Puzzling load test

[pigbrother]

I been trying Sinterfire bullets. For the first test with 75 gr 380 auto I looked at the Sinterfire data and it has one load (Titegroup), which is exactly the same as 100 gr 9mm using 231. So I backed away from that load and looked elsewhere. The only other load I could find was in the Shooters World load data using Clean Shot. I had some Clean Shot but have never used any of it. They show 4.0 to 4.5 gr for velocities of 862 to 1000 fps. So, I created a ladder in 0.1 gr increments, 10 rounds each starting at 4.0. Then I went out to test them with a chronograph (Labradar). Starting with the lowest load, the first round felt and sounded normal but the gun jammed (P3AT). The fired case was half way out of the chamber with the next round pushing into it. So the slide traveled back enough to get the next round but didn't eject the first round. The chronograph showed 1116 fps when I was expecting less than 862 (the barrel is pretty short). The spent case came out reasonably easy, the primer looked fine, but there was an excessive bulge in the brass. I packed up and went back to the bench.

 

The case is bulged more than normal with a slight "blister" above the base. It is similar to the pictures I have found of overpressured brass but much less severe. The case diameter is 0.014 larger than the unfired case and about 0.008 larger than other fired cases I have. The loaded rounds drop out of the case guage easily and about zero crimp, I wouldn't expect to have cracked a bullet. I don't know if a cracked bullet can cause overpressure like this. I verified the powder in the load data, on the bench, and in the measure, it's correct (Clean Shot). The measure continues to throw 4.5 gr, the last step in the ladder. I recorded the weights of each step in the ladder as I loaded as well as the setting of the micrometer of the Hornady LNL powder measure. I can see from what I wrote that what was in the fired round is much less than the 4.5 I ended on. I load a single powder weight, place them in a box, label the box, and then move to the next weight. The fired round came from box labeled 1, 4.0 gr, micrometer 2.74. The last was labeled load 6, 4.5 gr, micrometer 3.18. I don't think I could have fired the wrong loading. The Clean Shot powder was measuring very consistently.

 

At 4.5 gr the bullet is sitting on top of the powder, I was going to be watching that closely as I worked up to the higher loads. The 4.0 load had a very small air space and should not have been too much or compressed.

 

I haven't found any other load data for the 75 gr Sinterfire and I'm reluctant to use this loading again. Any thoughts on why a minimum load that almost fills the case would overpressure like that?

 

[Hi-Power Jack]

18 minutes ago, pigbrother said:

  I don't think I could have fired the wrong loading.  

 

Four possibilities that I can think of :

 

1.  That's one possible problem - you are not Positive that the round was not a 4.5 gr.

 

2.  you used a case gauge instead of your gun's barrel/chamber - the round may have jammed a bit into the rifling

 

3.  you fired only one shot and got one chrono reading - might have been a bad reading, depending on which

     chrono you used and the lighting situation.

 

4.  could have been something in the empty case before you filled it with powder

 

See what anyone else can come up with      

[Steve RA]

I've found, thru the years, that it works better if you weigh the powder on a scale for test loads.  This does away with any question of getting slightly different powder weights thru a powder measure.  Also it really doesn't take that much time as I only load five of any weight that I'm testing.  I also only load one brand of brass per caliber I load so that removes another variable from the result.

[pigbrother]

Thanks. I'm enough of a pessimist that I wouldn't rule out any of these.

 

1) True, and I  have been thinking on that one a lot. Pretty close to postive though, the 10 identical rounds  went into a box and it was closed and labeled before any other round  was made. The box was not opened again until I was loading the mags just before firing. At that time, no other boxes were open. After firing, the box number was verified, correct box and label. 

 

2) Right. I pulled the barrel and checked the remaining 9 rounds. all chamber to the same place as factory, just below the barrel hood. No way to know if #1 was seated longer.

 

3) I would definitely distrust an optical chronograh, but  I have not yet seen the Labradar give results that were both plausible and wrong. Sometimes wildly wrong though. 

 

4) Very possible usually, but when I'm testing a new load, and 10 at a time, I take a real good look at the inside when they go into the loading block. I would think this is the least likely. 

 

[Hi-Power Jack]

I'd load up 10 rounds at 3.5 gr and chrono them.

 

BTW, I don't see any reference in your first posting what the OAL was.

Rounds can pass The Plunk Test and be too short - could cause higher

pressure and velocity.

 

Also, did you test bullet setback for your rounds ?   Push the bullet in as hard

as you can by hand, pressing against your reloading bench - then measure the

OAL and see if they shortened at all - could also decrease the OAL and cause

higher velocity.

 

Sounds like an exciting project - good luck with it    

[pigbrother]

I like that plan, I'll try 3.5 gr as soon as I have the chance.

 

The OAL was 0.97 with some measuring as short as 0.963. The load data indicated 0.95 and I didn't want to crowd the powder more than necessary.  Of the 9 unfired rounds, one shortened to 0.943, the others didn't change or just a few thousanths. I'll shorten them a little for the next test.

 

Thanks for the suggestions. This wasn't supposed to be exciting before 4.4gr. 

[Hi-Power Jack]

5 hours ago, pigbrother said:

 one shortened to 0.943.  I'll shorten them a little for the next test.

 

I'd run The Plunk Test again, and see if you can lengthen the OAL, rather

than shortening it.  That could reduce pressure.

 

I'd also check more rounds for bullet setback - that can be a problem and

increase pressure.     

[chevrofreak]

Their recommendation of that much powder is ludicrous.  Look at the Hodgdon data for pretty much any bullet in .380 using Titegroup and it will be significantly lower.   Also, keep in mind that your frangible bullet is longer for its weight than an FMJ or JHP, which takes up more room in the case and increases pressures.    You should be closer to 2.7gr of Titegroup.

[pigbrother]

Fortunately there were a lot of things wrong with that Titegroup load which I discovered before I tried it. Except for the powder, it is identical to a 9mm load, including bullet weight and OAL.

 

[pigbrother]

Loaded another 10 rounds w/3.5gr Clean Shot. Taking Steve's suggestion, brass was Starline and powder charges were all +- 0.02 gr. The Plunk Test seems to indicate that I could chamber at least 1.029  OAL. The bullet was barely seated and much too long to go into the magazine. 0.98 was about as long as the magazine would allow. I set the crimp to  just snug the case, about 0.001 crimp as best I could tell. All rounds passed the setback test.

 

The first 6 rounds were 0.984 with average velocity 1033, S.D. 16.6, E.S. 42. The next 4 rounds were shorter, I was monkeying with the seating die. The shortest one was 0.97 so I used them as-is. Only 3 of the 4 registered on the chronograph. 

 

Overall, average was 1031 fps, S.D. 13.65, and E.S. 43.  The published maximum load had a velocity of 1000 fps which I assume comes from a longer barrel than mine. I think I'll reduce the powder until I get to 1,000 fps and call it good. It seems the load data I had was just too hot.

 

I've had the Keltec for quite a while but just now got around to handloading for it. Looking at the brass it doesn't have the blister I saw with the 4.0 grain charge. But the cases do seem too bloated. It looks to me as if this chamber is both long and fat and a little hard on the brass.

 

Thanks for everyones help.

[Hi-Power Jack]

1 hour ago, pigbrother said:

 

I've had the Keltec for quite a while but just now got around to handloading for it.

 

I've done some loading for my P-11, and have had a LOT of FUN

with very light loads - easier on the gun, and on my hand, and they

still hit the target at 10 yards    

 

I load them down so they still feed properly, but very little noise,

recoil or strain.