No. 4 "Compensation" Tests

I first did one 10 shot group at 300 yards.  The first 9 shots were within 3.1 inch spread, 1 MOA.  The last shot opened the group to 4.2 inches, 1.4 MOA.  I think nerves got to me thinking of how nice a 10 shot 1 MOA group would be at 300 yds.  Happy with these results. 

After some sighters at 600 yds, I proceeded with the ladder test of the following load:

PPU Case Neck Sized

WLR Primer

Varget Powder - Charge Weights 40.0, 40.3, 40.6, 40.9, 41.2, 41.5, 41.8 and 42.1 grains

174 gr Sierra MatchKing

3.07” Cartridge Overall Length

I shot these in a “round robin” approach, one shot of each powder charge working my way from 40.0 to 42.1 grains, then repeated this for a total of 5 rounds of each charge weight. This spreads out the environmental factors fairly evenly over the 40 round total.

Each shot position (x and y) was recorded off the monitor along with muzzle velocity. 

Here is an example of one of the plot sheets.  A 1 MOA is overlayed on the 600 yard scale target for reference. This is standard 8.5x11 inch letter paper, so a 1 inch grid on the plot sheet. 

Group centers were calculated and plotted on this sheet:

Note that Loads C, D and E (40.0, 40.3 and 40.6) have very similar Mean Point of Impact despite the 82 fps velocity extreme spread.  At 40.9 gr, elevation takes a step increase and rises steeply for each additional 0.3 grains. Clearly, the rifle does not compensate for velocity increases from powder charges above 40.6 grains (MV = 2391 fps), very likely that bullets are leaving the barrel as it is moving downwards. 40.3 grains seems to be an accuracy node at a 2365 fps possibly with the muzzle at the bottom of its displacement in the vertical plane. 

I may redo the test and lower the charge weights to 39.4, 39.7, 40.0, 40.3 and 40.6 grains to confirm if the 40.3 gr charge is at the bottom of muzzle deflection. Slower charges may then compensate nicely at 600 yds. 

My last 600 yard group (only had 9 rounds left) was with the 40.9 grain load. It was looking quite good until I had a case head separation, which resulted in a flier in the 5 ring at 12 O’Clock (shot #5). Shot #6 was sloppy.  This group had a fairly tight ES at 38 fps, SD at 13 fps. 

I’m using a Harrell’s precision measure, it will typically throw charges to within +/- 0.1 grains. I usually only weigh out every charge for my 600 yd and long range (800 to 1000 yds) loads.  Short line loads (300 yds and less) get dumped from the measure directly into the case. 

It is not likely that this rifle is an anomaly regarding how shot POI elevation is affected by muzzle velocity variations, I suspect it’s inherent to the No. 4 (T) and could well be part of the reason that snipers were discouraged from taking shots beyond 600 yards.  Snipers were expected to be able to make reliable hits on the body out to 400 yds and head shots out to 200 yds with the No. 4 (T). But, I’ve shown here with a good bullet and good load, head shots are assured at 300 yds (4 inch ten shot groups) providing the range is accurately estimated.  At 600 yds it becomes a bit tricky and not 100% assured.  

One of these days, I’ll visit the unknown distance range which is right next to the 600 yd known distance range. It’s a whole bunch of steel plates.  I’ll see how I do with estimating the range and how successful I can be with a first shot hit.  This is how the sniper matches really should be run. 

My post had commented that one of the virtues of the No. 32 Scope was its ease of dealing with range. While the 1 minute elevation adjustments might seem crude in comparison to the contemporary USMC 8x Unertl scope with 1/4 MOA click adjustments which is desirable for a target scope, but the No. 32 scope 1 MOA adjustments for purposes of hitting a man size target out to 600 yards is perfectly adequate.  With just 4 clicks per 100 yards (from 100 to 500 yds) and the elevation drum range markings very visible, what could be easier to use!  

I’ve witnessed two of my good friends shooting the 03A1 sniper rifle getting lost on counting up the clicks from 300 to 600 yards during a match and they could not get hits on paper!  

OK, I missed that one.

Just guessing still