Bullet Setback

[Nick Caprinolo]

Am I nuts?

I have been told to set as close to the lands as possible and then work backwards until I find the sweet spot. In many cases bullet setback is usually withing 30 thousands.

Recently, on two stock rifles I own, I am finding that the best groups are obtained within close proximity to SAMMI standards. I am very stubborn and hard headed to boot, so it takes me a long time to get old ideas out of my head.Also, I shoot with three other guys who are exactly like me.

I have a Remington 700, 22-250, that I could not bet groups better than 3/4 of an inch. Yes they are better than most, but did not seem good enough for me. So after much discussion with my friends, who all advised me not to change anything as it was shooting the best that could be expected, I finally decided to rebel against them. I did a reverse ladder test, starting with a slight jam and going down ten thousands at a time found that accuracy increase the further down I went. This rifle has a 190 thousand jump using SAAMI standards and I found that 120 thousands is giving me many 3/8 groups and a few much smaller.

Next was a Ruger PRP, in 6.5 Creedmoor. When I first bought this rifle, it was giving me 1/2 in groups with factory ammo. Well we all know that loading your own ammo, using years of past experience, will make things better. Not always true MaGee! I am now 20 thousands over SAMMI standards and am getting many very tight groups usually all touching and some very close to one holes.

My shooting pals scratch their heads in disbelief. While they are all great shots, they just can't get themselves to try it. Now I am 83 years old and the rest of them are all over 75.

Now I am not saying that this is the case in all chambers, because I have proved that close to the lands works on some rifles. But since I changed my attitude, I am winning more money from them than I had in the past.

 

[ebb]

Your Mistake was letting them know what you are doing to get these groups.

 

[Bill K]

Ya never should have told them, just keep beating them. As for your information.. sort of proves the old saying "What ever floats your boat, do it" Thanks for the information and the process you used to get your groups better.

 

[Paddyd]

I do not think you're nuts. I'm of the belief that IF everything is concentric, bullet jump doesn't hurt accuracy at all. I've always found that SAMMI recommended lengths are the best place to start. I always start my load development at the recommended C.O.A.L. . IF I don't get the desired shotgroups after loading 5 rds each in .2g increments, I will then take the best charge and start playing with seating depths to see if it improves or not. My Savage 308W with IMR4350, will shoot 5, 175 SMK's into slightly over 0.300" center to center @ 100 yds. The best yet is .303" this is at a book overall length of 2.800". In this case I never felt the need to try playing the on or off the lands game. Seating to or in the lands can get people into trouble if they don't carefully work into it. I may be the exception, but have always found the best shooting loads with some jump. Some with n awful lot of jump at that.

 

[Murray Brook]

Had the same thing happen to me with my 7mm/08 heavy barrel. Had about 700 rounds through it with many different powders and bullets. The result were groups in the .75 MOA range. Had some fellow shooters say it wasn't bad but I knew better. I had always gotten my best accuracy with my other varmint barreled rifles with a slight jam to appx .060 off. Well I done a ladder test for seating all the way to .140 off instead of stopping at .060 which I had previously done.At .120 I was shooting between .3 and .4 MOA. I said at last. Why didn't I do this 600 rounds ago. I revisited certain bullets which I had gave up on with this new seating depth only to find they too would shoot .3-.4 MOA. I will never make this same mistake again. Some barrels shoot their best with a lot of jump. JME
Nick You are certainly not nuts.

 

[spclark]

Some barrels shoot their best with a lot of jump.

Yep, s'truth!

Hard changing made-up minds though what with all the 'truths' to be found out there!

 

[Ned Ludd]

Nick - unless you're using very high neck tension (interference fit), once you jam a bullet somewhere around .020" to .025" into the lands, seating it out any further only results in the bullet being pushed deeper into the case neck as the bolt is closed. In other words, once you've reached a "hard" jam, seating the bullet out any further is not productive, because the force require to push the bullet any further into the lands is greater than that which holds it stationary within the neck. Obviously, there is not an "exact" measurement for a hard jam, and heavily worn rifling may allow the bullet go seat deeper with less force.

As far as your initial question, most people with any knowledge on the subject will acknowledge that loads with jammed bullets can show extremely good precision. It's not at all surprising that putting the bullets into the lands tightened up your groups. Just be aware that there are some general considerations to jamming bullets that you might not have had to think much about when using jumped bullets, including:

1) pressure spikes (i.e. - sometimes you may need to back off on charge weight by a tenth grain or two for jammed loads).

2) the optimal setting depth windows are sometimes more narrow than for jumped bullets (i.e. - you may need to re-visit seating depth more often as the lands erode in order to maintain optimum precision.

3) un-chambering an unfired round may leave the bullet stuck in the rifling, dumping powder out inside the chamber.

None of these are deal breakers in any way, they simply require a certain level of attention to details you may not have been concerned with when using loads with jumped bullets. The bottom line is that you tried something new and it worked. Well done!

 

[Nick Caprinolo]

Nick - unless you're using very high neck tension (interference fit), once you jam a bullet somewhere around .020" to .025" into the lands, seating it out any further only results in the bullet being pushed deeper into the case neck as the bolt is closed. In other words, once you've reached a "hard" jam, seating the bullet out any further is not productive, because the force require to push the bullet any further into the lands is greater than that which holds it stationary within the neck. Obviously, there is not an "exact" measurement for a hard jam, and heavily worn rifling may allow the bullet go seat deeper with less force.

As far as your initial question, most people with any knowledge on the subject will acknowledge that loads with jammed bullets can show extremely good precision. It's not at all surprising that putting the bullets into the lands tightened up your groups. Just be aware that there are some general considerations to jamming bullets that you might not have had to think much about when using jumped bullets, including:

1) pressure spikes (i.e. - sometimes you may need to back off on charge weight by a tenth grain or two for jammed loads).

2) the optimal setting depth windows are sometimes more narrow than for jumped bullets (i.e. - you may need to re-visit seating depth more often as the lands erode in order to maintain optimum precision.

3) un-chambering an unfired round may leave the bullet stuck in the rifling, dumping powder out inside the chamber.

None of these are deal breakers in any way, they simply require a certain level of attention to details you may not have been concerned with when using loads with jumped bullets. The bottom line is that you tried something new and it worked. Well done!

Ned
I think you took the wrong meaning from my post. I am not jamming into the lands in these two rifles. Far from it. When taking my first measurements, I try to insert th bullet softly against the lands. To me that is the freebore point I want to measure from.

What I found here was that I got the utmost accuracy by setting the bullets closer to SAMMI published lengths.

Now I have a 6 PPC that wants the bullet fully seated as the bolt closes. It is a true one hole gun as most PPC's are.

 

[Ned Ludd]

Ned
I think you took the wrong meaning from my post. I am not jamming into the lands in these two rifles. Far from it. When taking my first measurements, I try to insert th bullet softly against the lands. To me that is the freebore point I want to measure from.

What I found here was that I got the utmost accuracy by setting the bullets closer to SAMMI published lengths.

Now I have a 6 PPC that wants the bullet fully seated as the bolt closes. It is a true one hole gun as most PPC's are.

I see...other direction. Regardless, the starting point is a reference point only, where you end up is what's critical, and only the target can tell the true story. Well-tuned loads with bullets jumped a country mile are not unheard of either. The good news is that you went outside the box and found a way to get the results you were after.

 

[K22]

Several years ago Sierra published an article on this subject noting that some rifles do better with a considerable jump. I have found this to be so with many of my Rem 700's. As you may know, they tend to have quite a bit of free bore.

I normally start load development at .020" off the lands or more if necessary so the round will fit the magazine and there is enough bullet depth (I like one bullet diameter) in the case to provide adequate bullet tension and minimize run out.

However I never jam or get closer than .005" to the lands due to variations in bullet ogives. Never found it necessary to jam the bullets into the land to achieve excellent accuracy even for precision varmint shooting. I don't want a bullet to stick in the lands when I'm in the field and extract an live round. Also I don't want create a high pressure condition which jamming can cause.

 

[joshb]

Hi Nick! You’re not nuts! You did it right. Keep “experimenting” if a gun won’t shoot the way you want it to. A lot of times, conventional wisdom works. Sometimes it doesn’t.
A thought: Seating a bullet deeper in the case reduces internal case volume and can raise pressure. You have two things going on there.

 

[Steve Donlon]

Great post Nick. I'm a old guy too and have always thought that jamming a bullet into the lands was just a short cut to accuracy with some very undesirable effects. Of course accuracy is the goal and I understand why people insist on doing it. But there are other options and you have gave proof of that with your situation. If you have less lead than the options are not as many but I see no reason to jam a bullet into the rifling if you have other options. If the bullet goes in straight it will come out straight if all else is good.