Jam length in a bolt rifle?

[USSR]

If your bullets are accurately produced, the ogive/base will be the same on all of them.

Different makes and types of bullets have their ogives in different positions in relation to the point at which the seating stem contacts the bullet. Hence, a bullet where the ogive is farther from the point at which the seating stem contacts the bullet will locate the ogive farther from the leade than a bullet where the ogive is located closer to seating stem contact. That is why you use the exact bullet being used to determine maximum chamber length (jam length).

I don't see a lot of the Stoney Point dealies at benchrest matches. I see a lot of the Sinclair nuts...

That's because the maximum chamber length is already known by the shooter at the match (ie. they measured it at home - and not by "jamming" a bullet into the leade). It's not something that is done every time, whereas taking a base to ogive measurement is something that is done each time you set up your seating die to reload, so as to insure that you are producing rounds with the correct base to ogive dimensions.

a) Insert the case into the seating die via the press handle. If the press cams over, hold it at the cam point (I _do not_ like seating with a "standard" press). Now screw in the seating stem until it hits the bullet. This is your jam length. Screw it in about 0.003" more, and you should be good to go.

While this will work, it is not as precise as using precision instruments to setup your seating die. Also, please explain how you measure 0.003 turn of a seating stem?

Don

 

[bogie]

Different makes and types of bullets have their ogives in different positions

Uh, right... Anyone who tries to shoot a consistent group with bullets from different manufacturers or different lots is _seriously_ wasting his time.

That's because the maximum chamber length is already known by the shooter at the match (ie. they measured it at home - and not by "jamming" a bullet into the leade). It's not something that is done every time, whereas taking a base to ogive measurement is something that is done each time you set up your seating die to reload, so as to insure that you are producing rounds with the correct base to ogive dimensions.

I beg to differ... You already know your chamber length, because you've set up your sizing die to just barely bump size your brass. Most people will do this at the range where they're loading... It's easy. Take the firing pin out of your bolt, and insert a fired case. Notice how hard the bolt is to close. Now, with the sizing die screwed out, size the case. Does it still chamber hard? It should. Now, screw the sizing die in a little. Size the round. Chamber, etc., etc., until you have just a little feel when you close the bolt.

As for ensuring that you're producing rounds with the same base to ogive dimensions, if your bullets aren't all the same, you _really_ need to find another supplier.

To determine maximum OAL, and set your seating dies accordingly, the most accurate way to do this is to jam the bullet.

While this will work, it is not as precise as using precision instruments to setup your seating die. Also, please explain how you measure 0.003 turn of a seating stem?

I guess us benchresters have been really doing things wrong then... I suggest that you look at back issues of Precision Shooting magazine, the Sinclair precision loading handbooks, etc...

As for measuring three thous (which is actually a pretty big number... I got whupped like a rented mule by Jack Sutton at the NBRSA Nationals this fall - I finished a yardage in fifth place, with a 0.2005" aggregate, and he finished it with an 0.2004" score...Argh...)... It's easy.

With a standard Wilson die, take your seating stem out, stick it in your calipers, and note the measurement. Then loosen the lock screw, and turn the stem three thous in the direction of the seater... Check with the caliper, and when it's right, tighten the lock screw. You can also calculate the amount that a screw turn will advance the stem, but I generally never bother.

I also use the Sinclair micrometer tops, which are pretty close, and own two of Jim Carstensen's seating dies, which are just dead nuts accurate on their adjustments (0.00125/click).

If you're using press seating dies, a little trial and error with a Sinclair nut will get you there.

I _will_ shoot with you for money.

 

[USSR]

I beg to differ... You already know your chamber length, because you've set up your sizing die to just barely bump size your brass. Most people will do this at the range where they're loading... It's easy.

Ahhh, a benchrester. First, 99.9% of reloaders don't reload at the range. I am assuming the guy who started this thread is a casual shooter/reloader using a press with normal 7/8"-14 dies, and not the straight line Wilson dies. If not, sorry. What I was referring to with "maximum chamber length" (it is assumed that the case has been properly resized) is the distance from basically the bolt face to the point in the leade where the bullet ogive makes contact when the bullet is seated out as far as possible. This is a known distance (although it will lengthen over time) and is what I believe is being called the "jam length". We are both finding this length, you by gradually seating the bullet deeper in the case until you find it, and me by using the OAL Guage. It's just a question of which is easier to do. As for me, I am an F Class shooter, shoot at Williamsport, PA, and use the Redding Competition Dies.

Don

 

[bogie]

FWIW, I use a full length size die that's very similar to the redding dies - takes the same sizing buttons.

Only I use carbide sized in 5 tenth increments...

I shoot groups, out of St. Louis Benchrest Rifle Club, and use... Sheesh...

Butt Ugly gun (Stolle Panda, Lee Six Teddy stock) uses a Harrell FL die to size (in a Partner press), and a Carstensen seater.

Black and Blue gun (Kelbly Grizzly II, Kelbly Six stock) uses a Carstensen FL sizer (in an RCBS JR-3 press), and a Wilson/Sinclair micrometer seater.

Green Rail gun (Kelbly Grizzly II, Rush River rail) uses a Harrell FL die to size (in a Harrell press), and a Carstensen seater.

Precision reloading is _NOT_ that far removed from "stuff the thing with a primer, powder, and a bullet. It just requires a little more attention to detail.

If you shoot at Williamsport, we've probably got a few friends in common.

 

[Bullet]

USSR
“What I was referring to with "maximum chamber length" (it is assumed that the case has been properly resized) is the distance from basically the bolt face to the point in the leade where the bullet ogive makes contact when the bullet is seated out as far as possible.”

I thought chamber length didn’t have anything to do with the lands or your bullet. Just the size of your chamber.

“This is a known distance (although it will lengthen over time) and is what I believe is being called the "jam length". We are both finding this length, you by gradually seating the bullet deeper in the case until you find it, and me by using the OAL Guage.”

I don’t think this is what bogie is doing. I think he is referring to Jam 2 seating his bullet into the lands then backing out .003. Which will probably be still in the lands. Nothing to do with where the lands start.
bogie please correct me if I’m wrong.

I thought that just about every thing we know to do with accuracy / precision reloading came from the Benchrest Shooters.
bogie “I don't see a lot of the Stoney Point dealies at benchrest matches.”


bogie
Do any of the benchrest shooters seat their bullets off (or out of) the lands?

 

[bogie]

Jam it hard, which is pretty much the max, and then back it off. This ain't rocket science, and it's remarkably easy to do, including taking the bolt down, getting the size, making adjustment, and then loading, all within about 45 minutes.

Seat the bullets where they shoot. You know where hard jam is. That's a given. Start there (at low pressure...) or at about 3 thou, and go out in three thou increments. Some folks will jump 'em a pretty good distance, but you gotta have a starting point. It's really dependent upon barrel...

 

[USSR]

Bullet,

The chamber of a rifle includes everything from the point just in front of the extractor groove to the leade. In your initial post you said "Who cares how far into or out of the lands you are if wherever you are shoots best. Am I missing something?" I've tried to tell you that accuracy and pressure are related to whether the bullet is "jammed" into the leade or, if not, how far off of the leade you are. Since this site doesn't really deal much with precision shooting, I would suggest you check out several other sites that do.

For benchrest shooting: http://www.benchrest.com/forums

For Tactical Rifle shooting: http://www.snipershide.com

Hope that helps.

Don

 

[bogie]

There is no single magic number.

There are only starting points.

 

[Bullet]

What got me interested in Jam length was a friend of mine (he shoots in competion – service rifle) told me that in just about every rifle he has he gets the best accuracy when seated into the lands. I haven’t seen any posts here about this. Most of the posts I’ve seen are about finding the lands and then backing of. This is probably the way to go if your using a magazine but if you can load into the lands and get better accuracy why not. A couple valid reasons to be leery of loading into the lands are –

1 – You might have to extract a loaded cartridge and the bullet could or will remain in the lands and dump your powder.

2 – If you start adjusting seating depth (after you’ve found your powder charge) from just touching the lands and then seat into the lands pressure will rise.

Both of these seem to be avoided easily by –

1 – Use more neck tension or seat your bullet into the case a little more.

2 – Start from Jam length - bogie - “Jam it hard, which is pretty much the max, and then back it off. This ain't rocket science, and it's remarkably easy “


I really don’t under stand why some people seem reluctant to try loading into the lands where you could possible get better accuracy. Maybe they just don’t have enough info about this.

USSR
“Aren't you using your comparator in conjunction with a Stoney Point OAL Guage? If not, why not?”

Because this only measures to the lands and if you start here and seat into the lands pressures will rise.

bogie - To determine maximum OAL, and set your seating dies accordingly, the most accurate way to do this is to jam the bullet.


USSR
“What I was referring to with "maximum chamber length" (it is assumed that the case has been properly resized) is the distance from basically the bolt face to the point in the leade where the bullet ogive makes contact when the bullet is seated out as far as possible.”

USSR – “The chamber of a rifle includes everything from the point just in front of the extractor groove to the leade.”

Just to make this clear –

CHAMBER –
That part of the bore, at the breech, formed to accept and support the cartridge.

LEADE - See throat or freebore

THROAT –
That area of the bore ahead of the chamber, tapering to the point where the rifling starts.

FREEBORE – The distance, if any, which the bullet travels upon firing before it contacts the rear portion or origin of the rifling.

If you want to measure your rifles chamber you might try this –

http://www.sinclairintl.com/cgi-bin/category.cgi?category=RESDTCL&item=G-308&type=store

I still by my original statement – (with the exception of magazine length)

“Since all the above is to try to get more accuracy out of a rifle why would knowing the distance to the lands be of any value. I believe that knowing the distance to the lands doesn’t matter and that using the second meaning of jam listed above would be the way to go since you only seat your bullets into the case more to find the OAL that shoots best. Who cares how far into or out of the lands you are if wherever you are shoots best.”

Part of the reason I posted this was to see if there was something I wasn’t aware of and also with the hope that someone might have enough info to try this in his or her rifle and possibly find that it shoots better with the bullets seated into the lands. Plus if this works you don’t need to buy something to try to find the beginning of the lands. I’m no expert but thought this might be interesting to some others too. If anyone can add any info that has not been covered I’d like to hear it.

Thanks to all that have posted here.

 

[The Bushmaster]

Oh My...And I tried to stay out of this...I would never seat my hunting rounds into the lands (rifling) no matter how much more accurate it made them. I must unload every night after the hunt and having to drive a stuck bullet out of the rifle every night let alone cleaning the powder out of the works over coffee is not my idea of relaxing after a long day on the hunt.:banghead: The accuracy gained by doing so is not worth it. Instead I fit my cartridges so the bullet is just short of the lands by .003 to .005 of a inch. I have found that .010 is the best accuracy that I can get out of my .30-30 Winchester when using pointed bullets. Yes...I said pointed bullets...And not rubber tipped. And I have NEVER had to "jam" (seems like the lazy way to do it...) the bullet to achieve the above...

 

[Bullet]

The Bushmaster – “I have found that .010 is the best accuracy that I can get out of my .30-30 Winchester when using pointed bullets.”

Jam length in a bolt rifle?


Bullet – Quote - “I also agree that if there is not enough neck tension and you eject a round the bullet could or will remain in the lands (not to good).
I have neck bushings so I can control the neck tension but I do admit that this is not for everyone or every rifle.”

I might add that for most hunting rifles seating into the lands will probably have no value. But for Varmint rifles or precision rifles accuracy might be improved.

 

[The Bushmaster]

I hate to tell ya this, but Winchester (Marlins too) lever actions DO, indeed, have a bolt. I still would never use your "jam" method to seat a bullet or find maximun seating depth.

 

[Bullet]

The Bushmaster

You are absolutely right my marlin has a bolt, but I’m not talking about lever actions. What would be the proper term?


“I still would never use your "jam" method to seat a bullet or find maximun seating depth.”

This is not my "jam" method. I believe this is how some of the precision shooters find their seating depth.

 

[The Bushmaster]

Are you a pricision shooter? Or a hunter???

 

[Bullet]

All I do is target shoot. I’ve got a pretty good rifle and am trying to find the most accurate load in it. Seating depth seems to be part of the equation. To me and maybe I’m wrong but when I hear of a bolt rifle I don’t think of a semi-auto or a lever action.

 

[bogie]

Guys... If you're shooting a lever action, I don't think that playing with jam length is going to gain you any appreciable accuracy. In that case, I'd just load to "functions perfectly" length, and then adjust powder up.

And yeah, I own lever actions too...

As far as unloading... I do not load a round in my competition rifles unless I firmly intend to fire it.

Yawn. You either get it, or....

 

[The Bushmaster]

No problem Bogie. I have experimented with pointed bullets of 165 grain flat base and no crimp in my Winchester .30-30 and only chamber loaded them and moving the bullet depth to .010 from the lands on mine did make an improvment. I would never load these in the tube though...!!

Bullet: Pricision shoot, huh??? No problem then cram...Aah Jam-em in there then and have a ball.

 

[USSR]

I believe that knowing the distance to the lands doesn’t matter and that using the second meaning of jam listed above would be the way to go since you only seat your bullets into the case more to find the OAL that shoots best. Who cares how far into or out of the lands you are if wherever you are shoots best.

Bullet,

I've given you a couple of sites that deal exclusively with long distance target shooting. I guarantee you make the above statement on either of those sites and you will either be set straight or laughed off the site.

Don

 

[bogie]

Keeping notes is good, but don't get too hung up on a particular distance from jam. Shoot whatever works best. Period.

 

[Bullet]

USSR

I posted this question on both sites. I already had it posted on the benchrest forum and there are only a couple of replies.