jump to jam

[LabRat2k3]

I've been reloading for about 6 years now, so I'm still pretty new at it. I have really only loaded hunting rounds. I have always just worked to find what charge weight gave the best groups and seated them to the COAL from whichever manual I got the load from and called that good enough. However, I have started working up a load for my new range gun that I built in hopes of printing the smallest groups I can. I have the charge figured out, but need help on finding the right seating depth. My question is what range of depths most of you cover while testing a load. How much of a jump do you start with? How far into the lands to you go, and in what increments do you shorten or lengthen your seating depth?

[Dennis]

First, give us a little info on your gun.

Second, tell us what bullet you plan on shooting.

Some bullets like being on or in the lands a little, some like to be off a little.

[LabRat2k3]

It is a Stevens 200 with a CBI .223 Ackley Improved barrel. I'm single feeding them so mag length is no issue to me. I'm shooting 69 grain SMK over 25.5 Grains of TAC powder, CCI primer, Lake City brass.

[GaCop]

First, give us a little info on your gun.

Second, tell us what bullet you plan on shooting.

Some bullets like being on or in the lands a little, some like to be off a little.


+1, you won't know what your rifle likes until you try different seating depths, there's no hard/fast rule. Let your barrel dictate what it likes.

[seanhagerty]

You are going to need to do a little development. Find out what the OAL jam length is for the specific bullet you want to use.
Once you have that, seat bullets to that depth, then do load work up from published minimums, looking for overpressure signs.

Do not seat bullets longer than your developed length. Pressure can build rapidly as you increase jam.

[LabRat2k3]

Thanks guys, I didn't know if there was some point most folks start at like say 0.025 jump and work up in 0.005 steps until you are in the lands. Sounds like its pretty much trial and error. So I guess I'll start with them touching the lands and shorten by 0.005 and see if i hit a sweet spot.

[Nor Cal Mikie]

Everything I shoot is "jammed" .010" into the lands. Mostly BR rounds. 22,6,6.8 and my .221 Fireball.
Build your load with them jammed. Find the sweet spot with the best group. Then, back off and see if the accuracy changes. As a rule, larger calibers prefer a jump to the lands. And only change one thing at a time. Keep the same powder charge and adjust the seating depth.
Being that you're single loading, you don't have to be concerned with mag length. ;) Throat length may be a factor. You don't want the bullets to be falling out of the case neck while trying to reach the lands.

[Dennis]

Most VLD's like to be in the lands a little. .010 or .020

SMK's either touching or off a little, or sometimes SMK's like being off .050 or better!

Throat length is a factor, on my 22-250 shooting 55gr NBT's, I can't get close to the lands! I measured a Federal Factory round and set my COAL accordingly!

Get a COAL guage and you will know exactly when your bullet hit's the lands.

[rjtfroggy]

When making up new rounds I uaually take a dummy round and seat a lubed bullet long and gently chamber to get the jammed length. Then I subtract .015 and start there.
In my experience I normally end up .018-.020 off the lands for my most accurate rounds.I use Sierra matchking for all my bench shooting.

[frank1947]

I have never found any particular place for any bullet all barrels seem to have their own personallity of what they will shoot one may shoot a hornady and one of the same out of the same cnc machine may not, I start with a Hornady OAL gauge at touch I start from there loading and shooting, going a .005 jump from touch , if I jam then I do the same .005 jump from jam, but I start from a gr or so from max , going to end up there anyway.

[Dennis]

I was waxed today by a person shooting a 308 with 175smk's! His COAL is what the book recommends!!!!!!

Has no clue how far off he is from the lands!

[frank1947]

dennis that can happen.

[Dennis]

PS: Nobody else was even close to us!

[frank1947]

was it a match and you two were like neck and neck in points

[Dennis]

I/we were waxed!

I took second place by one point! This one person was 11 points ahead of everyone, basicallly shooting a factory rifle with factory ammo!

It was very windy, wind wasn't consistant, very hard match!

His 175smk's set at Sierra's book COAL was doing the job!

[frank1947]

I hve a gun it just seems to shoot the same no matter what, before I bought it I read all the reviews and that was what I found, it is a Rem 700 R5 Mil Spec SS .308 it has a long throat and the only bullet that will touch the landa is a 175GR according to Mil Spec hence the name.