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Posted: 12/2/2009 7:54:17 PM EDT
| Can someone please tell me what the average/standard flash hole diameter is for the .50 bmg ? I've been looking for several hours now online and in my various cartridge books and can't find it anywhere. I'm going to get a machinist friend of mine to make me a decap die and need to know. Also the approx. length the decap pin needs to be to make it thru the case head would be nice to know. I don't have an empty case yet nor reloading dies to get a measurement from. Thank you. |
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Per your post above, you're way ahead of yourself. Just get a die set to punch the used primer and reload the brass and then get a K&M or another high end viable hole debur tool.
You don't need a custom made tool set. Do more research and save yourself a bunch of time, money and headaches. Regards, SOG |
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Flash hole diameter in the half dozen different year cases measures approx. .138-.142 with one SL43 case with a flash hole diameter at .136". I use a 1/8" diameter pin in my handmade punch to punch the primers out. The pin needs to extend "out" of the punch a minimum of .750" to get the spent primer out of the case as the crimped in primers tend to stretch and the flat head of the primer bulges out . If that dimension of .750" sticking out of the rod is too long the pin can always be shortened. The decapping pin in my RCBS sizing die is approximately .093" in diameter and the overall length is 1.200" removed from the decap rod. It only sticks out of the rod about .475" and I have had a few primers that wouldn't come out of the pocket because of a tight primer crimp and the primer head stretching. Primer pocket depth on a 50 case is approximately .220". The primer pocket diameter is approx. .311-.312" while the primer diameter themselves are about .316". Now a primer pocket without the primer crimp removed will vary as the crimp amount varies. My 1/2" rod for my decapping punch works fine but some bent case necks have to be straightened before the punch will go into the case. I'd of course have a couple extra pins made plus the decap die should be made so that pins could be replaced if bent or broken. Once fired military cases can be .030-.040" longer than the trim length of 3.910" One case I measured is 3.940" long before trimming. Distance from the mouth to the inside bottom of the case is approx. 3.610" but the bottom is not flat . Thickness of the case head from inside to outside is about .330 at the flashhole but as said the bottom tapers at the case walls. Don't know exactly what you're making but hope this helps. Don't blame me if these dimensions don't work.
These dimensions are approximate and I don't have a print of a 50 BMG case handy either. I do highly recommend a primer pocket uniformer such as the K&M tool to uniform the depth of 50 BMG primer pockets. |
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SOG-sniper - No, I'm not ahead of myself. I've been reloading many different calibers for over 40 years, just new to the .50. I always decap brass & tumble before I do any other work on the brass, I use the RCBS universal decap die. Sizing & expanding go so much smoother and dies stay alot cleaner when working with clean brass. I just happen to have a machinist friend that will make a simple decap assembly for the press for free so why not ?
Skip |
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rg1 - Thank you very much for all the info. I looked in my reloading books, Cartridges of the World, and a couple others with drawings and none gave flash hole dimensions. My machinist is going to make a simple 1.5"-12 punch holder to go in the press and make the punch & replaceable pins. I'm thinking the punch diameter should be around .509 - .510" and have a slight taper at the end to help get it started in a neck that might have a small dent etc. in it. The decap pin will be held in the end of the punch with a recessed set screw in the punch. Very basic rig but I needed the specs to get him started on it. We'll figure in variances between cases for actual pin diameter & length etc. and adjust as necessary. I realize a simple hand punch is all you need but I like decapping in the press and this won't cost me any money. I decapped by hand for many years with my Lee Loaders back in the 1960's as a teen - also primed with that Lee rig - I remember the occasional detonated primer when I didn't hold my ass just right too, tapping that primer in !! I learned quick not to keep excess primers or powder on my reloading bench.
Thanks again for the info. Skip |
| While a decap rod at .309-.310 would work it might be a little big. Fired cases vary in inside neck diameter from about .314-316 in the few I measured. The dents from military once fired cases can and will be smaller than .309" That would mean that a straight rod would drag on the dents for the entire stroke. Even my .500 rod does. Possibly a stepped or recessed rod would work better? Plus for an off-center flash hole it wouldn't have any play? So I wouldn't make the decap rod .309-.310 for the entire length. The tapered end of the rod is a good idea. Just something to consider. |
| Geo.Az doesn't post here but makes some really good tools for reloading, here's a link to follow http://www.biggerhammer.net/barrett/wwwboard/index.cgi?read=222050 from there you can search the board for him. There are pictures of all his tools posted, you just need to do the leg work and find them. |
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Geo.az 's decap rig is exactly what I had in mind. Since my last post I've also found a guy with a bunch of .50 reloading equipment for sale at what seems like a great price that I'm considering and part of the equipment list includes one of Geo.az's decap rigs. It just so happens this guy lives about 50 miles from me and I'm going to check the equipment out within the next couple of days.
I appreciate all the responses from everyone - I'm sure I'll have more questions as I get into this new caliber more. It's a slow go, I've had my rifle for about 2 months now and still haven't got to shoot it yet, just been too busy for recreation. I just ordered scope rings (thought I had some ) and hopefully can get the rifle ready to shoot by next weekend or so. Skip |
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