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OAL for accuracy

This is a discussion on OAL for accuracy within the The Ammo Can forums, part of the Armory Talk category; You have to remember that OACL can't exceed the max. OACL recommendation because your rounds won't fit the magazine and may be too long for ...


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Old 01-21-2013, 09:41 PM   #11
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You have to remember that OACL can't exceed the max. OACL recommendation because your rounds won't fit the magazine and may be too long for the chamber unless you're using a custom pistol like a 1911. Your cast lead loads have to be shorter than the max. allowable for the chamber, where the bullet first contacts the lands. Like I said earlier, shorten by .005 - .010". Then you have to make sure that the load fits the magazine.

For most SWCs, I used 1.135".
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Old 01-21-2013, 11:11 PM   #12
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Originally Posted by MTgrizz View Post
After some trial and error, I cannot get my 155 gr SWC lead bullets to contact the rifling at all. The rounds get long enough that they will not fit in the magazine.

I loaded a couple long dummy rounds and dropped them in the chamber to see if I could get contact. The long rounds would not eject when I tried to clear the chamber. I suppose I can play around with a couple .001 and see what happens, but it doesn't look like there is much room to play with oal in my XDM.
Pistol bullets jambed into rifling offers you nothing but problems. At the worst, pressure spikes, at teh least, a round that sticks in the bbl & when you have to hand cylce it out, it either jambs or leaves the bullet in the bbl & spilled powder in the gun. Get it out of your head that you gain any accuracy advantage trying for this, you do NOT.
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Old 01-22-2013, 01:48 AM   #13
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Loading long in any particular pistol caliber only gets you some reduced pressure effects. In my experiments I do not notice much if any accuracy difference from various OAL/bullet combinations. The common wisdom about loading as long as the chamber will allow is viable only insofar as it reduces slightly the pressure from maximum loadings.

However, pressure can and does INCREASE if your pistol bullet is touching or is too close to the lands. Pistol powders are not like rifle powders. They are, as a class, much faster than rifle powders, and if the bullet is touching or very close to the rifling in the barrel, then the bullet cannot move sufficiently at the start of the combustion process to give the proper pressure cycle.

Do not load pistol bullets into the lands. You will spike pressures beyond what the "book" tells you you should expect, and if you are loading near the maximum things could go wrong.
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Old 01-22-2013, 04:09 PM   #14
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JSG is correct, at a given powder charge, the longer the OACL, the lower the pressure will be. It might be slight in some cases, depending on the powder used, but if you're loading near or at a max. charge, it can help to keep your handload from exceeding the max. recommended pressure.

The only time a bullet should touch the lands is with a "dummy" round where you put a bullet into an inert/fired case, put in the chamber and push by hand or very light taps with a plastic mallet until the case stops. Remove the bullet and measure for OACL. Repeat the process until you've done it about 5 times to make sure the OACL is consistent. That is the MAX allowable OACL. Then you reduce that OACL when you begin loading/seating by .005 - .010", or in the case of the .40 S&W, 1.125" for JHPs, 1.135" for LSWCs should work just fine.
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Old 01-22-2013, 06:41 PM   #15
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An easier way to measure that max COAL is put an empty case in the chamber, close it, measure w/ a rod down the bbl & mark the rod. Then put just a bullet in & hold it in place against the lands. Now measure that w/ a rod again. Then just subtract the diff. Easier & more accurate IMO, works for rifles & pistol.
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Old 01-22-2013, 10:18 PM   #16
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Sounds good in theory, fred, but you lost me on the accuracy part when you said "mark the rod". That would take some pretty accurate marking.
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Old 01-23-2013, 12:24 PM   #17
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I did not intend to load any live ammo with a bullet touching the lands. I was referring to finding the length that just touches the rifling, and then backing off to set OAL for live ammo. It doesnt seem to matter as the max length the magazine can accomodate is the limiting factor in my pistol with this bullet. Thanks to everyone for the replies.
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Old 01-23-2013, 04:17 PM   #18
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Yeah, I think some of us jumped the gun and thought you were talking about ammo you had loaded. Sounds like you have a handle on it and in this case the magazine is the limiting factor. I've used 155 and 170 gr. SWCs in my forties and after establishing that the length wasn't too long I loaded them to 1.135" and got very good results. Particularly with a CZ 75B in .40 S&W.
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Old 01-23-2013, 04:22 PM   #19
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On bit of advice, LSWC are tricky. My XD doesn't like them too long. They have to be seated just at the edge of where the wadcutter starts otherwise I'll get failures to feed.
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Old 01-23-2013, 05:41 PM   #20
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Sounds good in theory, fred, but you lost me on the accuracy part when you said "mark the rod". That would take some pretty accurate marking.
See, we are back to that discussion of accuracy in dims. A fine line SHarpie is plenty thin enough to mark a rod. Then of course one has to be able to measure & read calipers correctly. All within 0.002" tolerance & your gun/load will not know the diff. What you are trying to do is get off the lands, so add 0.01" & you are way good to go.
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