185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

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185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby pitted bore » Sun Jun 21, 2009 7:40 pm

Part 1

At the end of the trials described in Chapter 1, I had fired three loads of 5 rounds each, at 44, 45, and 46 grains of Lil'Gun behind the Hornady encapsulated 185-gr SWC bullet #45137. There were no observable or measurable signs of excessive pressure. Velocities showed a lot of variation around average velocity.

Because of that variation, there was little evidence that an increase in powder charge produced any significant increase in velocity.

I decided to increase the amount of powder to find whether such increase would produce higher velocities, or result in a decreased variability of velocity, or show any evidence of excessive pressure. I intended to halt the test of increasing charge should any signs of too-high pressure appear.

In this attempt, my first trial series started with a charge where the previous attempts had left off. I used the loading techniques outlined in the post of Chapter 1, Part 4 (15 June 09), except that here I loaded once-fired cases instead of new cases.

I used two cases for each load of 46, 47, 48, 49, and 50 grains of Lil'Gun.

I shot from a bench with the rifle clamped in a Lohman "gun vise"
http://southernhuntingsupplies.com/lohm ... unvise.htm
I put a sandbag of about 45 pounds on top of the barrel and action, and added another such sandbag behind the butt. The midpoint of the chronograph screens was set at nine feet from the muzzle. I pulled the trigger using a string, after I had stashed my tender torso behind a large tree about 20 feet away from the sandbagged gun. (Our club range is unused during much of the day, so I was worried only about spilling my own blood.)

Temperatures were a mild 76 F.

Ater the 10 shot series, the rifle had not disassembled itself. Here are the velocity readings (fps) from the chronograph:

Lil'Gun Trial 1 Trial 2
-------------------------------
46 gr - - - xxxx - - - xxxx
47 gr - - - 2858 - - - xxxx
48 gr - - - 2712 - - - 2879
49 gr - - - 2815 - - - 2750
50 gr - - - 2949 - - - 2900

(xxxx = no reading from the chronograph, or an obvious wacky reading.)

The cases had no measurable expansion at the head just in front of the extractor groove. The primers showed no evidence of flattening; there were no marks on the case head from the extractor. The bolt opened easily after each shot.

(Part 2, next post)
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby pitted bore » Sun Jun 21, 2009 7:44 pm

Part 2

The results of the trials with the 46- to 50-grain load series showed no clear increase of velocity with increasing powder amount. The two loads at 50 grains were suggestive, but given the variation at just a grain less, I was not ready to consider this as really positive.

The lack of pressure indications encouraged me to try to increase the powder charge further.

The cases were getting pretty full of powder at 50 grains. I got an estimate of the maximum possible charge by dumping powder into a fired case, putting a bullet on top of the powder column, measuring OAL, and then adding or taking out a bit of powder until the OAL was the usual 2.040 for this bullet.

At the OAL of 2.040, with the bullet resting on the powder, the charge of Lil'Gun was 53.5grains. So I made up another trial series with two cases at each of 50, 51, 52, 53, and 53.5 grains.

The rifle was set up as in Part 1 above: in the vise, sandbagged, and triggered via a string. The chronograph was set up similarly. I made sure my large hiding tree was not hollow and would probably absorb the shrapnel, and then commenced yanking the trigger string.

Here's what the chronograph showed:
Lil'Gun Trial 1 Trial 2
-------------------------------
50 gr - - - xxxx - - - xxxx
51 gr - - - 2814 - - - 2823
52 gr - - - 2889 - - - 2798
53 gr - - - 2767 - - - 2949
53.5 gr - - 2752 - - - 2830

(xxxx = no reading from the chronograph, or an obvious wacky reading.)

Temperature was 80 F.

Again, there were no pressure signs, and no expansion of the case heads. The variation was again large.

Here's a photo of the case head of one of the 53.5-grain loads. I cannot see any evidence of excessive pressure.
Image

I know that examining cases can be deceiving, and that by the time any pressure evidence appears, the specified pressure limits have probably been exceeded. I'm usually in the camp of those who during load development use the chronograph as an indicator of pressure. Unfortunately, this approach requires some data from pressure tests in a good lab; such data are still absent for the .450b.

(Part 3, next post)
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby pitted bore » Sun Jun 21, 2009 7:52 pm

Part 3 -What's going on?

I'd like to solicit responses from the forum about these results.

For this cartridge, and with these bullets, I've apparently reached some sort of plateau, where additional powder does not produce any additional velocity. I have some hypotheses about why this is happening, but I'd like to let the forum members make suggestions without my ideas to distract them, and to avoid biasing good explanations.

I'm also open to ideas on how to increase velocity above the approximate maximum of 2900. Faster powder? Slower powder? Other?

I suspect I've omitted some important information you may need to help interpret what I've found. Please ask for it.

Thanks!
--Bob
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby gunnut » Sun Jun 21, 2009 8:25 pm

I'm No Expert here! But, Generaly speaking. To me it seems that the 185gr. bullet Does Not offer enough resistance to build excessive pressures in YOUR GUN. Reguardless of powder charge.With generaly accepted reloading practices observed.
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby BD1 » Mon Jun 22, 2009 7:02 am

I believe that you're in the range where you have more powder than you can get lit with a small rifle primer behind that light bullet in that length of barrel. IMO you are getting an incomplete burn and the amount that does get burned is varying shot to shot. The lack of crony readings could be caused by clumps of unburned powder following the bullet through the screens.

I've had similar experiences trying WC 680 behind heavy boolits in the .44 mag. In the end I did get a good load for the .44 using a compressed charge and the heaviest crimp I could apply.

In the .450B I doubt that you are going to be able to get the start pressure up on that bullet high enough to get a good load out of it with a full case of LilGun as the bullet is too short to start into the lands with a good crimp.

BD
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby BD1 » Mon Jun 22, 2009 5:25 pm

PB, take a look at the WC680 data I posted under the "cast boolits in the .450 B" thread on this forum. Very similar results.

IMO this is powder too difficult to get lit. Probably a squib at 20 below.

BD
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby wildcatter » Mon Jun 22, 2009 5:31 pm

BD1 wrote:I believe that you're in the range where you have more powder than you can get lit with a small rifle primer behind that light bullet in that length of barrel. IMO you are getting an incomplete burn and the amount that does get burned is varying shot to shot. The lack of crony readings could be caused by clumps of unburned powder following the bullet through the screens.

I've had similar experiences trying WC 680 behind heavy boolits in the .44 mag. In the end I did get a good load for the .44 using a compressed charge and the heaviest crimp I could apply.

In the .450B I doubt that you are going to be able to get the start pressure up on that bullet high enough to get a good load out of it with a full case of LilGun as the bullet is too short to start into the lands with a good crimp.

BD


BD is probably in the ball-park. I see you're at 9fett for the screens. I burn so much powder that 15 feet is better and if I can get 18 that's better yet. I was losing to many rounds to negitice readings.

Try 296/h110
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Re: 185-gr SWC, Chap. 2: Trying to Blow Up the Rifle

Postby pitted bore » Mon Jun 29, 2009 8:10 pm

I appreciate the hypotheses about the problems I've described above.

You all are likely correct in thinking that there is not enough resistance with the light bullet to generate enough pressure to get the powder burning properly. I noted some powder grains on the bottom of the bore after firing this series. I suspect the force of the primer is sufficient to push the bullet into the lands, and it happens so quickly that the resulting increased chamber volume lowers max obtainable pressure considerably. The extra powder that might be burned to increase velocity above about 2750 fps or so is just getting blown out the barrel.

Some of the "no readings or wacky readings" were my fault. While piling on the sandbag I disturbed the barrel from its centering through the screens. The one really wacky reading was 4770 fps, and may have been due to the powder grain phenomenon you described. I had not seen this reported before, and appreciate learning about it here as a possibility.

One of the readings at 46 grains (Part 2) was 3008. This may have been real, since it occurred with a cold, fouled barrel, which might have increased pressure enough to burn a bit more of the powder.

Chapter 3 follows, with results based upon Wildcatter's suggestion of 296.

--Bob
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