Gents,

How far forward of the rebate do you measure for case head expansion?

I'm working up loads for my SA Ruger Bisley and I'm filling in my notebook. I'm changing to non-magnum primers

RP Brass
CCI 300 LP primers
21.5gr H110 (min) 23.0gr H110 (max)
BTB 300gr WFNGC
COAL 1.600 (But when crimped it moves down to 1.585)
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On the sized case, I measured about 1/16" foward of the rebate with a dial caliper and got 0.4760 as consistently as I could with the tool.
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On the min loads, I measured 0.4760-0.4763
On the max loads, I measured 0.4765-0.4769
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Again, the measurement accuracy is only as good as the tool, and it's not graduated for the ten thousanths, so that numerical value is a guess.
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I don't think I"m in trouble, but I'd like some more info if anyone can provide it.
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When I was using magnum primers, I started to get marks on the headstamp from the frame and slightly flattened primers at 22.5gr H110.
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With non-mag primers, I do not have any flattening or any addition head stamp marks up to 23.0gr.
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I reamed the chambers and firelapped the barrel. I have a consistant .452 from cylinder throats to muzzle. I don't think there is a problem, but I want to check with you folks.
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BTW-My best accuracy of 2.5" @ 25 yards came with the 22.5gr and non-mag primers, matched only by 21.5gr and mag primers.
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My next step is to put both loads over a chrony.

Your thoughts are appreciated.

EMC2

I assume this is for the .45 Colt.

A couple of things. First, a dial caliper isn't going to cut it. Too much spring in the jaws. You need a micrometer that can read 0.0001", and preferably, half of that (50 millionths). Also need the touch to use it.... not an easy thing.

Second.... traditional signs of high pressure just aren't going to be helpful at the 30,000CUP level that Rugers are often loaded to. Think about it.... how can those pressure signs be remotely useful at both 30,000 CUP and also for other cartridges in, say, the 40,000 CUP range? They can't work for both (and are probably of dubious value even in the higher pressure cartridges).

Frankly, I think your best bet is to chronograph the loads and see how they are doing vs. what the loading manual predicts.

Using the slower H-110 powder, I have always found it best to stay with the magnum primers...

As far as measuring case head expansion, usually about 1/4" or so in front of the rim will give you your most consistant measuring point for case head expansion...

If you are getting right at .001 of an inch where you are measuring at, me personally, I'd have to back off the load at least one full grain. Your measuring point should show no expansion at all, measuring that close to the base...

A

I'll agree with both posts above. Need a good microcrometer for such measurements.

H110 and similar powders do indeed, need mag primers to light them off sufficiently.

I also agree with above posters- I found for the 45 LC that 21.5 gr H110 under a 300 WFNGC was the best load with out any pressure signs- also the most accurate! Mag Primers yes always!!

Thanks for the input whisperers...:D As much as I agree based on everything that I've learned, I must admit that getting an extra grain in the case with non-mag pimers and no pressure signs is impressive indeed.

I also agree with above posters- I found for the 45 LC that 21.5 gr H110 under a 300 WFNGC was the best load with out any pressure signs- also the most accurate! Mag Primers yes always!!

Gunnut45/454,
I'm shooting out of a 5.5" bbl. What kind of velocities can I expect with the 21.5gr H110, 300 WFNGC and mag primers?

They closed the outdoor range closest to me, it could be a while before I get to travel and set up the chrony again:(

EMC2

Sorry, measuring case heads or pressure rings is not a reliable indicator of even relative pressure.

http://www.shootingsoftware.com/ftp/dbramwell%20july%2019%2004.pdf

All literature where the CHE or PRE methods are compared with pressure testing equipment show that it is not worthwhile. Lyman found that some loads that were well below safe pressure were indicated to be way over pressure while some other way too hot loads were deemed safe by case measuring methods.

Another thing you will find in all of the discussion of measuring case heads is that there is no single method, there are variations, and there is no agreement on what the measurement thresholds are or what they mean. In addition, most people are incapable of consistently making such measurements, we are talking about measurements to the ten-thousandths of an inch along an indeterminate area of the case where the positional measurement may vary hundredths of an inch.

You'd be better off getting a chronograph as at least there is a correlation between velocity and pressure.

For the 45 Colt in strong pistols, according to Hodgdon, 23.5 grains of H110 is a maximum load with a 325 grain cast bullet seated to a 1.68" COL. 22.2 grains of H110 is a maximum load for a 300 grain jacketed bullet. Hence, with less bearing surface of a softer material, 23 grains of H110 is likely a good maximum load for a 300 grain cast bullet.

Double "Hear Hear!" dittoes to all the above.

1. H110 (and W296) require not only a magnum primer but a tight bullet pull and a firm crimp to boot, or they simply not ignite consistently. If you don't, of 100, 98 may seem to fire fine, one may produce a squib shot leaving a case full of black tar - and the 100th might seem to detonate like a grenade.

2. Mo powda ain't mo betta if you risk the above.

3. I was a firm believer in measuring the PRE, until a very good statistician (Denton Bramwell) proved to me beyond doubt that it's a worthless tool for guessing pressures. I bought a strain gauge system to test Denton's claims. He's right. You may as well paw through chicken innards as measure case expansion. Without a strain gauge setup, follow book loads, analyze what the chronograph is telling you and when you reach EITHER the book max OR the book velocity, STOP.

You gentlemen exemplify the integrity of this forum. I thank you.
EMC2