6mm BR Load Development: 107 SMK, 95 TMK, 70 SMK, and 55 BlitzKing

The 6mm Benchrest (6mm BR or 6BR) is a nifty cartridge.  The combination of a low recoil impulse and excellent performance at the 600 yard line have earned it a great reputation among the target shooting crowd (It is such a great cartridge, Paul at Accurate Shooter/6mmBR.com actually built a website around it).  

Next to its contemporary counterparts (above, left to right; 6mm BR, 243 Winchester, 6×47 Lapua, 6 Creedmoor, 6,5×47 Lapua, 6.5 Creedmoor, 260 Remington and 308 Winchester), the 6mm BR (above, left) sticks out as a stubby little round.  Don’t let its appearance fool you.  While it may require a little bit of fiddling around to get it to work from a magazine, it burns less powder than it’s competition and is quite pleasant to shoot.

It has a short case that is hard to feed and eject, that means it is traditionally relegated to single shot applications.  Use of the 6mm BR in a AICS magazine requires a new spacer and follower system. Lately, the 6mm BR (and its improved versions the BRX and Dasher) have found more acceptance in field type rifles.

In this post I am going to take a look at the 6mm BR in a chassis rifle with a detachable magazine.  The 6mm BR diehards may be upset with my groups.  While my gun shoots fairly well, it doesn’t match the performance of some of the bench guns that are out there, and I am OK with that (one of traditional stock guns I built managed a 1.5″ 5-shot group at 600 yards a couple of years ago).

I’ve built three 6mm BRs over the last couple of years.  The first two used Remington 700 actions, the gun I am using for this test was just recently built.  It is different from the others in a few ways: first, it is built on a Tikka action, and second, it is very much a chassis gun.  In this case using a Modular Driven Technologies (MDT) ESS chassis.

I built the gun using the action from a Tikka T3 in 22-250.  It looks nothing like when it started.  The parts, which I ordered from Brownells include:

The rifle is topped with a Sightron SIII 6-24x50mm scope in a GG&G mount.

I covered a broad cross section of bullet weights and types, I decided to test the rifle with the Sierra (above, right to left) 107 gr. MatchKing (SMK), 95 gr. Tipped MatchKing (TMK), 70 gr. SMK, and 55 gr. BlitzKing.  I used new Lapua brass with CCI 450 primers.

WARNING: The loads shown are for informational purposes only.  They are only safe in the rifle shown and may not be safe in yours.  Consult appropriate load manuals prior to developing your own handloads.  Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

All shooting was conducted prone, from a bipod with rear bag.  Target distance was 100 yards.  Ballistic data was gathered with a MagnetoSpeed V3 Barrel mounted ballistic chronograph.

The rifle did pretty well with the 107 SMK and Varget.  I ran these loads with a .003″ jump.  Muzzle velocities ranged from 2,609 to 2,865 feet/second with standard deviations ranging from 6.7 to 16.2 feet per second.  Group sizes ranged from .395″ (.377 MOA- 4-shots) to .917″ (.876 MOA) with an average size of .703″(.671 MOA).

The 95 gr. TMK and Varget produced acceptable results, however, we did have a couple of groups open up over an inch.  Muzzle velocities ranged from 2,711 to 2,911 feet/second with standard deviations ranging from 5.1 to 14.0 feet/second.  Group sizes ranged from .642″ (.613 MOA) to 1.118″ (1.068 MOA) with an average group size of .850″ (.812 MOA)

I’m becoming quite the fan of H4895.  One of the most versatile powders on the market, it can be used for everything from match to reduced loads.  Muzzle velocities ranged from 2,589 feet/second to 2,677 feet/second with standard deviations from 2.0 to 9.9 feet/second.  five shot group sizes ranged from .451″ (.431 MOA) to .983″ (.939 MOA) with an average size of .779″ (.744 MOA).

Things really get moving when the bullet weight drops.  The 70 SMK and Varget offered muzzle velocities ranging from 3,206 feet/second to 3,317 feet/second with standard deviations from 9.6 to 22.2 feet/second. Five shot group sizes ranged from .499″ (.477 MOA) to 1.089″ (1.040 MOA) with an average group size of .808″ (.772 MOA).

The 55 gr. BlitzKing, as expected, offered the highest velocity of the bullets tested with muzzle velocities ranging from 3,289 to 3,427 feet/second with standard deviations from 6.7 to 24.9 feet/second.  Group sizes ranged from .793″ (.757 MOA) to 1.162″ (1.110 MOA) with an average size 1.018″ (.972 MOA).

Overall I was happy with the performance of the rifle.  In case you were wondering about how I got the magazine to feed, I ended up trying a couple of different systems- none of which worked with 100% reliability in my rifle.  I finally ended up cutting a factory follower down and using a spacer in the rear of the magazine.  While this worked most of the time, it did occasionally result in a nose dive with the longer bullets.  When using the shorter 70 and 55 gr loads the system worked 100% of the time.

I would have liked to see some more bug holes, maybe next time!

In other news, Zeiss has signed on as a sponsor of this site.  If you get a chance, please visit their website.  They offer a wide variety of quality optics for the rifle shooter.