Internal ballistics frustration.

[goodgrouper]

I have run into this a bunch in my reloading of big cases (over .515" at the web).

From what I understand of your problem, the brass fits when new, then each successive reloading from there gets harder and harder to chamber and especially extract. If this is the case, I would say that the problem is in your FL die. It is short enough to bump the shoulder back (which if it's an RCBS die is flat out amazing) but it is incorrect dimensionally in the web area of the case. These big cases need clearance in the web area more than smaller cases. If your chamber is small to normal in the "arse" end and your die is large for spec in this area, cases go in snug to fine but are an absolute ^&#*# to come out.

Check the diameter of the web of some virgin brass and then compare it to some that have been fired once and then to some that have been fired twice or three times. Then measure the web of some that have been fired a few times and have also been resized by your FL die. If there isn't much diff in the measurement of the sized brass vs. the 3x fired brass (.001-.002") than you have a chamber dimension to die dimension problem.

Remedy: get a new FL die. Preferably a Redding or custom.

 

[Michael Eichele]

[ QUOTE ]
then each successive reloading from there gets harder and harder to chamber and especially extract.

[/ QUOTE ]

Almost. After resizing, in all cases the cases chamber perfectly. Its only the extraction on the sencond and third time fired. The case head expands about .002" Slightly less. When I resize them, they remain .002" bigger than a factory new case. The drawing I have on the chamber specs show the head to be .5479" The cases new are .545". When fifed they are .547". After resizing they are .547". Would that contribute to this problem despite them chambering easily?

 

[Michael Eichele]

[ QUOTE ]
Is it perfectly straight or can you see any expansion bands around the body of the case.


[/ QUOTE ]

From what I can tell. it seems to be straight without any rings.

[ QUOTE ]
Do you have even bolt lug contact and has your receiver been accurized and trued?


[/ QUOTE ]

Yes and yes.

[ QUOTE ]
It does seem odd that you need to set the shoulder back that much to chamber easily with a sized case.

[/ QUOTE ]

I never had to set it back that much to get them to chamber easily (.005") They expanded .003" from new and I would set them back .003 to get them to new size + .002" hoping that would allow a little more case expansion for less pressure spikes. The new cases fired once will chamber back in perfectly whether resized or not. In all cases, if I resize them, even just setting the shoulder back .001" from the fired size, they chamber perfectly. I think I am dead wrong in setting them back that much. The reasoning was if the new ones extracted so easily, a lillte smaller would extract even better. I see now that this may be a bad idea. Do you think this could contribute to the problem? Is this creating more pressure than normal?

I am on my way to the range to see if setting them back less will help.

Thanks for all of your guy's valuable input.

 

[Michael Eichele]

I just got back from the range. I shot 5 rounds with twice fired cases and one 3 times fired case that was a bad offender. After resizing them to just bump the shoulder .001"-.002" instead of .005" helped quite a bit. They all had slightly difficult bolt lift, but not too bad. Slightly difficult meaning that, I can feel some resistance while lifting the bolt, then to get it to pop all the way up, it takes some minor to minorly moderate force. The actual extraction (act of pulling the bolt back and case out) was easy. Just the bolt lift required a little persuasion.

None of them pulled my extractor apart this time. Next I am going to try .0005-.001" and see if that improves it any more.

 

[Fiftydriver]

Did you shoot them over a chrono, it sounds like your running some higher presures as well. I have heard this with the Nosler cases that their internal capacity is smaller then say a Rem RUM case.

That bolt lift tightness would make me think that. At the top of the bolt stroke is where the mechanical extractor cam goes into effect. Do you need to give the bolt a slight pop to get it to go this last little bit and then the bolt comes back easily, I would check your velocities and see what they are saying with these loads.

On another note, that extractor pulling out would have me a bit worried. When Sako extractor is properly fitted to a bolt, the more pressure back on the bolt should pull the extractor down into the bolt, not out of the bolt. I would look into this as well, that is not right for some reason.

Kirby Allen(50)

 

[älg]

Why dont you try some just neck sizing?? It may give you a clue.

 

[Norz]

[ QUOTE ]
Why dont you try some just neck sizing?? It may give you a clue.

[/ QUOTE ]

This has ocurred in my 300ultra, it did however disappear when I necksized only.

 

[Michael Eichele]

[ QUOTE ]
Did you shoot them over a chrono, it sounds like your running some higher presures as well.

[/ QUOTE ]

Yes, I shoot most of my rounds over a chrono. Velocities for the 200 ACCUBOND are 3134 FPS average (corrected for 15') with 95.5 grains of H50BMG. If it is pressure, I have no idea what would cause excessive pressure with this load in a 27.25" 12 twist barrel.

[ QUOTE ]
Do you need to give the bolt a slight pop to get it to go this last little bit and then the bolt comes back easily,

[/ QUOTE ]

That is correct.

 

[Michael Eichele]

I will try neck sizing only, but with once fired brass only for now.

 

[goodgrouper]

[ QUOTE ]
When fifed they are .547". After resizing they are .547". Would that contribute to this problem despite them chambering easily?

[/ QUOTE ]


Bingo! You have the problem I mentioned. I absolutely positively guarantee it. The reason they go in ok is due to the taper in the case from the head to the shoulder. It is shaped to go in ok, but is opposite of what it needs to be to come out as easy.

Your brass started out undersized enough to get by with some possible hot loads, but after a few firings, it got blown out .002" and was not being sized back in enough to afford enough clearance. Your die is pushing the shoulder back plenty, it's just not squeezing in the body at all. Or if it is, it is not squeezing it in enough to offset the spring back in the brass.

Get a Redding FL die and see if it squeezes it enough. If it doesn't, a custom die made from your brass will work marvelously.

BTW, on my 338 thunder dies, I had to have them made to squeeze in the web area about .003" to give .001"-.00075" clearance on a chambered round after springback. Until that clearance was there, it was super hard to extract cases. The fatter and straighter a case is, the more likely it is that extraction problems will be encountered.

Hope this helps.
Good luck.

 

[Michael Eichele]

50,

I have a Redding body die on the way. I have had it coming for a few days now hopping that might help. I did go back to the range after bumping the shoulder a tad less and it seems to have helped even more. I had much less popping and the end of the bolt lift cycle. Hopefully, the .547" at the arse end is only one of the contributing factors and hopefully it will be resolved soon.

BTW, this last trip to the range I adjusted my powder charge .5 grain to offset the less sized brass and shot a .684" 3 shot group at 300 yards! This of course with a barrel that should be 60-70% shot out. I think shot out is a subjective term.

Thanks again to all for the help.

 

[Ballistic64]

I think GGs right,when you get your body die adjust it so the shellholder comes up against it tight and size one of your offending cases (besure to lube it).Then chamber it,your bolt pop at the end of the lift will probably be absent and will be much less prevalent after firing.You may later find that you can adjust the body die up off the shell holder slightly and accomplish the same results or just get a set of the comp shell holders.

 

[goodgrouper]

[ QUOTE ]
shot a .684" 3 shot group at 300 yards! This of course with a barrel that should be 60-70% shot out. I think shot out is a subjective term.



[/ QUOTE ]


I once had an extremely accurate 22-250 AI that shot well it's entire life. Then at about 1200 rounds or so, I shot several 5 shot groups in the .1" back to back. Then the next day, I went out and fired the gun and it was so inaccurate that I almost destroyed my chronograph. It lost it's accuracy overnight.

Sometimes they go quick and sometimes they gradually fall off. But believe me, pushing 95 grains of powder down a 30 caliber hole will be hard for any barrel and it will probably be done sooner rather than later! /ubbthreads/images/graemlins/frown.gif

 

[Michael Eichele]

[ QUOTE ]
Sometimes they go quick and sometimes they gradually fall off. But believe me, pushing 95 grains of powder down a 30 caliber hole will be hard for any barrel and it will probably be done sooner rather than later!

[/ QUOTE ]

Amen to that!!

I was a bit sckeptical about getting such an overbore caliber at first due to this fact. That and the cost of powder and the ability to load it into the case with a shovel, plus the recoil. I had been a die hard 308 finatic. I still am. But the trade offs are worth it when I have a 1500#+ critter in the crosshairs at 650 yards. This rifle has as much energy at 600 yards as my 308 has at the muzzle. For the reason that the barrels burn out so fast is why I had it set up as a switch barrel. I also have an ABS barrel in the works and hope to get some loads developed and I think after some initial testing and verification, I will for the most part quit shoting that barrel. I will then get another Lilja to replace the one I have for the amount of shooting I do. He?? its only money right! /ubbthreads/images/graemlins/grin.gif

Also, that .002" expansion at the base that I cannot get rid of with my die, my chamber is .5479 and the cases are .547. After FL resize, the chamber and extract perfectly before they are fired. My question is this. Scince I started bumping the shoulder back less, the problem is starting to iron itself out. Why would bumping the shoulder .005" back and then firing it cause this?? I would have thought it would generate less pressure. I do know that some time ago, I set some back .025" and after firing the first one, it literaly blew the case in half around the case head. In other words there was complete case head seperation. The funny thing was, the chrony read a lower than normal velocity. This too seperated my extractor. ARRRGGG!