Measuring OAL

[bobh918]

Hey guys, I don't know if I am having an off day or what, but my problem is I am trying to find the OAL to the lands in my 300RUM. I have been using a hornady OAL guage with the comparator with previous rifles and it has worked like a charm. For some reason today, I cannot get a consistent reading to save my life. I have even tried using a fired case with enough tension in the neck to let the bullet slide to determine the length to the lands and that is even getting mixed results. Are there any other tips or tricks you guys use to determine length to the lands? I appreciate any help or advice you can offer!

 

[bobh918]

Nevermind guys, I was having an off night last night and was able to get consistent numbers this morning.

 

[sp6x6]

The hornady gauge has built in error IF it is their supplied case and not one fire formed to your chamber, I have seen this to be .002-.007 differnce.

 

[bobh918]

Yeah, I read a couple of posts after I posted mine and didn't think about that last night. I measured the difference in expansion between the hornady case and one of my fired cases and the difference was only .002 to my surprise. I took that into account and also used a sharpie to mark the ogive and was getting repeatable results no matter which method of determining OAL I used. I never thought to color the bullet to see the marks left from the lands, just goes to show what you can learn by using the search function!

 

[Nimrodmar10]

Soot from a match or candle works even better than a sharpie. You can see the lightest touch of the lands.

 

[MMarshall]

I've used the system with repeatable results in 19 rifles to date. However, with my 300 RUM a few days ago while measuring a 180gr E-Tip I ran into a very frustrating condition.

Due to the shape of the bullet and where it contacted the lands or throat I was getting huge variables. It was the first time I've ran into this problem. I tried other bullets to make sure I wasn't doing something wrong. Only the E-Tip would give inconsistent readings when compared to Accubonds, Partitions and VLD's.

I could feel the bullet touching but continuing a little deeper with every attempt. That resulted in a different reading with every check. Other bullet shapes would come to a repeatable stop every time.

On a bright note, I did develop a great shooting load with 98gr of Retumbo, Nosler brass and CCI 250's shooting 3340fps and putting three shots inside of a 1/2" at 100 yards. I went with max magazine length minus .015 and gave up on the OAL tool with this bullet design. I'm around .200 off the lands give or take .025

 

[Bart B]

Due to the shape of the bullet and where it contacted the lands or throat I was getting huge variables. It was the first time I've ran into this problem. I tried other bullets to make sure I wasn't doing something wrong. Only the E-Tip would give inconsistent readings when compared to Accubonds, Partitions and VLD's.

The pointing die used to put the ogive on a jacket stuffed with lead or whatever doesn't make each bullet's ogive curve the same. There's always a small spread.

Sometimes that difference will cause accuracy problems. If it does, then seat bullets such that they hard seat against the rifling in the chamber's leade. You may have to drop a grain in powder weight to make up for the very slight increase in pressure, but it's usually worth it. Seating bullets about 5 thousandths too long probably will still let them be pulled out with the case if you need to unload. Any longer and they might stick in the lands. Then you get to clean all the powder out of the action.

 

[tackdriver10]

Yep Bart, I've done that several times in the past. What really sucks is when you're out in the field with a chamber and action full of powder, and you don't have to tools to clean it up, or even push the bullet back out of the lands..

That can ruin your day in a hurry.