Don Fischer
New member
I got to where over the years I seldom have to stand a case on a flat surface to see if a primer is seated enough. In the beginning, I found a lot of them not quite deep enough even though they seem to be.
Ogive differences
- Thread starter cdoc42
- Start date
I got to where over the years I seldom have to stand a case on a flat surface to see if a primer is seated enough. In the beginning, I found a lot of them not quite deep enough even though they seem to be.
Hollow point bullet jackets are made much the same way as cartridge cases. They've got shape dimension tolerances. When a lead core is pressed into the open end of the jacket then a pointing die shapes the ogive, it too, will have shape dimension tolerances.
Twist gently a bullet ojive in the muzzle of a barrel. Measure the distance from its mark to the bullet's base then to its tip. Repeat this with 9 more bullets recording each dimension. Note the spread of each.
Now twist each bullet ogive in the seater stem. Measure the stem mark to muzzle mark then record the numbers for each bullet. Note the spread.
Twist gently a bullet ojive in the muzzle of a barrel. Measure the distance from its mark to the bullet's base then to its tip. Repeat this with 9 more bullets recording each dimension. Note the spread of each.
Now twist each bullet ogive in the seater stem. Measure the stem mark to muzzle mark then record the numbers for each bullet. Note the spread.
best tool I have found for checking primer pocket depth and seating depth. Lots of used ones in good shape. Mine was given to me by a guy who has retired and had 4 or 5 in his garage/home shop. Just unscrew the contact from the spindle and it is the perfect diameter. Mine is so old the face is yellow so I guess it is vintage
Starrett 25-141 Ebay
Starrett 25-141 Ebay
Bart B. That small group you posted is over 20yrs old. Do you have anything current.
This is from your old site.
https://groups.google.com/forum/?fromgroups=#!topic/rec.guns/iL7zv-cktJc
This is from your old site.
https://groups.google.com/forum/?fromgroups=#!topic/rec.guns/iL7zv-cktJc
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SAAMI also defines the throat:
SAAMI is a concensus standards organization, so that will be the definition the industry accepts. Just as the tapered shoulder portion of a chamber is where a rimless bottleneck cartridge seats, so is the throat where the bullet seats if you load for zero bullet jump.
Cdoc42,
I think you will find two factors can cause a pressure difference. One is that your longer ogive bullet leaves more powder space under it, and that tends to lower pressure a little. Second is that a longer ogive radius means, when bullet jump is the same, that the annular ring is a little smaller, so less gas bypass can occur during the time it takes to get to the throat. These two influences tend to be oppositely directed, so they tend to cancel, but they won't have the same significance, so they won't do it perfectly. This will result in slightly different barrel times and exiting at a different point in the barrel flexure from firing could account for the POI shift you mention.
SAAMI said:
SAAMI is a concensus standards organization, so that will be the definition the industry accepts. Just as the tapered shoulder portion of a chamber is where a rimless bottleneck cartridge seats, so is the throat where the bullet seats if you load for zero bullet jump.
Cdoc42,
I think you will find two factors can cause a pressure difference. One is that your longer ogive bullet leaves more powder space under it, and that tends to lower pressure a little. Second is that a longer ogive radius means, when bullet jump is the same, that the annular ring is a little smaller, so less gas bypass can occur during the time it takes to get to the throat. These two influences tend to be oppositely directed, so they tend to cancel, but they won't have the same significance, so they won't do it perfectly. This will result in slightly different barrel times and exiting at a different point in the barrel flexure from firing could account for the POI shift you mention.
Mid Tompkins shot forty Lapua 185 gr. FMJRB bullets from his Hart barreled 308 Win M70 match rifle that went inside 2 inches at 600 yards back in 1971. Some 10 shot groups were under an inch.
The quality of centerfire barrels and bullets has improved little over the last several decades.
22 rimfire match ammo quality declined in the early 1980's. 100 yard prone 40-shot any sight records set before then still stand, as do some at 50 yards. Barrel life is now half that possible back then.
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I think gear is only a third or a fourth of the equation.
That sub 2" 40-shot group back in 1971 was shot from a rifle clamped in a free recoiling accuracy cradle. Exactly like this one belonging to David Tubb.
http://www.flickr.com/photos/12787226@N00/sets/72157594303093714/detail/
Ten or more were made back in the 1960's for NRA high power match rifle competitors.
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well Joe I used a Wilson seater without a micrometer adjustment when originally seating that batch. Once adjusted the lockscrew on the adjustment stem was tightened and never touched. When I reseated all 75 of those loads I never touched the adjustment on the die and it was still at the same adjustment used in the original seating. The only difference was I made sure I applied sufficient pressure so the seating portion of the die bottomed out on the die body every time
USA military teams used similar ones using that 3 point rest design. The USN match conditioning shop used one testing Garands. 7.62 versions testing handloaded Sierra 190's got half MOA groups at 600 yards in their tests.
Ogive differences , also bullet differences . One is a flat base the other a boat tail . I only shoot Sierra 168gr MK and there are differences from lot to lot . With bullet ogives the seating depths will also change , then how you size your cases from base to datum could add changes in your jump or jam settings . Doesn't surprise me that with the same ogive setting with different bullets his POI is different .
Except good equipment producing best accuracy reveals more precisely ones marksmanship abilities.
First thing to learn is how to call shots very well. One learns fastest with the least number of shots using a rifle and ammo that shoots no worse than 1/3 MOA.
They're amazed they can sight in their new rifle with 2 or 3 shots standing without a sling. And never put a bullet dead center on the bullseye.
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Most of the new CNC machined rifles with department store glass can get do .3 on occasion and .5's consistent. Guy at the club shoots a off the shelf Ruger Precision 6.5 CM with a scope that was part of the package and regularly shoots mid 190's in matches with an occasional clean in mid and long range.
Pretty much any off the shelf modern rifle can be turned into a sub .5 long range shooter by bedding it in a $200 Boyds stock and with the right person shooting it
Times have changed as far as equipment but the skills of guy pulling the trigger is still the major part of the equation in my opinion. If you can't read wind and mirage or jerk the trigger or can't keep a consistent cheek weld a rifle that shoots .1's won't do you any good
Pretty much any off the shelf modern rifle can be turned into a sub .5 long range shooter by bedding it in a $200 Boyds stock and with the right person shooting it
Times have changed as far as equipment but the skills of guy pulling the trigger is still the major part of the equation in my opinion. If you can't read wind and mirage or jerk the trigger or can't keep a consistent cheek weld a rifle that shoots .1's won't do you any good
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Benchrest long range aggregate record's groups won't all fit inside a half MOA.
Off the shelf rifles won't cut that mustard. That's all shots inside half MOA 800 yards and further to 1000.
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