COL Problem

[Jayhawker]

Hello:

A brand new CZ 527 Varminter, .223 caliber. My plans will be to try different loads with the bullet, different distances from the lands. The problem is that if I check this with Stoney Point OAL guage and comparator, it will give me consistent readings but they are about .050" shorter than when I do it the "old" method of using a fired brass and driving the bullet home with some magic marker on it. That method provided me with a consistent readings also but like I said, were .050" longer than when using the Stoney Point.

Any ideas here on what I should do?

Thanks.

Pete

 

[Lennyjoe]

I just did it the old fashion way and my rifle was .025 longer than what the manual calls for.

This is in a 30-06 Savage bolt. I posted it at this link. Maybe we both can learn something tonight.

http://www.thehighroad.org/showthread.php?t=121507

 

[larryw]

Probably just had to do with how hard you were engaging the lands when jamming it home vs. the Stoney Point gizmo. When jamming it home, do you see marks on the bullets from hitting (as opposed to touching) the lands?

Before I got the Stoney Point thing, I had special cases that I used to check chamber length: the case was necksized and then I hack sawed the neck to the shoulder (parallel to bore) so the bullet could move when hitting the lands without deforming.

 

[redneck2]

Fwiw

absolutely pure guess, but I suspect that, as noted above, the point on the Stoney Point is made of harder material and won't "give", and makes hard contact. The jacket of the bullet is soft enough that it may deform very slightly

Also, remember that you're contacting "on the curve", the ogive of the bullet. Since it's rounded so much at that point, you can move a long way (relatively) forward and back and not change the contact much

check Varmint Al's site. He has a method outlined there that's probably as good as any. In the end, the measurement isn't probably so important as what the rifle likes

 

[Lennyjoe]

No marks on the bullets. I sized the brass just enough to retain the bullet and when it engaged the lands it would slide in the brass rather easily.

Its a crude way of doing it but I thought it was interesting to try. I plan on getting the Stoney Point guages for proper chamber measuring.

 

[larryw]

If no marks on the bullet, then it's possible your bolt face isn't square and is slightly pumping the case as you rotate the handle.

Stoney Point tool works well, just takes some 'touch' to get consistant readings. Also get one of the tools that allow you to measure from the ogive (curve of the bullet) instead of the tip for more consistant readings.

 

[Lennyjoe]

Also get one of the tools that allow you to measure from the ogive

Thats a "must have" in mey eyes.

Expecially if your using any bullet with a lead tip IE. Winchester Power Point bullets.

 

[Bullet]

To learn the OAL where your bullet is just touching the lands try this. My seating die has a micrometer so I can adjust it by .001 of an inch at a time. This makes finding OAL easier but you can use a regular seating die too. First load a cartridge just the way you intend on shooting it but seat your bullet long. Next get a candle and smoke your bullet. Chamber your loaded cartridge then extract it and check to see if your bullet has any marks from touching the lands. If you loaded it long enough there should be a mark from the lands. If there is not a mark from the lands you didn't load it long enough. Once your bullet is showing marks from the lands start turning your die down .001 at a time to make your OAL shorter. Use a new cartridge with a smoked bullet each time you do this. If you continue to do this you will find that spot in your seating depth where your bullet nolonger contacts the lands. Since I use a micrometer seating die when my bullet doesn't contact the lands I'm .001 or less off the lands. Too touch the lands back the seating die out .001. My die is now set. Take your previous cartridges that were to long and run them back through. Once your OAL is known you can adjust your die from there for other seating distances. If you measure OAL on a cartridge make sure to measure from the Ogive for distance to the lands.

 

[Jaywalker]

Pete (since our handles are so similar),

There are a few issues to consider in addition to those already mentioned.

First, the Stoney point Comparator collar simulates the point of rifling on any given barrel, but it does not necessarily match it. I use both methods, but settle on the one for any given barrel that seats deeper in the case if there's conflict, in order to avoid possibly disastrous results if bullet is in contact with the lands.

Second, steel is harder than copper jacketing material and the jacket will "score" into a shelf across the bullet. I started noticing that my bullets would "click" (audible/tactile) into place in the barrel when used with the SP OAL Gauge. It's easy to make that mistake - push one way with the OAL Gauge "pusher," then free it from the lands with a long wooden dowell rod, then push again, progressively lighter, all the time feeling for the "sweet spot" that indicates the start of the lands. I finally realized I was scoring the jacket by pushing too hard through the OAL Gauge - that meant I was no longer feeling for the lands, but rather the shelf I scored. I fixed that issue by segregating any bullet that I'd previously used with the OAL Gauge and not use it for that again, though it's okay to shoot it.

Third, depending on the bullet brand, you can see some really wide variances within any given box. I "Comparator"-ed one box of 100 Speer .264 140g HotCor and came up with a variance in ogive length from 0.729" to 0.743," a pretty wide variance when .005" from the lands change is significant. A box of Hornady showed variance of .006, and, IIRC, Nosler Partition was .001. I stopped using Speer, and my process became noticably more regular.

Last year I varied only seating depth while maintaining a targeted powder amount. I finally came to the conclusion that the tried and true way was easier - I now target a range of powder loads - possibly 2 to 3 grains - then adjust the seating depth on the one that has most promise. BTW, I now start at .030" off the lands - I sleep easier and sometimes that is the most accurate.

Jaywalker