Inconsistent Measurement of OAL

J

jaykchan

Inactive
I am trying to measure the OAL of the 8mm Mauser cartridge with the bullet touching the land. I am doing this to figure out the suitable OAL of my hand load. The problem is that I have used three different methods and they give me three totally different measurements. One of the method gives me two significantly different measurements depending on how I position the measuring instrument. I am very confused. I would like to hear your opinion to learn what has gone wrong.

Some background info: I find that the extreme spread (ES) of fps from my hand load is very wide (can be as large as 160 fps of ES). I am trying to figure out what causes this large ES. I have ruled out powder weight variation and neck tension variation have anything to do with this problem. Now I am trying to see if OAL has anything to do with this problem.

First method: I started with seating the bullet quite long, and then tried to chamber the round and close the bolt, and kept seating the bullet into the case until I could close the bolt. Unfortunately, this resulted with the bullet seating very long. It was so long that I worried if the bullet might become cock eyed when I chambered the round from the magazine. I don't keep the measurement because it was so long that it was not usable.

Second method: I seated a bullet into the case loosely and long, and chambered the round slowly and closed the bolt. The bullet should be stopped at the land, and it was pushed inside the case. I inserted a long wood dowel through the muzzle slowly until it touched the tip of the bullet, and I made a mark on the wood dowel. Removed the round and closed the bolt. Inserted the long wood dowel until it touched the face of the bolt. Then made another mark on the wood dowel. The distance between those two marks was the OAL measured using this method, and this happened to 3.162". Strangely this measurement is very close to the OAL of factory round. At this point, I was very confused because I expected the result to be longer than the OAL of factory round. Therefore, I bite the bullet and ordered the Hornady Lock-N-Load Overall Length Gauge with a Modified 8mm Mauser Case that fits the Hornady LnL OAL gauge.

Third Method: I used Hornady Lock-N-Load OAL gauge. This time I found two significantly different measurements. If I rotated the gauge in a way that the thumb screw was facing up or facing left, the measurement would be significantly shorter than all other measurement: approximately 2.97". On the other hand, if I rotated the gauge in a way that the thumb screw was facing right, the measurement would be like 3.165" (that is very similar to the result that I got using Method # 2). I had tried multiple times, and the result were the same.

Would you please tell me why the measurement can be vastly different?

Thanks.
 
First method: I started with seating the bullet quite long, and then tried to chamber the round and close the bolt, and kept seating the bullet into the case until I could close the bolt. Unfortunately, this resulted with the bullet seating very long. It was so long that I worried if the bullet might become cock eyed when I chambered the round from the magazine. I don't keep the measurement because it was so long that it was not usable.
Click to expand...

This is the method I place the most stock in. Use your bolt to gently seat the bullet in a case which is trimmed to length. The bullet will stop when it hits the lands and that is what you have for that given bullet in that case. If the rifle has a deep throat, then it has a deep throat and there is nothing you can really do about it.

I have an old Remington 700 BDL VSSF where if I seat based on that method I would have very little bullet in the case. I just seat to the load data and quit chasing the lands. On a good day at 100 yards that .308 Win can pull under a 0.5" group. Why chase the lands?

Again, if you can't chase the lands then you can't chase the lands.

Ron
 
I suggest that you set the bullet to the manual for now. The focus on the Extreme Spread (ES) is getting lost. Have you tried other powders? I would try other powders first. When you find a powder that brings down the (ES) then work on your Primers. After you tune that then work on your seating depth. If you still are not happy with that try some other weight bullets...

Of course the rifle is solid?

That's my thoughts.
 
Because I know I am going to do it I drill the flash hole/primer pocket out in fired cases that have not been sized in my chambers. I drill the primer pocket/flash holes out for the sole purpose of having a way to push the bullet out of the neck of the case.

I am not timid about tight necks, I want all the bullet hold I can get because I will use the test case as a transfer when setting up the seating die.

Reminds me of forming cases, there was a time I would order 1,000 30/06 cases and then neck 200 of them up to 338/06 and another 200 up to 35 Whelen. My favorite cases are cases that have been fired in chambers I do not have. My favorite case is a case that has been fired in a trashy old chamber. I know, reloaders do not agree, I had no ideal reloaders had so much sizing cases.

F. Guffey
 
Here's the deal, each one of those methods are effective, but the "test equipment" you are using are not calibrated to one another. So you may get close, yet different results.

But, this is not a problem, as long as you use the same equipment when seating bullets. Here is my method:

I take an old FL sized case and with a dreammel tool I cut a slit down two opposing sides of the neck all the way to where the neck ends. I then take a dowel, bolt or something and slightly stretch the neck so that I can push the bullet into the case but there is enough resistance that it doesn't slip easily. Also, like Mr. Guffery, I drill a hole through the primer pocket so I can push the bullet out with a dowel. I also color the bullet with a black sharpie to make sure I can see the Rifling marks and, it shows how far down into the case the bullet was shoved if the bullet gets stuck in the rifling when I extract the case. Then I seat the bullet long, chamber and slowly chamber it.

I then use the Hornady Base to ogive set to see long it is....NOT COAL but base to ogive. Then, I use the same Hornady Base to ogive kit and micrometer to seat bullets. The fact that I use the same tool to measure my chamber and to seat bullets hopefully means that if it is off, it is consistently off. This means that if I change equipment, I have to re-measure everything.

All I'm saying is, just stay consistent and you are fine. It doesn't matter if YOUR measurements are 10/1000 off from another method, provided you don't change anything between measuring the chamber and how you measure OAL.

It would be nice if tolerances in test equipment were tight enough and uniform enough that it didn't matter, but that's not the case here.
 
I would also measure a few bullets tail to head. If you are using bullets with a lead tip you will notice they they are all a little longer or shorter.
 
I have used the Sinclair bullet seating depth gauge for about 25 years for bolt action rifles without any problems. It can be purchased from Brownell's and the catalog number is 749-004-6540WS. The cost is $23.99. It has worked well with the following calibers: 22-250, 270, 7mm-08, 7mm Remington mag., 30-30, 308, and 30-06. you do not need additional bullet seating depth guides for the above calibers.
 
Thanks Everyone

To Reloadron:

You are quite right. The Method#1 doesn't need any additional instrument to measure, and I can use my fired case to measure instead of using one from the vendor, and there is less likely to make measurement error because there are few variables. Somehow this method didn't work well in the other day when I used that method -- too many false negatives (when the bullet actually touched the lands and I thought it wasn't). Today I decide to paint the bullet with Dykem layout dye, and measure the bullet seating depth of that same Mauser 98K rifle one more time. This time the measurement is quite reasonable and matches my expectation. I also try this method with another mauser 98K rifle, and the measurement is also quite reasonable.

I have also tried the other two methods (wood dowel method and Hornady LnL OAL gauge method) on my second Mauser 98K rifle. Wood dowel method gives me a similar result as the method#1 and is acceptable. The Hornady LnL OAL gauge method again gives me two vastly different measurements depending on the position of the thumb screw -- just like the result from measuring the first Mauser 98K rifle. I believe this is the last time I will use that instrumnt.

To Longshot4:

I didn't know that I can adjust the extreme spread by using a different powder. Thanks for letting me know. Currently I am using IMR4895. May be I will try IMR4064.

To NHSHOOTER:

I am hoping for 2" group in 100-feet. Currently I am getting 3" to 4" group. I notice that bullets that traveled near the same fps tended to group together. Bullets that travelled in vastly different speed tend to scatter. Therefore, I am hoping that by minimizing the extreme spread, I can reduce the group size.

To All:

As mentioned above, I will stick with Method#1 to determine the maximum bullet seating depth and take 0.003" out of it. As of the fact that I get vastly measurements using Hornady LnL OAL gauge depending on which way I position the thumb screw, I will not try to figure this out.

I will also try different powder to see if this can reduce the large extreme spread.

Thanks everyone who has responded.
 
In the .30-06, with 4895 loads I have seen a difference of 80 fps just from tipping the gun down instead of up before firing. This determined whether the charge was forward with the bullet or back over the flash hole in the case. If your case has a lot of empty room in it, inconsistent powder position is likely part of the problem. If you have a lot of empty space in the case, try switching to a magnum primer, as magnum primers make more gas and pressurize empty space better. That is why they are made. Magnum cartridges have more room in them and need more gas to fill the space between the powder grains even if they are full with powder.

Second, check how your primers are seated:

"There is some debate about how deeply primers should be seated. I don’t pretend to have all the answers about this, but I have experimented with seating primers to different depths and seeing what happens on the chronograph and target paper, and so far I’ve obtained my best results seating them hard, pushing them in past the point where the anvil can be felt hitting the bottom of the pocket. Doing this, I can almost always get velocity standard deviations of less than 10 feet per second, even with magnum cartridges and long-bodied standards on the ’06 case, and I haven’t been able to accomplish that seating primers to lesser depths."

Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.​


Finally, if the cases are well used, and especially if they have different load history from being fired in different chambers different amounts of time, you want to look into annealing the necks and shoulders to improve the uniformity of the brass hardness.

On several occasions, when using the Hornady tool, I have found the bullet seems to catch in the chamber a little, producing the second, short seating result you describe. I always wiggle it on the way in to be sure it is all the way in place.
 
I use the Hornady Lock 'N Load like you have.....I've also made my own dummy rounds slitting 2 slits in the neck after sizing it, used the dowel measurement.....came up with that myself and LOL'd at myself at how unscientific my method was .....glad to see I'm not the only one.....great minds.:D I have also made my own modified casings prior to being able to buy the Hornady. Did that with my 7.65X53 Argentine Mauser. Can't source a tap in that diameter/pitch though locally.

One I just saw yesterday was to have a fired unsized case.......clean up the inside of the case neck real nice and then apply hot glue inside before pushing the bullet in. You leave the bullet seated far out and then run the bolt up until it closes and pushes the bullet inside the case. Leave the round in place to let the glue dry and then slowly remove it and take measurements.

Best to use the Hornady L'NL comparator inserts to measure with yeah? To the ogive?

I think what Longshot4 said about powder choice is important to consider. Perhaps being really anal about weighing and sorting bullets and cases and being super accurate down to the exact grains with powder drop is way up there also. Do you have a trickler? Calibrate and check your scale. If you have a cheap digital it might be off here and there. Maybe only use a balance beam scale until you have sorted the ES.
 
Welcome to tfl!

I am very confused. I would like to hear your opinion to learn what has gone wrong.
Click to expand...

I also am confused. My manuals list a maximum overall length with bullet for the 8mm Mauser as 3.250" Any round loaded to this length, or less should not have the bullet touching the lands.

However, longer overall lengths without touching the lands are possible, depending on the shape of the bullet, since touching the lands happens on the shoulder of the bullet, not the tip.

The standard COAL length is intended to allow all the common bullet styles to avoid touching the lands and work through the magazines as well. There are many guns where, if you seat the bullet to touch the lands (or be just off that) the round will be too long to work through the magazine.

Which brings up some additional questions. Specifically, what rifle are you using? What load? (warning, those answers will lead to other questions :D)

I'm afraid I have no experience with the Hornady gauge, so I can offer no help there.

Your method #2 (dowel down the muzzle) is not precise enough to be relied on for very small measurements. When looking at differences less than .1" variations on how a mark is made can result increasing the margin of error.

OK, you're shooting a Mauser 98k and looking at 3-4" at 100 FEET?? I don't know what else you have looked at, but first I would be looking at the rifle, and not worrying about seating to the lands or anything else just yet.

What Mauser 98k, and what is the condition of the bore?? I've had a lot of mauser 98s over the years, and they aren't match rifles, unless specifically built into one. When you say Mauser 98k, I think of the WWII German infantry rifle in issue condition. Is that what you have??

Have you shot the rifle(s) with other ammo, commercial ammo of assumed good quality? What were the results? (and for now we will assume its not you, but that can be a factor)

If you're looking to improve the performance of your rifle & ammo, the more information you provide, the better we can compare it with our experience and share the results with you.
 
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