Obturation compensation?

James W. Miner

Active Member
Can you shoot a 1" target at 100 yards? Most of my guns will but I am getting too old to hold steady..
Rick you are close to my age. Neither of us can do what we did.
The years have not been kind.
 

Doug

Member
Well Jim, I'm familiar w/ the "beagling will add roundness" consideration, and as I'm only adding .002" make this another check box for trying beagling first. As for that neck tension--wow. But I gotta go w/ our particular specs on this one--the best shooters in our BPCR game use no neck tension, or .002" at most. BUT, beautiful grouping sir. Fraid we're also limited in our BHN, and softest you'll find at comps is 30:1, w/ most bein at 20:1 or, at most, 16:1 for long bore riders against nose slump. (We tend to use "slump" for the nose and "bump up" and "obturation" for the seal.) And what Quick asks has also come up in my research and perhaps ties in here--in my case it's 1/18 for both, one @ 30" and other @ 34" for 500-535 grainers.
 

James W. Miner

Active Member
I did not size brass for most BPCR either but used boolits a little over groove and with the browning, even went to ..464" due to a pound cast. Browning's are close to a Marlin micro groove so need fatter. I found the Rapine 500 gov't shot best at .461" The Lyman boolits at .457" was rock tossing. So were RCBS molds.
 

James W. Miner

Active Member
Well Jim, I'm familiar w/ the "beagling will add roundness" consideration, and as I'm only adding .002" make this another check box for trying beagling first. As for that neck tension--wow. But I gotta go w/ our particular specs on this one--the best shooters in our BPCR game use no neck tension, or .002" at most. BUT, beautiful grouping sir. Fraid we're also limited in our BHN, and softest you'll find at comps is 30:1, w/ most bein at 20:1 or, at most, 16:1 for long bore riders against nose slump. (We tend to use "slump" for the nose and "bump up" and "obturation" for the seal.) And what Quick asks has also come up in my research and perhaps ties in here--in my case it's 1/18 for both, one @ 30" and other @ 34" for 500-535 grainers.
I fully agree about BPCR and hard does not work as well, tried it and got leading and no better accuracy at all. You sure do not want to do to a BP case what I do for revolvers.
I shot a lot of BPCR and I never tamed the beast, shoot my 45-70 BFR revolver better. My best 5 shot group was 2-1/2" at 500 yards with the revolver.
I shot with the best at IHMSA and BPCR at Shippensburg but there was a difference. Top IHMSA shooters took you under a wing to help as I tried to do. But BPCR shooters were secret.
Many shooters themselves are reluctant to take advise. You need an open mind and test things without trying to dig a deeper hole.
Everyone shooting a .44 back then used 4227. I told them to drop it but the next shoots they still used it and to hear the cussing on the line made me throw my hands up! I told them the .44 needs 296 and a Fed 150 STANDARD primer but to even pry them away from a mag primer because the book said so was beyond comprehension.
How I wish a BPCR shooter at the top would share but it never happened.
I can make a ML shoot and won so many prizes and groceries, clubs changed rules so a guy that hit 10 out of 40 got the same amount of groceries. I quit that stuff. It got like the handicap system when bowling or early archery competition. many sandbag all year and go nuts at the end.
 

Doug

Member
Well Jim, I'm a cherry to this BPCR game but fortunately I'm in it for my own reasons/what all the prep work and experimenting does for me. I even like the time (wiping) b/t shots. And casting 300 bullets does as much as a summer in a Zen monastery. Haven't ventured yet into primer-land, 'cept that I wanna try Fed'l BR. But I feared I'd be hamstringing myself if I limited myself to BPCR considerations only, so I read over at 6mmBR site too, and some others, and came here of course. Now the guy I just got my Browning Creedmoor f/ once posted at the BPCR site, "what effects do harmonics come into it for us?", and to a man every single post-er thought he was askin about null point. Fraid a lotta the BPCR crowd mite be limited in their approach to ALL THINGS ballistic. But what do I know? For me, it's been a good intro to shooting. BTW, just came across a neat site for resources

http://castpics.net/dpl/index.php

Lots of books, articles, and even owner's manuals. Cheers,
 

Rick

Moderator
Staff member
Yep Doug, castpics is one of the very finest info/reference sites on the web.
 

Doug

Member
Well Everyone,

Thank you all. Beagling was a great success, and if anything I even gained a little roundness, maybe b/c the caliber/bullet/block is so large. All I can say is that my wife will be very happy tomorrow--fortunately this proper fit is coming early enuf to show her some tighter groups and will help in her confidence and enthusiasm. And just in time for the upcoming match too. Much thanks.
 

James W. Miner

Active Member
I just wish I could have figured out BPCR, Now I can't hold the gun up anymore from shoulder injuries.
Been wanting to sell the Browning. No takers yet.
 

Doug

Member
Well if yours is the Miroku version w/ Badger barrel you might talk to Wayne over at

http://www.texas-mac.com/

As for the beagling, strange thing...It rounded the nose but oblate-d the base. Ran it through the sizer wh/ reveals that I need a thou larger sizer and I'll be absolutely set.
 

Doug

Member
The beagling worked. Kate's group was halved and she shot 2 MOA all 2 hours w/ 2 bullseyes and last 2 shots touching. Ordered a .459" sizer to try but may not need it. Success. Thanks.
 
9

9.3X62AL

Guest
AWRIGHT! Love it when a plan comes together. She is doing some fine shooting, I would say.
 

Doug

Member
LOL. She says it's my fine bullet casting and attention to detail, but truth is she's my official tester cuz she really is the better shot. Really like watchin her over the rifle. Glad she got rewarded today. Thanks again. Now I know what I have to do for the 90 next. Call me beagle.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Guy I used know shot muzzleloaders, not BPCR, but MUZZLELOADERS at 1000 yds (or more IIRC) in national comp. He talked barrel harmonics, yaw, BC, etc. with rifles that started out at a MV of something in the area of 1400fps. I saw a lot of his targets and many were groupings a man with a modern, scope sighted deer rifle would be ecstatic over at 100 yards. And he was 70 something and using open sights! I don't put anything past anyone if they have the time, brains and talent.

Jim, what was your handle on boolits? I've forgotten.
 

Doug

Member
Bret, That's absolutely amazing. Now that's what I'm talkin about...use it all! Most encouraging. Just beagled the lower half of another mold. Great stuff. New lube-sizer on its way. Our bullets will at least fit, and that's a good start.
 

fiver

Well-Known Member
Bret, Jim is 44 Man over there.

Doug it sounds like things are starting to come together.
 

James W. Miner

Active Member
Many of you know me and I am also bfrshooter here and there. I am old and set in my ways, been called everything under the sun.
I like this place best of all, you fellas have less discourse and get along the way it should be. I am amazed at how well you come together as friends and am proud to be with you, so thanks for putting up with me.
 

Brad

Benevolent Overlord and site owner
Staff member
Jim, that is exactly what we were after!

We don't always have to agree but by golly, we can do so in a polite manner. Just because we don't agree on something doesn't mean we need to try to destroy each other.
 

Doug

Member
Well Jim, I actually did give her a hug from you. We had a good laugh.

And fiver, we know we have at least one good bullet for her rifle. Attempts to partially beagle the new mold failed--I wasn't happy w/ the bit of slop in the nose at the muzzle end, and have been searching high and low for nose engraving, but 2 things: first, light nose engraving may be happening due to obturation, and secondly, the profile of this particular bullet seems a poor fit for the chamber. We'll try it, of course, but this particular mold seems better suited to my rifle. There's one more mold I'll try beagling on--the smallest bullet of the three--and we eagerly await the arrival of our .459" sizing die.
Here's what I'm working from:

"For those of you interested, below is a diagram of the bullet. It should be noted that the bore-riding section MUST be at barrel-bore-diameter at the chamber end of the barrel, not muzzle end. This is important due to the long nose ogive (unsupported nose.) Testing has shown that if the bore-riding section's diameter is too small for the bore, accuracy can be abysmal. And, a harder alloy is required for this high ballistic coefficient bullet design so the ogive does not bump-up and potentially reduce both accuracy and ballistic coefficient."

To me, this is just an iteration of what I first read here, the importance of chamber fit rather than barrel fit.
 
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