not sure if this is real but it has been noted repeatedly. i am working up loads in a 6x47(based on the 222 rem mag) slightly modified case...30degree shoulder and slightly reduced case taper and using LT 30 powder. found a good number of 222 rem mag brass, unfired. expand neck to 6mm and turn neck slightly. this brass expands .003 across case body/shoulder area after firing. mvs and small group noted. i fl size with a whidden type S fl bushing die, which is made based on the reamer print. very little sizing just a shoulder bump of .001. now the question: i reload with the same charge and will get a mv FASTER than when "fireforming". the group opens with this faster mv which is not unusual. my suspicion is that a lot of energy is being used to expand the brass which makes it unavailable for mv while in the "fireformed" case, more energy goes into the mv. if i reduce the charge for the "fireformed" cases the mv drops to the original mv and the small group returns. my chronograph is consistent. am i seeing something that is real or what.
an increased mv with same load in fireformed case?
- Thread starter lpreddick
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What do I see? I see another thread that is headed for 10 plus pages without an answer.
I chamber a round, fire, then eject a once fired case. The one thing that will never be explained on this forum is the difference between firing minimum length/full length sized cases and a formed case.
F. Guffey
Sounds like you might have it figgered out already! -----my suspicion is that a lot of energy is being used to expand the brass which makes it unavailable for mv while in the "fireformed" case, more energy goes into the mv,
At best seems you get your groups back where you want them.... if i reduce the charge for the "fireformed" cases the mv drops to the original mv and the small group returns.
At best seems you get your groups back where you want them.... if i reduce the charge for the "fireformed" cases the mv drops to the original mv and the small group returns.
I have seen the same thing in a 308 Baer. After they are formed it takes a half grain less to retain the same velocity. I contributed it to moving the brass like you think. According to MikeCr and his ballistic programs it is Impossible. I had at least 5 different barrels and they all showed the same thing over an Oehler 33. We had many arguments over this and I gave up arguing with him. He just kept saying that it is impossible to increase capacity and not gain velocity. This is one of the reasons I don't believe everything in ballistic programs. Good luck on your answer but I believe you are correct. Hopefully you can find the next node up or bullet seating depth will bring the accuracy back. In the case with my 308 Baer I was right at the limit of the brass and the 240 Sierra didn't like a jump. Matt
dmoran
Donovan Moran
Matt -
My pressure test results basically say the same thing as my chronograph, just as yours does !.!.!
Internal ballistic programs do not account for many effecting variables, that should be looked at as basis and for predictions, not as factual. There often wrong, and at times by a lot.....
Donovan
My pressure test results basically say the same thing as my chronograph, just as yours does !.!.!
Internal ballistic programs do not account for many effecting variables, that should be looked at as basis and for predictions, not as factual. There often wrong, and at times by a lot.....
Donovan
I've seen the same thing and reached the same conclusion with absolutely no scientific tests to arrive at that opinion. It takes energy to move that brass. Seemed to make sense to me.
Case in point was a 6ppc neck sizing and FL sizing with an off the shelf Redding die. Not a perfect match between chamber and die like most ppc shooters would want.
Turned out to make little difference to me because neck sizing a ppc is a fairly futile excercise anyway
If fguffey has another theory I have no problem listening. He could have expressed it already. This is a shooting forum not a mystery novel.
Case in point was a 6ppc neck sizing and FL sizing with an off the shelf Redding die. Not a perfect match between chamber and die like most ppc shooters would want.
Turned out to make little difference to me because neck sizing a ppc is a fairly futile excercise anyway
If fguffey has another theory I have no problem listening. He could have expressed it already. This is a shooting forum not a mystery novel.
Jay Christopherson
Not An Admin
lpreddick said:
This seems like an excellent question for the ballistics forum. It's internal ballistics, but I bet you can get a cogent answer there.
If you have the explanation that the OP is looking for then why don you share it rather than just filling every thread with passive aggressive nonsense. You seem to know all things about shooting/ reloading/ ballistics, but you refuse to share any real information. Every one of you posts is a bash on someone else rather than an informative or constructive response.fguffey said:
If you fail to see the pride that we take in this forum or the value of it, I suggest you do one of two things. Either provide informative responses to the questions and topics here or leave.fguffey said:
fguffey said:
At least I expressed an interest in hearing your opinion. Obviously much more civil and opened minded than yourself. The moderators are more than welcome to edit, delete or ban me if they feel I've breeched decorum. So far I do not see a moderator badge under your name. I'm still listening for your alternative theory...................................
milo-2 said:
I have no education either.IMO it's not the volume of the case so much as it's the volume of the chamber. That's of course dependent on the brass being of equal thickness.
Size a case considerably smaller than the chamber and force will be used to expand it to the size of the chamber. If a case is already close to chamber dimensions less force is required to expand.
That's how I see it.
dmoran
Donovan Moran
The answer in my opinion is very basic and simple:
To iron the structure of a smaller case in a chamber it takes more force to do so. That extra force needed is why there is both pressure and velocity loss to the pushing of the bullet down the barrel, because some of the pressure is rubbed to iron the smaller sized case structure to the chamber walls.
Results from a pressure trace system and chronographs repeatably have shown me that even small amounts of variance between case sizing effects pressure (and velocity). And that is any time a case is stretched further to iron and adhere it to the chamber walls, it is at a loss to peak pressure, exit pressure, barrel time, and velocity.
My 2-Cents
Donovan
To iron the structure of a smaller case in a chamber it takes more force to do so. That extra force needed is why there is both pressure and velocity loss to the pushing of the bullet down the barrel, because some of the pressure is rubbed to iron the smaller sized case structure to the chamber walls.
Results from a pressure trace system and chronographs repeatably have shown me that even small amounts of variance between case sizing effects pressure (and velocity). And that is any time a case is stretched further to iron and adhere it to the chamber walls, it is at a loss to peak pressure, exit pressure, barrel time, and velocity.
My 2-Cents
Donovan
Has the smoke cleared yet? I think this is the same phenomenon seen when fire-forming Ackley Imp. cases. Fire-forming with max charges for parent case yields low MV's. The SAME charge in a F/F'd case yields much higher MV's. (about 225 FPS in my .257AI) You will probably find that your F/F'd case is also slightly shorter, just like the AI cases....... I have 3 AI's and all have had the above result. My .223AI doesn't yield as much MV increase as my AI's with larger case capacity. It all seems to hinge on case capacity before and after F/Fing...... Not scientific, just practical experience.
I think this is the same phenomenon seen when fire-forming Ackley Imp. cases. Fire-forming with max charges for parent case yields low MV's. The SAME charge in a F/F'd case yields much higher MV's. (about 225 FPS in my .257AI) You will probably find that your F/F'd case is also slightly shorter, just like the AI cases....... I have 3 AI's and all have had the above result. My .223AI doesn't yield as much MV increase as my AI's with larger case capacity. It all seems to hinge on case capacity before and after F/Fing...... Not scientific, just practical experience.jo191145 said:milo-2 said:
IMO it's not the volume of the case so much as it's the volume of the chamber. That's of course dependent on the brass being of equal thickness.
Size a case considerably smaller than the chamber and force will be used to expand it to the size of the chamber. If a case is already close to chamber dimensions less force is required to expand.
That's how I see it.
Well I'm about to find out yet again on this, just had a 6CM built, fireforming brass with 47.3gr of IMR 7977 behind a 115 Dtac. I'll chrono the 1st 5 and report back. I firmly believe vel will drop here. Waiting on a die to size right now.
milo-2 said:jo191145 said:milo-2 said:
IMO it's not the volume of the case so much as it's the volume of the chamber. That's of course dependent on the brass being of equal thickness.
Size a case considerably smaller than the chamber and force will be used to expand it to the size of the chamber. If a case is already close to chamber dimensions less force is required to expand.
That's how I see it.
Well I'm about to find out yet again on this, just had a 6CM built, fireforming brass with 47.3gr of IMR 7977 behind a 115 Dtac. I'll chrono the 1st 5 and report back. I firmly believe vel will drop here. Waiting on a die to size right now.
Well I would expect you lose velocity while fire forming also. I just think your original post is a little contradictory. You can't have less velocity while fire forming and then expect less velocity from fire formed also. Maybe I'm reading it wrong.
I think dmoran stated it quite well in post #15. He should up his rates to 3 cents.
Brians356
Gold $$ Contributor
fguffey said:
What do I see? Another thread wherein several surly, recalcitrant chaps (who BTW would fit in quite nicely over on the Guns And Ammo campfire and bean-eating contest) get into a p__sing match here, a lot of dung gets flung, some inappropriately-prurient animation gets posted, and the thread gets "disappeared" by the Admin.
But before that train eventually wrecks: The "energy diverted to expand the brass" explanation seems plausible. Especially since several AI case formers claim to have documented the same phenomenon.
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