Measurements are they exact or averages

Bill Daniel · June 19, 2011, 06:45 PM

I have a Savage FCP in 308 and have been searching for the perfect target load. I have started with SMK 168 HPBTs and found 44 grains of Varget to give me my best groups so I am now trying to tinker with seating distance off the lands. I have a Hornady LNL Classic single stage press and use a Redding competition seating die. My brass is trimmed to 2.05" and is fire formed Lapua. I use a Hornady comparitor and a Dillon dial caliper (which I just noticed was made in China). Having said that with no change to the set up my lengths to the ogive on the bullet will vary 0.001" to 0.002". When people report that their load is 0.01 or 0.005 off the lands is that absolute or an average of a certain number of cartriges.
Thanks, Bill Daniel

TXGunNut · June 19, 2011, 07:43 PM

IMHO it's a tolerable range. They won't be exact because of slight variations in components and loading processes. An average could have measurements outside of a tolerable range. When I measure headspace I know it's not an exact number, more of a benchmark or starting place. Seating a bullet .01-.005" off the lands isn't always the best strategy, BTW. Sometimes it works, sometimes it doesn't.

Jim243 · June 19, 2011, 08:00 PM

For me it is an absolute. I use a Hornady L-N-L case length gauge and cartrage for measurement for each new bullet brand and type and weight.

That gives me the MAX OAL for that bullet "IN MY RIFLE". It would be different in YOUR rifle. From that OAL I back off 0.050 inches and that is the OAL that will place the bullet 0.050 off the lands.

Simple.
Jim

**Unclenick** · June 19, 2011, 09:35 PM

Bill,

General consensus seems to be that few guns can show a difference of less than a hundredth of an inch. People seeking the best seating depth usually tune in 0.010" steps for than reason, then discover they actually have a range of 0.020" to 0.030" of the lands that's best and aim for the middle of that range. No telling where it will be. A lot of people just assume it will be close to the throat because that's typically better than standard seating depth, but it doesn't always work out. Berger has shown it's VLD's like to be as much as 0.165" off the lands for best accuracy, so be prepared to go from near the throat all the way to full seating short of the ogive starting to vanish into the case mouth.

Because pressures vary with seating depth, knock your load down to 40 grains before you do this. Find what works best with that load, then work the charge back up to tighten the groups to best performance from there.

cracked butt · June 19, 2011, 10:20 PM

edit: oops nevermind, I see that OP was using a oal tool to measure off ogive....

June 19, 2011, 06:45 PM	#1
Bill Daniel Senior Member Join Date: February 10, 2000 Location: Bowling Green, KY. Posts: 518	Measurements are they exact or averages I have a Savage FCP in 308 and have been searching for the perfect target load. I have started with SMK 168 HPBTs and found 44 grains of Varget to give me my best groups so I am now trying to tinker with seating distance off the lands. I have a Hornady LNL Classic single stage press and use a Redding competition seating die. My brass is trimmed to 2.05" and is fire formed Lapua. I use a Hornady comparitor and a Dillon dial caliper (which I just noticed was made in China). Having said that with no change to the set up my lengths to the ogive on the bullet will vary 0.001" to 0.002". When people report that their load is 0.01 or 0.005 off the lands is that absolute or an average of a certain number of cartriges. Thanks, Bill Daniel __________________ Prosecute criminals to the fullest extent of the law and their weapons will become harmless. "Let us speak courteously, deal fairly, and keep ourselves armed and ready." Theodore Roosevelt 1903

June 19, 2011, 07:43 PM	#2
TXGunNut Senior Member Join Date: January 16, 2010 Location: If you have to ask... Posts: 2,860	IMHO it's a tolerable range. They won't be exact because of slight variations in components and loading processes. An average could have measurements outside of a tolerable range. When I measure headspace I know it's not an exact number, more of a benchmark or starting place. Seating a bullet .01-.005" off the lands isn't always the best strategy, BTW. Sometimes it works, sometimes it doesn't. __________________ Life Member NRA, TSRA Smokeless powder is a passing fad! -Steve Garbe I hate rude behavior in a man. I won't tolerate it. -Woodrow F. Call Lonesome Dove My favorite recipes start out with a handful of used wheelweights.

June 19, 2011, 08:00 PM	#3
Jim243 Senior Member Join Date: January 5, 2009 Location: Just off Route 66 Posts: 5,067	For me it is an absolute. I use a Hornady L-N-L case length gauge and cartrage for measurement for each new bullet brand and type and weight. That gives me the MAX OAL for that bullet "IN MY RIFLE". It would be different in YOUR rifle. From that OAL I back off 0.050 inches and that is the OAL that will place the bullet 0.050 off the lands. Simple. Jim __________________ Si vis pacem, para bellum

June 19, 2011, 09:35 PM	#4
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Bill, General consensus seems to be that few guns can show a difference of less than a hundredth of an inch. People seeking the best seating depth usually tune in 0.010" steps for than reason, then discover they actually have a range of 0.020" to 0.030" of the lands that's best and aim for the middle of that range. No telling where it will be. A lot of people just assume it will be close to the throat because that's typically better than standard seating depth, but it doesn't always work out. Berger has shown it's VLD's like to be as much as 0.165" off the lands for best accuracy, so be prepared to go from near the throat all the way to full seating short of the ogive starting to vanish into the case mouth. Because pressures vary with seating depth, knock your load down to 40 grains before you do this. Find what works best with that load, then work the charge back up to tighten the groups to best performance from there. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 19, 2011, 10:20 PM	#5
cracked butt Senior Member Join Date: December 22, 2001 Location: southeastern wisconsin Posts: 537	edit: oops nevermind, I see that OP was using a oal tool to measure off ogive....