Degree of testing

Ammo Junky · November 22, 2006, 10:04 PM

When working up a rifle load, I usualy get some new preped win cases, win primers, The hodgedon powder or two I want to use and the hornaday or sierra bullet I want to use. I set oal for .005 jump and work up the charge in .5gr incrimets. I pick the charg that looks the most stable, promissing and gives near the target velocity. I then load some rds with that charge at dead length, .005, .015, .025 jump and Mag length if the longer oal will not fit. Of corse there is the horrible throat of rem 308 :barf: that cant really be loaded properly

so I only test at mag length

. My question is how many of you have tested your oal / bullet jump in small incriments of .001 or .002? Has anyone seen big changes on paper from .002" change in oal?

Thanks
AJ

P-990 · November 22, 2006, 10:22 PM

.002" change in OAL is very small. Unless you're using a comparator, you can get that much difference in just the bullet tips of match hollowpoints.

I wouldn't worry about jump too much, honestly. As long as you're safe, let the targets tell you what needs to be done. I've got some .223 AR-15 loads that jump over .025" and they shoot fine. I'm currently loading 52gr Hornady's jumping about .015" (they're well below mag-length, actually, about 2.21" OAL) for 100-yards and I'm confident they'd group within an inch for ten from a rest. There doesn't really seem to be any accuracy advantage (IME) with my long-range loads which only have to jump about .02".

As always, YMMV. And besides, tinkering can be half the fun!

(But yes, I consider .002" OAL changes to be borderline madness-indunction.

)

mrawesome22 · November 22, 2006, 10:30 PM

What I do is start with the ogive .030" off rifling, then work up to max charge. This has always produced groups that are plenty accurate for me. Maybe I just have accurate guns? All going closer than .030" did for me was make pressure's go too high and made my groups fall apart. I know .030" seems like a mile when all you hear day to day is .005" this and .010" that, but look at a tape measure, if it has 32nd lines, look how tiny that is. I'm no competitive benchrest shooter either though. I'm a hunter. And a 1" group at 100yds is all I need for killing hogs and coyote's at 400yds. Sure I'd love to shoot 1 hole groups. But I'm sure that dead coyote is gonna care less.

And I've have to agree with P-990 LOL, .002" would have to be seen with an electron microscope LOL.

**Unclenick** · November 22, 2006, 11:12 PM

Traditional method is to move the bullet in either .005" or .01" steps, using a moderate target velocity load to find minmal group size. Once you've found the best seating depth, start adjusting the load until you find the smallest group size for that seating depth.

Often you have trouble testing the best seating depth if you aren't neck-sizing only. In most HP rifle, each .01" step will produce a pressure change similar to 0.1 grain of powder, increasing as the bullet seats deeper. The exception is seating out to touch the lands, which, owing to the bullet now having its static rather than its kinetic coefficient of friction to overcome in entering the rifling, creates a jump in pressure equal to adding about 0.5 grains of powder typically. The difference is bigger in bigger bores.

The reason it is often hard to tell a result if you aren't strictly neck sizing is most comparators measure the bullet position from somewhere on the ogive (which is why the tip variance doesn't affect the reading) to the casehead's face. If the cartridge headspaces on the shoulder, then how big the chamber is determines how far forward the shoulder and neck slide into the gun when the firing pin strikes. So, it is the bullet's seating depth with respect to the shoulder and not the casehead that actually matters. Only when you fireform the cases then neck size-only does this dimension not change from one round to the next. If you full-length resize you will often find two to four thousandths of variation in the shoulder location with respect to the casehead from one case to the next (depending on the cases and their load history). This alters how far the firing pin drives the case forward into the chamber before the case shoulder strikes the chamber's shoulder and stops. It is this that determines where the bullet is when it stops moving forward.

Nick

Bullet94 · November 22, 2006, 11:31 PM

Unclenick

I copied this from Benchrest Central. What do you think?

“MY point is simply QUIT dinkin' wi'ddit! Just PICK a good solid setting that allows he rifling lands to aid in centering the bullet and work on other stuff.

ONLY with a true-blue BR rifle capable of "shooting in the ones" will you EVER see a gain from "tuning" with seating depth (and even then it gets more play than mebbeso it should )

For regular stuff it's all about INTO the lands and OUT OF the lands (like ten thou out, or more, like to fit a magwell)”

November 22, 2006, 10:04 PM	#1
Ammo Junky Senior Member Join Date: March 11, 2006 Location: IL Posts: 537	Degree of testing When working up a rifle load, I usualy get some new preped win cases, win primers, The hodgedon powder or two I want to use and the hornaday or sierra bullet I want to use. I set oal for .005 jump and work up the charge in .5gr incrimets. I pick the charg that looks the most stable, promissing and gives near the target velocity. I then load some rds with that charge at dead length, .005, .015, .025 jump and Mag length if the longer oal will not fit. Of corse there is the horrible throat of rem 308 :barf: that cant really be loaded properly so I only test at mag length . My question is how many of you have tested your oal / bullet jump in small incriments of .001 or .002? Has anyone seen big changes on paper from .002" change in oal? Thanks AJ __________________ Will work for brass. I apologise in advance for spelling errors.

November 22, 2006, 10:22 PM	#2
P-990 Senior Member Join Date: May 2, 2002 Location: Only1/2WayThere Posts: 1,316	.002" change in OAL is very small. Unless you're using a comparator, you can get that much difference in just the bullet tips of match hollowpoints. I wouldn't worry about jump too much, honestly. As long as you're safe, let the targets tell you what needs to be done. I've got some .223 AR-15 loads that jump over .025" and they shoot fine. I'm currently loading 52gr Hornady's jumping about .015" (they're well below mag-length, actually, about 2.21" OAL) for 100-yards and I'm confident they'd group within an inch for ten from a rest. There doesn't really seem to be any accuracy advantage (IME) with my long-range loads which only have to jump about .02". As always, YMMV. And besides, tinkering can be half the fun! (But yes, I consider .002" OAL changes to be borderline madness-indunction. ) __________________ NRA Master, Highpower Rifle, Across-the-Course NRA Expert, Highpower Rifle, Mid-Range Prone

November 22, 2006, 11:12 PM	#4
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Traditional method is to move the bullet in either .005" or .01" steps, using a moderate target velocity load to find minmal group size. Once you've found the best seating depth, start adjusting the load until you find the smallest group size for that seating depth. Often you have trouble testing the best seating depth if you aren't neck-sizing only. In most HP rifle, each .01" step will produce a pressure change similar to 0.1 grain of powder, increasing as the bullet seats deeper. The exception is seating out to touch the lands, which, owing to the bullet now having its static rather than its kinetic coefficient of friction to overcome in entering the rifling, creates a jump in pressure equal to adding about 0.5 grains of powder typically. The difference is bigger in bigger bores. The reason it is often hard to tell a result if you aren't strictly neck sizing is most comparators measure the bullet position from somewhere on the ogive (which is why the tip variance doesn't affect the reading) to the casehead's face. If the cartridge headspaces on the shoulder, then how big the chamber is determines how far forward the shoulder and neck slide into the gun when the firing pin strikes. So, it is the bullet's seating depth with respect to the shoulder and not the casehead that actually matters. Only when you fireform the cases then neck size-only does this dimension not change from one round to the next. If you full-length resize you will often find two to four thousandths of variation in the shoulder location with respect to the casehead from one case to the next (depending on the cases and their load history). This alters how far the firing pin drives the case forward into the chamber before the case shoulder strikes the chamber's shoulder and stops. It is this that determines where the bullet is when it stops moving forward. Nick __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

November 22, 2006, 11:31 PM	#5
Bullet94 Senior Member Join Date: September 8, 2004 Location: Kansas Posts: 723	Unclenick I copied this from Benchrest Central. What do you think? “MY point is simply QUIT dinkin' wi'ddit! Just PICK a good solid setting that allows he rifling lands to aid in centering the bullet and work on other stuff. ONLY with a true-blue BR rifle capable of "shooting in the ones" will you EVER see a gain from "tuning" with seating depth (and even then it gets more play than mebbeso it should ) For regular stuff it's all about INTO the lands and OUT OF the lands (like ten thou out, or more, like to fit a magwell)” __________________ PRO-SECOND AMENDMENT - Live Free or Die

November 22, 2006, 10:30 PM	#3
mrawesome22 Senior Member Join Date: November 9, 2005 Location: Ohio, Appalachia's foothills. Posts: 3,779	What I do is start with the ogive .030" off rifling, then work up to max charge. This has always produced groups that are plenty accurate for me. Maybe I just have accurate guns? All going closer than .030" did for me was make pressure's go too high and made my groups fall apart. I know .030" seems like a mile when all you hear day to day is .005" this and .010" that, but look at a tape measure, if it has 32nd lines, look how tiny that is. I'm no competitive benchrest shooter either though. I'm a hunter. And a 1" group at 100yds is all I need for killing hogs and coyote's at 400yds. Sure I'd love to shoot 1 hole groups. But I'm sure that dead coyote is gonna care less. And I've have to agree with P-990 LOL, .002" would have to be seen with an electron microscope LOL.