CASE CAPACITIES (a bit wordy!)...

[BCB]

WARNING: This contains discussion/questions that deal with condom bullets�not cast bullets…

Well, with the disclaimer out of the way, I was shooting my T/C Contender, 16� barrel, 223 Remington today. I was using 28.0 grains of WC-844 and the 40 V-Max bullet. I consider 28 grains of this powder to be MAXIMUM�but I may be wrong with that thought. Maybe it should be MAXIMUM PRUDENT load!

I was originally using LC-85 cases and decided to load a box of PMP (not PMC) with the same load. To my range I went to fine tune the point-of-impact out to 200 yards so I can use this Contender for ‘chucks as the summer progresses. I got the handgun shooting exceptionally well with the LC-85 cases. As a matter of fact, I shot my first “bug hole� at 100 yards with it today. Might just frame that group! I was doing some casual shooting at plastic soda bottles filled with water using the LC-85 and PMP cases. I noticed quickly that I was not doing as well with the PMP cases�bullet impact always seemed high. So I placed a target at 200 yards and sure enough, it was over 2� high and an inch to the right�the LC-85’s were zeroed at 200 yards. Contenders can be discouraging at times�just the nature of this beast I think�and I was a bit bummed out. So I came home and decided to weigh the cases. Knowledge that exists in my brain but is sometimes forgotten!

Here seems to be the problem. The PMP cases were 10.75% heavier than the LC-85’s! I suspect the 28 grain charge in these cases would be OVER MAXIMUM. Luckily I only fired a few of them, although they didn’t show any blatant signs of pressure. Since these cases are 10.75% heavier, does that mean that the capacity is approximately 10.75% less? I am planning on trying 25 grains of WC-844 in these cases as that would be approximately 10.75% less powder than used in the LC-85’s. Does this sound like something that might produce the same velocity as the LC-85 cases or is this not a likely scenario? I do have a chronograph, but I was just curious before taking the chrony to my range. Thanks…BCB

[StarMetal]

No the weight won't correspond into volume proportionally. You need to do a volume check, like fill to the mouth with say fine walnut media or something like that then weigh the charge.

If you got the same charge of powder in both the LC and PMC cases then your target impacts are telling me that the PMC had the lower velocity. That is the barrel is recoiling upward at ignition and the slower bullet will result in a longer barrel time, thus exit the barrel when the barrel is at a higher lever then the faster bullet.

If the PMC don't have as much volume as the LC cases and you used the same charge of powder, I'm at a loss.

Joe

[BCB]

StarMetal,
I agree with the bullet impact higher with slower velocities in HANDGUNS, but I am uncertain that the T/C's act like handguns, especially with "rifle" cartridges. I think the velocity of the PMP is higher. But, you are correct in that I should weigh one of each with water and calculate the volume. Maybe I'll do that now. My basement is cool--it is near 90 out of doors...BCB

[StarMetal]

I've seen it happen with both handguns and rifles. Not always a for sure thing though.

Joe

[BCB]

StarMetal,
You are indeed correct that the volume is not proportional to the differences in weights of the empty cases!
I just weighed two primed empty cases, a PMP and an LC-85. I then took a bullet and cut a groove lengthwise in it to let water exit as I seated that bullet. I filled each case to the mouth and then seated the bullet. I then weighed each case filled with water and the bullet seated. Results: PMP = 28.12 grains of water…LC-85 = 29.35 grains of water. Or a 4.37% increase in volume.
Wouldn’t this lead to greater pressure in the PMP case with equal charges (28 grains) of powder? And wouldn’t that mean a bit faster velocity unless I have reached super maximum pressure and crazy things are happening. But, that is not observed with these loads…BCB

[StarMetal]

Yes, the pressure would be greater if you used the same charge of powder. Theoretically it the PMC case load should have shot lower as it would have a faster barrel exit time. But like everything else this theory doesn't always hold true.

By the way for the LC case, was your load max or close to max? If not I don't think the PMC load would be supermaxed out.

Joe

[StarMetal]

I reread your first post. 844 is suppose to be similar to H335 and my jug recommended H335 data for loading. Well they were wrong with my 844, it's a bit faster then H335.

Joe

[felix]

The next question, Joe, is what version of H335 do you have? Fast or slow or just right? ... felix

[BCB]

StarMetal,
I believe with the LC-85 case I was right at maximum. That is according to data using H-335 and the 40 grain V-Max. My lot of WC-844 has proven to be approximately 1 to 1.5 grains slower than H-335. So, 28 grains of WC-844 should be right at or a bit over maximum�no indication of excessive pressure has been observed. Actually, I was a bit nervous firing it today in the 90°+ temperature. But all went well. Guess I will just have to get the chrony out the next trip to the range…BCB

[felix]

Joe, a 5 percent case variation in volume won't be noticed with a slow powder for the bore. As the speed of the powder is increased, or the bore made smaller, you will notice more case differences. This is because of the powder's ramp time to max pressure. A stiffer case will make this time shorter, and increase the pressure for a fast burning powder. ... felix

[Herb in Pa]

I recently returned from a varmint expedition to Idaho and thus had a good sample of empty 22-250 cases to examine. My varmint load utilized Federal Premium cases but due to their being discontinued, I had to also load some with Remington cases.

The 20 case sample of the Federals weighed in at an average of 163.9 Grains, with the lightest at 161.9 and the heaviest at 164.6.

The 20 case sample of the Remingtons weighed in at an average of 154.1 Grains, with the lightest at 151.5 and the heaviest at 156.2.

My standard load with the Federal cases uses 37.0 Grains of Varget with a 50 grain Moly VMax and chronos and average of 3815 fps.

The Remington cases required 38.2 Grains to achieve a similar result.

[Scrounger]

You guys totally dismiss the possibility that the phase of the moon, the atmospheric pressure, or the brand of Jockey shorts worn could be a factor in this?

[swheeler]

You said you own a chrono, so you have the tool to get the job done! Load the PMC cases to match the velocity of your LC 85 brass- case closed.
Scooter