185-gr SWC, Chap 5: SRP vs LRP Cases

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185-gr SWC, Chap 5: SRP vs LRP Cases

Postby pitted bore » Fri Jul 24, 2009 1:51 pm

b]Part 1[/b]

(NOTE: My reports in this thread are based on my bolt rifle, using a barrel that likely does not conform to SAAMI specs for the 450B. If you try to duplicate what I describe, do not expect similar results. Do not forget that this is internet information, which very often does not resemble reality.)


In Chap 4, I indicated three possiblities for exploring solutions to the problems of erratic performance obtained in Chaps 1-3. These three were mechanical (e.g. crimping), using powders faster than Lil'Gun (e.g. Blue Dot), and using hotter primers (e.g. LR primers in modified 284 cases.)

This report is of some results with hotter primers in LRP cases.

I gratefully acknowledge the kindness and thoughtfulness of BD1, who furnished some 284 cases that he had fully prepared for use with the 450B. He described his techniques in some June 22 posts on the "284 to 450B cases" thread in this forum. He indicated the cases he sent me had been fired once or twice. THANK YOU, BD1!.

BD's cases measured 1.700" long, +0.000", -0..002", which is pretty precise. Level full, they held an average of 55.1 grains of my lot of Lil'Gun. My 2X-fired factory 450B cases held 58.6 grains, which indicates there's some extra brass in the 284 cases somewhere.

I loaded three trial series of cartridges. Each series was made of five single cartridges having 42, 44, 45, 46, or 47 grains of Lil'Gun powder. The first series was put into factory 450B cases, primed with CCI BR4 small rifle primers. The second series was put into the converted 284 cases, primed with Federal 215M large rifle magnum match
primers. These rank pretty high on most charts that rate "hotness" of primers. The third series was put into converted 284 cases, primed with CCI 200 large rifle primers, which are usually noted for being fairly "mild".

I selected the charges based on previous experiments, reported in Chap 1. The 42-4 series included the loads with about the highest velocities obtained with Lil'Gun. It started low enough, I thought, to find if the LR primers produced pressure problems, so I could end firing a series without damaging pressures. The upper end of the series I hoped would run high enough to allow the LR primers to demonstrate their superiority to the SR primers, if indeed they were superior.

I did not put in more than 47 grains, because that load left a seated bullet directly on top of the powder in the 284 cases. In the 450B cases, some air space was present, equivalent to about 3 grains of powder.

As in other trials, I used the 185-grain Hornady SWC fully encapsulated bullet. These were seated to a COAL of 2.000", and taper crimped to a case mouth diameter of 0.476".

(Continued in next post.)
Last edited by pitted bore on Sun Sep 27, 2009 6:49 pm, edited 1 time in total.
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby pitted bore » Fri Jul 24, 2009 1:52 pm

Part 2

At the range, the middle of the chrono screens was put at about 9 feet from the muzzle. I started firing each series with the low charge, looking for pressure or other problems as charge weight increased. I let the barrel cool to about ambient between each series. Here's what the chronograph read in fps:

charge - - SR - - - - LRM - - - - LR
----------------------------------------------------
42 gr - - - 2697 - - - 2804 - - - 2802
44 gr - - - 2736 - - - 2867 - - - 1484 ??
45 gr - - - 2764 - - - 2914 - - - 2767
46 gr - - - 2770 - - - 2674 - - - 2897
47 gr - - - 2829 - - - 2704 - - - 2544

Charge is grains of Lil'Gun, SR is the small rifle primer in the 450B case, LRM is the Magnum Federal 215M primer in a 284 case, and LR is the CCI 200 primer in a 284 case.

Some observations:
(1) I doubt that the 1484 reading is real; recoil of the shot was not appreciably less than others. Recoil with all of these is noticable, approximating a stiff '06 load with some shots.

(2) The first three shots of the LRM series had me happily thinking that the LR primers had solved the ignition problem. The fourth shot (46 gr) put those hopes to rest, with a drop of 230 fps accompanying a 1 grain increase in powder.

(3) There was no evidence of high pressures.

As in earlier chapters, the SR loads showed sooting of the case back to the head, except for the 47-grain load, which only the front half of the case sooted. The LRM cases had the front 1/4 of the case sooted for the first two loads, some sooting near the mouth only for the 45 grain load at 2914 fps, and complete sooting for the 46 and 47 grain loads. Of the regular LR cases, the 42, 45 and 46 grain loads were sooted only near the mouth, while the 44 and 47 grain loads were fully sooted.

It does not appear that using hotter primers solves the problems associated with using 185-grain bullets in the 450B.

If I've omitted some information necessary for interpreting my results, please ask for it.

--Bob
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby gunnut » Fri Jul 24, 2009 4:56 pm

Have you tried the Modified Lee 45-70 factory crimp die? or a side crimp? To me this makes one heck of a differance! I worked up to 42gr. of Lil Gun in my 284 cases under a 230gr. fmj. 42grs. was a pretty stout load! I don't have a chrono. So, I backed off to 40grs. Any help with the effect of the F.C.D. would be appreciated. A word of caution here! I only use FMJs! The other thin skinned ones are easy to damage when crimping and WILL come apart! Should be call negligee's, Nice to look at. But, Not a jacket. and Don't help when the rubber meets the road!
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby pitted bore » Fri Jul 24, 2009 9:36 pm

gunnut-

I have not yet gotten to crimping as a way of solving the problem of ignition with light bullets. I hope to try that in a couple of weeks.

The 185-grain bullets I'm working with are Hornady's SWC fully encapsulated, so they are like totally jacketed. The jackets on these particular bullets are pretty strong, unlike the copper plating on some other 185-grain SWC bullets. I initially selected these in response to some posters' worries that the 185-grain bullets might fly apart as a result of high velocity (about 3X what the 45 ACP produces) in a fast-twist barrel. I've seen no evidence of jacket failure yet.

Thanks for your comments.
--Bob
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby BD1 » Sat Jul 25, 2009 6:31 am

I'm going to offer a theory: As the charge weight approaches a full case, and begins to bear against the base of the bullet, the explosion of the large rifle primer is pushing the bullet out of the case before the powder is ignited, or at least before it's fully ignited. This would greatly increase the effective cartridge capacity at full combustion, lowering the pressures. I think some form of better crimp is needed.

I would also suggest that a sample size of "one" makes it pretty tough to draw any conclusions.

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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby wildcatter » Sat Jul 25, 2009 2:04 pm

BD1 wrote:I'm going to offer a theory: As the charge weight approaches a full case, and begins to bear against the base of the bullet, the explosion of the large rifle primer is pushing the bullet out of the case before the powder is ignited, or at least before it's fully ignited. This would greatly increase the effective cartridge capacity at full combustion, lowering the pressures. I think some form of better crimp is needed.

I would also suggest that a sample size of "one" makes it pretty tough to draw any conclusions.

BD


BD,

I think you're hot after it. It's called "Bullet Pull" and there needs to be a slight hesitation or things to start cooking. Traditionally a roll crimp is the best crimp as the bullet is held in place for a sufficient length of time to allow complete ignition. A Taper Crimp is ok, but there are several problems with it. One is, if the Taper Crimp is not adequate, then the bullet can move in and out of the case during cycling. Another is the powder won't ignite well and a faster burning powder is needed. Now, taper crimps have been around for a long time and they are useful, 9mm & 45auto, attest to their usefulness. The accuracy of the Hornady 450 ammo says, "What's up Chuck, you wanting egg in your beer, or what"? Suggesting, we should be happy with what we have, Right? Well, Not Right, I want better and if a better crimp gives us the kind of bullet pull we need to burn the powder much more efficiently, and allows more powders choices and thus better performance, then I say let's go for it.

The real question is what kind of crimp is better than the roll crimp, the one we can't use, for fear of increased head spacing. Let me reintroduce the LeGendre Side Crimp, which accomplishes everything I needed to further develop the 45 Professional and now the 450 Bushmaster. Can one of you guys go over to Cal-Guns and get that dissertation I did on the side crimp and do a cut and paste here for our new readers, their going to need this. And for you new guys, there are some heavy hitters here that are using this crimp with great success, ask them about it, they'll tell ya all about it..
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby gunnut » Sun Jul 26, 2009 10:57 am

Move these comments to "Crimp & neck tension" Maybe?
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby pitted bore » Sun Jul 26, 2009 11:30 pm

BD1-

The theory you're offering is likely correct, from what I've obseved and learned. The primer ignition is pushing the bullet out of the case before the gas pressure resulting from burning powder can increase sufficiently to cause burning of the full powder charge. I posted a reference to an article about this phenomenon on the thread titled "Is anyone using magnum primers" in this site's Reloading forum. Here's a relevant quote from the article by Barsness:

"For instance, in a very small rifle cartridge such as the .22 Hornet, a 'hotter' primer might start to dislodge the bullet itself before the powder really gets going. Instead of a relatively gentle, slowly accelerating push, the bullet gets cruelly dumped into the world like a fledgling eagle pushed from the nest. This is why some Hornet fans use small pistol primers, with much milder brisance than small rifle primers."

I'm guessing that in a straight case like the 450B, moreso than a bottlenecked case, there's a pretty critical teeter-totter balance between faster and slower powders for light bullets. With faster powder, the pressures can build rapidly enough to get a good burn while the bullet is exiting the case from the primer's pressure and some initial powder ignition. The limitation with the faster powders (like Blue Dot for the 450B) is that velocities cannot go as high as we'd like. If more powder is added to increase velocity, pressures rise to unacceptable levels.

Slower powders result in the problems seen here. They don't ignite rapidly enough to raise pressures high enough to take advantage of their slower pressure rise. The bullet is propelled from the case, increasing the size of the combustion chamber, which results in lower pressure which results in lower velocity. Adding more powde doesn't work; it is simply blown out the barrel or burned without increasing pressure very much while the bullet moves down the barrel.a few inches.

(I think I said about what you did, but I used about 40 more sentences. It's ok; electrons are cheap.)

Using the LR primers to get the fire lit quicker didn't help, because they shoved the bullet out of the case quicker and further than the SR primers.

Your idea is an intriguing variation on this, in which adding more of a slower powder decreases size of the combustion chamber size, resulting in an increase in the pressure of the primer pushing out the bullet. I suppose this could be tested by substituting an inert powder-like material for the powder. The effect of the decrease in chamber size could be measured by how far the primer could jam the bullet into the lands with various charges. I suspect that the two percent decrease in interior volume with each grain of powder might not have a major effect. However, there are likely threshold effects with the pressures of the burning powder so your theory might be exactly right. Verifying it would require pretty sophisticated measuring equipment.

It is perhaps going to be impossible to get the teeter-totter to balance with bullets as light as 185 grains. There are the two remaining manipulations: a powder with a speed somewhere between Blue Dot and Lil'Gun, and playing with crimps.

--Bob
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby pitted bore » Mon Jul 27, 2009 12:54 am

BD1 wrote:I would also suggest that a sample size of "one" makes it pretty tough to draw any conclusions.

BD-
You're right - a sample size of one usually is inadequate, because more than one observation is needed to obtain an idea of variation. In this case, however, the increasing values of the powder charges produce a sort of replication.

Consider the results for the SR primers reported above:

charge - - SR
------------------
42 gr - - - 2697 fps
44 gr - - - 2736
45 gr - - - 2764
46 gr - - - 2770
47 gr - - - 2829

It looks like there is a continual increase in velocity with increasing charge. If I make an assumption that the increase in velocity is linear with charge over the range of charges, I can use conventional regression techniques to estimate variability in this range of charges. For example, a pretty good estimate of the velocity that would be produced by 44.5 grains can be calculated (2751.9 fps), and a confidence interval for that value can be found too.

The problem, of course, is the assumption of linearity, which rarely applies for any considerable range of charges in reloading. What I'm really interested in with these trials are points at which the assumption of linearity breaks down badly.

This happened with the LR magnum series:

charge - - LRM
--------------------
42 gr - - - 2804
44 gr - - - 2867
45 gr - - - 2914
46 gr - - - 2674
47 gr - - - 2704

The positive relationship of increasing velocity with increasing charge held through 45 grains, and then fell apart at the 46-grain charge. When this occurred, I was pretty sure I was no longer dealing wtih a linear relationship. I might anticipate some departure from the continual positive one, due to do variation in the system. For example, I would not have tossed out the assumption of a positive relationship if the 46-grain value had dropped to something like 2907, and the 47-grain value had been back up to something like 2935. However, the decrease from 2914 fps at 45 grains to 2674 fps at 46 grains is too much to attribute to usual variation I expected at 46 grains, based on values at 42, 44, and 45 grains. I concluded that something is messing up the expected positive relationship between charge and velocity.

We enter trials like this knowing from experience approximately what the variability of velocity around an average velocity should be. That's why we can say that an extreme spread of 9 fps for ten readings at a given charge is "good", and an ES of 200 fps is "poor". It is this experience that allows us to say that something is amiss.

You're correct in thinking that I would have been more confident of my conclusion of a messed-up relationship if I had obtained more than one reading at each charge. However, since I'm looking for large effects, the single trial values are adequate.

If a different powder or crimping were to show the positive charge-velocity relationship, then it will be necessary to do lots of replications at each charge level to convince skeptics that the cure is real.

(Another reason for a single value is that the tests use costly bullets. I've reached the point that my employer does a direct deposit of my paycheck with Midway, who monthly refunds to me the pittance that remains after deducting my expenditures there.)

Again, a big THANK YOU for furnishing the cases for the trials.

--Bob
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Re: 185-gr SWC, Chap 5: SRP vs LRP Cases

Postby BD1 » Mon Jul 27, 2009 6:46 am

"(Another reason for a single value is that the tests use costly bullets. I've reached the point that my employer does a direct deposit of my paycheck with Midway, who monthly refunds to me the pittance that remains after deducting my expenditures there.)"

This is the driving force behind my search for a cast boolit load. Over the life of a brass chucker like the AR in .450B the cost of pulling the trigger will far out way the cost of putting the gun together. The 250 grain FTXs cost me about 60 cents a bang. A 300 grain cast lead gas checked boolit about 2 cents.

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