Re: 5mm smc
Been reading your post again and I think I understand your comments that all the powder ignites at the same time, but is not totally burnt up at the same time.
So I assume you feel there is a progressive burn of the powder, In the case, as the bullet travels down the barrel.
I guess I can not argue that point with enough solid data to make the debate worth my time in any way.
The question I do have for you is about powder being pushed down the bore while burning. I am not sure if you have ever experienced what I call powder bridging??? Probably not because from your explination, this could simply not exist.
In my world, when I was developing the 257 Allen Magnum. I Felt that with the 95 gr powder charge capacity of my magnum and using a 130 gr FB HP Wildcat Bullet that Retumbo would be pretty hard to beat for top performance.
I started with this powder, loaded up 80.0 gr which was around a 75% load density. I was expecting hangfires from this load as well. In stead, one shot would hangfire, another would blow the primer out of the case.
I figured the problem was the low load density and probably had to do with the position of the powder at the time of ignition. Worked up the powder charge until I was around 85.0 gr Retumbo. First two shots, worked perfectly, this was during fireforming brass as well. Those two cases formed perfectly, mild pressure, nice round shoulder on the primer, no cratering, case shoulder was formed right at 95% with just a slight radius left on the shoulder.
I was in the chips, had my fireforming load. Loaded up 15 rounds to do the barrel break in and form some cases.
First shot literally blew the primer pocket. When I ejected the case it fell out in my hand.
Second shot was perfect with mild pressure, third shot again opened the primer pocket dramatically.
I had no idea what in the hell was going on. Tested with some other powders and had the same results. In fact H-50BMG would blow primer pockets out at any load you put in the case. Even one that should have really not even been up to around 35,000 psi blew the primer pockets clean out of each case on the first firing.
I was very unhappy and a bit nervous as well and was very close to bailing on the project all together until I set at the loading bench one day playing with things. If I poured the stick powders into a funnel to quickly, every time, the powder would lock up and the powder flow would stop unless I tapped on the funnel and sometimes very smartly to get the powder flowing again and then it would again stop after only a small amount passed through the funnel.
I then grabbed an old can of H-870. I dumped a good charge into the same funnel and the powder flow never stopped one time. It was smooth and consistant until the all the powder had passed through the funnel.
I loaded up 80.0 gr into my 257 AM under the 130 gr bullet. The handfire was terrible but pressures very mild. I jumped up 5 grains to 85.0 gr and the round fired perfectly but still very low pressure. I upped the load to 87.0 gr and the shoulder on the case rounded up to where I wanted it with still very mild pressure.
A light went off in my noggin. I grabbed a piece of 1.750" barrel shank stub and machined,, as close as I could match the inside dimensions of the 257 AM case to represent the powder chamber of the round. I then reamed a 0.250" hole through the end of it. I poured 80 grains of Retumbo into the hole and it stuck right where it was. I had to vigirously tap the side of the chamber to get the powder to work out of the .250" hole.
I then poured in 90 grains of H-870 and it flowed through with perfect consistancy from start to finish.
I loaded up 15 more rounds with H-870 and every one was VERY consistant in pressure and all cases formed perfectly with no strange pressure spikes of any kind.
By this time my order of WC872 had arrived so I started working with this powder and the new at the time 156 gr ULD RBBT. I started at 80.0 gr and worked up to a max working load in that rifle of 92.0 gr with a muzzle velocity of 3340 fps at the top end. At every step velocity increases were predictable and consistant. Never were there any stange pressure spikes.
I repeated these similiar tests soon after when my 6.5mm Allen Magnum was up and running by reaming out the hole in the machined powder column part to 0.264" with nearly identical results to the 257 Allen Magnum which makes since as they are so similiar in bore diameter and case volume.
Then I did the same test with the 270 AM and was suprised to find out that Retumbo worked extremely well in this round when it was matched to the appropriate bullet weights, generally in the 130 to 140 gr range worked the best with Retumbo. It was consistant, predictable and showed no sign of any strange pressure spikes. Why was this, I went back to the bench. The case volume on the 270 AM is roughly 10 grains more then that of the other two smaller rounds because it is based on the full length 7mm RUM case compared to the shorter ones based on the 338 RUM.
I reamed the center hole out to 0.280 and interestingly enough, the stick powders flowed much better though this diameter hole, no change with the ball powders, they flow through anything. There were some minor hang ups but only a very gentel tap on the cylinder would get the powder flowing again if it did stop.
When my 300 Allen Xpress was up and running, I though Retumbo may be the very best powder for that round using the 180 gr class bullets and I was not wrong. I got the highest velocity levels with this powder of any other powder with this bullet weight. With the heavier 220 to 240 gr pills, US869 gets more velocity and with the 240 up to 265 gr bullets, WC872 got the highest velocity potential.
Again to test my powder bridging theory idea, I reamed the cylinder hole out to around 0.310" and now the stick powders flowed MUCH better. Very rare was it that the powder locked up and stopped flowing.
I then tested H-50BMG which is significantly larger in granular size then Retumbo and while there were slightly more powder stopages, it was still pretty rare.
I then reamed the hole out to .340" and I could not even get H-50BMG to stop flowing through the cylinder.
My theory was and still is this, the smaller bore on the 257 and 6.5mm AMs simply would not allow the stick powders to flow freely through the neck as the round was ignited, the powder would lock up in the shoulder area and at times cause severe pressure spikes which would result in the blowing of the primer pockets.
In the 270 AM, this problem pretty much went away with the stick powders and any of my rounds larger then 7mm have never shown any sign of this no matter what powder is used.
Again, even with H-50BMG which I tested in the smaller rounds as well thinking it may have been a simple burn rate mismatch made the problem even worse.
Why would this be if your theory is correct. H-50BMG and H-870 are very similiar in burn rate but H-50BMG would blow primer pockets out every time where as H-870 would and has never once has this problem???
If the powder was staying in the case while it burns, there would never be a problem.
I am curious to hear your explination as to why YOU believe this problem was occuring and if the powder never leaves the case intact, how or what was causing this problem to occur????
In my opinion, with all due respect, while some of your points are right on, some do not match up with actual real world test results.
Again, I never have claimed to know near what you do about internal ballistics, I simply observe what happens, tests some things out to try to reproduce similiar results and try to figure out why they happen and what to do to correct these conditions.
I am 100% convinces that the powder was bridging in the shoulder are of the 257 AM and 6.5mm AM with the stick powders and I would doubt you could ever convince me otherwise because it makes perfect since especially after finding powders of the same burn rate that work perfectly well and only are different in granular dimension, i.e. ball form that flows VERY easily.
Again, if your theory is true, my problems never could exist as they happened. Are you saying that the problems I encountered could not have possibly happened?
Just curious how you would explain such occurances if you happened to see them in one of your rifles?
Again, no flame intended or disrespect, just asking your opinion as to why these things happen.
Interestingly enough, I have talked to many shooters using the several versions of the 25 cal wildcats based on the 300 RUM case. IN every instance, those that used a shoulder angle shallower then 25 degrees had very few issues with what I call powder bridging with stick powders. With shoulder angles in the 30 degree range, this started to occur more often, with shoulder angles over 35 degrees, no stick powders were usible.
Again, logical thinking tells me this is because of the angle at which the powder is funneled into the neck of the case. Again, if all the powder burns inside the case, this should make no difference at all to inconsistant pressure spikes.
Let us know what you think, very interested to hear your response.
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