INDEXING CARTRIDGES IN BOLT AC
INDEXING CARTRIDGES IN BOLT ACTION RIFLES
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- Last Post 14 October 2014
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It seemed to work for Stan D, back when he shot.
Good ole Stan. A really great guy!!! He did a 32 cal GC bullet mold for me, to my design back in the early 90's when I was shooting CBA.
Do you know if he's still with us?
Frank
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Bill,I'm very sorry to hear that. Rest his soul. He was a real terror in the production class in my day. Frank
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good test, joe:: i always wondered about that.
still, if we can find nothing that makes bigger groups ... why are there bigger groups ? does that mean we therefore can find nothing that makes smaller groups ?
i have always wanted cba to put out a business card sized ” top five rules for cast accuracy ” ... so far we have a couple of ” usually/maybe s ” . ::: bullets should be nearly tight in the throat ... and longer bullets are more accurate ... :::
usually and maybe.
ken
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I've wondered the same myself, but with my modified scoped 1917 Enfield and other positive-feed actions where the extractor securely grips the rim. So the trick will be to make the case rotate the same amount from round to round while keeping the bullet unmoved against the lands :wnk:
Match Director
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I've wondered the same myself, but with my modified scoped 1917 Enfield and other positive-feed actions where the extractor securely grips the rim. So the trick will be to make the case rotate the same amount from round to round while keeping the bullet unmoved against the lands :wnk:
Why not test? Mark a few cases, bolt out, case held by extractor, bolt in-turned-then opened. Pull the bolt back and see if the case turned.I don't have a mauser-claw-extractor gun.
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Perhaps the variations in rim diameter or rim thickness cause some of the cases to turn. The bolt head may grip the fat ones more firmly.
Both dimensions can vary 2 or 3 thousandths.
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Why not test? Mark a few cases, bolt out, case held by extractor, bolt in-turned-then opened. Pull the bolt back and see if the case turned.I don't have a mauser-claw-extractor gun.
That is a logical suggestion but I would urge that the testing start a step further back than: can you index reliability with a bolt action?
The first question should be, does indexing improve accuracy? (To find out use a falling block so indexing is reliable.)
If the answer to that is yes, then try to pin down -- with what types of bullet imperfections is it helpful?
I know it can be shown that by making large defects in bullets you can create a situation where indexing improves accuracy but does it really happen with real cast bullets that are decently cast?
Frank Marshall tested both indexing and sorting by weight and published his results in “Cast Bullets” published by the NRA in 1979. He found that indexed and sorted by weight bullets shot groups less than one quarter the size of the same bullets unindexed and unsorted. These are fantastic results and very persuasive -- until you try to duplicate them yourself. Marshal must have had really bad bullets because I don't believe anybody has ever been able to replicate those results or anything close to them. At least I haven't seen such results published.
My own, admittedly less than comprehensive testing, give little evidence that either procedure amounts to a hill of beans with decently cast bullets. However, I would be pleased to see evidence that indexing really improves accuracy so I could use it to improve my shooting.
John
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I'll test a few rounds.
What is a statistically-relevant number....100?
Now measuring, thinning, and polishing rim and extractor interiors will be next...groan...
Match Director
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Why not test? Mark a few cases, bolt out, case held by extractor, bolt in-turned-then opened. Pull the bolt back and see if the case turned.I don't have a mauser-claw-extractor gun.
That is a logical suggestion but I would urge that the testing start a step further back than: can you index reliability with a bolt action?
The first question should be, does indexing improve accuracy? (To find out use a falling block so indexing is reliable.)
If the answer to that is yes, then try to pin down -- with what types of bullet imperfections is it helpful?
I know it can be shown that by making large defects in bullets you can create a situation where indexing improves accuracy but does it really happen with real cast bullets that are decently cast?
Frank Marshall tested both indexing and sorting by weight and published his results in “Cast Bullets” published by the NRA in 1979. He found that indexed and sorted by weight bullets shot groups less than one quarter the size of the same bullets unindexed and unsorted. These are fantastic results and very persuasive -- until you try to duplicate them yourself. Marshal must have had really bad bullets because I don't believe anybody has ever been able to replicate those results or anything close to them. At least I haven't seen such results published.
My own, admittedly less than comprehensive testing, give little evidence that either procedure amounts to a hill of beans with decently cast bullets. However, I would be pleased to see evidence that indexing really improves accuracy so I could use it to improve my shooting.
John
The great advantages to this test is that it can be done in ten minutes, is cheap, easy, no travel, quiet and safe. ALMOST as easy as no test at all!
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I'll test a few rounds.
The first one that turns tell the story; if none turn in 30, that's close enough.
What is a statistically-relevant number....100?
Now measuring, thinning, and polishing rim and extractor interiors will be next...groan...
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There's 'indexing' and then there's “indexing". I always mark my cases and orient them when feeding into the chamber. I've been aware that they do not all end up precisely positioned every time. My thinking is returning the case into the chamber each time roughly the same way has to help. Anything within around 20 degrees works for me. The benefit may be only mental. I hold no records yet.
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In my mind indexing is only relevant for oval chambers. Stan was doing his with a 1903 in the military matches.
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Bill;Don't oval chambers kind of index themselves? I mean If they are so ovate that the fired case will not chamber unless it is in a particular orientation? Brodie
B.E.Brickey
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There's 'indexing' and then there's “indexing". I always mark my cases and orient them when feeding into the chamber. I've been aware that they do not all end up precisely positioned every time. My thinking is returning the case into the chamber each time roughly the same way has to help. Anything within around 20 degrees works for me. The benefit may be only mental. I hold no records yet.
When I shot the M14 with 80Div Large bore rifle team, I'd check for runout and index the high point of each round to the top when placing in the mag. IT MADE A DIFFERENCE. Runout was from .004 to .007 for the matches, worse was plinking ammo.
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I think indexing would work best with snug fitting bore rider bullets. Case may spin when closing bolt, but bullet will not...I think Mark the bullet, not the case
Better yet, mark (Sharpie) the bullet and case at neck to see if bullet slips in neck when closing bolt.
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I actually think a better test for fixed ammo is to measure the bullet run out in the case and index the run out into the chamber.
As I said earlier, I don't believe a perfectly round bullet will benefit a indexing test. So, if your going to do index testing, make sure you have a out of round bullet to do it with.
That reminds me of another issue.......... centering sprues on the cavity. For the molds that I shoot in competition, I always make the sprue plates centered on the cavity by indicating the cavity in the mill and center drilling the sprue plate on the mold.
The reason is, in one of the publications done by Harrison or Marshall or?, they sectioned the bullet and in the area of the sprue flow, there was a distict difference in metal texture. I believe that bullets were indexed in the rifle, with the bullet cast with the sprue on the edge of the cavity and it made a difference in accuracy. Do any of you remember that article?
Frank
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frankeore: sprue area on bullets ... maybe that is why back when i wuz trying to get more accurate cast shooting; i found that making a lathe cut on the base of bullets improved most but not all bullets. i figgered some of the bullets had problems bigger than their base deformities. this would give better score shooting. maybe those nose-pour molders have something !! ( g ) .
it takes a very sharp y high rake cutter; lead is so gooey.
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frankeore: sprue area on bullets ... maybe that is why back when i wuz trying to get more accurate cast shooting; i found that making a lathe cut on the base of bullets improved most but not all bullets. i figgered some of the bullets had problems bigger than their base deformities. this would give better score shooting. maybe those nose-pour molders have something !! ( g ) .
it takes a very sharp y high rake cutter; lead is so gooey.Here's the easy way.
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