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Modding 300BLK cases to take Large Rifle Primers


StuBeef302

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Anyone have any experience in opening up a 300BLK primer pocket to take a large rifle primer?  I can't find any small rifle primers AT ALL.  and I really want to throw some 300BLK downrange.  I have plenty of large rifle primers.  I have a lathe to make the primer pocket perfect size and depth, I also have access to CAD and can do an analysis of the strength of the altered brass, but in general, the chamber and bolt face take all the load.  I'd start low on powder and work up looking for pressure sign, so I'm not trying to be stupid, but any thoughts would be appreciated. 

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No experience...

 

but I have to wonder....

 

7.62X39 takes large primers right?

 

getting a 7.62X39 bolt, barrel and mags might be easier than machining brass for primers....

 

 

that said, Hornady does make primer crimp removal tools (bits) that can be chucked in a drill.

 

I don’t know if a large Hornady reamer would actually enlarge a small primer pocket.

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Thanks Chills, I wasn’t planning to mod a ton, maybe 100 rounds.  Good point about 7.62x39, I just am all setup for reloading the 300BLK and I use it for hunting and home defense so I just wanted the trigger time on that particular gun.  And reloading is a fun past time. Just those darn small primers are unobtainable. (Except from gougers on GunBroker. Even though that makes $ and time sense over modded cases too 😂)  I’ll give a batch of 10 a go and see how they turn out.  Thx.

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Whoops!

 

with respect to my comment up above... 

 

that’s ASSuming you could find any factory 7.62X39 ammo to start out with or once fired brass.

 

which is probably just as UNobtanium as small rifle/small pistol primers now.

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If you are not loading "HOT" you could try using small pistol magnum primers. For the AR15 it is recommended to use primers with a cup thickness of .025 to help prevent slam fires. "BUT" many reloaders use the CCI 400 primers without ill effect.

 

CHOOSING THE RIGHT PRIMER - A PRIMER ON PRIMERS

http://www.sksboards.com/smf/index.php?topic=56422.0

 

CCI 400 -thin .020" cup, not recommended for AR15 use by CCI/Speer.  Good for .22 Hornet, .30 Carbine.  See Note 1 at the bottom of the page

 

NOTE 1:  According to Speer/CCI Technical Services - Both the CCI 550 Small Pistol Magnum and CCI 400 Small Rifle primers are identical in size.  Both primers use the same cup metal and share the same cup thickness.  Both primers use the same primer compound formula and same amount of primer compound.  They can be used interchangeably.

 

QJM65zp.png

 

 

Edited by bigedp51
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Here's what we know so far, it's easy to do with a Rcbs trim mate using Lyman large primer tool and a Rcbs large primer carbide tool.   Going to do ten and just shoot the cartridge with primer and TB plugging the end.   Next will be with wax bullets.   Start with the Lyman first (one on the right)

 

MY TEST will be done with a Bolt GUN not an AR.

C43F9956-E468-45F2-90B4-3523627DAE4D.jpeg

Edited by dannyd
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I did model a 5.56 case up in CAD to run a pressure simulation, but quickly realized that there is significant head thickness variation from manufacturer to manufacturer.  So much that some thinner ones with small primer pockets yield more than thicker ones with large primer pockets.  So as far as head strength, that shouldn’t be a significant issue when using thick brass.

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  • 1 month later...
  • 1 month later...

Thinking out loud on this idea...For wax bullets you may be fine but I would be a little concerned that your idea “could” reduce the thickness of the surrounding primer pocket brass thus possibly causing the rear primer area of the case to rupture if you intended to try this with real 1000 fsp loads....

 

Please know - I do not claim to know or understand the difference in the amount of material that surrounds the primer pocket but I would think removing this much brass could prove to “weaken” the structure of the brass case in this area...

 

Interested to read your trial results with hopes that you and dis-prove my aforementioned concern....

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Hi p226, I did mention above that I analyzed that already 

On 11/11/2020 at 7:47 PM, StuBeef302 said:

I did model a 5.56 case up in CAD to run a pressure simulation, but quickly realized that there is significant head thickness variation from manufacturer to manufacturer.  So much that some thinner ones with small primer pockets yield more than thicker ones with large primer pockets.  So as far as head strength, that shouldn’t be a significant issue when using thick brass.

But!  It’s been the pit of winter for a couple months where I live, but we should have a few above freezing days in a row, I’ll get out and post some pics.

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5 hours ago, Sigarmsp226 said:

Thinking out loud on this idea...For wax bullets you may be fine but I would be a little concerned that your idea “could” reduce the thickness of the surrounding primer pocket brass thus possibly causing the rear primer area of the case to rupture if you intended to try this with real 1000 fsp loads....

 

Please know - I do not claim to know or understand the difference in the amount of material that surrounds the primer pocket but I would think removing this much brass could prove to “weaken” the structure of the brass case in this area...

 

Interested to read your trial results with hopes that you and dis-prove my aforementioned concern....

I does weaken the brass, so the number of times it can be reloaded may go way down.  Haven't tried them yet also working on large rifle in 357 magnum cases.  In 1935: 357 magnum used large primers, so I will be checking it out.

Edited by dannyd
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Thanks Danny for responding. Again do not claim to know what I am talking about. Was really asking more than stating I knew...Mark

 

Stu - Thanks Sir for your response. The first time I read your post I was thinking “head” being the projectile end of the brass. After re-reading your post I realize your post addressed my post thoughts.  Thanks for not slamming me for my mis-post....

Edited by Sigarmsp226
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