Fire forming 7.62X39 ?????????

[rasp65]

Another step I add is to lube the case with some gun oil to keep the case from grabbing the chamber while it is forming.

[Reno82]

No. You have to size the 7.62 down to 6.5 first. Then firing it in a 6.5 will force the shoulder and taper to expand and conform to the chamber of your barrel. The result will be a new 6.5 grendel casing.

OK..... I was doing it right.

[txgunner00]

I place a single-ply circle of toilet paper over the powder and top off the case with C.O.W. Then, using a case as a punch, I knock out some circles from a styrofoam cup to make a plug to keep the C.O.W. tidy while chambering the round gently. Make sure you rotate your gas block to keep the stuff out of your gas system. Don't underestimate the power of such a charge. It's still deadly.

Hoot

I don't separate the powder and COW with TP. Not sure it's necessary but can't hurt. I like the styrofoam plug idea. Sound faster than making TP wads.

[Malchira]

Another step I add is to lube the case with some gun oil to keep the case from grabbing the chamber while it is forming.

Rasp, any concerns about increased bolt thrust when doing this?

[longdayjake]

Hmmm, what do you mean by grabbing the chamber? I have never heard of this. Is this a COW fireforming issue?

[tacticalj]

So the problem I'm having with this is that I can't seem to get the shoulder bumped down far enough to chamber up, without sticking, in my grendel. I'm using a Hornady new gen FL die and when compared to Factory Hornady brass, the shoulder is taller on the resized 7.62 brass than on the Hornady brass. I even ground a couple thousandths off my shell holder to get it deeper in the die. The shoulder is still slightly taller than the Hornady brass, but when you chamber a round, it takes alot of force on the charging handle to get the bolt to open. The first ones I did, would not fire, as the bolt was not locking up all the way. I think it's the same problem still, but just not as bad. I haven't tried firing any of these and am seriously contemplating scrapping the whole fire forming project! I don't need it, but I thought it might work and give me some cheap brass, as all of it was given to me and I only have about 100 peics of Hornady brass built up. Not sure, but it seems that I'm having more difficulty then everybody else that I've talked to. Most say they resize and fire form with no problems, using the same die that I'm using. My necks aren't too long, the inside of the neck is fine and doesn't need to be turned. It just simply won't bump the shoulder down far enough to match the Hornady brass and it bothers me. Apparently it bothers my rifle too!

[pinzgauer]

So the problem I'm having with this is that I can't seem to get the shoulder bumped down far enough to chamber up, without sticking, in my grendel.

Just curious, Have you tried chambering just an empty case? And ruled out bullet seating depth? Lot's of folks get caught by that, and blame the dies, etc.

Also, have you shot this rifle with factory ammo? Or shot 6.5 Grendel cases resized with that die?

I ask because something is not right if the die moves the grendel shoulder correctly but not the 7.62 brass. Could you post what barrel / bolt combo you are using?

My experience with IMI 7.62x39 brass and Forster dies is that it puts the shoulder right where it needs to be. Functions fine, shoots good. I'm seeing 8-9 reloads before small case neck splits, usually where the feedramps scored the brass and created a stress fracture.

[tacticalj]

I'm using a Sabre Defense 18" barrel with matched bolt. I've shot my reloads in hornady brass and I've shot Hornady factory Amax 123gr ammo through the gun with no problems. I've got the shoulder within about .020" of the factory hornady brass, of course this is just a rough measurement with a set of dial calipers, but it was at .040" before. I have 6 rounds loaded with this shoulder dimension and I'll see what happends. At .040" it would not lock up and fire. It would allow the trigger to pull and sounded like the firing pin went, but no bang. When I pulled the upper off and checked on it, the bolt was just barely in the locking lugs.

I also checked any my OAL of the 7.62 brass was the same as my reloads, which were at 2.20" then. I figure that if I can put a round in with an OAL of 2.300" and not have a bind or get into the groove/lands, then it must be the shoulder of the brass not getting far enough into the chamber to allow the bolt to lock up properly. I may be wrong, because that's just my logic. I also forced a couple 7.62 cases deeper into the die, by means that I'm not going into as I don't need to hear the fallout, and it bumps the shoulder to right about where it should be. All resizing that I've done on hornady brass seems to be fine.

I'm at a loss on it and the only other thing I can think to try is a different resizing die, but I don't know if I want to spend the money on that venture or not. It's not really a big deal because I have over 100 peices of Hornady brass that is either 1xfired or virgin, so I'm not hurting for it. This was just something to do and a way to expand my knowledge and skill set for reloading. It necks em down just fine, but the shoulder is where the problem lies, or at least in my eyes.
Thanks guys

[rasp65]

Rasp, any concerns about increased bolt thrust when doing this?

Honestly I have only done it about twenty times in the Grendel. I did not find any signs of high pressure. The oil allows the case to conform to the chamber walls without sticking. I stopped because I did not want to get any of the crap in my gas system.I have used this method hundreds of times before in a Contender pistol and a Ruger No1 rifle with no problems. Like LR said fireforming with bullets is still pretty accurate.

[pinzgauer]

sounds like you are not likely to have bolt/barrel related headspace problems.

Have you tried the case with no bullet? Just measuring COAL is not enough if using different projectiles, though it should not be an issue if it's the same projectile and same COAL.

I'd also give a try with the poor mans "correlator".... measure the base to shoulder distance using a 9mm case over the neck. Just a handy way to measure the shoulder distance at a known index point. There are many more expensive tools you can use for that, but it's much more accurate than trying to measure the start of the shoulder with a caliper by itself.

I see no way physically for the shoulder on the fireform brass to be further forward than the grendel ammo. The die should not allow it. I've taken a photo of a raw 7.62x39, sized but not fired, and fireformed side by side I'll post later. The grendel die absolutely has to push the shoulder back as well as necking down. The shoulder transition nearest the base is not moved, as the die does not contact it. (It actually needs to move toward the neck during fireform)

the only other possibility I'd be on the lookout for is some other problem, overall case length, a bulge/buckle on the neck, etc.

With IMI even after resizing and several reloads they are still a hair short for all but a few. But other brass could be different.

Just some more ideas to try to help resolve the mystery.

[pinzgauer]

Here's a shot showing from Left to Right: Raw IMI 7.62x29, Sized to Grendel, Fireformed



You can see the shoulder start at the neck is pretty much identical after a pass through the grendel die, but where it joins the body is different (and smaller) until blown out to Grendel size by fireforming.

[Clod Stomper]

Actually, I have had that very problem when forming one case from another, and not just with the Grendel. I guess there is just more "spring" in the case after it has been formed to that extent. I could not get my cases to chamber even after tightening the sizing die down to a worrisome extent. What I had to do was turn a few thousandths off the top of the shellholder. That allowed me to bump the shoulder back that last little bit.

BTW, to the OP, a case headspace gauge is really a necessity when loading the Grendel, especially if you are forming cases.

The Grendel isn't the only case which I've found to be this way. I've formed 7.65x53 cases from .30-06 and .300 Savage from .308 Win. and ran into the same problem. The first time it happened I thought I had a bad die. I turned a few thousandths off the bottom of the die to make it work. DON'T DO THAT. File a bit off the top of the shellholder. If you don't have a lathe, you can use a file or a sander, but be sure to take enough off that it won't contact the die because it probably won't be square. Mark that shellholder and remember not to screw the die all the way down to contact it.

I'm not sure that this is the OP's problem, but it actually does happen. A shellholder/die combination that will size factory cases perfectly well can fail to set the shoulder back far enough to overcome the "spring" when forming one case from another. It looks like Pinzgauer hasn't had that problem.

All that being said, I have given up on making cases. I read LR1955 when he wrote that the fireformed cases have less capacity, but I thought "well, I'll give up a bit of capacity for the less expensive cases." Well, the loss is actually pretty significant. A charge that will fit behind the bullet in a factory case will almost fill a fireformed case to the case mouth. I figured that out after necking down hundreds of cases. I still haven't fireformed them all. I have yet to buy a factory loaded round and the only factory cases I have came with a used barrel. From here on, I'll buy Hornady (or Lapua if I find a really good deal). I'll use the fireformed cases I already have with lighter bullets for shorter range targets or hunting.

Good luck,

Will

[tacticalj]

That's exactly what I ended up doing. I removed a couple thousanths off the shell holder and it got me pretty much what I needed. I did that because I didn't want to mess with my die just in case there was something wrong with it and wanted to get with Hornady on it, besides the shell holder would be cheaper if I screwed something up, so I ordered 2 of em! Problem solved, but to what extent the cost was worth the gain, who knows. Anyhow, thanks for the help there guys and just for info, I loaded up some cases today and will hopefully see how they shoot tomorrow, pending I want to go out to a muddy range. This was my plan for today, but it rained this morning.

[mseric]

Here's a shot showing from Left to Right: Raw IMI 7.62x29, Sized to Grendel, Fireformed



You can see the shoulder start at the neck is pretty much identical after a pass through the grendel die, but where it joins the body is different (and smaller) until blown out to Grendel size by fireforming.

What load do you use to Fire-form your brass? It may be the photo, but it looks to me that the shoulder is still round and not fully formed. Frome left to right, 7.62x39, Grendel sized 7.62x39 and fire-formed x39 brass.

[pinzgauer]

I see what you are referring to. I don't know if that's the difference between chambers or what. Your once fired does appear sharper than even my "many fired" IMI cases as well as unfired & fired Hornady & Wolf factory loads. I do not have any AA factory ammo for comparison.

The shoulder to body radius is supposed to be .030" based on the dimensions I've seen, which is pretty sharp. That's sharper than the neck to shoulder radius at .075, so who knows. I do know this is an area that is often different between reamer mfg's even in other cartridges. I have both an AA barrel and a licensed non-AA producing similar shoulders even at full pressure, so don't know what may be the difference. Which chamber/reamer was yours sample shot in?

From reading it's not uncommon for milder (90%) fireform loads in other cartridges to not completely blow out the shoulder. Most of reported it does not produce a significant variance, at least not that they could measure. So I won't rule that out, but from visual comparison of full power factory & reloads fired cases mine are pretty consistent.

My sample was fireformed with 27g of AA2520 behind 120g projectile. (Speer hot core or Sierra matchking 120g). I've also fireformed with 100g hornady and AA2230, which was milder. (but quite accurate and shot very close to same POI as full power 120g did).