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| <.> |
I have a .223 Ackley for which I'm working up load data. 45 gr. Hornet bullets and 31 gr. of H-335 pushes the primer back into the firing pin hole: --http://pages.chatropolis.com/general/geo/primer.jpg-- (Sorry, you need to cut/paste . . . tight assed ISP won't allow hot links.) I also got ejector marks on the rim of the brass. This is with the bullet sitting on the lands. I backed off 0.020" from the lands, reduced the load to 29.5 gr. and this reduced pressure/velocity. But I'm still getting some "cratering" of the primer. Very slight cratering, a rough edged dimple around the firing pin. The primer is not backing into the firing pin like the photo above. What's "acceptable" for the primer? I see bullets seated from right on the lands to 0.005" to 0.010" . . . to 0.020". I realize this is part of tuning the load, but what's a "nominal" set-back from the lands? Standard neck chamber. Brass trimmed to 1.750" Thanks. ------------------ | ||
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| new member |
Genghis, there could be a couple of reasons for primer cratering either hot loads or the firing pin hole in the bolt face is a good bit larger than the firing pin. Extractor marks on the case head sound like 31 grs of 335 is a little hot. Is this the only lot of this powder you have used with this cartridge? I have found that H335 can vary from lot to lot and it is somewhat picky about any changes in cases( in 308 WIN don't work up a load in civilian cases and then switch to GI brass). I have found that if I stop working up when the primer is flat but not cratered that I have gone about as far as I can before there are other pressure signs like hard extraction marks on the case heads. New primers have a slightly rounded appeareance and low pressure loads don't usually flatten the primer out. Factory loads in many modern calibers are loaded close to SAAMI limits so look at the primers in fired factory ammo, you will see that the primers are flattened somewhat but there is still a distinct line between the edge of the primer pocket and the fired primer. I know with wildcats there is a whole lot of feeling your way along but hope this helps a little. | |||
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| One of Us |
Joe is right. The problem COULD be in your bolt head, but it looks like to me the easiest way to find out is throttle back a little more on the load. No valid reason to push it that hard. Loading on the razors edge is never smart IMHO. ------------------ | |||
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one of us |
One frequently overlooked cause of cratered primers is the metal used in the primer cup itself. They DO vary, even in the same manufacturer. Primer cratering tells you nothing about the load most of the time. | |||
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| <.> |
quote: Federal 205's . . . small rifle. I think about going to something a bit heavier in the cup. The primer is not flowing into the primer pocket. It's backing into the firing pin hole. I should be able to get 3650 fps velocity from this load. Right now I'm getting about 3510 fps. Rifle is a Rem. 700 PSS. Should be in good shape. ------------------ [This message has been edited by Genghis (edited 05-11-2002).] | ||
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| one of us |
Point is, why worry about it? 205M's is what I use mostly, and in some very hot loads. They crater whether load is mild or not. | |||
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| one of us |
While I rarely if ever try to motor my guns at the top end, velocity is one of the last things I consider. Accuracy, dependability, brass life span, and several other things are looked at before I consider velocity. It kinda falls where it falls. Since you have 'fast' barrels and 'slow' barrel within the same make of rifles, I'm not sure its a good idea to arbitrarily take a velocity figure and try to work to it. | |||
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| <.> |
quote: Yeah, but a flat trajectory goes hand in hand with velocity. 3456 fps is what the books show for standard Rem. I expect that the Ackley Improved will provide more velocity -- like about 3650 fps at a charge weight of 29.5 gr. Accuracy is fine at this weight. I just wonder if the cratering is a pressure index or if it's something that I don't need to worry too much about.
[This message has been edited by Genghis (edited 05-12-2002).] | ||
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| <.> |
quote: Yeah, the chamber is chrome lined in the AR-15. You don't want to do the rechamber for several reasons: First -- rechambering requires that you set-back the barrel. This moves the gas port. You don't want to mess with moving the gas port. Second -- Ackley Improved brass gets neck sized. The case is straight walled with a steep shoulder. In theory, this is not an optimal shape for a semi-auto feed system. Third -- Neck sized brass may or may not feed into your chamber just because it's "tight" rather than full-length resized. Ackley Improved is more or less intended for bolt actions. It's a wildcat load that can get sort of "fussy" about spec. I neck turn my brass, and otherwise spend a lot of time polishing, trimming, deburring, uniforming, weighing, etc. Last thing I want to do with this stuff is have a semi-auto ejector fling it across the range and onto the ground! Generally, wildcat loadings get out on the edge of pressure spec. As strong as the action is on the AR, it's not designed like a bolt action system. The 223 Ackley increases case capacity about 10% -- 12%. And then we increase the load by the same margin with the intention of getting gains in velocity of about 10% - 12%. Standard velocity for 45 gr. bullets is about 3456 fps. I'm looking to get 3650 fps. That's about 17% gain in velocity. But we're seeing pressure signs at the primer/firing pin. Mostly what I've gained in going to Ackley is a barrel with no "free bore" a new chronograph, lots of chronograph stats, a lot more time spent at the bench, and some real working insight into internal ballistics and ballistics software. I like it. Some would not. ------------------ [This message has been edited by Genghis (edited 05-13-2002).] | ||
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| <BigBob> |
GENGHIS, You may want to check your manual to find out what type of rifle and barrel length the cited velocities were tested in. If it was a 26" barrel frm a bolt action it may be a little difficult to duplicate without the same type of rifle. Manuals are guides, nothing more. What a manual shows as a midbook load may be dangerous in another rifle. A listed max load may not even a starting load in another rifle. There are several causes of primer cratering. What does the rest of the primer look like? How far down the case does the pressure ring go? How does the firing pin fit the the firing pin hole in the bolt? To small a diameter of the firing pin, or to large a hole will lend itself to cratering. One cause of cratering that is often overlooked is a weakened firing pin spring. A weak spring will allow cup material to be extruded into the firingpin hole. I hope that this is of some help. Good luck. ------------------ | ||
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