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I was at the range this morning working up loads for a new 243 Ack Imp. I had fireformed brass at 41 Gr. IMR-4350 with 80 Gr. Hornady FMJ. These loads gave better than MOA with velocity around 3100 with SD of 24. In my fireformed brass, I was working the load up 1/2 Gr. at a time looking for pressure signs; I was using 100 Gr. bullets and started with 41 Gr IMR-4350, 3048 FPS. At 43 Gr. I had a tremendous pressure spike. It was hard to extract. The brass had flowed back into the ejector slot. The velocity was only 3178. This is the worst pressure spike I've ever had. ------------------ | ||
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I wonder if it might not have been one of those pressure excursions we sometimes hear about? Paul B. | |||
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| <.> |
Several possibilities . . . Some brass is soft, and you may have found a defective piece. I assume uniform brass / production lots / etc. but I see a lot of people firing mixed brass. If your barrel got hot, you could get a spike from just heating up the load while it sits in the chamber. Brass is a very excellent conductor of heat. The interior wall of your chamber will be hotter than the exterior surface of your barrel. PO Ackley talks about "bore capacity" -- the point at which incremental increases in charge weight do not provide the same incremental increases in velocity. If each 0.5 gr increase gives you let's say 75 fps increase in velocity, and then you start seeing 35 fps increases, there's a good chance that you're at the top end of the load. You increase pressure, but you don't gain velocity. I wonder if you got to bore capacity without realizing it. I confess to not seeing slight primer cratering in small rifle primers on my .223 Ackley. Realizing that this photo is greatly enlarged, this is the primer that made me review my load data -- --http://pages.chatropolis.com/general/geo/primer.jpg-- (Sorry, you'll have to cut/paste. ISP won't link images.) I'm working up loads as we speak. I assume that you're watching the seating depth on your bullets, and ensuring that brass is trimmed to length so that the bullet doesn't get pinched in the end of the chamber by a neck that extends into the lands. Please forgive me if all this sounds patronizing. I have buddies who don't trim or measure brass and shoot range pick-ups. That's why I mention the obvious. It's just not obvious to some. ------------------ | ||
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Gengis....you've mirrowed my thoughts about seating depth. When working anywhere near max pressure, or where you think is max pressure, differences in seating depth ie distance off the lands can be very important and can cause disproportinate increases in pressure. Get something like the StoneyPoint tool and measure every round when you are close to the top. | |||
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Genghis: The brass was uniform and trimmed to the same length. The fireform loads were seated hard against the lands. I used two different brands of brass during the fire forming with no problems, Federal and Rem. 3 of the Federal brass fatigued near the shoulder and were discarded druring fire forming; maybe the Federal brass is no good. The one that showed high pressure was Federal; I have not loaded any of the fire formed Remington yet; I've still got about 30 to fire form. I had loaded 3 Fed. at 43 Gr., so when I had the pressure spike, I measured the other two and then weighed the powder charges. They were off the lands by .01 and were charged with 43.0 Gr. Maybe the cartridge did get warm in the chamber, but I was touching the barrel between shots to make sure it wasn't very hot. It's possible that I could have short stroked the reloading press and had this one round touching the lands as well. I'm going to switch to Remington brass and start working up again, but I've got to put this project on hold for a week or two. ------------------ | |||
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JD check the primer hole on that case. Ooops-- just saw your "seating hard against the lands". That explains it. [This message has been edited by aladin (edited 05-15-2002).] | |||
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quote: I believe he was fire forming at this stage. | |||
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eldeguello: There was no pressure sign prior to the one at 43 Gr. Primer hits were fine, and I mic'ed them as normal size after the spike. The high pressure one did expand .001. aladin and scout: I was fire forming when the bullet was hard against the lands. ------------------ | |||
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You can also get increased pressure by setting the bullet deeper in the case. | |||
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| <.> |
Seating the bullet deeper in the case affects pressure on handgun loads where seating depth significantly affects case volume. This shouldn't be an issue in a rifle case. I hear rave reviews about Winchester brass as compared to some of the other brass. Nothing to base it on except what I've heard. Although I've heard this a fair amount. O.010" off the lands should be fine for seating. Should be. Seating against the lands drives pressure/velocity very significantly. ------------------ | ||
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Check the case weight and the capacity of your Federal cases compared to the other brand. I regularly find Federal brass to be considerably heavier and volume less. In my 300 Sav. loads max out at 1.5 grains less powder than in W.W.. Rem brass usually falls in the middle. My 30-06 requires 2 grains less in Fed cases than with W-W. 257 Ackley similar. Velocities are nearly the same regardless so pressures are very comparable despite different qty. powder. I generally find Fed. brass to be strong but have separate load notes for their brass. | |||
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I went back to the range a couple of days ago with new loadings for Federal. I had weighed all my brass and segregated them to eliminate this as a problem. At 42 grains the primers started to flatten a bit; so I'm thinking I must have missed this in the previous loadings. I then fire formed about 30 Remingtons using the 41 Gr. IMR 4350 with the bullet hard against the lands. The last few Remingtons had a slight amount of primer flattening, so I think my barrel must be getting fouled very quickly. Also, the last few Remingtons had slowed down by about 40 fps. [ 06-09-2002, 23:17: Message edited by: JD ] | |||
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| <Powderman> |
For fireforming, I would probably use a lighter load. You're not looking for gilt edged accuracy, or trying to get good velocities. As a matter of fact, I would probably use some real "pud" loads (short and weak) just to get the brass to flow. As a suggestion, try light charges of a faster burning powder, and the lightest bullet you can use for the purpose. Also, to cut down on pressures, you might try inside reaming the neck prior to loading. | ||
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Did you check neck clearance? Dutch. | |||
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