small caliber distance to lands

[spitballer]

Recently I went from touching the lands to backing off .030" from the lands with my favorite .223 Rem thin-jacketed bullets because of possible pressure signs. Accuracy was still acceptable, but SD doubled to 46 and group size increased accordingly. Seems to me I read somewhere that small calibers like 22 shouldn't be seated into the lands like bigger bores, maybe something to do with relative thickness of jacket? Anyone know anything about this?

I'm inclined to close up the gap at least a little bit, perhaps to .015" but the jacket theory seems sound to me. Can anyone shed some light on this small caliber stuff? Thanks in advance.

 

[MtnCreek]

I don't know about small cal or not.

When you went from seating at the lands to seating off the lands the pressure changed and could have thrown you out of your accuracy node. I'd rework at 0.015 or 0.020 off, then make slight seating adjustments after finding your charge weight (or just stick with it if shooting well enough).

 

[rsrocket1]

Recently I went from touching the lands to backing off .030" from the lands with my favorite .223 Rem thin-jacketed bullets because of possible pressure signs.

What pressure signs did you observe? Flattened primers? Incipient head separation? Bolt marks on the face? Or was it "worried about potential high pressure from interweb posts"?

Seating a .223 bullet 30 mils deeper certainly can increase pressures (maybe around 1000 psi) but certainly can change barrel harmonics. You shouldn't see SD going up from 23 to 46 fps, unless you really were causing super high pressure with the bullet stopping at the lands while the powder is early in its burn phase.

What was the load?

 

[spitballer]

What pressure signs did you observe?
What was the load?

Well quite frankly I didn't see anything at the breech end that would be an indication of excessive pressure with the Nosler 55's, but recent experience with the heavier flat based 64's has gotten a lot of us jittery. My concern stems from the appearance of flyers when seated on the lands. A recent group of 16 seated on the lands had two flyers to the right, one high and one low. As soon as I saw the high one I quit and cleaned the barrel. Would fouling from excessive pressure be causing this?

This would be a 27 1/2 grain max .223 load of H-Varget..

I've been scouring my manual trying to find the reference to this issue but can't find it. I thought for sure I'd read somewhere that seating smaller calibers on the lands is counterproductive. Maybe it was something web-based like you suggest.

 

[ess45]

Try these articles.

http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/
http://www.bergerbullets.com/setting-loads-optimum-accuracy/

 

[jhansman]

I keep my 60gr. .224 fast, pointy thingies .020 off the lands of my target Howa 1500, and the primers look just fine. You might want to work up some loads in .010 increments to see if the signs of pressure stop, and you can still maintain accuracy. BTW, the Hornady OAL guage is invaluable in determining how long is too long; that, and whether you can close the bolt on a chambered round with ease.

 

[Charliefrank]

I keel my 22 Hornet back about 3-5 thousandths back from contact. That's her sweet spot. And I always use the same bullet and same AOL. Using 40gr Nosler Ballistic tips, btw.

 

[Blue68f100]

It all depends on the chamber and bullet combo. I've had some guns that you can reach the lands very easy, min spec chambers. Then I have/had one that the only way you were going to, was single feed the round and use a heavier bullet for the added length. If I have the option I like to start around 0.030" or recommended OAL by the mfg. If I recall once you go less the 0.020" the pressures start going up quickly.

 

[Charliefrank]

Typically once you start going longer than the OAL, they may not feed through the magazine. My hornet is a single shot, so no worries there. I have never had any pressure issues. That being said you never want the bullet contacting the lands as that would create a (possibly catastrophic ) spike in pressure.

 

[spitballer]

ess45, good links - clearly illustrate the mechanics of this issue. Charliefrank I'm inclined to try your method of positioning just off the lands as opposed to scrunching up against them and I've made up a batch at .002" off. When seated into the lands the fouling shots were lower, but when seated .030" off the fouling shots were higher so t'll be interesting to see what this new batch does.

Won't be this week though, not until I get a break from driving these %$#@%^& trucks..

 

[Charliefrank]

ess45, good links - clearly illustrate the mechanics of this issue. Charliefrank I'm inclined to try your method of positioning just off the lands as opposed to scrunching up against them and I've made up a batch at .002" off. When seated into the lands the fouling shots were lower, but when seated .030" off the fouling shots were higher so t'll be interesting to see what this new batch does.

Won't be this week though, not until I get a break from driving these %$#@%^& trucks..

I used black soot from a burning candle to mark the front end of the bullet, (a dummy round of course ), so I could accurately determine initial contact of the lands. I referenced my notes this morning and I'm exactly. 003" off the lands. This method should be used with neck size only. Of course it goes without saying when fabricating ammo this way, extreme attention must be paid to the process as you are leaving no room for error.

 

[Charliefrank]

One other thing, if you change bullet style you must start over again as it will change distance to lands.