Some time ago I bought 2 Howa mini barreled actions; a 6.5 Grendel and a 7.62x39. Both have 20” lightweight barrels. Howa mini’s are smooth actions with nice hunting trigger. My only complaint is the bottom metal. ‘Nuff said.
A consummate tinkerer, I decided to try 7.62x39 improved version. There was no good reason for this. The hope was to get 30/30-ish performance out of the rifle/cartridge combo.
CH4D had 28 degree dies on the shelf. Whoda thunk? Mike Bellm had a reamer and did the rechamber job to match my CH4D dies. “Conversion” is as simple as firing factory ammo in the rifle. Nothing else. Capacity before/after fireforming is roughly 3 grains of AA1680 powder or 11%.
I built a Mannlicher stock for the barreled action(s)s. Mannlicher stocks can be frail so I reinforced it with pillar and full length bedding. There are 3 recoil lugs supporting the stock. An old Nikon fixed 4X scope is mounted in Tally base-rings. The unloaded rifle weighs exactly 6lbs.
When I fireformed a box of WW boxer primed 123 ammo average velocity was about 2250 fps. Today I loaded the same cases with 30 grains of AA1680 powder over Hornady 130 (.308) spire point bullets. This is about a 95% load with a COAL= 2.230”. Chronographed velocities = 2594. 2602, 2598fps. Accuracy for 3 shots at 50 yards was ½” cloverleafs. Encouraging results for a first try.
I believe 2500 FPS is possible with 150 grain bullets and a COAL = 2.390”. This is the limit of the Howa magazine. Generic 123 grain 7.62 bullets might approach 2800 FPS.
All disclaimers apply . These results exceed SAMMI specs for the cartridge because it was designed for the AK platform. However, these PSI levels are well within the capability of the Howa bolt action, which is chambered for other cartridges in the 50-55,000 PSI range and a similar bolt face. At any rate, in my rifle, extractions was easy, primers are tight, bases are not expanded. I see no excess pressure signs.
The little Howa carbine wonderfully accurate & potent. The “conversion portion” of the project cost me about $200. Besides learning something, I got quite a bit of extra performance.
Next steps, test 150 grain bullets, try .224 saboted [ Accellorator] ammo, and finish the rifle.
