Has anyone else noticed or do I need my meds reduced ??

[Reg]

After many weeks of not being able to get in any bench work finally decided today was the day or at least before the wind got up too high. Being tested was a pistol in .22 Jet caliber using cast bullets, Recluse lube and a light , 3.5 gn. charge of Bullseye. Actual object of the test was to compare any differences there might be between Hornaday and homemade aluminum gas checks. This load has been proven to be extremely accurate in times past.
All charges weighed, everything was held as close as possible to all being exactly the same. Only difference was in the gas checks.
When testing, I always set up the Chroney to help with any comparisons.
First string was fired using the Hornaday checks, velocities recorded and a average in FPS was determined.
Second string was the aluminum checks. Velocities recorded and a average determined.
I noticed that there was a 24 FPS difference between the two and didn't think too much about it. Fired a second string of each and low and behold there was that same difference. The aluminum checks were faster.
I fired four more strings of each and without fail the FPS difference stayed there every time.
Looking over the fired casings for any difference, I did notice that the primers in the cases with aluminum checks did seem a tiny bit flatter. Now I know one is not supposest to use primers as a pressure indicator but I feel they can pose as a relative indicator. No other difference was noted in accuracy , ejection or anything else.
Due to surgery earlier and a couple other things I have been taking some stout stuff this winter but have been fully off of all of it for a few weeks now and to me this repeatable difference should not be there.
What am I missing ???

[RickinTN]

My guess is that the aluminum checks create less friction in the bore and therefore your difference. Nothing else comes to mind at the moment that could be the reason.
Rick

[slim1836]

Were the copper checks the same thickness as the aluminum? I would think if they were not, then the thinner checks may be the faster due to less resistance.

Slim

[Reg]

Were the copper checks the same thickness as the aluminum? I would think if they were not, then the thinner checks may be the faster due to less resistance.

Slim

I just checked, the copper checks were .013 or so and the aluminum were .0045 but both were sized to .2230.

[abqcaster]

I believe your looking at the opposite of what the others are saying. The aluminum might be softer than the copper alloy used in the copper checks. It could be obturating more or sooner, and INCREASING the pressure, which your seeing in the way of primer flow. If, that's the case it would make sense that a relatively slight increase in pressure would cause a proportionate increase in velocity.

[Reg]

I believe your looking at the opposite of what the others are saying. The aluminum might be softer than the copper alloy used in the copper checks. It could be obturating more, and INCREASING the pressure, which your seeing in the way of primer flow. If, that's the case it would make sense that a relatively slight increase in pressure would cause a proportionate increase in velocity.

This very well could be. Had no choice but to use the thinner aluminum as a thickness of .010 to .012 caused a lot of deformation with sizing. Just too much pressure. This was also one of the reasons for the accuracy test as I have heard that very thin aluminum dosn't work too well with gas checks. I did notice it took a bit more effort to get good checks with the thinner material, tearing etc.
I know we are talking very minor differences here and considering the load it will never be a problem it's just one of those things that pop up from time to time and you have to wonder why.
Am glad the accuracy part showed no change whatever. This has always been a accuracy load that I have used in the Jet and if the wind isn't gusting to 60 or beyond, it is easy to keep all shots in less than a inch at 50 feet. Not perfect by any means but as good as I can do with any handgun.

[detox]

Due to surgery earlier and a couple other things I have been taking some stout stuff this winter but have been fully off of all of it for a few weeks now and to me this repeatable difference should not be there.
What am I missing ???

Withdrawal may have caused you to leave out accuracy results...copper vs aluminum.

[longbow]

I am with abqcaster. I think any difference the frictional resistance between checks would be so small compared to the bore friction of the boolit as to not make any difference. A bit better sealing though would have a significant difference.

Longbow

[Reg]

OK, it is fes up time.

I have gone back twice now and with the identical materials tried to achieve the same results. The only factor of variance would have been temperature.
I did the first shooting when it was just below freezing and have since done it at 14 degrees and again the other day at 48 degrees.
At 14 degrees the crono results were so out of wack they made no sense at all. All the way from 980 fps. to 6905 fps.
The last day all readings, no matter what , were within 20 fps. On both days no signs of a pressure difference were noticed in primer flatness. Everything looked normal accuracy was excellent.
The primer flatness difference was there on that first shooting, wish I had taken a picture. Now it no longer is.
The velocity readings were there on that day and were repeatable. I deliberately ran a second string because I just didn't believe the first. Now they are within the normal range of error.

I think some of this might be attributed to the display on the chronograph. Normally I try to do chronograph work on better days but we have so few good days this winter it was one of those "go for it" deals. I didn't think it would make a difference but have been told that it actually does and based on what I have seen--- yup, it does.
The fact that it repeated itself is what has me stumped.

Guess if I have learned anything from this, it is to not say the sky is falling until I do a double check and make danged sure it isn't.

Sorry if any of this has caused sleepless nights !!
Reg

PS.

One thing I did learn for sure was in some respects what I was out to find in the first place.

1. There seems to be no accuracy difference between the two checks. Both shoot very well.

2. I recovered a good number of the aluminum checks at the 100 yards backstop. All showed excellent orbitration and showed they stayed on for the whole trip down range. None showed any signs of gas cutting.

Unless I can be shown any other reason to not use them, I would say the aluminum checks are a excellent replacement for the copper checks.