Obturation compensation?

Doug

Member
Well, this new money mold drops perfectly, nice and round and w/ a .459" base, but at a .449" nose that needs to be .450" Tried beagling 5 different ways so am lapping the nose for .001" and "Lee-menting" the whole thing afterward. I'll be goin slow--by hand and not by drill--so should be ok.
 

fiver

Well-Known Member
you can pour through a nut and use that to turn the lap.
but whichever way you go, go slowly, and be neat about where you put the lapping compound.
I have found that just removing the blueing from the inside of the mold is close to .001 and working on roundness rather than diameter will pay off better.
make some test casts along the way and don't try to rush things.
 

Doug

Member
Thanks fiver. Success! Don't mind sayin I feel a fair bit of accomplishment, but was a little concerned when the mold seemed to go through its break-in process each time I made a new plug. But it's done, and exactly at .450. It lightly engraves--more a nice scuff actually--at the leade. Interestingly also I was only able to find one of these molds that specifies a .450 bore riding section. Wasn't really sure whether or how to proceed til I found that quote above by the designer of this bullet, but it jived w/ what I've seen here about the need for a chamber fill.
 
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James W. Miner

Active Member
I loved to go to BPCR shoots but never got my Browning to shoot like I wanted.
One fellow had one like mine and cleaned the turkeys so shot a long run. I think he had 37 or 38 before he missed. I never learned what he shot.
I bought the 500 gr Lee mold and it plain sucked and was told by top shooters, the nose slumped off center from no support.
I could get good groups at 200 meters but spotter would see boolits go off course well before 500 with any boolit so rams were hard to hit. It came to luck only.
I have a 1 in 18" twist and My revolver will out shoot it at any range. My 45-70 BFR has a 1 in 14" twist so I wonder what a faster twist would do?
Most had custom rifles that cost more then my property but nobody ever told me what twist or load.
I bought a mold at a shoot once. Expensive type for a heavy boolit. No sprue plate or handles but for $5 I had to have it. I make my own molds so I made a plate and the boolit will not shoot. I think you can go too long and heavy. This mold might work with a 45-110 or so.
With a pile of molds, I still think the Rapine 500 Gov't works best at .461". But many 45-70 rifles have worked much better down to 300 gr bullets/boolits. Even an original trapdoor and a roller shot my 317 gr into one hole at 50 meters.
I think my mistake was the heavy boolits.
Fit is so important but so is a twist rate and spin for long range.
 

Doug

Member
Well James,

We recently had a chance to shoot the modified money mold I lapped. We're limited presently to a 200 yd range but shot a 200/300/600 yd match a week ago. Til then I'd only managed 60 shots w/ the new Browning to fire form some brass, and might have had about 2 MOA groups at best before lapping the nose section. The match was the first test for the enlarged nose. This bullet is long and heavy (535 gr) and the bore riding section has to support against the slump of wh/ you speak, so the added diameter there and an 18:1 alloy were where I'd placed my hopes. BUT, we have an 18 twist on both rifles, tho I've read that the current fad is toward 16. We had great results, much improved to sub-MOA even out to 600.
 

James W. Miner

Active Member
Sounds good. Everything you find is of interest to me even if I can't hold my rifle any more. There is still the bench.
I could never shoot the gun off hand any more. I tripped and fell in the barn, landed on my fore arm and must have torn something in my shoulder plus my right shoulder was injured at work just before I retired and is bothering me.
I can't raise my left arm to open the door even with just a news paper in it.
Eyes are getting worse too.
 

Doug

Member
Forgot to add that we also beagled the base to accomplish .460 bands wh/ either shrink down or, if new, can be sized down to .459 to snugly thumb seat into the fire formed brass. Obvious best case is no sizing anywhere. As for off hand shooting, we haven't broached that yet and my tighter groups were no doubt helped by our first time shooting prone. My wife actually had back trouble for days after trying 5 off hand shots and is now refusing to compete next week in that part of the match requiring off hand. Can't say that I'm looking forward to it either. But we'll both join the 1K side match, and will see just how this bullet holds up at that distance. Should also mention that we've since modified our other working molds accordingly. Glad we found this site and learned that Fit is King, maybe especially for we who rely upon these long bore riding sections.
 

James W. Miner

Active Member
Sorry about the wife halving back problems. Carol has knee problems big time. It is funny I have no pain but can not lift things, like a wall in front. A STOP like lifting an anvil. I can be 100% pain free all day but can't do things that were so easy a few years ago.
 

Ricochet

Member
I have a 1973 1895 Marlin with the 8 groove rifling they made as a transition between the 12 groove "Microgroove" and 6 groove "Ballard" rifling. Its groove diameter is right at .4585", right at the Marlin spec of .4584". I have a Lee C457-500-RF that drops bullets right at .457". Shooting them plain based at 1400 gives a little more leading than I'd like. I have three ideas for fixing it. One is to get some checks and size them to .460" and see if better sealing at the base will compensate for the slightly loose groove fit. If the chamber and throat will accept it I'll try patching these bullets. If that's too big to fit I'll run them through a .452" sizer and then patch them. Patching is no more work than sizing and checking, so whichever works best is what I'll stick with.
 

James W. Miner

Active Member
Marlin never got it right and Browning has the same problem with 8 groove and Marlin with Ballard. Grooves are the same depth as micro groove so they actually lose grip faster. I have slugged many and found .003" rifling in all of them. Bore sizes are close and still need a larger diameter boolit.
Ballard should have deeper rifling but they missed the boat or it sank.
Like a RB rifle barrel is best with .010" deep rifling and TC makes theirs too shallow now.
Too many guns are made only for jacketed or sabot's so cast is on the back burner.
Cast just starts at at least .004" grooves and .006" is better.
I really think the right fit in a micro groove is better then in Ballard with the same groove depth.
I am always the odd man out and think a revolver should have a faster twist then a rifle and as a barrel gets shorter, twist should get faster.
It is a fact that handgun shooters ignore twist. marlin lost their mind with the .44 lever gun with a 1 in 38". They had complaints over the .444 so they changed it to 1 in 20" so I complained to them over the .44 mag and they sent me the Greenhill formula and any one with a brain knows it doesn't work. If you can't drive a .444 to spin, how would you in a .44 mag?
Never ever base your gun on spin formulas, none ever work.
I also believe drive length of a boolit works better then overall length, what use is a nose that makes no contact with rifling? Measure length of a boolit, work out twist and you will be far too slow.
 

James W. Miner

Active Member
Hey fellas, back problems cropped up and Carol was in a car accident where a girl on a phone turned in front of her. Bulged 3 disks and one pressed hard on the nerves to her leg. She could not walk or sleep.
Don't get cut. We found a chiropractor with the machine that stretched the spine with a computer controlled machine plus they gave her nutrients and tenz treatment. Expensive because it is elective. It cured her FAST. After the first treatment she walked out. Took time but her disks healed.
PLEASE don't go under a knife unless there is no hope but you will never be right.
Maybe the Teeter hang up would do the same.
Doctors have ruined so many of my friends it is unreal.
My daughters had rotator cuff injuries and had surgery. Wire a tendon to bone, grind away bone. The wires break and poke out of the bicep. Both lost jobs. They are still not right.
Fuse the spine---NO. Not a single person that had shoulder surgery I know can work. Your back can heal done right.
 

fiver

Well-Known Member
holy cow James.
glad the back issues were fixable without surgery.
some of the doctors I have seen work have no cutting skills they just saw at the tissue and make things worse.
 

James W. Miner

Active Member
I worry about all of you. Your body can fix itself. but might need a little help. I have shoulder problems but no quack will wire tendons to bone.
I got in trouble at work once. Hurt my knee big time with a bolt in the airplane pit that I kneelled on. Swelled twice the size but I would not go to the company quack that was being sued from many. I went to another doctor. Orthopedic surgeon, an Indian by the way. He said no draining or surgery. Just wrap it and don't walk on it. A supervisor seen what happened and said he will stand by me. Joke of course. I was home on the couch, wrapped from hip to foot and the bell rang. Stinking same supervisor to see if I was faking. I needed a paper from the doc to confirm it was industrial but got nothing. I stopped at the mail box before going to work and found the letter. I just punched in and the Union guy asked where I was, had a hearing but I was not told. I gave him the letter and was saved from being fired.
Look out if hurt on the job. Those bastards do not want a claim and will fire you right quick. Both of my daughters were let go from shoulder injuries. Everyone I know that were injured on the job are not working.
 

fiver

Well-Known Member
my old company took a different tact.
they sent you to a physical test before you could come back after a surgery or lost work time, which was much different than the initial job test.
they made you do sit up's and push up's, carry weights up and down a hall-way and a bunch of stuff like that.
when you looked around a new class of guy's you could tell who didn't have to go to that physical as many of them couldn't do 5 sit up's or push up's in the stretching class they made you take as part of the new hire orientation.