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Thread: Chamber and throat relationship.

  1. #21
    Boolit Bub
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    excellent visual, thanks.
    Ray

  2. #22
    Boolit Buddy vogironface's Avatar
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    I recently measured the relationship between the throat and bullet of my 9mm. I do not think it would be possible to load a boolit that would fit properly with any boolit appropriate for the caliber. the distance is best described as a chasm. Accuracy is a frustration with that gun. Is inaccuracy what one would expect with a boolit seated to far back? I know accuracy can be improved in rifles (and I assume handguns) by seating just off the lands and I infer from that that an extremely poorly fitting boolit might have the opposite effect.

  3. #23
    Boolit Master jabilli's Avatar
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    Stinking Brilliant. Thanks! (Where'd you get that cutaway?)
    Is it a common occurrence for reloaders to not fill the throat? :-p
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  4. #24
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    Quote Originally Posted by vogironface View Post
    I recently measured the relationship between the throat and bullet of my 9mm. I do not think it would be possible to load a boolit that would fit properly with any boolit appropriate for the caliber. the distance is best described as a chasm. Accuracy is a frustration with that gun. Is inaccuracy what one would expect with a boolit seated to far back? I know accuracy can be improved in rifles (and I assume handguns) by seating just off the lands and I infer from that that an extremely poorly fitting boolit might have the opposite effect.
    In a 9mm about the only thing a fellow can do is load a fat boolit to help align the boolit in the throat/chamber and load the cartridge as long as the magazine will allow. Chances are you'll never get your firearm to shoot cast boolits accurately, and chances are just as good that jacketed ammo will not improve accuracy significantly. Some guns just aren't built in a way that is inducive to accuracy.

    Edd
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  5. #25
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    Quote Originally Posted by jabilli View Post
    Stinking Brilliant. Thanks! (Where'd you get that cutaway?)
    Is it a common occurrence for reloaders to not fill the throat? :-p
    I cut away the chamber area on a old 03-a3 barrel that had been removed from a friends rifle. We put on a much better barrel and I thought the visual would be helpful to some. It appears I was correct.

    As far as loading to fill the throat to help improve accuracy, we can do a lot to improve fit by knowing what our chamber and throat are shaped like and what boolit we use to help fill the void. THAT is precisely why you'll see the expression "Fit is king".

    Edd
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  6. #26
    Boolit Master jabilli's Avatar
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    Quote Originally Posted by badgeredd View Post
    I cut away the chamber area on a old 03-a3 barrel that had been removed from a friends rifle. We put on a much better barrel and I thought the visual would be helpful to some. It appears I was correct.

    As far as loading to fill the throat to help improve accuracy, we can do a lot to improve fit by knowing what our chamber and throat are shaped like and what boolit we use to help fill the void. THAT is precisely why you'll see the expression "Fit is king".

    Edd
    Makes me wonder- ammo when you go grab it off some shelf...Considering all things equal (which, is certainly not the case) some brands/designs will work better for some guns and not so well with others... Gunmakers...Knowing this...can they and do they somehow make their product more able to shoot whatever someone grabs off the shelf accurately?
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  7. #27
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    Quote Originally Posted by jabilli View Post
    Makes me wonder- ammo when you go grab it off some shelf...Considering all things equal (which, is certainly not the case) some brands/designs will work better for some guns and not so well with others... Gunmakers...Knowing this...can they and do they somehow make their product more able to shoot whatever someone grabs off the shelf accurately?
    Considering the chambers I have found in some commercially built rifles, my guess is they build rifles to be a good (adequate) fit for the maximum SAAMI ammo. I suspect ammo makers in general make their ammo to fit the minimum SAAMI chamber. Throats seem to vary quite a bit with some manufactures seeming to always have long throats. I'm sure that in our litigation society, everyone is trying to cover their posterior. At any rate, we as handloaders can improve ammo for our particular firearm by loading to fit OUR gun. I don't see any way a manufacturer can load ammo that will be accurate in all firearms chambered for any given cartridge.

    Edd
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  8. #28
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    Quote Originally Posted by badgeredd View Post
    No, the chamber/cartridge combo is not limited to this particular boolit. I used this particular boolit because a) it was readily available and b) it pretty much demonstrated what I wanted to show.

    The idea is to fill the throat as much as possible with a boolit regardless of its shape. If the boolit shape doesn't lend itself to mostly filling the throat, one cannot expect good results. A person MAY be pleasantly surprised, but the likelihood of a boolit working well and not at least mostly filling the throat is not in one's favor.

    Edd
    New to shooting lead boolits in rifles. Have read of what you said. NOW that I have seen it, I understand it. In this case (for me) the thousand words are made clear by the pictures. Thank you.

  9. #29
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    Excellent addition to the board, thank you!
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  10. #30
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    So, Edd, I think you are saying to size cases as large as will fit/cycle reliably, same for the body of the boolit/throat, with the nose sized to barely engrave the rifling. For best accuracy. The average caster probably sizes the CB body to fit the throat, possibly with slight engraving, then sizes the case to prevent reducing the body and provide proper neck tension. Thus sometimes grossly oversized CBs for the BORE slug.

  11. #31
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    Bottle neck rifles, as shown, are slightly different than normal handgun ammo. You always want your bottle neck rifle brass to be fire formed to the chamber and then work with your neck sizing based upon your bore slug. Bottle neck rifle brass in semi-autos is also different, such as an AR-15. You would always FL size that bottle neck brass.
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  12. #32
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    Brilliant photography AND essay. Pictures are worth many thousand words..

    I worked over a M77 in .308 and the last thing I did to it was something that cut groups totally in half and put it under an inch @200yds shooting from laying prone with no sandbags. I had loaded with fire formed brass, but crimped in the cannelure of a 180gr plain base. Groups were manageable for a hunting rifle but nothing to write home about. The last thing I did was assemble a dummy round with no crimp, just the neck tension, and closed the bolt on it, letting the rifling seat the bullet. I pushed it out from the muzzle with a cleaning rod, stuck it in a seating die and adjusted the plug down until it touched. Took the dummy out and turned the die 1/2 turn farther down and locked it. I used that measurement to load all the subsequent rounds with, and collet crimped them. Amazing what that 1/2 turn of freebore did for the groups.

  13. #33
    Boolit Master
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    Very good sir, that should be a sticky for sure. Nothing explains as well as pictures.

  14. #34
    Boolit Master popper's Avatar
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    So I chambered an unsized 165 TC 40SW in XDm. Interesting, not engraved, a step between throat and chamber - case mouth is 0.422. CB is 0.404, throat is 0.401, I slugged the groove 0.400. I can see where the throat is on the CB, see a .001" ring .03 from the mouth, throat is >.05 long. I've been sizing to 0.401, should I size to 402 and let the throat size to 401, groove to .400? Looks like I can also seat longer to get closer to the rifling. I need to run the same test on the rifles.

  15. #35
    Boolit Master 303Guy's Avatar
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    Something about the term 'free-bore' - technically it's a portion of the throat that is groove diameter but has no rifling. Some super magnum rifle manufacturers gave their guns long free-bore to reduce chamber pressure, something in the order of a full bullet length comes to mind but I don't actually remember. So a standard chamber could be free-bored by cutting the rifling out and moving the rifling leade further forward. This differs slightly from a chamber with a long throat which is cut to accommodate a long seated bullet - compare the 303 Brit with the 308 Win or better yet the 6.5 Swede or 7x57 with the 308. The 6.5 has a long throat but the leade is still fairly close to the bullet ogive.
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  16. #36
    Could you add a pick of an unfired cartridge with the same boolit in the chamber? I'd like a better sense of the 'before ignition' scene. Namely how far the boolit moves before it engages the throat. Thanks!
    Last edited by ylexot; 05-18-2013 at 10:08 AM.

  17. #37
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    Quote Originally Posted by ylexot View Post
    Could you add a pick of an unfired cartridge with the same boolit in the chamber? I'd like a better sense of the 'before ignition' scene. Namely how far the boolit moves before it engages the throat. Thanks!
    The idea is to load your boolit so it DOESN'T jump to the throat. If the boolit fit is correct there is no run to engage the throat. The last picture is of a loaded round in the firing position, pretty much filling the throat and leade.

    Edd
    Last edited by badgeredd; 05-28-2013 at 09:22 AM.
    Charter member Michigan liars club!

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  18. #38
    how do you know how what the COL of the reload will be?

  19. #39
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    Quote Originally Posted by graphic914 View Post
    how do you know how what the COL of the reload will be?
    Perhaps others will chime in with their methods to determine COL.

    I set the COL this way. First I insert a cast bullet I intend to try into the chamber using light pressure to insure it is actually touching the throat, I then use a cleaning rod from the muzzle to touch the inserted bullet and mark the rod with a piece of tape. I them remove the bullet and then touch the breach face with the same cleaning rod and mark the rod. Then I measure the over all length on the rod. I load ONE dummy to a length .025 to .050" longer ( sometimes I go even a bit longer initially) and check the feed and seating of the dummy in the rifle. IF it appears to function in the magazine and chamber, I load 5 to 10 rounds and try them. If it seems the dummy is too short, I adjust the bullet out or if it is too long I try a shorter COL. One needs to do his/her own work to get it done. There isn't a substitute for taking the time to fit and try a cartridge. Obviously, different bullets need to be adjusted for the optimum COL.

    Edd
    Charter member Michigan liars club!

    "The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in Government." -- Thomas Jefferson

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    Beware of man who types much, but says nothing.

  20. #40
    Boolit Master Slow Elk 45/70's Avatar
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    Just my openion, this would make a great stickey, more info for "New Shooters , IMHO
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check