Now that I had these perfectly made up cartridges I took the Stoney Point comparator and set out to measure the length to ogive for the different bullets. I was shocked to find that the different bullets varied up to .085 from each other. Theoretically shouldn't they all measure the same since the lands and the comparator should match? The biggest difference was between a 175 gr. Grand Slam and a 139 gr. Hornady SST, but there were differences among all of them.

Any insights which might help me to understand this would be appreciated.

Thanks,
Rick

Welcome aboard (first of all). I would rather call a desire for accuracy an obsession as opposed a disease [however].

Notwithstanding, there are a series of variables affecting your metrics in so much as 'an implied' linear value is derived based upon volume, and a geometric surface. Understanding those and putting them into their correct perspective will eliminate any doubt and raise your level of confidence.

Studying the mathematics behind a secant-tangent or tangent ogive projectiles might help one if they wanted to get into the nitty gritty behind it. I have built an excel spreadsheet to examine the dynamics and graph such items if you are interested. The idea is the ensure consistency by deriving a point circumscribing the center of form at an area to the rear of the point of the bullet. Since various sizes and configurations essentially make up different volumes, several constants can be counted [as you already know] on to ensure that one has achieved and accurate round made up to the particular firearm.

Recommended starting points:

1. Ensure that the caliper instrument is properly calibrated
a. Does it zero correctly when fully closed?
b. Does the offset dialed-in match the implied zero point?
2. Ensure that initial lot of bullets being used have the same degree of consistency by weight, length and diameter. Undoubtedly this step might seem trivial, but confidence it built by sometimes eliminating or ruling out elements which may generate a negating affect on the overall process.
3. Once a dummy round is created, where does it compare to the SAAMI spec of the maximum for the cartridges� overall length (COL)?
a. If greater than, an incorrect measurement was obtained for the firearm. Resume by taking another measurement
b. If less than or equal, make a process judgment of acceptance or rejection.
4. Ensure round chambers as expected for the firearm. If it is too stiff to chamber, the round is too long.
5. Ensure that the seating die is set to the correct seating depth. If the reloader does not have confidence in the delivery of consistent seating, then examine entire sizing, charging and seating process.
6. Establish an acceptable tolerance once a measurement is accepted (e.g. +/- .0005)

Obviously, this only starts the process. One has to shoot off several rounds to actually put the litmus test on the subject matter. The only caution to really pay attention to is the amount of charge. As a reminder, please use less powder than published and work up incrementally! Since the ogive [supposedly] rests on the bearing surface of the lands, pressure builds rapidly! I am sure that you want to continue to use that 7mm for a long time to come, and we surely don�t want to read about a fellow forum member going �down range�.

Please let us know how you make out!

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Best regards,
Alex

Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote! - Benjamin Franklin 1759

[This message has been edited by Alex Szabo (edited 03-18-2002).]

I never saw this before, the rifle is a new M-70. Can anyone help ?

quote:

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Originally posted by JHook:
...longer then SAMMI specs. ...Can anyone help ?

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JHook,

There are a number of facets governing the concept of "seating to the lands". From all of the conventional wisdom I've learned over the years and especially on this forum, is that one would simply use regualar factory rounds to "break in the barrel" prior to any form of customized loading. There is [as a matter of fact] another thread here started within the last month, if you wish to reference it in terms of proceedure, should you need to reference it.

Other than that, if the unit is factory spec and it is larger than SAMMI spec, then I would simply assert that the following conditions must be true:

1. Incorrect measurement obtained from the firearm
2. once fired brass NOT being used to obtain the measurement within the firearm.

After chambering the dummy round, is it tight or does the bolt chamber smoothly?

I personally have only seen SAMMI specs exceeded if and only if it was a custom carved unit. And even that is most egregiously rare as a competent craftsman most likely cut those barrels to spec!

Hope this helps and please let us know your final outcome or remedy.

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Best regards,
Alex

Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote! - Benjamin Franklin 1759

Thanks,
Rick

If I have to I will simply have to break in the rifle with factory rounds. I'll pick up a box on the way to the range. I will measure the factory rounds and then work up, or down, from there.

I dont think it would be wise to fire these loaded reloads yet, until I figure this out. On the plus side they will all be seated long and easy to seat deeper.

Ive never had this problem with a rifle before...............thanx. I will repost when I get to the bottom of this!

Remember first that it is to compare that a comparator is used for. Each bullet and bullets within a brand have a different ogive curves and what you are doing is finding out where THAT particular bullet touches the lands in relation to the over all length.

Bullets do have variance within a box. Measure 10 or so and take the average or take the longest or shortest whatever you want to do. Unless you are benchresting you don't have too much to worry about.

Once you have established the length to the lands using the comparators then you can begin the seating depth process relating to the accuracy you want.

I found over the years that dummy rounds just get lost or missplaced or I ended up with a bunch in a box for that rifle and didn't use them again. It is quick to set your dies up each time if you have the micrometer style seaters, just note the micrometer setting with the load data.

I have run a few tests with bullets of the same weight from different makers using the seater setting for one accurate load and seating the other makers bullet without changing the setting. Sometimes there wasn't much change in group size, sometimes there was a big change in group size. I didn't run enough tests to establish anything other than the fact that there isn't very many things in this sport that are carved in stone and you just have to try things out. I learn new things everytime I read a new post and adjust my thinking and proceedures. You have to have an open mind to be able to advance.

I try loads I read on this forum that shoot small groups for that person and his rifle and load combination. Sometimes I get the same good results, sometime I need to tweak a little, sometimes it's just no good at all.

Use the comparators as a beginning reference only. Also remember, you just learned a very good lesson, keep asking yourself and others questions when the thing you are doing doesn't seem right. That is the first step in the ongoing learning process.

I also found Sinclairs bullet seating compareter quicker to use than Stoneys. Just measure a bullet, push it into the lands, put the rod guide in the bolt guide, slip the rear collar on the rod and push the rod in until it touches the bullet base, lock the collar, tip up the rifle and drop a short piece of brass rod down the barrel and the bullet will pop out, push a sized case into the chamber, put the second collar on the rod and insert into and touching the base of the case, lock the collar. Measure the distance between the collars and add the bullet length to the measurment and you have the over all length of the cartridge touching the lands.

It takes longer to tell how to do it than to do it.

I keep these measurements, the case and the bullet I used in a plastic tube so I can always return and reuse as a reference.

When I start a load development and find a good load, I use the previous "touching" LOA and subtract the current LOA to find just how far off the land the bullet is. Sometimes this information is of some value later on, you just don't know until you need it.

quote:

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Originally posted by rickdm:
...I guess I did not pose my question clearly...

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RickDM,

I understood the question, and was attempting to recommend a series of processes, which would help in discovering WHY this anomaly or axiom is occurring.

The only question I failed to ask was the actual full-length or overall measurement. I have not seen you post a result on that nor have I asked.

What is the overall length of each of the rounds in question by bullet-type? I assert that the circumscribed (center of form) perimeter behind the point or full length should [inevitably] yield identical results. I only stuck in the seating because it is [in my estimation, a critical success factor] the focal process enacting this result set.

Please keep us posted as we are interested in knowing the process and its outcome....

------------------
Best regards,
Alex

Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote! - Benjamin Franklin 1759

[This message has been edited by Alex Szabo (edited 03-19-2002).]

I don't think you have to concern yourself too much over the length of the factory rounds (unless that helps you).

It is more important to have the firearm worked up to a 'ready state' so that you can make the most accurate round possible.

From my own experiance, I have learned that the seating [from an implied point relative to the lands] and amount of charge governs the whole shabang.

Look forward to your results!

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Best regards,
Alex

Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote! - Benjamin Franklin 1759

Like Curley, I've got a real long throated Rem 700 ADL -06. I have never measured the length (as I'm not concerned), but it is long enough that it won't fit in ANY rifle with a box magazine or any other brand chamber that I have tried it in. I does fit in one other Rem 700. Both were made in 1967. I'm also not bothered by that as both are sub 1/2 MOA rifles.

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The older I get the better I was.

quote:

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Originally posted by JHook:
Im haveing a funny problem with my new .375 H&H. No matter how I measure off the lands Im ending up with a finished cartridge thats longer then SAMMI specs. Im useing both the "empty case" methed and an RCBS screw on cartridge micronmeter.

I never saw this before, the rifle is a new M-70. Can anyone help ?

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Jhook, I just bought a new Mod 70 Safari Express in 375 H&H. I placed a Nosler Partition in an empty, slightly crimped case and chambered the round. When I ejected it, I found an OAL that wouldn't come anywhere near fitting in the magazine. (Didn't measure it).

I guess I'll just settle for seating the bullet to the cannelure...

So much for making full use of my fancy Forster Ultra Seater Micrometer die.

Rick.

[This message has been edited by curley (edited 03-19-2002).]

Rick

My RCBS presicion Mic is worthless for the throat of this rifle. OCL for .375 H&H is 3.600 and all my measurements find that Lands at 3.840. I never experienced this with a rifle before.

Well Im going to break in the barrel this Sun with a box of factorys and see how she shoots. As long as it groups ha;lfway decent Im not going to worry about it, and If I have to I'll just have to full length all my cases, trim to minimum, and seat to max OCL. Im sure as hell not going to fire a cartridge thats .24 over max OCL.

I'll keep you posted on this..................J

Glad to see you figured it out. I was going to post yesterday, but when someone else answered, I figured he understood your question and I hadn't. Wrong again.

I don't think there's anything wrong with the Sinclair "nut," although I now use a Davidson clamp-on for convenience. It is different. I doubt that there is an industry standard for throating. I think you need to settle for using the comparator to measure case-head to bullet-datum line for ONE bullet, so as to seat consistently off (or on) the lands, but the whole thing is by comparison to your dummy round WITH THE ONE BULLET seated to the lands.

In my opinion, your measuring hole size in the comparator shows that you understand exactly what's going on, but the "standardization" you would like to see doesn't really exist.

[This message has been edited by Recono (edited 03-20-2002).]

Glad you have found a pathway. I have attempted to duplicate your condition, but have been unsuccessful.

I deliberately used an incorrect depth for the barrel measurement, and generated dummy rounds which were incorrectly sized. They still maintained consistency in the comparator's value based on the ogive.

If I find the sweet spot, I'll let you know.

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Best regards,
Alex

Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote! - Benjamin Franklin 1759

You hit the nail on the head when you realized you were mixing Stoney Point and Sinclair tools. Although both are excellent tools and both are made to measure the same thing, they are still two different tools. It's kind of like taking a 1/2 inch socket and a 1/2 inch flat wrench and using them to turn the same nut. It's likely that one of the two will fit a little tighter.

Seems to me all you need to do is make sure you're comparing apples to apples by using one comparator or the other for your measurements.

One other thing occurred to me that may be coming into play. When I clamp my Stoney Point comparator to my calipers, I have to re-zero the gauge. The comparator (with caliber insert) measures something like 1 inch plus 10-12 thousandths. So I re-zero my gauge and then just subract an inch from whatever the measurement comes out to be. If you aren't re-zeroing that gauge, that might throw you off by 10-12 thou or so. Just a thought.

Rick

Bullets have ogives, which as I understand it basically is the shape of the curve from the bullet tip to the major bullet diameter. You mentioned that the bullets you loaded varied from at least 175gr to 139gr, right? Since these are very different weight bullets and likely from several makers, the ogives are likely to be quite different, even if they look almost identical to your eye. It doesn't take much "eyeball" difference to amount to many thousandths when you're measuring.

Anyway, you used two comparators, one with a .271 opening and the other measuring .274. OK, lets assume all the loaded rounds with all the various bullets measure the identical length on the .271 comparator. Common sense would tell you that they should also measure as being identical with the .274 comparator as well, right? But if their ogives are different, then when you switch to the larger diameter comparator some of the bullets are going to slide in just a fuzz deeper or shallower, depending on the ogive shape. I hope I'm explaining clearly enough what my concept is.

Same is true when you seat all those different bullets to just touch your rifling and then they don't measure the same on the comparator. The reason is that your comparator diameter doesn't perfectly match your rifle's bore, so bullets with different ogives aren't going to measure the same when checked with your comparator (either of them).

Since you now understand what the problem is, or at least what we think it is, I still believe that you'll be fine as long as you use one comparator or the other, and simply realize that they are slightly different. As long as you use ONE comparator, work up your most accurate load from seating depths with that ONE comparator, then you should be fine. Just be sure that when you write down the optimum seating depth in your loading manual, you specify which comparator that measurement is from. Make sense?

[This message has been edited by Kentucky Fisherman (edited 03-21-2002).]

However as soon as you load for a new type of bullet you need to stick it in the barrel to determine the distance to lands for that particular bullet, because the comparator cannot be counted on to determine distance to lands among different types of bullets (unless you get lucky and your comparator happens to perfectly match your lands). It is not a big deal to do this, I was just confused about what I could use a comparator for.

Thanks,
Rick