7.62x39 to 6.5 Grendel Brass Conversion (2024) Experience

[That_Aussie]

I've been converting once fired 7.62x 39 brass to run in the Grendel for three reasons.

1. Affordable Grendel brass has proven impossible to find in my part of Australia.

2. I regularly lose brass while hunting pigs at night in swamps, long grass and down cracks in blacksoil paddocks.

3. I had a couple of bags of once fired 7.62x39 brass gathering dust in the man cave.

My experience thus far:

S&B 7.62 brass necked down to 6.5 extremely easily, almost no pressure required with just a hint of lube.

Fire forming load with 120gr Sierra Pro-Hunter & a very cautious load of AR2208 for a lazy 1,800 FPS blew the brass out perfectly and has proven effective for knocking over close range pigs. No wasted primers, powder or projectiles, just load and hunt.

Interestingly, the fire-formed S&B brass (full length resized after forming) and Hornady Grendel brass from factory ammo (also once fired and resized) have the same water capacity of 39.7gr.

The formed S&B cases weigh 119.8gr with a spent primer while the Hornady factory brass weighs 120.8gr (on my old beam scales).

On my next trip to the range I will send some test loads in the fire formed S&B cases loaded with 140gr pills and AR2206H over the chronograph & compare pressure signs and velocity between this and Factory brass.

[That_Aussie]

Typo, Should be 120gr Sierra Pro-Hunter. (and I've now found the edit button)

[VASCAR2]

When I first started shooting the 6.5 Grendel brass was not readily available and I used fire formed 7.62x39 brass. I used this FF brass for hunting so I wouldn’t loose my Lapua/AA or Hornady 6.5 Grendel brass. My FF x39 brass didn’t take but a few reloads until the primer pocket got loos or the neck split enough to ruin the brass. I never tried annealing brass. Brass quality varied between 7.62x39 brass manufacturers. I had several pieces of IWI brass which seemed more difficult to size to 6.5 Grendel. I finally got enough 6.5 Grendel brass I quit using the x39 brass. I bought a brass goat brass catcher for my AR-15’s and I rarely loose brass now from my AR-15’s.

I only used my FF x39 brass for short range pest control or short range target shooting. I still have a few 7.62x39 brass and will hang onto them as you never know when I might need them. I never loaded my FF x39 brass any where near max pressure but was satisfied with moderate powder charges.

[Constitutionalist]

I fire formed about 600 rounds of 7.62x39 to 6.5G when I first got into the caliber for the same reason - brass was unavailable back then. I was always pleasantly surprised how accurate the fire forming loads were. Unfortunately my ARs wouldn't feed them from the magazine reliably until they were formed.

[NightStalker]

I have some of 7.62x39 I need to adapt. Just took a break from the Grendel for a while.

[lazyengineer]

My own experiences with 7.62x39 brass has been very good. I tend to get better accuracy when using 7.62x39 brass, than actually Grendel brass, but split necks very quickly. Now that I anneal, i'll wet tumbling clean, anneal, resize to 6.5, anneal again. Trim. Mandrel back up. I load up to a spec load that's dedicated just to that brass (90 TNTs and BenchMark, with LR primers). And get very very good accuracy and performance. Now that I anneal, neck splits have stopped, and I'm up to 6 loadings so far on some of the brass.

I have never lost a single casing of 6.5 Grendel due to loose primer. not one, and not a single 7.62x39 converted case. I'm not quite sure why, and am wondering if my loads are maybe too light or something? Not sure. Maybe that'll change as fast as next week (who knows!). Now that I'm annealing, neck splits have stopped, so next failure mode is probably going to be primers eventually - I guess.

As to headstamp, I find PMC is my favorite, but do decent with all of them. GECO and LAPUA are my least favorite, as they are the most difficult to size down to 6.5Grendel and I have to fight chambering them. They also have thicker rims that fight the shell holder.

[That_Aussie]

I visited a friend's bush block on Saturday morning for my oldest son to sight in his Christmas gift from me (a long story) and to put several of my Grendal loads over the chronograph.

Fire formed 7.62 S&B brass loaded with 140gr Game Kings and a stout load of Win748 gave an average velocity of 2199fps. Accuracy was on par with all of the loads I shot in Hornady Grendel brass on the day. Primers were slightly flattened but no cratering and bolt lift and extraction were perfect.

I also shot a group with hornady brass loaded with 90gr Speer TNTs and Benchmark for an average of 2578fps with no pressure signs. There's room for more velocity with these pills but I'll do some more testing for the most accurate load. I do like Benchmark for accuracy in a lot of my rifles.

120gr Sierra pro-Hunters over ADI 2206H gave the best groups of the day (by a tiny margin) with an average velocity of 2352fps.

Note: these are through a 16" bolt gun.

With the Speers 90s sighted to be 1.5" high at 100 yards, I'm only 1.5" low at 200.

[Highbrow]

I have had some issues with 7.62 brass when converted to 6.5Gr with the rim diameter being a bit larger than Grendel rims. This caused some feeding issues with ARs and ejection problems. No problems with a bolt rifle though.