Affect of COL on velocity?

[Bigpike]

Seems like I'm having some difficulty in making Major with my .45 XD, 4".

Loading Clays under a Precision Delta 230gr FMJ. I'm loading to COL of 1.25

Went to the range with a friends chrono yesterday and got these numbers (these are average of high 3 of 10).

3.6 gr. 642 fps for PF of 147.8

3.8 gr 671 fps for PF of 154.5

4.0 gr 715 fps for PF of 164.5

I've got a number of options I think. One is changing powder, but I really like using Clays since it's also my shotgun powder so that simplifies my life.

It was suggested to me that shortening the COL to 1.20 might increase velocity.

Does anyone have any knowledge of just how much of an increase I might get with that adjustment? Any other pros or cons of shortening things up a bit?

Another suggestion was loading up 4.1 grains and 4.2 grains of Clays, but I'm a bit leery of that since the Hogdon manual recommends 4.0 as the max. However I've got no flattened primers or other signs of overpressure.

Any thoughts will be appreciated.

Thanks--Steve

[Sarge]

I don't load 45 or use Clays. But shortening oal will increase velocities but I don't think there is a magic formula to tell by how much.

OAL will affect feeding if too short. I learned that by mistake.

Most powder makers use conservative numbers which quite a few shooters routinely go over and above with caution of course.

Did you search the 45 reloading section?

[dirty whiteboy]

I would try 1.225 first. If you don't want to add powder.

I load to 4.1+ with no issues. This load is still under what used to be run when the PF was required to be above 165,000. You can leave the COL at 1.250-60

Edited May 10, 2010 by dirty whiteboy

[Sarge]

I found this: http://www.brianenos.com/forums/index.php?showtopic=103180&view=findpost&p=1207101

[Pro2AInPA]

I would suspect the 4" barrel is the root cause of your issues . . .

[G-ManBart]

I've got a number of options I think. One is changing powder, but I really like using Clays since it's also my shotgun powder so that simplifies my life.

It was suggested to me that shortening the COL to 1.20 might increase velocity.

Does anyone have any knowledge of just how much of an increase I might get with that adjustment? Any other pros or cons of shortening things up a bit?

Another suggestion was loading up 4.1 grains and 4.2 grains of Clays, but I'm a bit leery of that since the Hogdon manual recommends 4.0 as the max. However I've got no flattened primers or other signs of overpressure.

Any thoughts will be appreciated.

Thanks--Steve

If you know some/all of this I apologize, but if you don't, it might help.

Decreasing the OAL is the same as adding more powder as far as pressure goes (and vice-versa), so there really isn't a free lunch. You've got a couple of basic variables in any load that significantly (important distinction there) influence pressure, which increases or decreases velocity:

Case volume (they're all a little different), bullet weight/diameter/jacket material, amount of powder used, primer and OAL. OAL really should be called the amount of case volume used, but it's really hard to come up with a reliable way of measuring that, so we use OAL, but it's tied to a specific bullet...sort of an indirect case volume measurement. If the case has less volume it will increase pressure and velocity over one with more volume. If the bullet is seated deeper (using more case volume) it also increases pressure and velocity, just like having a case that starts out with less volume. More powder we know increases pressure and some primers slightly increase or decrease pressure.

So after all of that, loading to 4.0gr at book max, with the same exact bullet they used, but loading to a shorter OAL, is the same as going over 4.0gr would be.

Pressure is pressure (pretty much) and it takes X amount of pressure to drive a specific bullet to Y velocity, so if you change something and the velocity goes up (or down), you've changed the pressure.

As Pro2A mentioned, it's probably the barrel length (and maybe a somewhat slow barrel) that is causing you to get numbers below the book values.

Generally speaking, pick the OAL based upon what the gun likes, so long as it's within the normal min/max OAL range for that cartridge and look to the other variables to get the velocity you want. R,

[kgunz11]

I don't load 45 or use Clays. But shortening oal will increase velocities but I don't think there is a magic formula to tell by how much.

Correction, COAL will effect chamber pressure. While that sometimes causes changes in muzzle velocity, it still directly effects chamber pressure. NOT a good thing to play with using Clays. One minute it's fine, but the SLIGHTEST little hiccup with Clays can be catastrophic.

To the OP, you might be better served with another powder that will allow you to safely increase the powder to a point where you can make major with your shorter barrel.

Might I suggest trying a 5" 1911? You'll be much happier in the end.

[njl]

IIRC, 1.20" is the min COAL for the data from Speer. I wouldn't go straight there from 1.25. Having just done some experimenting with Clays, PD 230gr FMJ, and a G21, I'd say you could expect a boost of 20-30 fps by reducing from 1.25" to 1.23". That would be enough to just make major with a little room to spare.

I did an initial test run of 3.7, 3.8, 3.9, and 4gr of Clays at 1.25 and with my G21 got just a bit more velocity than your numbers. Looking to make a mild load with a bit more speed, I loaded some 3.7gr at 1.23" and got a boost of 30fps.

[Sarge]

I don't load 45 or use Clays. But shortening oal will increase velocities but I don't think there is a magic formula to tell by how much.

Correction, COAL will effect chamber pressure. While that sometimes causes changes in muzzle velocity, it still directly effects chamber pressure. NOT a good thing to play with using Clays. One minute it's fine, but the SLIGHTEST little hiccup with Clays can be catastrophic.

To the OP, you might be better served with another powder that will allow you to safely increase the powder to a point where you can make major with your shorter barrel.

Might I suggest trying a 5" 1911? You'll be much happier in the end.

Got me on a technicality! I don't load to max with much so I guess its a different story. Every time I shorten oal I get more velocity along with the increase in pressure.

[CocoBolo]

BigPike - I run Clays in my 45 with 200gr Bayou at 4.3gr. The Jacketed bullet is harder to push and does not seal as well as Moly or Cast bullets which I think most 45 shooters are using with Clays. You might want to try some http://www.bayouBullets.net or so Precsion Bullets (not delta). This will get you the PF you need and the gun will be more enjoyable to shoot. To be honest I've never shot a jacketed bullet out of my SS 45, only Moly and Gator Snot coated.