Stoney Point tool lying to me? Help

[CamoWildcat]

I've got a problem I'm hoping someone can help me solve. :?
I have a Stoney Point OAL gauge. I also made a 'dummy case' for each cartridge I load by cutting 2 slots down the neck. I took a test bullet and put it in the Stoney Point tool, pushed it in the chamber, and while pushing on the tool, I pushed on the bullet, then locked it. The COAL measured 2.253". I then took the SAME test bullet, put it in my 'dummy case', put it in the chamber and closed the bolt. When I removed it, I kept a small amount of pressure on the bullet tip with a cleaning rod just to make sure the bullet didn't back out any as I removed it. This COAL was 2.262". I then seated the SAME test bullet in the dummy case and seated it in my seating die to 2.261" (someone suggested seating to the lands in my 243wssm, so I thought I would try it in my 223wssm also). I then took the first bullet to be loaded and tested it in the Stoney Point tool - it measured 2.245" COAL. I seated it in the first case to be loaded and it measured 2.259" COAL. I then chambered the round and it showed land marks, but the COAL did not change. How can the dummy case measure longer COAL unless the bolt is not inserting it all the way into the chamber? Is that my problem with the 223 wssm accuracy trouble? Which should I believe, the Stoney Point or the dummy cartridge? HELP!! :?:
This is a 50 grain boattail bullet which measures .774" OAL, giving me .174" inserted into the neck. Is this enough?

 

[Charlie-NY]

IMO the StoneyPoint OAL gauge will give you more accurate information than using the split neck/dummy round method. The dummy round technic is really hit & miss.

You can get very accurate measurements with the StoneyPoint after you have used it for awhile and "gotten a feel" for its use.

 

[Jaywalker]

Cartridge OverAll Length is a poor measurement.

First, bullets have different tapers - "ogive" - so the an OAL for one bullet will be wildly different for a bullet with a different ogive.

Second, even within the same bullet box, the ogive might differ markedly. Think about it - if the weights of the bullets vary and the OAL is the same, where is the extra weight? It's in ogive differences. If you seat to the same OAL, the distance from the lands will differ, as will its its Jump To Lands, and that's the critcal value.

Third, bullet tip deformation changes OAL.

Finally, It's really easy to screw up a Stoney Point measurement. A copper bullet is softer than the steel lands - pushed too hard, the copper will score and sit too far forward. Using that as your "Land Zero" will will lead to a bullet too close to the lands.

I'd believe my eyes - land marks mean move the bullet farther back. If you want a tool that's better than the OAL gauge, get Stoney Point's Bullet Comparator. That attaches to your calipers and allows you to record Ogive Length in inches, and that measure, unlike OAL, is repeatable among bullets.

Jaywalker

 

[Blaine]

I took a test bullet and put it in the Stoney Point tool, pushed it in the chamber, and while pushing on the tool, I pushed on the bullet, then locked it.

I have no idea what you mean by this statement. Do you mean the S.P. OAL gauge AND the modified case? If not, I have no idea how you got the S.P."tool" into your chamber.

What Jaywalker said is exactly and precisely correct. You cannot use OAL from base to tip and get anything near the same measurement from round to round.....too many variables in tip/ogive. The S.P. comparator (or similar) is the only way to duplicate the "jump" from round to round.

Blaine

 

[CamoWildcat]

Jaywalker,
If you will re-read my post, you will notice I said I used the exact same bullet for all the measurements. I normally measure to the ogive and I have the comparator, modified case, ogive inserts, and headspace gauges. So, measuring to the tip of the EXACT SAME bullet is actually more accurate when comparing one tool to another since even ogives vary from bullet to bullet.

Blaine,
Yes I was using the SP tool with the modified case.

What surprised me was the dummy case / bullet COAL was longer.

 

[rick smith]

Measuring to the ogive is a far more accurate method of knowing how far off the lands your bullet is seated. Your measurements are using the "SAME" bullet but when you start loading your ammo you will be using different bullets and the location of the tip of the bullet as measured to the tip doesn't tell you where the ogive is in relation to the lands. I usually make my own modified cases but can tell you what I have done to help with the factory modified cases. Close the modified case in the action via your bolt. Need to make sure the case will properly fit your action. Measure to the datum line on the modified case and compare that number to a fired, unsized case from that rifle. A bullet should just slip through the neck of a modified case, if it is tight, open the neck so the bullet will just slip through. Be aware that the amount of force you put on the rod that slides through the modified case can drastically alter your results. You can easily push the bullet 20 thou into the rifling. I have tried several methods of finding ogive to lands including the split case. I have been using the Stoney Point method well over ten years and find it to be the best for my uses.You are using both methods to look for the same number and it should be very close with either method. Since I can't be there to watch how you do each of these methods I will not attempt to make suggestion to these. But with either method you should take a minimum of 3-5 readings and average them. Technique with either method should give you readings within a few thousants of each other.
After you have your number. Seat a bullet to that length, at the ogive, and try it in your rifle.Rick.

 

[Jaywalker]

Sorry if I misunderstood the issue, but I guess I still do. Lots of swapping things back and forth, and I've read it another couple of times and I'm still missing it. Is it that the seating die is the issue? If so, I doubt the seater is pressing on the ogive at the same point that the bullet touches the lands. A change of bullets requires a change in the seating die, even if we want the same Jump To Lands distance.

If that isn't the issue, then just chalk it up to my lack of reading comprehension.

Jaywalker

 

[Blaine]

Rick makes some excellent points, to reiterate:

1) make sure you take several readings to be sure you are getting a consistent one.

2) How hard you push on the bullet "pushing" rod before you lock it down can vary your results by a lot, just because of the flex of the thin plastic rod.

3) Also how hard you push the rod (and the bullet) just before you lock it in can determine how far you push the bullet ogive into the rifling...it doesn't take much pressure to actually "seat" the bullet into the rifling a few thousandths.

4) It takes quite a while to get the "feel" of using the S.P. Although it is a very good and useful tool, it could have been designed a little better; like with a metal bullet push rod that wouldn't flex.

My suggestion is that you start from scratch again and when you take your initial measurement, do it about 10 times and record the length each time. I think it will surprise you how inconsistent the measurements are. I've seen the time when I did the test 10-15 times before I finally settles on an average. Sometimes when you're having a bad day, you just can't seem to put a constant amount of pressure on the push rod.

Another issue is with the plastic rod, the more you use it with about the same length seating, the more the place on the rod that takes the set screw starts to wear and instead of the screw locking where you want, it tends to "wander" just a bit till it finds a spot to seat.

As I said the S.P. could use some design changes, but it is still one of the best tools out there. You just have to get used to the feel of it so that you can get the best readings possible. Hope this helps....thanks Rick for pointing out some of these issues.

Blaine

 

[CamoWildcat]

Jaywalker, Rick, And Blaine,
I wasn't real clear in my original question. I took ONE measurement with the SP tool and ONE with the 'dummy' case. Then I wondered why the two measurements didn't agree.
Thanks guys for all your help.
I push firmly on the plastic rod on the SP tool since I didn't realize you can actually push the bullet into the lands. I also squeezed the neck in a little after cutting the slits in the dummy case - in an effort to keep the bullet in the case when it is withdrawn from the chamber. So I am probably pushing the bullet into the lands in that case as well. I like the idea of putting the modified case in my chamber and closing the bolt. And I will do a datum point measurement before and after.
BTW, I took two more measurements from the muzzle end using a cleaning rod - one with the SP tool and one with the dummy case. These were referenced from a closed bolt face. Of interest, the dummy case measurement was the same as the original SP tool measurement.
One more BTW. I have my full length sizer die set up to bump the shoulder back .002" and the dummy case was made from one of these sized cases. I probably should have used a fire formed case, but I wanted the case sized as I also use it to test bullet seating depth when setting up the seating die.

 

[Jaywalker]

CW,

When using the Stoney Point tool that pushes the real copper bullet into the lands, I only use that bullet for measurement one time. Once it's been pushed into the lands and scored, you can shoot it without concern, but it will no longer yield valid measurement results for subsequent measures.

Before I realized that, I wondered what that "click" was when seating the bullet - you know, the tiny back-and-forth Stoney Point in, cleaning rod out, repeated until you're sure you've just the tiniest pressure into the lands. The "click" was the scored bullet seating into a pre-scored position in the lands, much farther forward than you think it is. Once the bullet "clicks" in, it's a shooter (and it was for the previous measurement, too), not a measurer. Ignore this part of the test and live to wonder why measurements are 0.050" (!) different. When that happens, change bullets.

When I do it now, I use the first bullet as a practice round to get the delicate feel that's necessary, then I withdraw it and change bullets for the real test. Push too hard once - start over.

Jaywalker

 

[Charlie-NY]

In my original response I ASSUMED that you were using the SP bullet comparator with the OAL gauge. As stated by others, measuing off the bullet point is all but useless.

When I take measurements I push the plastic rod lightly with the ball of my finger tip. It is not all that hard to determine when a light contact is made with the rifling. Pointy bullets can easily be pushed farther into the rifling if you are not gentle and careful.

I normally take 12 consecutive measurements. Then I drop the highest and lowest reading. Take the remaining 10 measurements and average them for a final measurement.

Any measurement that is WAY off should be automatically discounted and not used in the average.

 

[DevilDawg]

I have found that when using the SP gauge, you want the bullet to slide easy in the neck. Then when you push it with the plastic rod, as soon as you feel pressure on the bullet you are in the lands. Lock the rod and take it all out of the chamber. If the bullet falls out, so what,just put it back in the neck with the rod locked and take your measurement. Just make sure you are not putting a lot of pressure on your dial indicator when you take the final measurement. Do everything with a light touch and it should work out for you.

 

[Tiny]

I have found that when using the SP gauge, you want the bullet to slide easy in the neck. .

Ditto to the above.

Seeing as you got 2.253 OAL with the S.P tool and a longer 2.262 with the same bullet with the Dummy Round.

I would just about bet that the SP modified case has a rough spot in the neck which is stopping the bullet from being pushed all the way into the lands.Ran into the same promblem with one of myself.

Try pushing several bullets through the case with the tool.If any fail to be pushed out with ease everytime. Take a small round file and file the inside of the case untill they do.