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Thread: Fireforming 7.62x39 to 9x39

  1. #1
    Boolit Master

    Sig556r's Avatar
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    Fireforming 7.62x39 to 9x39

    Need advise from gurus who perfected the art of fireforming.
    I've successfully resized 7.62x39 brass & fireformed to 6.5Grendel wihtout seating all the way to the rifling since it still headspaces partially on shoulder.
    On the 9x39 however, the tapered wall of the 7.62 puts the shoulder just a tad wider than the neck of the 9x39 chamber that loading it on an AR pushes the round forward that the extractor doesn't engaged the case head & jams. Manually engaging the round to the extractor prior to chambering forces the round to headspace from the casehead & will work but it'll be tedious even on a sidecharging upper..
    Any insight is appreciated.
    ...Speak softly & carry a big stick...

  2. #2
    Boolit Master



    skeettx's Avatar
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    Fireforming in an auto is a pain in the BUTT !

    But the easiest way is to leave the magazine in place.
    Load one cartridge into the chamber and close the bolt gently
    The trick is to seat the bullet out to the rifling to hold the cartridge back.

    YES, I do like your word tedious

    Mike

    p.s. the other way is to expand the neck to .375 or so and then size back till the case is a tighter fit

    He he he, lar45, I see we think alike !!!!!!!!!!!! Posted at the same time
    NRA Benefactor 2004 USAF RET 1971-95

  3. #3
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    You might try expanding to .375", then run it back into the 9x39 sizer to establish the shoulder where you want it.

  4. #4
    Boolit Master

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    Thanks guys.
    I actually opened the casemouth with a 9mm lyman M-die after annealing & expanded just a bit to accept missouri #1 9.3mm boolits. I'm a tightwad & still resisting that $150 redding die set & plans to cut-off an old 35rem sizer, so I seat the boolits using the max out 35rem seater & crimp with a redding 7.62x39 taper crimper. They actually load from the magazine & ejects manually with visual lands contact. May need to disengaged the gas port for this effort.
    ...Speak softly & carry a big stick...

  5. #5
    Boolit Master

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    Fireformed some 7.62 brass to 9.3mmx39 last night.
    Jamming the projectile to the lands did pose a few ftfs, but all in all, was able to form a couple of hundreds.
    Not really paying attention on accuracy but with iron sights at 50yds, not bad with loose brass.
    Ejection was consistently between 3-4 o'clock but seems undergassed at times most likely due to low charge.
    Li'l Gun was on the dirty side & probably get worse suppressed so will experiment on other 'whisper' powders. No visual leading on the bore & running a mop on the gas line seems to be ok as well.
    Will fireform some more with my own PC cast.
    ...Speak softly & carry a big stick...

  6. #6
    Boolit Mold
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    What load?

    Quote Originally Posted by Sig556r View Post
    Fireformed some 7.62 brass to 9.3mmx39 last night.
    Jamming the projectile to the lands did pose a few ftfs, but all in all, was able to form a couple of hundreds.
    Not really paying attention on accuracy but with iron sights at 50yds, not bad with loose brass.
    Ejection was consistently between 3-4 o'clock but seems undergassed at times most likely due to low charge.
    Li'l Gun was on the dirty side & probably get worse suppressed so will experiment on other 'whisper' powders. No visual leading on the bore & running a mop on the gas line seems to be ok as well.
    Will fireform some more with my own PC cast.
    What loads are you using on Missouri bullet 9.3? I just ordered some. And what mags are you using. D&H is making mags for 9X39 and are supposed to send two to me for testing. They are just about to start manufacturing (note on their website is wrong about timing). Using KAK dies I bought when they had 25% off. I have gotten tired of fire forming using jacketed bullets. skeettx is right about extending out to the rifling. And you have to load them one at a time. I love this round so much that I have three AR uppers and a bolt gun built on a black collar arms chassis. All using KAK barrels. I, too, am suppressing and using a Griffin Optimus with tri-lug adapter. I am using the KAK recipe for fire forming but even the cheapest Nosler Accubond jacketed like they use are too much at half price of $25.45 for 50. (Shooters Pro Shop sells Nosler seconds).

  7. #7
    Boolit Master

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    Quote Originally Posted by mhames View Post
    What loads are you using on Missouri bullet 9.3? I just ordered some. And what mags are you using. D&H is making mags for 9X39 and are supposed to send two to me for testing. They are just about to start manufacturing (note on their website is wrong about timing). Using KAK dies I bought when they had 25% off. I have gotten tired of fire forming using jacketed bullets. skeettx is right about extending out to the rifling. And you have to load them one at a time. I love this round so much that I have three AR uppers and a bolt gun built on a black collar arms chassis. All using KAK barrels. I, too, am suppressing and using a Griffin Optimus with tri-lug adapter. I am using the KAK recipe for fire forming but even the cheapest Nosler Accubond jacketed like they use are too much at half price of $25.45 for 50. (Shooters Pro Shop sells Nosler seconds).
    D&H mags are a bust, lotsa complaints especially with the hype & expectations prior to release.
    I did use KAK loads with fireforming but I bumped them a tad to ensure cycling.
    Missouri 9.3s are $0.22/ea at Graf's
    ...Speak softly & carry a big stick...

  8. #8
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    Always wondered about short chambering a barrel with a 35 Rem Reamer and using X39 brass and cut down 35 Rem dies, then the 350 Legend came along and the project got shelved for now

  9. #9
    Boolit Master

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    Quote Originally Posted by rockrat View Post
    Always wondered about short chambering a barrel with a 35 Rem Reamer and using X39 brass and cut down 35 Rem dies, then the 350 Legend came along and the project got shelved for now
    Thought about the 350Legend for a while but I still preferred bottlenecks on my DI AR.
    Recent issues with rim-extractor incompatibility for the 9x39 kinda explained the hard-extraction regardless of care in sizing brass.
    Looks like someone needs to figure out a matching extractor or re-rim headspace for standard 7.62x39 bolt to smoothen extraction.
    ...Speak softly & carry a big stick...

  10. #10
    Boolit Mold
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    Look up Type I & II Grendel bolts. The best option is to recess the bolt case more so there is more extractor. From what I've read, that is what Colt and the better Grendel bolts are, but most 7.62x39 bolts and barrels are not. To use the better bolt, you have to change most 7.62x39 and 9x39 barrels so more case is sticking out. Steel cases might have harder extraction since they don't spring back as much, especially with the straighter 9x39. Higher remaining pressure when the bolt starts to move can also be a problem, which is why timing is more difficult with shorter gas systems.

  11. #11
    Boolit Mold
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    Regarding magazines, I would like to try using Grendel mags with a 2 diameter bullet (like the SIG 300 BLK) that will fit the magazine rib.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check