and 24.2gr, based on groups within that range falling to the same POI and having a nice tight group at 24gr N133 for a relatively low ES.

First to the RS50 and thanks to the innovation of the Custom Electronics Bluetooth gadget which attaches to my ProChrony, I was able to email myself the results of the load ladder straight from the field!  Data as follows:

Powder: RS50/Brass:  6F PPU/Primer: KVB223/COL 2.310 (50 thou jump but within mag length)

Load Ref in grains (see the chart below to cross reference):

1.  23.6

2.  23.8

3.  24.0

4.  24.2

5.  24.4

6.  24.6

7.  24.7

8.  24.9

9.  25.0

10.  25.1

11.  25.2

QL and RS data suggests a maximum load of 25.6gr RS50 for a max vel of 2871fps with a 69gr HPBT which has a similar bearing length to the 69TMK at a col of 2.26" so I was well within those parameters and decided not to go above 25.2 to allow some pressure leeway.

These were the results:

 

 

 

As you can see from the graph, there is a pressure insensitive region between loads 1 and 3 and load 2 was 23.8gr RS50 for 2726fps, giving a Strelok estimated terminal velocity of 1220 fps at 690yds, so this should be a stable load for 600m.

The next velocity plateau up seems to extend from loads 5 to 7, so taking the mid point, load 6 should be a good accuracy node at 2824fps.  That offers a little more velocity.  There's another possibility within loads 9 to 11 although load 10 dipped somewhat more than expected at 2868fps with 9 and 11 being 2943 and 2936fps respectively.  It could well have been a brass issue or some other inconsistency when loading.  At no point were there any obvious signs of pressure with case heads being clean although primers, whilst still not squared off or flattened, started to show slight cratering signs from around 24.6gr upwards, something I've noticed when using both KVB223 and CCI200 primers.  It could be down to primer cup thickness for these non-magnum primers so I might be wise to try some of the magnum versions with thicker cups and drop loads a little loading from 24.6 to 25.2 for the re-tests. I have found the KVB223 primers quite "hot" compared with their Magnum stable-mates and compared with CCI200 primers so if anything might expect velocities to drop a little with the magnum versions.

I did however note one or two cases with a couple of very thin streaks of soot starting to show in one or two locations (had to look carefully to notice) which made me suspect that primer pockets may not be in the best shape, but these cases have only had 7 firings and at modest loads!  (more on that later).

The conclusion here is that the lower load seems to be the least pressure sensitive and points towards a good, accurate load with velocities for the RS50 at 23.8 grains,  and with a load of 24.2gr producing similar results to me N140 23.6gr load. 

60gr Vmax: Continuation of OCW Tests

Following on from my previous description (see OCW load tests on separate thread) of the OCW test for N133/60Vmax, I had established a velocity plateau lay between 23.8 and 24.2gr N133 and on group patterns, I estimated that the best load may lay slightly at the lower end, so I loaded up 5 at 23.9gr and tested these for ES today.

These were all shot using 6F PPU brass shot through a Prochrony Digital using a CE Bluetooth link to  Dlink programme.  the results are as follows:

 

 

Possibly the very best results on load tests using very modest components which I've so far managed.

An ES of just 8, which would have been and ES of zero had it not been for one wayward load which wanted to shoot a little hotter!

SD was 3.

This is an excellent outcome and goes to show that even modest Lee Pace setter dies are capable of producing some very good consistent loads.  However, there was one rather unpleasant result which coincided strangely enough with the "flyer" and this was it:

 

I noticed a slight crack in the side of the primer, and my suspecions with the odd few cases showing very thin grey streaks were confirmed here, as this isn;t a particularly stiff load (Viht gives a max load of 24.7gr N133 for 3209fps.  This was 0.8 grains under that max and in my 26 inch barrel was giving 3214fps average and was about 3% under max recommended load, which normally I would have felt was ok given how conservative Viht load data can be.  This is either too stiff a load or it points to the primer pockets coming slightly loose but it's the first time ever I've experienced this after so few loadings.  It is confined to this particular batch of PPU so I can only conclude that it's a particularly "soft" batch of brass.  I have been annealing the necks after every firing and have been careful to ensure that I use tempilaq and only have the necks in the heat for a few seconds using propane to minimise  annealing time to prevent case head area getting too hot.  I've so far not experienced any such issues with my  .308 cases which have shot much stiffer loads.  Any other ideas?

Edit:  I spoke with a supplier of PPU and without saying how many times these had been fired asked about the average life expectancy with moderate loads. The answer was 7 to 10 times with PPU and perhaps 20 to 25 times with Lapua before primer pockets get too loose.  I've had more firings from PPU in the past but am not going to risk firing any more of the 7F cases and will pull the remaining ones.  Useful to know. 

However, tests on the deprimed cases showed that primer pockets weren't obviously loose, although probably well on the way.  Confused, I've since checked other Murom shot primers and have discovered a good number had cracked on firing....pinholes appearing in the sides of several and these resulted in the grey sooty streaks seen on cases.  The other thing to conclude from this as far as I am concerned, is that KVB-223 primers have a problem here, and having consulted with a reputable rifle smith a little earlier on, he confirms that he's had to deal with a few bolts where the faces have been gas cut...the common factor being that KVB primers were used.  I shall not be using them any more after this discovery.  I had a similar issue with one or two of the thicker, tougher KVB-223M primers although not to the same extent.  That was in a different rifle where marks were left on the bolt face.  The 223 bolt from the rifle used today has some very obvious signs of gas cutting on the bolt face, perhaps not yet enough to warrant the £200 repair job needed but nonetheless, a very unpleasant surprise, so be warned.

[Murph]

I found my best accuracy running the 69 tmks at 3100 fps using h4895 . I used 25.7 grains of it. In my lee reloading it showed its speed at 3000 fps!. Cci 400s are a very good primer for the 223 with a very hard cup design. My blaser lrs 2 has a 24 inch barrel.

 

 

[VarmLR]

I think I'll be switching to magnum primers for the 223, for the extra cup thickness, especially after issues encountered with standard primers.  Muroms gave by far the best SD and ES, much better than I found using CCIs but we'll see what CCI450's bring.