OAL and crimp questions...

[SpeedQuest]

Hey guys. Got my NEW XL650 almost 100% now. I am just waiting on a powder scale so I can begin dropping powder. In the meantime, I have been toying with the different stations and trying to establish my dies.

I am shooting a Springfield XD SubCompact 9mm.

Here are the components I am using:

MG 124 JHP

Used Remington range brass

Eventually, I will be using Alliant E3 powder and Winchester SP primers once I get the powder measuring calibrated.

Here's my question. I 'built' a round with an OAL of 1.120 after reading some of the recommendations and 'recipes' posted. However, this won't feed properly in my gun. So I measured the store bought rounds I currently use. They have an OAL of 1.068 - 1.080. Taking a cue from this, I started building rounds at 1.075 and they cycled well. As I 'extended' the length, I eventually found that my gun doesn't like anything beyond 1.099 OAL. Does this sound correct?

The crimp I seem to get is about .378-.379. How's that sound?

All of these powderless/primerless rounds also seem to have a 'Coke' bottle taper to them in that they bulge at the top, taper in the middle and then resume normal size at the bottom. They measure .385-.386 at the bottom, .373-.375 in the middle, and .378-.379 at the top. What causes this and is it acceptable?

I have been using the Dillon 9mm Case Gage to test all of these rounds and some were definitely 'tight' as the round reaches the last 1/32"-1/16". Running them through stations 4 & 5 a second time, seemed to eliminate this.

Also, as a side note, I am wondering how 'short' OAL is too 'short'? Will shorter OAL raise pressures and therefore speed?

Obviously the factory rounds that I have some measure 1.068 and still work.

Enough for now though. I appreciate you guys assistance!

[GrumpyOne]

Hey guys. Got my NEW XL650 almost 100% now. I am just waiting on a powder scale so I can begin dropping powder. In the meantime, I have been toying with the different stations and trying to establish my dies.

I am shooting a Springfield XD SubCompact 9mm.

Here are the components I am using:

MG 124 JHP

Used Remington range brass

Eventually, I will be using Alliant E3 powder and Winchester SP primers once I get the powder measuring calibrated.

Here's my question. I 'built' a round with an OAL of 1.120 after reading some of the recommendations and 'recipes' posted. However, this won't feed properly in my gun. So I measured the store bought rounds I currently use. They have an OAL of 1.068 - 1.080. Taking a cue from this, I started building rounds at 1.075 and they cycled well. As I 'extended' the length, I eventually found that my gun doesn't like anything beyond 1.099 OAL. Does this sound correct?

The crimp I seem to get is about .378-.379. How's that sound?

All of these powderless/primerless rounds also seem to have a 'Coke' bottle taper to them in that they bulge at the top, taper in the middle and then resume normal size at the bottom. They measure .385-.386 at the bottom, .373-.375 in the middle, and .378-.379 at the top. What causes this and is it acceptable?

I have been using the Dillon 9mm Case Gage to test all of these rounds and some were definitely 'tight' as the round reaches the last 1/32"-1/16". Running them through stations 4 & 5 a second time, seemed to eliminate this.

Also, as a side note, I am wondering how 'short' OAL is too 'short'? Will shorter OAL raise pressures and therefore speed?

Obviously the factory rounds that I have some measure 1.068 and still work.

Enough for now though. I appreciate you guys assistance!

Ok, first, you want the coke bottle effect. Do a search on here and you'll see the same question asked h7ndreds of times. The coke bottle effect prevents bullet setback, a good thing.

Second, with the OAL you are comparing apples to oranges. If the bullet you are loading has a different profile than the factory bullet, the OAL will be different. The shoulder of the bullet may extend further into the barrel than others and it may be hitting the lands. You can only compare OAL of your round if you are using the exact same bullet as the factory.

Third, drop the case gauge. Take the barrel out of your gun and use it instead....after all, that's what you'll be shooting them in, not the case gauge.

Fourth, you can go too short. As the bullet gets set deeper and deeper (with the same powder charge) pressures go up exponentially, and can cause catastrophic results. If you shorten the OAL, back off the powder charge.

Fifth, you aren't really crimping the bullet, just removing any bell\flair you put into the case to aid in seating the bullet. For your measurement, measure the diameter of the bullet, and the case wall thickness. Multiply the case wall thickness x 2, add the diameter of the bullet. That should be your crimp.

[GrumpyOne]

With the JHP, the shoulder will make the OAL shorter as the shoulder will hit the lands. My OAL for the same bullet in my Shadow was 1.085, but with a 147 rn, it's 1.150...and it could go longer.

Edited June 4, 2013 by GrumpyOne

[CZ85Combat]

Well you need to read this. This was for a 40 S & W but will work for all cal. Copied from a post by WOBBLY @ czforum

Well, books and help line people can certainly be valuable, but there's no substitute for knowing exactly how your bullet interacts with your barrel. As I said, the XTP is special and your CZ chamber is also special. So let's not guess, let's find out EXACTLY. Sound good?

There are several ways to do this, but here's my method.... Fit a new bullet into a fired case. (No powder; fired primer.) If you try 2 or 3 bullet/case combinations you'll end up with 1 or 2 where the bullet is a snug "push fit". Set the bullet out to an OAL of like 1.300". Any OAL longer than what you need. Working with your barrel REMOVED from the gun, slide this "test cartridge" into the chamber. At some point it will stop going into the chamber. In other words, whatever the bullet is striking is keeping the test cartridge from going all the way in. At this point, if you continue to push, the bullet will slide back into the case until the mouth of the case comes to rest on the end of the chamber. So whatever the bullet was striking has pushed the bullet back into the case. Follow?





Now, slowly and carefully withdraw the test cartridge and measure its new length. Do this with other bullets and other cases until you start to see the same number again and again. That measurement is your exact chamber length for that bullet in that barrel. Now of course we need a set-back distance off the rifling, so subtract at least .015" from that number to obtain your maximum OAL.





So let's assume your test cartridge keeps giving you a number like 1.177". We subtract our setback and get 1.177" - .015" to equal 1.160". You see I've backed off an additional .002" because 1) it's simply easier to read on a caliper, 2) the chances of finding a load for 1.162" is impossible, whereas 1.160 is probably pretty good, and 3) we're talking less than a human hair, so gee whiz give it a break!

With an OAL like 1.160" you can use any load for 200gr jacketed that is equal to or shorter than. So the load for the 1.155" from Hodgdon will work nicely. Can you follow all that? I hope so. Now you are armed with EXACT knowledge of your firearm and don't have to guess any longer.

[mlmiller1]

Instead of trying to "slowly & carefully" pull your test round out of the barrel without disturbing it's length, you can measure down to it from the muzzle end of the gun. Use a rod or dowel that is a close, not tight, fit to your barrel, slide it down muzzle with no round in the gun until it contacts the breech face. If this gun has a floating firing pin, be sure the pin isn't sticking out the breech face. Now, make a mark on the dowel exactly at the muzzle end. Then use your test round & follow all those previous instructions until you get the slide completely closed. Now slide your dowel down the barrel gently, mark the exact end of the muzzle again. Pull out the dowel, measure the distance from one mark to the other & you will have the maximum length round you can run in that gun with that bullet. Now, for reliability sake, take .015" or so off this length to make reliable length ammo that should always fit in this gun. You really don't want to run your bullet into the lands of the rifling as pressures build fast when you do so, therefore for reliability & SAFETY sake take off .015" or so.

Try that, in my mind it is a little easier than trying to pull the test round out very carefully without disturbing the length. Of course, you can do either or both just for double checking sake.