Bench Rest Evaluation Session

Tacoma Rifle and Revolver Club, August 1999.

Disclaimer:  I am about to mention three businesses in the North West USA area.  None of these businesses have paid me in any way for what I am about to say.  They have not given me anything to test and evaluate.  I rarely do a pitch for any business but my experience has lead me to trust the following companies whose equipment I used for this article.

I am providing my own personal load for the 185 grain target bullets I make using the 30-06 cartridge.  If you have problems with this load, it isn’t do to me as I have fired thousands of my 185 grain bullets with this load in both hot and cold temperatures without excess pressures.

 Bullets:  I swage my own match bullets in the 155 and 185 grain range.  The dies I use are originally of Corbin MFG in White City Oregon.  I recently sent some of these dies to Richard Corbin of Rich Corbin Enterprises in Phoenix Oregon ((541) 512-0440) for inspection and tuning.  Richard is a fanatical shooter and his single purpose seems to be making the best bullet swaging equipment you can find.   Richard evaluated them, modified some, swaged some bullets out of them, then returned them to me with a very professional note on what he did and why.  A true professional. 

Rifle:  The rifle pictured is a 30-06 Match Rifle made by Jim Cloward of Seattle.  Jim is a Wimbledon Cup holder, High Master Competitive shooter, and Big Game hunter (US and Africa).  Jim is a gunsmith and I don’t use ‘gunsmith’ lightly here.  He does spectacular work on both Match and Hunting rifles.  Jim has been in this business for forty years and if you want his services you can get him at his shop in Seattle Washington at (206) 632-2072.  Jim made the rifle and one-piece angled bridge scope mount that is in the pictures.

Optic:  The optic is a Leupold 16X Mk I scope.  No need to elaborate on Leopold’s reputation here.  While training US Army Special Forces and Ranger Snipers, the issued optic for the M-24 Sniper Weapons System was a Leupold M-3 Ultra 10X optic.  The five week sniper courses I ran at Fort Lewis Washington put these optics through more abuse than a life time of hunting, and I never saw one fail to function flawlessly even in the most extreme of weather conditions and after abuse that would render other optics useless. 

My last Goosepit article gave details about setting up the bench position for some simple evaluation of a rifle’s ability to shoot ammunition.  It pays to set this bench session up correctly to begin with rather than to find out at the end of the session – once you are out of ammo – that the guard screws were about to fall out or that the scope mount was so loose you could move the scope right and left.  You session is shot, the money you just spent on the ammunition is wasted, and your time is lost.  And all it took was some simple set up and rifle inspection prior to the evaluation.  For details on inspecting the rifle – go into the Goosepit Archives and read my article on this subject. 

Lets Shoot!

 On to the range session.  I wanted to evaluate the accuracy of the ogive design for three each 185 grain .30 caliber bullets.   From tail to tip, a bullet has a base, a bearing surface, which is what the rifling contacts, and the ogive, which is the curved portion of the bullet that leads to the tip, and the tip.  Ogives reduce fore body drag to various degrees and also distribute a weight of the bullet core along the axis of the bullet that in turn gives the bullet balance while in flight.  I had already fired these types of designs but Rich Corbin had done some alterations on some of my swaging components that would shift the center of gravity around so I had to evaluate them again.  My intent is target shooting at from 600 to 1000 yards so terminal ballistics is not part of my evaluation – only accuracy. The photo shows the three bullets next to each other – from left to right is a ‘8’, ‘10’, and a Very Low Drag or VLD ogive design.  Without going into detail on ogival design – the 8 is the least tapered, followed by the 10 then the VLD is the most tapered.   I use VLD only as a name as frankly I have never seen a bit of difference between a “VLD” design and a conventional ogival design in terms of reducing drag.  In other words – I need no less elevation at 600 or 1000 for the VLD as I did for the 8 or 10 ogive.  Therefore I view ‘Very Low Drag’ in name only.  In the past, the 8 ogive had given me the best accuracy and the VLD the worse accuracy, but now some things had changed so I had to evaluate them again.

My intent for the range session was to get an initial evaluation completed.  My view of these sessions is to get as much done with as few shots and as little time spent as possible so I chronograph my loads while testing them for accuracy.  A chronograph gives you velocity data but I will normally accept shot group size over velocity spreads – unless the spread between shots exceeds fifty feet per second.  It is pretty much assured that if you are playing with fifty feet per second spreads then you will have troubles with vertical strings at the longer ranges. 

My process for this evaluation was to load 12 rounds of ammunition for each type of bullet and shoot two fowling shots followed by two strings of five shots each at 100 yards.  I used what had been my best load for these bullets before RCE had done their modifications.   My personal load for this bullet and cartridge is 48 ½ grains of Reloader 15 and a Federal 210 Match Primer.  I use Lake City ‘Match’ brass for the ‘06’. 

Once set up, my evaluation sessions go pretty fast.  I will shoot at a  rate of about a shot per minute.   I shoot two shots to foul and warm the barrel, ensure the chronograph was working, and ensure the gun is zeroed.  Then I shoot my five shot string with my first load.  For ease of reviewing my groups, I will go right three minutes of angle and shoot five shots from the next load, go right three minutes again and shoot the third load.  Once the strings of five are shot, go down range and replace the shot target with a clean one and return to the firing line and repeat the process.  You now have two separate targets for comparison.   The chronograph has given the data needed for each string which needs to be recorded before the next string is fired.

I now have two targets with three shot groups on each for comparison as well as my velocity data for each group.  Some guys will shoot five or even ten strings of five shots  which is probably more precise but to me it’s expense in time and money, and does not give me a different opinion than by shooting two strings of five for each load.  For me, there is sufficient data now available to make decisions and I give this data a good 95 percent in terms of decision making. 

There are various ways of measuring a shot group for size so you can get some statistical idea of which is better.  I use two types – Mean Radius and Figure of Merit.  A mean radius is taken by determining the center of the shot group, then measuring the distance from the center of each bullet hole to the shot group center, and finally dividing the sum of all the distances by the number of shots.  The Figure of Merit is found by measuring the distance between the centers of the two most vertical shots and the two most horizontal shots --  add the two distances and then divide by two.  Normally I will use a Mean Radius at 200 yards and beyond and a Figure of Merit when the shots are so close together that they make one large hole.  For my evaluation at 100 yards I used a Figure of Merit.

My standards for High Power shooting are that the group must average under ¾ inch for a Figure of Merit at 100 yards.  A Mean Radius will get larger the farther away your target is but I will accept only those loads which hold ¾ Minute of Angle.  Most High Power shooters are not satisfied unless their loads hold ½ Minute of Angle but this may take far more time in load development than I am willing to take and my scores at 600 and 1000 yards are respectable.  Normally the bullet goes where I saw the barrel was pointed when the shot was fired which means that the bullets and rifle functioned just like they were supposed to.  Now, if I point the barrel in an 8 ring when the trigger is pulled and the bullet goes there – it surely was not the fault of the bullet, load, or rifle as I saw the barrel was pointed in the 8 ring when I decided to pull the trigger.

  Comparing my three groups for these bullets and loads, it is very rapidly apparent that the VLD design gave me the best accuracy -- at 100 yards anyway.  For reference, the black pasties are one inch square.  From left to right the average Figure of Merit and velocity data is in the table below.  The Standard Deviation for velocity is at the bottom.  This Deviation is basically plus or minus feet per second from the mean velocity of all the shots fired in the string.  Normally, a SD in velocity of under ‘12’ is good. 

 The above data is the average of only two strings of five shots fired at 100 yards.  The immediate conclusion is that the VLD design shot the tightest group but had the highest deviation from a mean in velocity – a little too high for what I consider a good standard of plus or minus 12 feet per second from a mean but I will always go with what ever group shows the smallest average shot group size so I decided to do further evaluations on the VLD design and the #8 ogive.

My intermediate step in evaluation then took place at 200 yards using the 8 and VLD design.  Again, the VLD design fired the tightest groups holding under 1 ½ inches (¾ inch Mean Radius at 200 yards) and the 8’s held just under two inches (1 inch Mean Radius at 200 yards).   Given the use of a 300 yard range, I would have skipped the 200 and fired the shots at 300 instead.  There is a shooters rule of thumb that says if the ammo will group to within standards at 300 then it will probably do just fine at 1000, provided the bullet stays supersonic. 

As there was no 300 yard range to work on, I loaded up twenty of each bullet and fired two strings at a 600 yard practice match from the unsupported prone with iron sights.  At 600 yards you must contend with how the wind and sun effects both the bullet and how you see the target and sights so this practice was more to confirm my confidence in the bullet and load as opposed to getting a solid mechanical evaluation.  I kept a score book at 600 and shot the normal twenty shot for record strings with each bullet.  The 8’s gave me a 98 average and the VLD gave me a 99 average.   Due to the variances in the environment at 600 and beyond, it is not a bad idea to  switch from looking at a Mean Radius to seeing raw scores and watching for shots that do not go to your calls.  Scrutinize shots that do not go to calls as normally your calls are good which means there was probably a mechanical problem.   The averages for my record fire is so close given the inconsistency in environment of shooting at 600 that it is difficult to tell if one was better than the other.  My final decision was based on how close my shots went to my calls – a purely human assessment whose value is dependent on the confidence the shooter has in his ability to see where his barrel is precisely pointed when a shot is fired.  My calls for the VLD design were far more consistent and precise than for the 8’s so my decision is made to use this VLD design for my long-range work.   The score book can also allow you to see general issues like vertical or horizontal spreads but only the shooter can conclude if problems at these ranges are caused by his human input or by some mechanical problem with his equipment. 

If you do not have a clue as to evaluating your rifle and ammunition combination – you now know how to sun your own evaluation session.  If you already have a method for these types of evaluations, you know another way.  For the next Goosepit article I will get into some practical uses of exterior ballistics in unknown distance shooting.   Until then – take advantage of the sun and good weather in the North West.

 Gene Econ