Seating into the lands , Pressures & velocities

I don't think bullets seated by the lands seating them X thousandths different with reduced loads will bring peak pressures up to normal or spec maximum levels. Way too many mechanical variables involved: Jacket hardness, throat angle and surface texture, diameters of bullets and bore cross section area.

Then the variables in bullet pull and those of powders further compound pressure issues.

Measuring peak pressures is better than assuming what it's gonna be. Safer, too.
 
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I know already what my fired cases measures head to datum in this specific rifle . Knowong that should help , also these are new Lapua cases which I’ve measured several case headspace on . Although pretty consistent there are a few that would be equal to bumping my shoulders 4 or 5 thou . If these cases don’t expand and fully fire form under these reduced loads . Not only will the measurements show that , I should also see some backed out primers .

I’ll be testing on the 18th , this theory will be tested then . I fully intend to post my results here . Maybe even updating in real time while at the range . I’ve done this before and if you’re online at the same time it’s always fun having a real time conversation while doing the test itself . I plan to be out there between 2:30 PM and 5 PM Pacific standard time .
 
Knowing the distance from case shoulder datum to cartridge bullet contact diameter on the chamber throat is 17 times more important.

Case heads typically don't touch the bolt face when fired.

If there's a 4 thousandths spread in case heads to shoulder reference, there's a 4 thousandths spread in bullet touch point to the throat if the case head rests on the bullet seater base when seating bullets. There's also a 4 thousandths spread in case head clearance to the bolt face.
 
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Knowing the distance from case shoulder datum to cartridge bullet contact diameter on the chamber throat is 17 times more important.
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yep , that's how I know how far my jam will be . I didn't just guess what the jam might be ;)

Case heads typically don't touch the bolt face when fired.
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I think you mean at the point of first ignition after the firing pin strike . Saying "when fired " indicates the entire firing process from pulling the trigger all the way to the point the bullet leaves the barrel . You can't get flat-ish primers if the case head is not pressed against the bolt face . Using the word typically would indicate ( to me ) most of the time or the majority of the time the case head is never in contact with the bolt face during the any part of the firing process . I don't believe that to be "typical" . :)

If there's a 4 thousandths spread in case heads to shoulder reference, there's a 4 thousandths spread in bullet touch point to the throat if the case head rests on the bullet seater base when seating bullets.
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Correct , are you just reiterating what's already been discussed above . :confused:

Me said:
I got to thinking that maybe .005 jam isn’t enough to be a consistent seating depth . I remember one load development I tried where I had the bullet just touching the lands and I had what may be the worst ES/SD’s I’ve ever had . I have always figured that the variance in case head space , base to ogive measurements etc. contributed to the issue . I’m not sure how much a .004 or .005 variance would be , meaning maybe sometimes the bullet was .002 or .003 off the lands while other times it was .002 or .003 in the lands???

I’m thinking maybe I should do at least .010 jam ??
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I'm not going to post the responses but they seemed to say pretty much what you're saying , If not , can you explain it using different wording because I may not be following your point ?:confused:
 
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When I say fired in this context, that's when the primer detonates. Case is against its headspace limit.

Now that I think this through, perhaps "starting the cartridge firing process" may be better.
 
No idea how some get such radical differences in measured base to ogive measurements. I measured 15 seated bullets (Berger 105 hybrids) and all base to ogive measurements were exactly the same. Lee press and Forster seating die with Berger 105 hybrids
 
I don’t know either . I’ll measure the ones I just loaded and see what the differences are . FWIW I use a Hornady classic press and Redding comp seater
 
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If the seater die touch point diameter on the bullet ojive is only a couple thousandths under bullet diameter, a few thousandths spread in X to ojive dimension is normal.

The closer to the bullet's tip that touch point is, the X to ojive spread from case head will be less.

This ain't the best way. Case shoulder to seater touch point on bullet is best because this is what happens in the chamber when the firing pin fires the primer. Assuming the case shoulder ain't set back too much in the process.
 
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toIFNN.jpg


Top line is where my seater contacts

Middle line is the Hornady insert = ES .001 , 30 measured

Bottom line is the Sinclair insert = ES .002 , same 30 measured

This ain't the best way. Case shoulder to seater touch point on bullet is best because this is what happens in the chamber when the firing pin fires the primer. Assuming the case shoulder ain't set back too much in the process.
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Agreed if you mean throat touch , I can't do that or at least I don't know how with the tools I have . This is why I intend to seat them long enough to be jammed no matter what .
 
That's what I've found, too. The Sinclair insert holes are close to actual throat dimensions, so they come very close to stopping on the real throat contact location. The Sinclair nut tool is, I understand, finished with actual throating reamers and these inserts look quite similar. I think it is possible because they are made of stainless steel, where the Hornady LNL inserts are aluminum and aren't tough enough to maintain such dimensions against the force of wedging against the bullet at shallow angles.

Here's what I found measuring 30 150-grain .308 MatchKings some time ago. Mind you, this is just measuring the bullets themselves and not seated in cases. The seating die will fix its contact point on the bullet as the reference point, so I have often thought what you really want is to measure the difference from the seater stem ram's contact point to the land contact point, and from there to the shoulder datum. That will tell you more about how consistently you can position the bullets off the lands.

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Agreed if you mean throat touch , I can't do that or at least I don't know how with the tools I have . This is why I intend to seat them long enough to be jammed no matter what .
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Soft seat a blackened bullet barely in a resized case neck then push the case full into the chamber. The case shoulder will be against the chamber shoulder and the bullet will be pressed against the chamber throat as it seats in the case neck.

Pull the bulleted case out and note where the throat marked the bullet. That bulleted case now has its bullet position where it will be when the round fires as the bullet is touching the throat.,
 
Unclenick, when did you get those Sierra 150 HPMK 2190 bullets? Their dimensional spreads are huge which sometimes happened in their California plant.
 
I think I must have got those in the mid-'90s. I remember I got them specifically to replace M2 ball bullets in pseudo Mexican Match style for 100-yard local reduced range matches.
 
Unclenick said:
I think I must have got those in the mid-'90s. I remember I got them specifically to replace M2 ball bullets in pseudo Mexican Match style for 100-yard local reduced range matches.
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I asked because Sierra often didn't change bullet lot numbers and packaging after minor adjustments to bullet making dies in their California plants a few years before moving to Missouri. Accuracy was barely acceptable but some bullet dimensions weren't always 100% up to snuff.

Mid Tompkins went to Missouri and convinced Sierra Bullets owner Bob Hayden and plant manager to change lot numbers when any change in the bullet making machine was made.
 
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with a comparator it really does not make a darn if the hole is throat size or not, just as long as it is smaller than the diameter of the bullets bearing surface. I did not have a 6mm insert for my Hornady when I first played with the 6 CM so I used the .22 cal insert. I loaded my rounds that way for a few weeks until I remembered to add a .243 insert to another order from Midway. My base to ogive measurement for the rounds changed but the base to meplat measurement did not
 
hounddawg said:
with a comparator it really does not make a darn if the hole is throat size or not, just as long as it is smaller than the diameter of the bullets bearing surface.
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It does if you want to be exact when you use the proper rear reference, the case shoulder.

Close only matters in 4H activities; hydrogen bombs, hand grenades, harassing fire and halitosis.
 
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It does if you want to be exact.

Close only matters in 4H activities; hydrogen bombs, hand grenades, harassing fire and halitosis.
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that is pure BS Bart

exact to what? A throat that erodes as it wears? Might want to look down a borescope sometime
 
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Bearing surface is that portion of a bullet’s outer surface that comes into direct contact with the interior surface of the barrel bore when moving through the barrel. Includes lands and grooves.

Exact measurement is from case shoulder to where ever the bullet touches the throat.
 
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