For a more universal and easy to find caliber choice I have a 24" .223 sporter barrel that was a gift from S. Pence. I made two recoil lug discs/spacers on the lathe. They were .187" and .189" thick, 1.30" OD and 1.065" ID. With the .187" lug the bolt wouldn't close so I fitted the .189" lug in place and it worked just fine. I recrowned the barrel and shot a few firelapping rounds down the barrel to smooth everything out and, yes detractors, increase the jam length about 15 thousandths. On the factory load side, the Black Hills 40 grain Ballistic Tip load left the barrel at 3470 fps, with a group of .5 MOA. With handloads, I had good luck with 24.5 grains of AA2495 in Nosler brass, BR4 primers and 55 grain Berger bullets. With a COAL of 2.317", I got 2960 fps and 3 shot groups averaging .6 MOA. The 52 grain Sierra Matchkings, also pushed by AA2495, are averaging .4 MOA. I feed the .223s using the AI 10 round plastic magazine. It has plenty of room fore and aft inside the magazine to load your cartridges out to an overall length of 2.55" (compared to normal AR-15 magazine length of 2.26").
Extra Bolt (top), wood barrel vise spacers and Surgeon action wrench tool for changing barrels (middle left), Borka adjustable torque wrench(center), nylon single round loading block (middle right), AI 5 round .308 magazine (bottom left), Alpha Industries 10 round .308 magazine (bottom middle) and AI 10 round .223 magazine (bottom right)
I purchased a used take-off 7-08 barrel for $45. It was blued, 22 inches long and .66" OD at the muzzle. I recrowned it on the lathe and broke the crown's edge with a .45 FMJ bullet smeared with 220 and then 320 grit lapping compound. I threaded it to accept a Ross muzzle brake threaded 5/8-24. The brake is Stainless Steel that I sand blasted with a Campbell Hausfeld sand blaster using play sand strained thru a screen. I wanted the hole to be .030"over bullet diameter so Ross, the brake maker, drilled it out to .314". The brake has 3 chambers with 3 top ports and 3 ports on each side. It cost $40 shipped and was money well spent. I made a spacer .080" thick to time the brake top ports to be top dead center.
I found that 7-08 cartridges won't feed through a 700 that has feed lips intended to feed .204 cartridges. I had read that this would happen but figured I would find out firsthand before I moved to the next step in the project - converting the rifle from a drop floorplate magazine to the detachable AICS magazines. In the mean time, I just single loaded my handloads. I forgot to mention that I have a second bolt to handle the 7-08 and .308 cartridges. Speaking of bolts, you may want to paint barrels and the appropriate bolt that works with them the same color. That is, the 7-08 and .308 barrel could be painted OD green to go with a .462 bolt that is also painted OD. The .204 and .223 barrels could be painted black to go with a .378 bolt that is painted black. If the colors match, you're good to go. That might prevent you from bringing your rifle to the bench with a .223 bolt and a 7-08 barrel. Ask me how I know this.
The jam length for this barrel is around 2.78" for the 7mm Sierra Matchkings in 150 grain and 168 grain weights. That's a pleasant surprise since that COAL is shorter than magazine length. Factory R7M081 ammo loaded with 140 grain PSP bullets averaged 2750 fps and yielded 2 MOA groups. I pulled the bullets and weighed the powder. I loaded some 'Mexican Match' ammo by dropping 2 grains of the powder (from 45 down to 43 grains) and seating 150 Matchkings at 2.766". I was rewarded with a quarter inch group with a muzzle velocity of 2640 fps. With R-P brass, 210M primers, 38 grains of Varget and the 168 Matchkings set at 2.77 ", I got 2454 fps and 3 shot groups just over half an inch. This is understandably a soft recoiling load since 41.5 grains is the max load in the Sierra loading manual. The same powder charge with the 150 grain Matchkings yielded 2480 fps and similar groups. With a compressed charge of 47.5 grains of H4350 in resized FC 308 cases (172 grains in weight) under the 150 grain Matchkings at 2.766", I got 2700 fps and .6 MOA 3 shot groups.
I was using a .185" recoil lug but found that the fired cases were SAAMI minimum minus .001". Consequently, I fitted a .186" lug that put me right at SAAMI minimum, based on the .308 Precision Mic. Checking the bolt lug engagement, I found that one side was carrying most of the load. I lapped the lugs using 220, 320 and 600 grit lapping compound and then made up for the lost metal by installing a thicker .188" recoil lug. This work brought me up to SAAMI minimum plus .001". Checking jam lengths at this point using the F.A. COAL gage resulted in the 140 grain Gamekings measuring 2.791", the 150 Matchkings measuring 2.781", and the 168 Matchkings measuring 2.782". I decided that I needed to try the Hornady 162 Amax bullets but wondered if they were too long to stabilize. The reps at Hornady gave me the length of the bullet as 1.425". Plugging that into the Miller twist rule equation for a 1:9.25 twist barrel and adjusting it for 2600 fps and 20 degrees F, I got a stability factor of s=1.37. That's pretty close to 1.4, so I figured it would work just fine. I bought a box, shot some groups at 25 to 30 degrees and got nice round holes at 100 yards. Varget gave me good groups of .3-.4 MOA at a COAL of 2.954". That's too long for the mag, but they load fine with the single round loading block.
I loaded up some 150 grain Swift Sciroccos over 43.5 grains of H414 and shot some bare 10% ballistic gelatin at 100 yards. The muzzle velocities (not impact velocities) were 2663 and 2664 fps and the bullets penetrated 22.5"and 22", weighed 143 and 141 grains, and expanded to .62" and .61". The 140 grain Accubonds at 2741 and 2745 fps, penetrated 23.5" and 24.5", weighed 110 and 105 grains and expanded to .53" and .54". The 154 grain Interbonds at 2691 and 2664 fps, penetrated 21.5" and 24.5", weighed 144 and 146 grains and expanded to .66" and .69".
The following shots were fired at 30 yards, rather than 100 yards. The 140 grain Trophy Bonded Bearclaw, fired at 2725 fps, went 20" in bare gel, weighed 137 grains and expanded to .65". The Winchester 140 grain Failsafe at 2733 fps weighed 121 grains and expanded to .39". The Speer 145 grain Nitrex Grand Slam at 2621 fps went 24", weighed 116 grains and expanded to .60". These were factory loads.
As I mentioned in the 7-08 section, the feed lip cuts in the action were set up to feed .204s and wouldn't feed the 7-08s. To continue the project I needed to solve this little problem. By switching from the drop floorplate magazine system to the AICS detachable magazine I could use the AICS metal magazines to feed the .308 and all its offspring (.243, .260, 7-08, etc.) and the AICS plastic .223 magazines to feed the .223 and its cousins (.204, .300 Whisper/Blackout, etc). The plastic magazine has the same width and fore/aft measurement as the metal magazine so both types of magazine fit in the same magazine well. My next step was to consider which bottom metal to go with. I had fitted Surgeon bottom metal to a couple of stocks and really like their system. I will use the Surgeon Bottom Metal and a McMillan stock for my youngest son's 700. CDI also makes bottom metal that is affordable but with which I have no experience. Another option, and the one I went with for this rifle, was to glue the action into a Tube Gun Kit. I found an excellent condition MAK XC (across the course) repeater tube gun kit, spare mag and nylon single round loading block for $495 at 6mmBR.com.
MAK (Mike, Archie, Kevin) tube gun kits have been covered in at least two other PS articles written by Robert Whitley (February and October 2004). The benefits of the MAK include ease of set-up as a switch barrel rifle, free floating barrels, no bedding to worry about, weatherproof (aluminum) construction, increased action stiffness and multiple stock options (any AR-15 stock will work). The kit is made up of an aft cap (to which the stock attaches), receiver sleeve (holds the action), sight rail (flat or 20 MOA slope), handguard and trigger guard. Holding it all together are thirteen screws, five of which hold the sight rail. To tighten these screws, especially the action screws, you can use a torque wrench, such as one of the fine Seekonk products. Another option would be to use a Borka adjustable torque wrench. The torque settings change depending on which hex hole you chose - the one shown in the photo allows settings of 36, 43, 50, 57, 65 and 72 inch-lbs. For its features, it's handy, light and priced right.
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