In my weekly study of internal and external ballistics, the 7mm-08 A.I. caught my attention some 20 months ago. I read, I called, I sent texts digging up as much information as I could find. When all was said and done, it looked as though it would be what I hoped it would be. And that is a very high performance short action on the common .470” bolt face, shared by the .308 Win, .243 Win, 6.5 Creedmoor ect. By performance, I am meaning lack of wind drift and energy on target (read flesh). I don’t even look at vertical trajectory. Correcting for it means dialing a turret farther, or holding farther down on a reticle. How much BC can we push at what muzzle velocity? Well, I’ve got thousands of rounds experience behind the standard 7mm-08, and I am a huge fan of it! But, can we make it stronger, faster, better? The most performance I’ve achieved out of a 7mm-08 is with a 1:9 twist rate, on a 24” barrel. Loaded with a 162 gr bullet, it can produce 2700 fps MV, maybe a tad more. So what can a 7mm-08 A.I. do? How well does the A.I. chamber shoot while fire forming brass? Those were my questions. Keep in mind, the 7mm-08 A.I. is by all means a “hand-loader’s cartridge”. You can’t short cut your way to brass shape short of a hydraulic forming die (which I have no experience with). .280 A.I. brass is available on the market, 7mm-08 A.I. brass is not. So this cartridge has been on my brain for a long time. Then David called…
David is one of my customers that I taught precision rifle shooting to almost a year prior to the phone call. His call was to get my opinion on what rifle to build. My standard line of questions for anyone with this project are as follows: Hunting rifle? Range rifle? Rifle to do both? Are you more concerned with muzzle velocity or a short, maneuverable barrel length? Do you want a long action, or a short action? He answered, a rifle to range shoot, and hunt. I want a short action, I don’t mind having a 24” barrel, and I loved shooting your 7mm-08, so that’s what I was thinking. And he said he wanted a “medium weight barrel”. David is a hand loader, and he told me he wants to get the best components on the market, but run a bullet that will hunt as well as target shoot. I proposed a 7mm-08 A.I. telling him that second loaded brass will cause a second load development project, adding more powder and therefore more velocity, but I don’t know exactly how much velocity. David said it sounded good to him. So I advised a Rem Varmint contour, stainless, and 1:9 twist rate. Lapua brass, CCI 200 or Fed 210 primers, Hodgdon-Varget, and Hornady 162 gr. ELD-X. David obtained all those components, and requested that I do the load development for him.
I looked at Hodgdon.com for minimum and maximum charge for the 7mm-08. They list 38.5 gr to 41.0 gr. My suspicion was that at maximum, and possibly above maximum, due to the brass making such a significant move to fill the chamber, that pressure signs probably will not show, meaning there is not a high pressure scenario happening. Therefore, I focused my attention around maximum listed charge of 41.0 gr. I began at 39.6 gr, and worked up to 41.4 gr. I shot these in a “ladder test” format at 300 yards, and in 85F ambient temp. The ladder test showed that 41.0 gr was where I needed to be. I reproduced it, and shot a three round group at 200 yards. Vertical dispersion was .25”, horizontal dispersion was 1” (that’s wind, not me ;). So we have technically a ½ MOA shooting load WHILE FIRE FORMING BRASS! I left my 300 yard test range, and went to the 800 yard steel range. I made a guess on velocity since my chronograph was loaned out, at 2700 fps MV. I plugged in Hornady’s published G-7 of .315 (G-1 .630) and got predicted corrections. Using a NF ATACR F-1 5-25X Mil-C, I dialed corrections every hundred yards out to 800 yards with center hits the whole way out. Project number one complete!
Two months later, a friend named Bill called me, literally with the exact same rifle goals as David, and I gave Bill the exact same answers. So we built a twin sister to David’s rifle. A Tikka T-3 action, Bartlein “Rem Varmint” stainless 1:9, and a West Texas Ordnance muzzle brake, McMillan A-3/5, CDI Precision bottom metal. I instructed Bill of what components to obtain so that I could fuel the rifle. Once the rifle was built, I suspected the load would match David’s load, But! This is a different lot of H-Varget and I had better test below, on, and above 41.0 gr. I went straight to group shooting this rifle at 200 yards, after 20 fouling rounds at 100. Sure enough, same barrel manufacturer, same contour, same finish length of 24”, same gunsmith, same reamer, produced the same “best shooting load” at 41.0 gr. Bill’s grouped 3 rounds .29” tall X .95” wide. But why didn’t I shoot the benchmark five shot group? Because we are fire forming here, and we will abandon this load in a month or two anyway. Same DOPE to 800 yards on Bill’s rifle as David’s. Then Bill and I went to his hunting lease, which contains a rifle range out to 1700 yards, with steel every hundred. We checked zero at 100, all was well. We skipped straight out to 600 yards, and the DOPE matched, even though we were in a higher DA than my range in Fannin County, Texas. We skipped to 800, same DOPE. Then consulted the calculator for 1000 yards. First shot, center hit. I was spotting for Bill, and asked him to maintain the same hold, and fire two more rounds for a thousand yard group. There was not even a tenth Mil variation. 1/10 Mil at 1000 yards is 3.6”, and we are still fire forming brass! We shot that rifle, and connected with steel out to 1400 yards, before we needed to pack up for the day.
Once home Bill told me to keep his rifle, and shoot the remaining virgin brass. I got that done in a couple of days, and now had 200 pieces of fire formed brass to work up a true Ackley Improved load. I asked David if he had done that on his rifle yet, and he sent me some group pics. On David’s rifle, his did well at 43.0 gr of H-Varget, so I concentrated my efforts there. I began at 42.4 gr and went up to 43.6 gr, skipping in .2 gr increments. Temps were 80F, fairly heavy mirage, and a 2 o’clock wind 2 to 6 mph. I group shot these at 300 yards. 42.8 gr grouped .80” vertical X 2” horizontal, but I had a wind gust during that group. I really only worried about vertical dispersion. 43.0 gr grouped .65” vertical X .75” horizontal, (that’s a real life quarter MOA) but I had slight extractor marks. I exceeded 43.0 gr and was showing extractor marks, but no flow-back on primers, and no flattened primers. I eventually found a hard bolt lift at 43.6 gr. So it’s a full load of powder, but not getting “danger close” yet. Due to the fact that 42.8 shot well, and showed no signs of pressure, I decided to roll with that powder charge. But how fast is it now? Well, let’s go out to 800 yards, and find out. When all was said and done, the DOPE matching in the calculator showed a muzzle velocity of 2820 fps. That’s a 120 fps gain from virgin brass to fired brass, and we are still talking about a 162 gr. bullet! Long story short, it takes the wind cheating ability of the 6.5mm short action chamberings, and also produces close in ft/lbs of the .308 Win, as well as delivers more foot pounds down range than any other cartridge/ bullet combo that will fit in the same action and bolt face.
Rifle project number three came along. My very own 7mm-08 A.I. I had been waiting on my Manners MCS-EH1 to build me a short, light bolt action. The stock finally arrived, so I got my gunsmith in gear, and we did an experiment. I asked him to take a Tikka 7mm-08 barrel and re-chamber it for Ackley Improved. We just needed the pilot to make it into the rifling for it to work, and it did. He chopped it down to 17” for me, and threaded and crowned the muzzle. The assembled rifle tips the scales at 6 pounds 10 ounces. I decided to experiment with a slightly faster burn rate, and small kernel powder, and I’m going to keep this one to myself. Again, the fire-forming load was at maximum for a standard 7mm-08. I got all that brass fired, and went another two grains heaver. I am also shooting a 162 gr Hornady ELD-X. It is making 2640 fps MV out of a barrel that short, wearing a Tiger Shark suppressor. By comparison, my 20” 7mm-08 with the same suppressor, is at the same velocity. So I’ve got 3” less barrel length, same suppressor, and making the same muzzle velocity.
All three of these rifles feed from an Accuracy International magazine, and all three do not give any trouble doing so. If it weren’t for potentially losing brass, I would compete in PRS style matches with the 7mm-08 A.I. The recoil does not seem any more significant than a 6.5 Creedmoor shooting 140’s at 2800 fps MV. But as of right now, mine will only hunt, and play on my range where I do not lose brass. This January, on a doe and spike hunt, I harvested a whitetail spike at 285 yards broadside shot, 7mm entry and a 1 ½” exit wound. The deer did not take a single step. Spike two at 265 yards quartering away, 1 ¼” entry (it clipped the last rib left side) 1 ½” exit center of right shoulder. The deer took three steps and fell over. I harvested a doe at 250 yards, perfect broadside shot. 7mm entry 1 ¼” exit. She ran 30 yards, and fell over.
The 7mm-08 A.I. is, in my opinion, the short action cartridge that can do it all. It cheats wind, it hits things hard, it flies into extreme range distances beyond 1000 yards, and shoots consistently. Using temp stable powders at 100% case fill, it is predictable. Once home from the last hunt I played with cold bore shots 300 to 800 yards, and it goes where expected every time. So, if you have the time, the facility, don’t mind load development twice for one rifle, I highly recommend the 7mm-08 A.I. and a 162 gr bullet.
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