"Jamming" bullet into the lands?

[Clark]

I have shot thousands of ground squirrels with 223 with the bullet jammed into the lands.

A ground squirrel at 250 yards is a harder target than a deer at 500 yards.

I have shot both.

In 2010 I was hunting with a 7mmRemMag 3.48", not 3.34", because I wanted the bullet jammed into the lands to get a little more accuracy.
It did not matter much, the longest shot deer I took in 2010 was at 380 yards with the scope on 1.75X.

Bart Bobbitt may shoot a 3" 20 shot group at 600 yards with his bullet jammed into the lands so hard that not shooting and then extracting, means spilling powder all over the action. But I only jam hard enough to get in there, but I can still extract the bullet.

 

[TnTom]

I have shot thousands of ground squirrels with 223 with the bullet jammed into the lands.

A ground squirrel at 250 yards is a harder target than a deer at 500 yards.

I have shot both.

In 2010 I was hunting with a 7mmRemMag 3.48", not 3.34", because I wanted the bullet jammed into the lands to get a little more accuracy.
It did not matter much, the longest shot deer I took in 2010 was at 380 yards with the scope on 1.75X.

Bart Bobbitt may shoot a 3" 20 shot group at 600 yards with his bullet jammed into the lands so hard that not shooting and then extracting, means spilling powder all over the action. But I only jam hard enough to get in there, but I can still extract the bullet.

The amount of jam was .040"? Base to rifling is 3.340 and your loaded round was 3.480 base to ogive?

 

[Clark]

The amount of jam was .040"? Base to rifling is 3.340 and your loaded round was 3.480 base to ogive?

No ogive measurement for me anymore.
I find the OAL [ cartridge Over All Length] threshold of touching the lands. I find the OAL threshold of unfired bullets getting stuck in the throat. I use as my load, an OAL half way in between the two, if I can. Sometime the bullet is not long enough or the magazine is not long enough.

The normal max AOL for a 30-06 based length cartridge; 25-05... 338 Win Mag is 3.34", and that is often the max the magazine length is designed to feed from with some margin for cartridge tipping up on one edge of the base.

I have loaded the 7mmRemMag for 2010 hunting, not at 3.34", but at 3.48" with 70 gr Re22 180 gr VLD moly 3025 fps which is 0.140" over max. Part of how I was able to get away with that was that it was a Ruger #1 single shot with no magazine. If I pull an unfired round from the chamber, there are definitely lands marks on the bullet, but the bullet does not get stuck in the throat.

This was a 380 yard shot in 2010.

 

[TnTom]

thanks for the feedback. Its easy sometimes to proceed with what seems like it would be of benefit we finding out latter that such wasn't the case.

Also from other posts it has been pointed out that even when a bullet it advanced into the rifling the engraving remains quite subtle and has been pointed out why it may be an advantage under the right conditions which are quite specific. Tom

 

[Clark]

There are disadvantages of jamming the bullet into the lands: too long for the magazine, pressure spike, and unfired bullets can get stuck, spilling powder all over the action and leaving the gun non functional.

There is one advantage to jamming the lands, accuracy.
It is more accurate, because it gets one end, at least, of the bullet concentric with the bore.

In the 1960's there was the NRA and US ARMY article "Gauging Bullet Tilt" By A. A. ABBATIELLO, that has a mathematical derivation connecting concentricity with accuracy.

In the 1960s Purdie was patenting his reloading inventions to make ammo more concentric.

In the decades that followed Bart Bobbitt was competing at Camp Perry and getting great groups and explaining on the foundling early internet about jamming bullets into the lands.

There is nothing new about jamming bullets into the lands.

 

[boomtube]

"In the 1960's there was the NRA and US ARMY article "Gauging Bullet Tilt" By A. A. ABBATIELLO, that has a mathematical derivation connecting concentricity with accuracy."

A very interesting American Rifleman article it was (and remains). I still have it around somewhere, lost in my nearly three foot high stack of old un-classified photocopy files. Few of us had any means of checking run-out at that time but the article encouraged the development of practical and affordable gages. Today they are readily available and easily within the reach of most reloaders; that makes me happy!


"There is one advantage to jamming the lands, accuracy."

Surely no one has said or even implied that run-out doesn't matter; it obviously does. The issue is, how effective is seating jammed for reducing run-out. Demonstrable fact is, it MIGHT help but, again, it might not, it's certainly not a given fact. Not only I but LOTS of others, including some very serious BR guys, can say that it really isn't consistant (especially in factory chambers) while there are ways to reduce run-out that ALWAYS work!

 

[Clark]

I can understand how a benchrest rifle has 6mmPPC ammo so concentric and so tight fitting that jamming the bullet into the lands does not improve the concentricity.

But for factory sloppy SAAMI chambers loosely filled with SAAMI ammo, I can't imagine the front end of the bullet not improving the concentricity by jamming into the lands.

 

[boomtube]

"But for factory sloppy SAAMI chambers loosely filled with SAAMI ammo, I can't imagine the front end of the bullet not improving the concentricity by jamming into the lands."

That does seem intuitive but it's that sloppy fit that makes jamming SAAMI ammo in loose SAMMI chambers inconsistant.

Just because we have centered the forward part of the exposed bullet into the bore doesn't do a thing for an out-of-line rear portion. That's why jamming tends to work pretty well (but not always) in tightly fitted BR chambers, the bullet is then aligned between two concentric points of contact.

 

[Gene]

As far as LR BR, there is nothing consistent there with either approach, or results. It's totally an abstract at this point. These shooters claim success yet with terrible winning percentages and lack of performance consistency below 1/2moa. Not one of their measures include single shot placement without sighters, or w/resp to center of mark(accuracy).
It's competitive group/score shooting, very specialized, and not so to contribute to hunting anymore than hunting contributes to BR.

I disagree completely. There is a clear correlation between long range competition/group or score shooting and long range hunting accuracy. Or would you rather cripple and lose a big game animal at long distance because you were not cognizant of the potential accuracy of your firearm? Long range hunters can and have learned much from various forums that espouse 1,000 yard shooting, etc. Yes, half MOA accuracy is a great goal. Achieving it consistently is very difficult. Usually, the guy who prepares his loads properly and reads the wind best wins the match and kills the animal cleanly. I daresay that many readers of this forum read comments and recommendations elsewhere from long range competiton shooters. In the end, both disciplines have the same objective.

The original poster did not say his question pertained to long range hunting, nor competition. He asks "In jamming a load are we talking about sinking the lands into the jacket by a specific amount, a point that is beyond just touching the lands or seating the bullet deeper into the case by chambering?" The correct answer is that yes, "jamming" does mean pushing the bullet slightly into the lands, which of course, does sink it very slightly deeper. There is no harm in jamming a bullet, excepting that pressures increase somewhat. The throat engraves the bullet jacket lightly and some believe this causes the bullet to align perfectly with the bore. This practice became popular in benchrest circles 40 years ago.

 

[BountyHunter]

You need to define the discussion a little more.

"Jamming into the lands" is commonly referred to soft seating with minimal neck tension and letting the bullet seat itself into the lands and still withdraw. That is what is formally defined as "the jam" by Tony Boyer in his book. Mike Ratigan in his BR booke defines it similar except he wants not visible marks on the bullet while looked at with a magnifying loop.

That is also done with the bolt stripped and firing pin removed.

That normally measures out as far as .050-.070 from the start of the lands.

That is the two most common ways to define jam and seating depths from the jam by BR shooters.

It is interesting to note that those two are probably the two best SR BR shooters today and both use a lot of neck tension. Most LR BR shooters are using a minimum of .0015 to .003 as the norm also.

"Seating into the lands from the start" can be anywhere from .005 to .040 into the lands as the norm. Normally that is done with enough neck tension and that you will not pull a bullet out. Final step of load tuning is normally neck tension over the .001 some use to as high as .004. Yes that can be used very successfully by LR shooters shooting single shot and with the right neck tension tuned load.

Key in all of this is an accurate measurement from the "start of the lands" ie, touching.

Soft seating a bullet in a case then measuring from that is normally a minimum of .040 into the lands to start and then if you go another .020 and only .001 neck tension, you will leave a bullet in the neck.

Big fallacy that it will produce a pressure spike always. Many pressure tests report the opposite as it is more air space in the case. Plus it depends on the powder as to what type of pressure spike it gives as a norm.

Yes it will it you use a max load with it way off and then jam into the lands. But then that goes against common sense reloading.

However, if you are going to run singleshot, start into the lands and work your way off. you will never be wrong.

If going to run a magazine, start a max magazine COAL and work back.

Bergers guidelines for jumps from in to .020, then .040, .080 and .120 off to find a sweet spot (and then narrow down) make good sense.

You will burn the barrel out moving .001-.005 at a time initially for most people.

Neck tension is important in load tuning for KLR hunting and if you are seating bullets where they can be pushed back in by hand, you are asking for trouble IMO. You should be running at least .0015 to .003 tension depending on what your load likes.

Now that fine tuning calls for neck bushings and annealing or you are just fooling yourself that you are controlling neck tension.

BH