243 Winchester load development: 70 SMK, 95 TMK and 107 SMK

The .243 Winchester (.243 Win) is a popular cartridge that is can be loaded with a wide variety of bullets making it a useful varmint and big game cartridge. First chambered in the lever-action Winchester Model 88 in 1955, the 243 Winchester uses the .308 Winchester as a parent case necked down to accept .244″ (6mm) diameter bullets. The combination of case capacity and small bullet diameter (sometimes referred to as “over bore”) makes the cartridge capable of pushing light bullets at extremely high velocities. This also adds fuel to the 243 Winchester’s reputation as a barrel burner.

A wide variety of hunting and match bullets are available in .243″ (6mm) diameter. The 243 Win high velocity 55 grain varmint loads can approach 4,000 feet/second, while the heavy 107 grain hunting and match bullets can often exceed 3,000 feet/second. While the varmint loads will kick more then most .22 caliber centerfire offerings, the 100 and 107 grain heavy loads offer a significant reduction in recoil for deer hunters when compared to more traditional options like the 308 Winchester. To accommodate the wide range of available bullets, the Sporting Arms and Ammunition Manufactures Institute Inc. (SAAMI) specifies a 1:10″ rate of twist, which should stabilize most bullets up to 100 grains. A link to the SAAMI specifications can be here.

The 243 Winchester’s design lends itself to longer barrels in order to obtain maximum velocities. In 243 Winchester- Effect of barrel length on velocity, Rifleshooter.com cut a 24″ .243 Winchester barrel back one inch at a time to 16.1″ and recorded the effect on velocity for 80 and 100 grain loads. For the 80 grain load, average velocity reduction was 39.6 feet/second per inch of barrel length. For the 100 grain load, average velocity reduction was 42.3 feet/second per inch of barrel length. For more information above this experiment, click here.

In this post, I’ll be using a factory Remington 700 SPS Varmint rifle chambered in .243 Win. In the hierarchy of Remington 700 models, the SPS is one model up from the bottom, the ADL which has a blind magazine (and is the least expensive version). I purchased this gun retail. After a limited time $75 rebate, it ended up costing just under $500. In many places, street price for the rifle (as of July 2016) is under $600. A complete review of this rifle can be found here, Review: Remington 700 SPS Varmint.

I equipped the rifle with the following accessories from Brownells:

The rate of twist on the 700 SPS’s 26″ barrel is 1:9 1/8″, faster than the SAAMI specified 1:10″, which would presumably stabilize heavier bullets better than the 1:10″. Since I was unsure how the 1 in 9 1/8″ twist would stabilize heavier bullets (online reports vary), I decided to work up some loads a wide weight range of Sierra bullets. I selected the 70 grain Sierra Match King (SMK) #1505– above, left, 95 grain Tipped MatchKing (TMK) #7295– above center, and 107 grain SMK #1570– above, right. You’ll note these are all match, not hunting, bullets. This is because I plan on using this rifle to punch paper.

A brief caveat- I approach load development for hunting rifles very differently. Normally in a hunting rifle, I focus primarily on velocity with an accuracy standard around 1 MOA. Compared to match ammunition, hunting ammunition is a different tool for a different job for a different job. In this post I am looking for precision and a low standard deviation with an acceptable velocity, typically in that order.

For reloading information: 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.

To develop these 243 Win loads I used Lapua brass and Wolf large rifle primers. While Wolf may synonymous with inexpensive centerfire ammunition, they make outstanding primers and match grade 22 long rifle ammunition. I’ve found their large rifle primers yield the lowest standard deviation in 308 Winchester sized cases.

To reload, I use the following tools:

The load development process occurred during multiple range sessions. I should note that I tend to run my guns hot during load development. I realize most reloaders prefer to allow the guns to cool and approach the process accordingly, I try to find loads that shoot from a hot gun. Most of the matches I’ll shoot will require strings of 22 rounds or more. I find this technique meets my needs.

To determine cartridge overall length (OAL), a Hornady length gauge and modified case were used.

All shooting was done prone, from a bipod with rear bag. The target was a 1″ orange dot shot at 100 yards. With the exception of the initial 95 TMK 3 shot group (I needed two rounds to get a rough zero on the rifle), all groups are 5 rounds

Velocity data was recorded with a MagnetoSpeed barrel mounted ballistic chronograph.

70 grain Sierra MatchKing loads

I selected the 70 grain Sierra MatchKing to show give an indication of some of the raw speed the 243 Winchester is capable of. While the 55 grain bullets can approach 4,000 feet/second, the 70 grains projectiles can approach velocities of 3,600 feet/second.

The 70 grain SMK has a G1 BC of .259. In the test rifle, overall length (OAL) of the 70 SMK was 2.695″ to the lands. I loaded these cartridges to 2.625″, for a .070″ jump. Looking at the profile of the bullet, it doesn’t seem that OAL would matter as much as it would on other VLD type designs.

I only worked up three loads, however, they were all sub MOA!

The 70 grain SMK Varget loads are shown in the photo above. I’ve had great luck with Varget in my 6mm and 6.5mm rifles. While this bullet is capable of greater velocities than those I recorded, however, each 5 shot group had a low SD and was sub MOA.

95 grain Tipped MatchKing (TMK)

I’ve had great success with the 130 grain 6.5 mm TMK, so I was excited about it’s little 6mm brother. The 6mm 130 TMK has a G1 BC of .490 up to 3050 feet/second and .500 above 3050 feet/second. In the test rifle, OAL of the 95 TMK was 2.885″, I loaded my cartridges to 2.860″ for a .025″ jump. This length also allowed the cartridges to function in an AICS style magazine. While the standard, BDL style hinged floor plate and magazine system of this rifle wasn’t as confined as an AICS magazine, I figured at some point in the future this feature would be updated on the test rifle.

I worked with three powders for the 95 grainTMK, H4350, H4831SC and IMR 4064. Note some of the lighter loads of H4350 showed higher standard deviations, however, case fill was pretty good. I didn’t have to deal with the compressed loads of the H4831SC, or excess space of IMR 4064. Once I pushed the 95 grain TMK past the 3083 feet/second with the H4350 group size opened up more than I liked it.

H4831SC loads worked well, however, the velocities were lacking. I would venture to guess a hot 6mm BR with a 28″ tube would be similar.

IMR 4064 shot well at 37.0 grains. I would have liked more case fill, however, the results speak for themselves. If you take a how the group shot above, note the four rounds in one small bug hole.

I loaded up 50 cartridges with 37.0 grains of IMR 4064 and the 95 grain TMK. Shooting three different five shot groups on an SR-21 center at 500 yards, I got some surprising results, 1.410″(.269 MOA), 5.840″(1.116 MOA) and 5.220″ (.997 MOA).

I’m still in awe of this 500 yard group! This was the factory rifle with the factory trigger. The moon and stars aligned for this one, 1.410″ (.269 MOA)!

Engaging steel out to 700 yards (the furthest distance at that range) was a piece of cake with this load. Note the vertical distribution on the steel plate in shown towards the end of the post.

107 Sierra MatchKing (SMK) loads

The 107 SMK has a G1 BC of .547. OAL in the test gun measured 2.862″ to the lands. Cartridge OAL was 2.850 for a .012″ jump. I wasn’t completely convinced the 107 would shoot in this rifle. Sierra recommends a 1:8″ twist and this gun is a 1:9 1/8″. The 107 SMK and Remington 00 SPS proved me wrong.

My initial 107 SMK groups were with Reloder 22 (not Reloader- no “a”) just to see if they would be stabilized. Well, they were. Both loaded were under 1 MOA, however, velocity was low and SD was high. I gave H1000, Varget and Retumbo a shot. While Retumbo yielded low SDs and high velocity, the accuracy wasn’t there. Varget, once again, gave low SD and sub MOA groups for 2 or the 3 loads, but lacked speed.

The 46.0 grain H1000 load seemed to give the best balance of low SD, velocity and precision.

I fired two different five shot groups on a SR-21 center at 500 yards and 4.875″ (.931 MOA) and 4.750″ (.907 MOA). Solid sub MOA performance from a factory rifle and trigger.

At 700 yards I left a VTAC E Silhouette set up to print a few groups. The results are below:

I didn’t make my wind calls very well, however, my vertical distribution for both loads (95 TMK top, 107 SMK bottom) were legit! Oddly enough the two groups are nearly identical, don’t ask me why.

Shooting the 243 was a pleasure. The recoil impulse for the 70 and 95 grain loads was mild, often allowing target to remain visible in the optic. The 107 load was a little more stout, however, still extremely mild when compared to larger cartridges like the 308. All three of these bullets offer great performance in the 243 Win.

While the 243 is capable of great accuracy, it does use quite a bit of powder when compared to other competing 6mm match cartridges like the 6mm BR, 6×47 Lapua, 6 XC and 6 Creedmoor- all of which offer respectable performance in match rifles. I’ll be comparing these cartridges in an upcoming post.

The Remington 700 SPS Varmint continues to be an excellent performer. I’m going to replace the heavy factory trigger with a Timney 510 and hope to see further improvement.

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