185-gr SWC, Chap. 7: Crimping is our Style

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185-gr SWC, Chap. 7: Crimping is our Style

Postby pitted bore » Sun Dec 13, 2009 10:11 pm

Part 1

(NOTE: The tests described below were carried out with my bolt rifle (LINK to Bob's bolt rifle). So, what I experienced may be very different than similar trials carried out with other rifles, especially the usual semi-autos. My barrel has a 1:16" twist and .451" grooves, and I don't have to be concerned about port pressures, etc. Do not expect my results to occur with any other rifle. Also, do not forget that this information comes to you on the internet.)

In previous chapters 1-6, I told how I learned that light-for-cartridge bullets, like the 185-grain bullets in a 450B, present a lot of problems. There's a reason Hornady doesn't recommend these. The problem boils down to getting a whole caseful of powder to ignite properly in this cartridge. I finally arrived at the same conclusion as many others on this forum: A crimp (or something like it) was necessary to increase bullet pull and rate of burn.

At the end of October I finally had the crimp die operational (see crimp die construction thread HERE.)

I decided to begin with Lil'Gun, and loaded a series of increasing powder weights. I did not load up a large number of cartridges for this initial exploration. Load procedures were much like those of previous chapters. I used the same Hornady encapsulated 185-grain SWC bullets (#45137). Working with Lil'Gun, I used Winchester SR primers. I began with new cases. Cases were prepped using the FL Hornady sizer and flared a bit with the expander die. Powder was weighed to the nearest 0.05 grains. Bullets were seated so the COAL was 2.000 inches, and then taper crimped with the Hornady die to a mouth dia of 0.476". I applied the Lee factory crimp, so that the center of the crimp was 0.070 below the mouth of the case, with the bullet being distorted as a result.

(See image posted on the crimp die construction thread.) Powder weights were 43-47 grains in increments of 1.0 grains.

At the range, the chronograph was set at 8 feet from the muzzle. With an air, ammo & rifle temperature of 40 degrees F, these were the recorded velocities:
43 grains . . 2441 fps
44 grains . . 2548
45 grains . . 2623
46 grains . . 2663
47 grains . . 2720

A factory load gave 2216 fps. Two of my handloads of the 250 FTX gave 2288 and 2291 fps.

There were no signs of excess pressure with the crimped loads. Case heads showed no expansion when measured immediately in front of the extractor groove. The pressures of firing ironed out the crimp in the cases almost completely.

This sequence was encouraging. The uncrimped loads loads put together with the same amount of powder and fired 4-5 months earlier had given higher velocities at the low end of the series, but were also more erratic. (See Chapter 1).

I decided to proceed with increased powder charges.

(continued in Part 2)
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Re: 185-gr SWC, Chap. 7: Crimping is our Style

Postby pitted bore » Sun Dec 13, 2009 10:13 pm

Part 2

I followed up the brief series in Part 1 by loading another series, starting at 49 grains of Li'Gun, and progressing to 53 grains. Except for the cases being once-fired, the loading process was the same as in Part 1. The temperature at the range was a nice 32 degrees F on 27 November.

The chronograph showed these velocities at 8 feet:
50 grains . . no reading
51 grains . . 2790 fps
52 grains . . 2857
53 grains . . 2948
54 grains . . 2932

As with the previous series, signs of excess pressure were absent, with no expansion of case heads when measured in front of the extractor groove. The pressures of firing ironed out the crimp in the cases almost completely, even though this was a second firing.

Again, I was encourage because there was no evidence for the plateau that developed in the uncrimped loads tested in June. The jump of 90 fps with a single grain of powder between 52 and 53 grains was unexpected, but I attributed it to usual variability, given the drop to 2932fps at 5 4 grains.

(Continued in Part 3)
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Re: 185-gr SWC, Chap. 7: Crimping is our Style

Postby pitted bore » Sun Dec 13, 2009 10:15 pm

Part 3
I wanted to get a better idea of how much variability there was in velocity at the upper end of these loads, so I put together 5 loads each of 53.0 and 53.5 grains of Lil'Gun with crimped bullets as above, using 2X and 1X fired cases, respectively.

Again, range temperature was a balmy (for the UP of MI) 32 degrees F.

The 8-foot instrumental velocities at 53 grains were 2934, 2938, 2899, 2902, and 2888 fps.
Average was about 2912, SD=22.4, and ES=50

For 53.5 grains, velocities were found for only 3 rounds; it was getting dark at 4 pm: 2964, 2992, 2981 fps.
The average was 2979, SD=14, and ES=28.

There were no signs of excess pressure, not even the ejector slot scrape at lower pressures that I've described before.

Velocities are very close to the 3000 fps ("lookit all those zeros") goal that started the work, and may be 3K when corrected to the muzzle. There's room in the case for a compressed load of 54 grains or a bit more. Since the range has pretty well closed with 3+ feet of snow in the last week, further work will be delayed.

I have no idea how accurate these loads will be. I'm really not expecting much, given bullet distortion, and a relatively fast twist, on top of old eyes with iron sights.

As a side note, these loads are becoming less fun. A 185-grain bullet at 2990 is what a 300 H&H mag produces, and this is a 7-pound rifle.

Again, beware of following these recipes. My reading of the tea leaves makes me think I'm OK with these loads, but I'm stuffing way more Lil'Gun behind these bullets than Hornady recommends for any of their loads with heavier bullets. In another rifle, pieces of metal and flesh might fly through the air at the pull of the trigger, and St. Pete could be measuring the shooter for a robe and harp. If they show some accuracy potential, I may have them pressure tested.

Please feel free to make comments or suggestions.

Thanks.

--Bob
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Re: 185-gr SWC, Chap. 7: Crimping is our Style

Postby MudBug » Sun Dec 13, 2009 11:21 pm

Great info. I think as soon as I get the new knowledge base up and running I'm gonna add all of your posts on this subject.
Eric

"A coward is much more disposed to quarrels than a man of spirit." - Thomas Jefferson

"War is less costly than servitude. The choice is always between Verdun and Dachau." - Jean Dutourd
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Re: 185-gr SWC, Chap. 7: Crimping is our Style

Postby wildcatter » Tue Dec 15, 2009 7:16 pm

The Side Crimp is working pretty good, wouldn't you think? I have my internal pressure goodies now but I'm soon to go out of country for a month (Sunday). Keep up the good work and when I get back we'll take some of these loads and test them for all kinds of goodies. For one, someone here suggested to do a test on the factory stuff before and after a side crimp, good idea and might tell us allot. We'll be able to see, on graphs, just whats-what and if we need more or less of a particular powder, what the primers are doing, are we getting good ignition or not, is the powder too slow or to fast, but the best thing this equipment will do is accurately catalog the SD's, hence giving us a real predictable snap-shot of what is actually happening. I now have two co-phased IR chronographs, one at the muzzle and the other at the 200yd line, this way we will have all the data for that particular round and as far as the velocities and BC's are concerned, there will be no SD's, in other words, that set up, using two sky-screens, eliminates the statistical need to predict the SD, because my SD, with this system, will be Zero. At that point what we'll be looking at isn't some kind of statistical average of the probability of a result, "A" will be "A" not a guess of is it A or B or C or D or E and what is the statistical probability it could be any of these or something entirely else..
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