OAL change due to tumbling with light taper crimp


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bds
January 20, 2010, 09:52 PM
From what I read on THR and other forum threads, the concern over powder breakdown seemed to apply to really older powders and not for newer modern smokeless powders.

Thanks to all the posters who have devoted much time and effort proving modern smokeless powder DOES NOT break down even after 24-48 hours of continuous tumbling. I used to tumble my loaded rounds for about 20-30 minutes, but now I feel much comfortable tumbling my loaded rounds longer to remove lube from lead bullets and making jacketed/plated bullets even more shiny (shiny bullets don't improve my shot groups, but make my smile bigger). :D

As to slight increase in chronograph speed, I think this is worth verifying whether the bullets are being seated deeper during the tumbling process with other bullets acting like "tiny jack hammers".

One variable is the amount of taper crimp used by different reloaders. Perhaps the real concern over tumbling loaded bullets has more to do with lightly taper crimped bullets being seated deeper causing increase in chamber pressure.

Would you consider doing some additional tests using different taper crimps and measuring OAL and recording chrono speeds?

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Canuck-IL
January 20, 2010, 10:06 PM
Taper crimp doesn't maintain the OAL length - neck tension does.
/Bryan

bds
January 20, 2010, 10:15 PM
Canuck-IL, yes I do agree. That's why I am curious just how much affect it has on tumbling after loading.

From reading other THR threads, I am comfortable knowing that tumbling loaded rounds DO NOT break down powder to increase chamber pressure.

I am trying to verify whether tumbling will decrease the OAL enough to significantly affect my shot groups for range practice/match shooting. I am guessing that if OAL is affected, the affect will not be equal for every round.

Also, I wonder if different bullet types (jacketed vs plated vs lead) have different response to tumbling.

bds
January 20, 2010, 10:47 PM
I believe if the taper crimp was sufficient, there would not be any problem. Concern is for "lightly" taper crimped bullets possibly being seated deeper in an over-loaded tumbler.

Many new reloaders read THR threads and may be lead to believe that tumbling ANY loaded rounds in a vibratory tumbler for an extended period of time maybe safe.

What if someone, after reading THR threads, buys some older looking reloads at a gun show and dumps them into an over-loaded tumbler. What if the reloader used old stock powder and light taper crimp that decreased the OAL of the rounds during the tumbling thus increasing the chamber pressure.

bonez
January 20, 2010, 11:00 PM
What if, what if, what if? You can take the question to ridiculous lengths. In order to move the bullet in the case you need to overcome the inertia of the bullet/case mass, AND overcome the neck tension, AND overcome the crimp tension. Not going to happen in a home vibratory cleaner, not enough force applied. IMO you are worrying about something that is not going to happen.

With this kind of outlook, I am surprised you shoot. you are much more likely blow up your gun with a factory loaded cartridge than move a bullet enough to cause you any issues in a vibrating tumbler.

bds
January 20, 2010, 11:39 PM
bonez, the thread question was OAL change due to "light taper crimp".

As to "what if", consider this:

As part of my quality control steps for reloading, in the past, I have found when I checked the crimp on my and other reloaders' loads by pressing hard on top of the bullets - some of them moved. This was done to duplicate the force a round goes through being pushed by the slide against the ramp (force of the slide against the round/ramp is quite hard during cycling).

When was the last time you pressed hard on a reloaded round to check the quality of crimp? I think we simply increase the crimp on the bullet until we can't move the bullet if we find the crimp insufficient. I think I may do OAL measurements before and after the reloads are chambered (once and several times) to see if there is a decrease in OAL as another quality control step.

If the crimp is light and not tested, especially for a 9mm case which is wider on the bottom of the case, tumbling may decrease the OAL (especially for the shorter 115 gr bullet) which will loosen the bullet crimp even more. During chambering, the force of the slide on the ramp may drive the bullet deeper into the case leading to increased chamber pressure. This will affect velocity and shot group accuracy.

ljnowell
January 21, 2010, 12:06 AM
If the case is good, taper crimp is irrelevant. Neck tension is what matters. This is a moot point.

bds
January 21, 2010, 12:15 AM
http://www.exteriorballistics.com/reloadbasics/crimp.cfm

Taper crimping is the best choice for any firearm which headspaces on the case mouth. Cartridges intended for use in self-loading pistols, such as the .45 ACP, should never be given any type of crimp other than a taper crimp. Because of the method of headspacing on the case mouth, a slight ledge must be left to provide positive positioning of a chambered round.

On these cases, the use of a roll crimp will result in poor ignition, unreliable functioning, and reduced accuracy. Few bullets designed for autos have cannelures, limiting the amount (and type) of crimp that may be applied. On any bullet, if the crimp being applied is heavy enough to cause any visible deformation, you are over crimping! Over doing the crimping reduces accuracy, so we strongly recommend using only the degree of crimp required for your particular loading application.

Regardless of which type of case a crimp is applied, one of the primary reasons for crimping remains the same; to increase neck tension, thereby ensuring proper powder ignition. In many cartridges, such as the .357 and .44 Magnums, large charges of slow-burning powders like H110 and Winchester 296 require firm initial resistance to the bullet’s movement. This building pressure aids in giving complete combustion, enhancing accuracy and shot to shot uniformity.

A firm taper crimp on ammunition intended for use in an autoloading firearm is intended to do exactly the opposite; to prevent the bullet from being forced deeper into the case during the feeding cycle.

Walkalong
January 21, 2010, 12:20 AM
Neck tension is what matters. This is a moot point.

Yep.

Tumbled vs non tumbled. Measured rounds were no different. I used very light neck tension and a sizer .002 larger than I normally use.

http://www.thehighroad.org/attachment.php?attachmentid=113800&d=1264050691

See it here (http://www.thehighroad.org/showthread.php?t=498890)

.

Walkalong
January 21, 2010, 12:22 AM
one of the primary reasons for crimping remains the same; to increase neck tension, thereby ensuring proper powder ignition.
It does not increase neck tension. It only affects a small amount of the "neck" holding the bullet. It increases bullet pull which aids in powder ignition etc.

No amount of crimp can make up for poor neck tension. It is only an aid to proper neck tension.

bds
January 21, 2010, 02:30 AM
Thank you walkalong.

mongoose33
January 21, 2010, 01:22 PM
Here's the part I don't get: People seem to think the bullets, if they move at all, are only moving deeper, not shallower.

I'd expect the opposite. Wouldn't pushing in increase the friction from neck tension, and thus be harder to do, than pulling action which would decrease teh amount of neck in contact w/ the bullet.

Wouldn't it require more force to seat, say, a 147gr 9mm bullet than a 115 or even lighter bullet, since there's more bearing surface in contact w/ the case? And thus, more force to push it further in than bring it out?

I've seen Walkalong's results, which reinforce my belief that there's nothing wrong w/ tumbling them for a while. However, I think it odd that the expected change would be deeper, rather than shallower.

rcmodel
January 21, 2010, 01:41 PM
All I can say is, if you can push a bullet deeper in a case without hurting your hand, you don't have enough neck tension to safely use the ammo.

And a taper crimp, as used on auto pistol ammo, is not at all the same thing as a roll crimp used on revolver ammo.

Excess taper crimp can actually make the bullet looser in the case, not tighter.

The reason is, the brass is more elasic then the lead bullet.

You can squeeze it down below bullet diameter, then the brass springs back slightly, but the lead doesn't.

A roll crimp "rolls" into a cannulure or crimp groove built into the revolver bullet, and the bent over case mouth has no effect on squeezing the bullet like a taper crimp does.
It in fact does add considerably more force to keep the bullet in place.

The bottom line is, if you are trying to use a taper crimp to make up for insufficient case neck tension on an auto-pistol round, you are doing it wrong!

rc

Vitesse304
January 21, 2010, 02:09 PM
quick question...how do you improve neck tension? I've got a few .38 spl cases where a .357 lead DEWC will just slide down into the case with finger pressure where some won't. These are all being resized by the same die, but for some reason, some of them don't have the same neck tension!

243winxb
January 21, 2010, 02:15 PM
.how do you improve neck tension? Smaller diameter expander button. Or a FLRS die that sized the brass down more. Depends on what one is not doing its job correctly. Take measurements. Case wall thickness is different between brands of brass, so the flrs die must oversize (make to small) the brass.Expander open it to the correct inside dia.

243winxb
January 21, 2010, 02:18 PM
modern smokeless powder DOES NOT break down even after 24-48 hours of continuous tumbling. I need proof on this one. Anytime the size/shape or coating on the powder is changed, the burning rate can also be changed. Deterrents coat the exterior of the propellant granules to reduce the initial burning rate on the surface as well as to reduce initial flame temperature and ignitability. The coating also broadens the pressure peak and increases efficiency. http://www.fbi.gov/hq/lab/fsc/backissu/april2002/mccord.htm#table1 The powder used in Hornady's new Superformance ammo would seem to be even more sensitive to tumbling. As far as OAL, i dont think a bullet with 35 lbs or more bullet pull is going to move any (5.56mm). http://www.bradfordherrick.com/sitebuildercontent/sitebuilderfiles/m855.pdf

bds
January 21, 2010, 02:54 PM
243winxb, plenty of posters/threads have done tumbler tests to prove this. Just do a forum search for tumbling loaded bullets http://www.thehighroad.org/search.php?searchid=6995265

Walkalong is doing some chrono test post 24-48 hour tumbling on this thread:
http://www.thehighroad.org/showthread.php?t=498890

rcmodel
January 21, 2010, 02:56 PM
I need proof on this one.Good grief man!
Haven't you been following this thread to it's logical conclusion?
http://www.thehighroad.org/showthread.php?t=498890

One more time again, tumbling doesn't break down powder.

rc

243winxb
January 21, 2010, 03:05 PM
i read, saw no proof. Goverment or military testing is need. http://www.fbi.gov/hq/lab/fsc/backissu/april2002/mccord.htm#table1 Shape and size have a profound effect on the burning rate and power generation of a
powder (Meyer 1987). Deterrents coat the exterior of the propellant granules to reduce the initial burning rate on the surface as well as to reduce initial flame temperature and ignitability. The coating also broadens the pressure peak and increases efficiency.

bds
January 21, 2010, 03:24 PM
243winxb, this thread is concerning "OAL change due to tumbling with light taper crimp" and not with powder breakdown.

Since other threads/tests have shown insignificant powder breakdown for longer time (24-48 hours) than what I plan to do (about 30 minutes), I am more focused on why there was slight increases in chrono speed of tumbled rounds.

I am trying to verify if this was due to bullets being seated deeper during tumbling and if this is the case, verify the cause (I am theorizing light taper crimp).

I am also interested in taper crimp vs slide/ramp affect on OAL to see if this may have caused the increase in chrono speed.

I added the "slide/ramp affect during cycling" to my title to clarify the objectives of the thread.

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