trouble finding chamber oal

[brokeasajoke]

Remy 700 30-06. Using the bullet in empty case method close bolt extract measure Im getting 2.599 consistantly with 165 noslerBT but with 180 corelokt im getting 2.830. Hows this possible? What am i doing wrong? This gun has been shooting minute of 8.5x11 paper with these 180s 54-56.5 h4350 rem 9 1/2mag primer and bullet seated to cannalure.

 

[Dusty Stevens]

Differences in ogive shape.

 

[brokeasajoke]

Im using dial caliper with hornady insert measuring on ogive.

 

[LHSmith]

Chamber OAL is the length from bolt face to end of neck portion of the chamber as machined with the chamber reamer. You want to find the length of the freebore of your chamber.
As Dusty said - ogive differences.

 

[brokeasajoke]

Wow I know Im a novice but i never would have guessed that much difference between bullets using hornady gauge.

 

[M-61]

Another thing to keep in mind is that using that gauge and the SAME bullet see if you can get the EXACT same reading 3 times in a row.
You'll wind up taking an average and using that.
Then take the SAME box of bullets and measure base to ogive....that will also surprise you. Soon you are sorting bullets into 3 piles that are ROUGHLY the same.
Now when you throw in another weight bullet it starts again.
Ir's not so much the Hornady gauge as it is the difference in base to ogive between the same lot of bullets and the way you use the tool.

Quote:
"This gun has been shooting minute of 8.5x11 paper with these 180s 54-56.5 h4350 ...."
I'm not sure what you mean by the above.

 

[Brians356]

You are measuring with a Hornady comparator bushing, but you are using a self-seating bullet method to create a dummy round, rather than using the Hornady tool to probe the chamber.

How tight is the neck on your dummy case holding the bullets? If it's pretty tight, you are forcing the bullets considerably into the lands, and different ogive profiles will go into the lands significantly different distances.

If you size the neck just right, to allow you to shallow "seat" the bullet with your fingers alone (with moderate force), yet tight enough not to let the bullet move of its own accord, the readings will converge considerably I'm betting.

PS have you slotted the dummy case's neck? That can help create the desired neck tension I described. But personally I use the Hornady (nee Stoney Point) gauge to do this.

PPS Some chaps want the "hard jammed" measurement, in which case you should go ahead keep doing what you're doing, and accept the measurements you are getting.

 

[brokeasajoke]

With the 165 nosler 5 tries yeilded 1-2thou difference. So this process must be done for each brand bullet/weight used. Im ordering a OAL gauage btw.

 

[Brians356]

So this process must be done for each brand bullet/weight used.

Definitely!

 

[brokeasajoke]

Well that helps cause seating these 180s to cannalure is give almost 1/4 in jump to lands.

 

[Brians356]

Well that helps cause seating these 180s to cannalure is give almost 1/4 in jump to lands.

They might group fine with that much jump, in fact I'm fairly confident you can find an accuracy node way out there somewhere - accurate enough, anyway. I assume these are big game hunting loads you are working up? "How much is enough, Gordon?"

 

[Catfish]

Now that you have been totally confounded and enlightened you still have no idea what seating depth will give you the best accuracy. Some guns shoot best with a long jump and others with the bullet jammed into the lands. To make things worse, if you do a lot of shooting the throat will get longer and you at some point will want to set your bullets out some.

 

[brokeasajoke]

4-5" groups so far. 1 group was 1.9" but not repeatable at 55.5gr h4350. Under stand eroision i have a 338LM savage which requires chasing them. I assumed bih variations measuring to meplate but not to ogive.

 

[Dusty Stevens]

Those shape bullets are made for loading to a mag length with no regard for accuracy. Theyre made for minute of deer accuracy but still function in a magazine

 

[lgwatson]

Try the Sinclair tool 749-004-650WB
Sinclair Seating Depth Gauge


Mfr Part: 594000

 

[Brians356]

With 30-06, if you load at or below published maximums, and do not feel resistance to opening the bolt, you shouldn't have to worry about chasing erosion, ever, unless you plan to also hunt prairie dogs en masse with it. 8)

 

[M-61]

With the 165 nosler 5 tries yeilded 1-2thou difference. So this process must be done for each brand bullet/weight used. Im ordering a OAL gauage btw.

Just like Brian 356 said....YES!
And to add to it, and I may have not made it clear, same box of bullets, you will find different lengths base to ogive. Really upsetting when you see this but it is a fact.

 

[Brians356]

Geez, given all this inexactitude, it's a wonder any old factory ammo can hit a pie plate at 400 yards, but most can. And down goes your ruminant ungulate for the count.

 

[ericbc7]

I have fought with getting Consistant chamber/cartridge length for a while now. To be clear I am looking for the distance from the shoulder (on bottleneck cases where round head spaces) to the ogive of the bullet.

The split neck -chambering regime is decent but since your Rem uses a spring loaded ejector you may not be getting the true bolt face measurement since the ejector plunger is the only point of contact between the cartridge base and bolt face (possibly).

Use a twice fired casing neck sized between firings to minimize the effect of the ejector. Split the neck, seat bullet long and lube the bullet well. This will give you a close measurement of the bolt face to lands measurement since the ejector plunger is more completely compressed ( due to better fit of case in chamber).

I also remove the firing pin to increase the "feel" when working the bolt.

This will get you to a measurement that well approximates the true distance from bolt face to lands for your rifle. At this point other things become more significant to precision.

My humble opinion, Good luck friend.

 

[brokeasajoke]

Thanks all. Im just chasing a 2" group on this bear gun.