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Showing results for tags '9mm XDM OAL COL first-time'.
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This one is not a question. It's for all the first-timers out there like me. (Everyone here has been extremely helpful. I'm trying to give back a little.) I am determining Maximum Overall-length (OAL, aka COL, aka COAL) for Hornady 115grain Full Metal Jacket Round-Nose bullets (115gr FMJ RN). Maximum Overall Length will be DIFFERENT for each particular chamber-and-bullet combination and must be determined by the user each time. I am making dummy rounds---no powder or primer---in order to find max OAL for my particular gun with this particular bullet, a 9mm XDM 3.8 Full-Size. Note the SAAMI OAL specification for 9mm is 1.169 inches. I make the dummy bullets by carrying them through the full cycle on my RL550B. (Note: The bullets have to be crimped (or "deflared", which is a more accurate description for 9mm) in position 4, or they will move when you try to measure the length.) Shortening things a little, I discover 1.173 inches will pass the plunk test easily on my chamber for this particular bullet-and-chamber combination. A little bit of a surprise since I am over the SAAMI specs by .004 inch. But nope, there's not the slightest hitch anywhere. (A "plunk test" is where you remove the barrel from your gun, drop a round into the barrel's chamber and see if it passes two tests. 1. The round must fall out when the barrel is inverted. 2. The round must spin in the chamber without effort. Try it with a factory round to see how it works.) 1.183 inches, however, does NOT work. Now the question becomes "WHY is this round not passing the plunk test?" I can solve this by using a method I found posted by somebody who apparently works for Dillon. (Don't have the link, or I'd post it.) The method is to take the sticking round, paint it black all over with the Sharpie, put it back in the chamber, and turn it. (My .02. You won't be able to turn it with your fingers. I had to use a pair of pliers.) Pull the round out. Where the round is sticking will have a bright line scored around it. I hereby quote from the post (saved it to a reloading file I'm compiling) 1) scratches on bullet--COL is too long 2) scratches on edge of the case mouth--insufficient crimp 3) scratches just below the case mouth--too much crimp, you're crushing the case 4) scratches on case at base of bullet--bullet seated crooked due toinsufficient case expansion (not case mouth flare) or improper seating stem fit 5) scratches on case just above extractor groove--case bulge not removed during sizing. May need a bulge buster. When I pulled the round out, I had the cutest little circle around the bullet. I attach a picture. The arc you see on the bullet goes all the way around. Case 1, the bullet is too long. Presumably it's hitting the lands. Conclusion. 1.183 is too long. 1.173 works. Max OAL for this particular combination is therefore somewhere between 1.173 and 1.183. 9mm magazines won't feed longer than 1.169". Therefore the OAL I actually use can only be 1.169" or less. I have selected 1.150" to allow for variation. I am informed, and some testing has shown, OAL variation on a 550B can be as much as 0.005". Also: The process of feeding the round causes the bullet to be knocked back deeper into the chamber and therefore decrease OAL. (Anything besides seating that knocks a bullet back deeper into the chamber is called "setback.") On my gun, feeding setback is around 0.001"-0.002". Next: After determining Max OAL, load dummy rounds into magazine and see how well they feed. A lot of the time Max OAL will not feed properly.
