zhunter Posted December 21, 2015 Share Posted December 21, 2015 How important is it to have a round plunk and spin when inserted in the chamber? I am working on "perfecting" my ammo and it's accuracy. Currently my bullets do not spin, so I am testing shorter OAL's. So it this a big deal for improving accuracy? Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted December 21, 2015 Share Posted December 21, 2015 Nothing to do with accuracy. If your rounds won't PLUNK, they might not feed - it's really all about feeding reliability. I'd keep shortening the rounds until they pass The Plunk Test, and then back them off just a little bit more, since OAL will vary from round to round. Link to comment Share on other sites More sharing options...
zhunter Posted December 21, 2015 Author Share Posted December 21, 2015 Nothing to do with accuracy. If your rounds won't PLUNK, they might not feed - it's really all about feeding reliability. I'd keep shortening the rounds until they pass The Plunk Test, and then back them off just a little bit more, since OAL will vary from round to round. I've been shooting non-plunking rounds all year, they feed fine and shoot well. I'm just looking to perfect my ammo Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted December 21, 2015 Share Posted December 21, 2015 My experience is that if your rounds won't spin, eventually you'll get a FTF - slide won't completely close and you will have to clear the "jam". Are you plunking in your own chamber? Link to comment Share on other sites More sharing options...
GrumpyOne Posted December 21, 2015 Share Posted December 21, 2015 Having the round not "plunk" may mean that the OAL is too long...while it may cause feed issues, if you are running anywhere near a max load in a fast powder, it may cause more than just the feed issue, it may cause case rupture because of the extra pressure of the bullet head sitting on the lands. Link to comment Share on other sites More sharing options...
C-Money Posted December 21, 2015 Share Posted December 21, 2015 I had some not pass plunk test... and blew my gun up (slightly). Tanfoglio and I would bet CZ guns can fire slightly out of battery. I do mean slightly. By having bullets hit the rifling you might also have problems during ULSC with rounds wanting to stay in the barrel. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted December 21, 2015 Share Posted December 21, 2015 may cause case rupture because of the extra pressure of the bullet head sitting on the lands. Yeah - much better response than mine. Thanks Grumpy. :bow: Link to comment Share on other sites More sharing options...
bigboy69 Posted December 21, 2015 Share Posted December 21, 2015 When you say plunk do you mean in your barrel or chamber checker? Link to comment Share on other sites More sharing options...
zhunter Posted December 21, 2015 Author Share Posted December 21, 2015 When you say plunk do you mean in your barrel or chamber checker? Barrel I do case gauge, but case gauge does not check OAL Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted December 21, 2015 Share Posted December 21, 2015 (edited) in your barrel or chamber checker? case gauge does not check OAL never mind... Edited December 21, 2015 by Hi-Power Jack Link to comment Share on other sites More sharing options...
bigboy69 Posted December 21, 2015 Share Posted December 21, 2015 Haha, I never heard it called plunk, I heard it called smack or something like that. Link to comment Share on other sites More sharing options...
zhunter Posted December 21, 2015 Author Share Posted December 21, 2015 I will also be switching from a .355 to a .356 bullet. Early testing in my barrel the .356 seems more accurate. Link to comment Share on other sites More sharing options...
Grump Posted December 22, 2015 Share Posted December 22, 2015 Ummm, this is all fine and good so long as the resistance to rotation is caused purely by the bullet contacting the leade. It will never happen if the case is the source of the "sticktion". Then you run the risk of chasing ever-shorter bullet seating all the way into unsafe pressures. UNlikely to blow the gun or the case the first 5 or 50 or 5,000 times, but I wouldn't want to go down that rabbit-hole. I suggest your isolate one variable at a time. With some chamber/case/bullet combinations, going too short on seating will compromise feed reliability by letting the case tip up too sharply, the bullet nose doesn't hit the top of the chamber, and the case wall on the bottom jams on the feed ramp. YMMV, of course, as this is very dependent on the details of the chamber and ramp. But I *have* seen it happen more than once, and going back a bit longer is exactly what fixes that feed problem. Link to comment Share on other sites More sharing options...
zhunter Posted December 22, 2015 Author Share Posted December 22, 2015 I have previsiouly been at 1.10", but at 1.085" I can spin the round in the barrel's chamber. I doubt that 1.085" is going to give me any pressure issues at 132 PF. I have not tested feeding yet. Link to comment Share on other sites More sharing options...
Wheeljack Posted December 23, 2015 Share Posted December 23, 2015 When checking spin, make sure your bullet and the chamber are free of lube. A heavy build up of lube can prevent spin and give the impression that the bullet is too long. Link to comment Share on other sites More sharing options...
IDescribe Posted December 26, 2015 Share Posted December 26, 2015 (edited) ZHunter, the issue with this is pressure, as was previously mentioned. This isn't myth or internet hearsay. This is discussed in reloading books. Because smokeless powder burns faster the more pressure it's under, and it builds pressure as it burns, AND the bullet travelling down the barrel is expanding the combustion chamber which works to relieve pressure, anything you do to decrease or delay the acceleration of the bullet increases pressure. That's what jamming it into the lands does. It delays the acceleration. The little bit of momentum that the bullet develops between the primer detonating and the bullet hitting the lands helps the bullet pass into the lands. By jamming it into the lands, you deny the bullet that momentum.Imagine it this way. You're sitting on a bicycle, and you roll the front tire right into the curb passing from the street into a driveway. With the front tire touching the curb and at a standstill, getting the bike to roll forward takes a lot of force applied to that bicycle pedal. You might have to stand up and put all your weight on that one pedal to get the bike to move forward at all. But if you back the bicycle up a foot from the curb, then pedal, that tiny bit of momentum helps the bicycle climb up and over the curb with ease.It's the same with the bullet jammed into the lands. It takes a lot more pressure to get that bullet moving when it's jammed into the lands than when it's just a few thousandths off the lands, and that extra initial pressure built before the bullet moves and the combustion chamber starts expanding means that you'll reach a higher peak pressure overall. And the effect is not a linear progression. It's a positive feedback loop with a geometric progression. I know it's worked out for you so far, but if you operate under the assumption that that means it's okay, you're teaching yourself a bad lesson, and there might be some future load you develop where the impression that this is an okay practice is the difference between "kick-ass!" and kaboom.You will sometimes find rifle data that specifies the bullet should be loaded into the lands, but when that's the case, the data was developed that way. If that's not specified, you should assume the data was developed with the bullet off the lands, and if you load into the lands, you're going to be at significantly higher pressures than the data would indicate for whatever charge level you are at. Basically, stay out of the lands. Edited December 26, 2015 by IDescribe Link to comment Share on other sites More sharing options...
bigboy69 Posted December 28, 2015 Share Posted December 28, 2015 I had a 38 super that loooooooooooooooooved .356 Link to comment Share on other sites More sharing options...
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