What's wrong with the AET ?

[Julien Boit]

I have a very strange question for you master reloaders:

A friend of mine recently put an AET .38 super barrel in his open gun.

He chronoed several cartridges using  SP2 powder and 124 grs bullets from several manufacturers.

The first shot is about 1350 FPs, the second shot is about 1270 FPs and the third shot is about 1170 Fps.

He did this several times and it's always the same schema : The first is about 1350 fps then the others goes down.

If he wait for a couple of minutes between the shots, they are all at the highest speed and are ok for PF.

But if he continue shooting through the chrono, the velocities colapses.

It doesn't happen with the N105 for Vitha with a charge to achieve the same PF.

Same bullet, same length, different results.

What could it be ?

For info, the charge with the SP2 is not at its maximum, the powder is not compressed into the case.

But the vitha is a little compressed.

Could this be a dilatation problem ?

Any help will be appreciated

DVC

Julien

[gm iprod]

I believe it is a powder problem. Not because the powder is moving about in the case, just the burn rate vs density.

Try single loading the pistol, as fast as you can. Point the pistol up hill then carefully aim across the chrono.

Try the same up hill the aim trick from a loaded magazine but shoot fairly quickly. You must remember to point pistol up between each shot.

Now do above again but point pistol downhill.

If the velocities on each string show the same variation downward then I believe the actual burn rate of the powder is at fault/not suitable. If the up shows significant improvement over normal shooting, and the down is even worse then I believe the problem is load density. Just MHO.

We used to do this for 38Spl when we pushed the 120pf a little for Service Pistol. But we used fast powders not treacle ( Molasses ) like burn rates.

[Carlos]

Another thought: 1st shot = cold chamber (and no heat transferred into the powder through the case wall). 2nd shot  = hot chamber, so some heat is transferred to the powder befor firing. 3rd shot = more heat transfer.  Perhaps the Vectan SP2 powder/load combination is very temperature sensitive where as the VV has additives to reduce temperature sensitivity.

[Julien Boit]

Carlos,

The thing is that it don't happen with a "regular" barrel.

I shoot 38 super through a schuemann barrel with the same load and I never experienced this.

Velocities are regular.

Also, as temperature increase, so should chamber pressure, it's the opposite.

I thought something happens when the bore is hot with this combo of powder/charge/rifling.

I'll email it to Wil Schuemann.

Thanks

DVC

Julien

[Flexmoney]

Does the brass look like it is getting some blowback from the case not expanding to completely seal off the chamber?

It seems that it is a bad lot of SP2 or the is cut in such a way that the brass isn't sealing at the pressure/speed of the SP2 load (which it should, right?).

I'd try a different lot of SP2.  If that doesn't do it...look toward the barrel as being the problem.

By the way, does that barrel have a fluted chamber?

[38supPat]

What is your load of N105?...is it a full hybrid/what porting?

Pat

[Julien Boit]

Of course the chamber is fluted.

I'll ask to my friend what the cases looks like.

The barrel has 8 or 10 little ports plus 6 chamber comp.

I'll ask to my friend about his N105 load.

[Julien Boit]

Ok, I have the datas :

Powder Vectan SP2 charge 8.8 grs

The comp is an EGW 6 ports plus 8 little ports on the barrel.

1st shot 1350 fps, 2nd shot 1270 and 3rd shot 1120 fps.

With 9.4 grs of N105 velocities are regular.

The guns only shoot new brasses, with old or once fired, it has extraction problems.

They look fine .

DVC

Julien

(Edited by Julien Boit at 11:29 pm on April 11, 2002)

[Flexmoney]

Julien,

I don't know why he would be getting the various readings.  

I am still in load development with SP-2 in 38 Super Comp.  It is looking like about 9.4 grains with Speer 124g JHP's.

Two different Open guns.  One has a three port comp and two hybrid holes in the barrel.  The other has a comp with four top holes and one hole on each side, and five hybrid ports in the barrel.  I don't have my load data in front of me, but velocity wasn't too different between the two guns.

Good load data here:

http://home.columbus.rr.com/jmaass/ipscload.htm

I'd try bumping the load up.  If that didn't work, I'd do some chamber measuring.

Might have him do a serious cleaning of the barrel.  He might have some leading from previous loads that the first round is scrubing out of the gun.  

(sorry...I'm not much help...just throwing out ideas)

[BSeevers]

Give Wil Schuemann a call or email. He is a nice guy and very responsive to questions. I don't think you are supposed to ream that barrel(fluted chamber and progressive rifling) so that might be a problem. You have too much load variation but that could be your loading technique or components. That is a very different barrel and just might be an isolated problem. I would not shoot it til you get it sorted out. I like 3N37 and you might look at 350.

(Edited by BSeevers at 7:04 am on April 12, 2002)

[Julien Boit]

Just receive an email from Wil Schuemann.

For Him, it might be only a problem of distance between the muzzle and the chrono.

The gases arrive before the bullet or at the same time and it disturbs the chrono.

Keep on investigating

DVC

Julien

[BamBam]

STOP THE PRESSES.  I believe I have the definitive answer!  I had the exact same problem shooting SP-2 from my AET open rig.  Let me ask you this... are the rounds being loaded on a Dillon?  I found that the Dillon powder feed does not consistently charge the SP-2 powder.  You are getting all different speeds because all different dumps of powder are happening.  V-V powders measure great from the Dillon powder measure.  I like the VV3N37 and also IMR 7625 for consistent powder feeding and for working well in the AET barrels.   If that does not solve the mystery, write again.  I may have a plan "B".

[Julien Boit]

Did you have that "thing" with velocities ?

First High, then the others lowered but regularly and always the same speeds ?

4 or 5 times in a row .

The thing is that my buddy weighted all powder charges as it was a test, I think he would have noticed this.

But We'll watch for it , thanks.

DVC

Julien

[BamBam]

I had the velocities scattered all over the place with huge 100+ fps swings.  It was so bad that I discarded all results and moved on to another powder forever, so I can't tell you the details of the shot by shot data.  

The only way to verify and eliminate this possibility would be to hand measure each powder charge for every bullet for absolute consistency BEORE reinserting into the press and continuing to load (that's how I do all my chrono test loads anyhow).  NEVER trust the auto powder charge with SP-2 powders, thus it hardly makes it worthy of major match confidence.  

If that does not help you, make sure you are using hot primers.  I find I have the best results with small-pistol-magnum or small-rifle for all my AET loads.

On another note, how many holes did you say were manufactured in your AET barrel and how many additional chambers are in your comp?  Is this a tribrid barrel?

[Flexmoney]

How about crimp?  Perhaps a light crimp is allowing the remaining bullets to move in the case under recoil.