Bullet seating depth trials

[Shootinstick]

Have been doing some initial testing with a new 6BR R5 Tube gun. 28" 5R Rock Creek Barrel. My first trial was with 30.0 grains of Varget for 25 rounds of 107SMks loaded .005" off the lands and another 25 Berger 108BTs loaded .008 off the lands. Results were not spectacular with the average of 5 five shot groups being around 1.4" - 1.5" at 200 yards. The Bergers gave a slight edge. I was using a B&L 6-24 scope with the duplex cross hairs so could not see the best. Switched to a Weaver T36 and loaded 5 more 107 SMKs at .020" off the lands. Group was 1.8" @ 200 yards. I next tried the 107's .010" into the lands and 5 shot groups shrank to 5/8" at 200. Another 5 shots seated .015 into the lands opened up slightly. I then tried another 5 shots with the Berger 108BTs loaded .010" into the lands and they also resulted in about a 5/8" group. Seems this gun wants them seated into the rifling.
On my next test I tried two 5 shot groups with 107SMKs just touching the rifling with resulted in a 1.5" groups. Tried .005 and .010 into the lands again which shrank the group back to 5/8".

I have never before seen this drastic an effect by changing bullet seating depth with other guns. I still haven't tried any other powders, charge amounts or tried jumping the bullet more than .020.
Any comments or suggestions from others more familiar with the 6BR?

 

[limbic]

It always amazes me what .010 change in seating can do to groups. It is pretty common for some guns/bullet combos to enjoy specific seating. I have a 6brx that eats scenars up at .020 in the lands. Common depth for alot of people. My 260 will eat whatever I feed it with alarming accuracy.

Like the saying goes. Different strokes for different folks.

 

[lynn]

http://qik.com/video/41832090

Here is a video of a rail gun and the affects of seating depth on group size.

ShootingStick
I generaly do the powder charge first but since you have your initial seating figured out you can now increase your powder charge in 0.2 grain increments looking for best accuracy.
Lynn

 

[cmillard]

try .020 ITL. that is what my 6BR shoots the 105 berger vlds best at. plus, if you run them over the chrony, the consistency from shot to shot is unbelieveable vs jumping

 

[bozo699]

It always amazes me what .010 change in seating can do to groups. It is pretty common for some guns/bullet combos to enjoy specific seating. I have a 6brx that eats scenars up at .020 in the lands. Common depth for alot of people. My 260 will eat whatever I feed it with alarming accuracy.

Like the saying goes. Different strokes for different folks.

My sons 6brx really likes 107smk's .012 into the lands, we are low on 107's so I decided to try some Lapua Scenars today, I left the die set where it was, I was multi-tasking and forgot to measure them, he shot 5 rounds on the mid 1's at 100 he loaded 5 more and I then thought to check, I did some quick measuring and some quick math and we were .020 jam so I reduced it by .008 and the next two 5 shot groups were over 3/8's went back out to .020 and they came right back in the low to mid .1's Yes a few thou. does matter
Wayne.

 

[lpreddick]

for many years i believed the key to accuracy was powder and a specific charge of same( assuming a match barrel, trigger, etc). several shooters have written on the effect of bullet seating depth on group size. i would almost shoot a barrel out trying to get tight groups until i discovered the magic one can work by simply seating a bullet 5 thous deeper. the lands have a gentle slope, so there are degrees of jam, from slightly touching to really engraved bullet jacket. at some point the bullet will be pushed into the neck, depending on neck tension. therefore a bullet with only 1 thou tension will seat quickly and if you think you have 20 thous jam, you don't. a very tight neck will continue to push the bullet forward until it also stops or seats. jumping bullets is very different. with the precise equipment available we can pretty much measure to the thou of an inch. the deeper you seat a bullet, the longer it takes for it to reach the muzzel ( a millisecd or fraction of). this timing and the barrels vibrations seem to affect accuracy very significantly. only 5 thous variation will change group size and location of the group. once one has the 'right"powder and Charge, load groups of 3 to 5 at the same depth, then 3 to 5 rounds 5 thous deeper and continue until about 30 thous jump. one will usually find a depth where the group shrinks to it's tightest, then start to open. the kicker: do this in the winter, and repeat in the summer...AAAAAAAGGGG!!! the temperature changes the bullet speed and subsequently it's barrel time and the group. seat deeper to slow arrival time at the muzzel and one often sees the tight group again. this really works.

if i can see you, i can touch you. bang!

 

[STP]

With my 6BRX I jammed into the lands from the start with moly coated SMK107`s, and ladder tested to start. Found this barrel`s sweet spot at 33.5grs of Varget right off the bat with CCI BR4 primers.

Just got a 26" 1/8 twist 6BR barrel for another Savage and will do the same with somewhat lighter bullets.

Have yet to see the need to seat off the lands with the 30-06, 243Win, 260Rem. My factory Rem700 in 308Win. has been the only exception, as it`s throat is a block and a half long.

Regards,

Scott

 

[bozo699]

With my 6BRX I jammed into the lands from the start with moly coated SMK107`s, and ladder tested to start. Found this barrel`s sweet spot at 33.5grs of Varget right off the bat with CCI BR4 primers.

Just got a 26" 1/8 twist 6BR barrel for another Savage and will do the same with somewhat lighter bullets.

Have yet to see the need to seat off the lands with the 30-06, 243Win, 260Rem. My factory Rem700 in 308Win. has been the only exception, as it`s throat is a block and a half long.

Regards,

Scott

and the magazine is only a half block long LOL

 

[Nodak7mm]

Keep us posted Jim. How you getting away from the skeeters??

Rod

 

[shooter63]

totally agree with ippredick i get less flyers with 105 vld bergers jumped 15th 272 no turn kreiger 30in. hv 1x8 twist brx barrel 33.2 gr. varget 32.5 gr rl15 268 nk bushing cci 450 mag primer tried jamming till i heard sam hall was jumping his tried it &works good for me will try 107 sierras. next of course each barrel is different plus temp changes load methods but jumping the vld definately works better for me thanks for my 2 cents shooter63

 

[Hatrick]

My 6br Broughten 5C 1-8 twist barrel likes a .020 jump best when launching the 107 smk. I am just now getting around to experimenting with other bullets, so I will be curious to know if any of them shoot better touching or jammed in the lands.

 

[BoydAllen]

One thought...
Often I read where a shooter posts about trying loading "jammed" with nothing further explained. I makes me wonder if he knows the degree of subtlety involved in finding the correct seating depth when seating into the lands. To do it correctly, a definite procedure should be followed and differences of as little a .002 can be significant. simply loading the bullet so that it is marked somewhat will not get you there. Also, jam, was I think originally used by short range benchresters to mean the farthest that a bullet can be loaded into the rifling (with the neck tension that is used for actual loading) without it being pushed back into the case. Anything less than that was/is described as so many thousandths off (shorter than) jam. From there shooters who were not aware of this meaning, and how it is used to indicate a more precise location have picked up, and used the term to mean anything that is longer than touch. This does not convey any real detail about what has been, or should be done, and I think that it would be better to say with the bullet seated so much longer than touching (or off jam, working from another reference) instead if jammed. In short, I think that we would do a better job of communicating what we have done, with a different choice of words.

 

[DennisH]

With my 6BRX I jammed into the lands from the start with moly coated SMK107`s, and ladder tested to start. Found this barrel`s sweet spot at 33.5grs of Varget right off the bat with CCI BR4 primers.

I know a person who broke there 6brx barrel in with naked 107SMK's .030 in the lands with 30.0 grns Varget. He was shooting bug holes forming brass.

He got a little upset when he started to find his final load as his groups were all over the place! He went through many power/bullet combinations during the process.

The gun was doing fine fireforming brass and he couldn't figure it out. And then one day he just decided to jam them .030 in again for the heck of it! Bingo, that's where his gun wanted them!!!!!!!

To make it short, he ended up using around 32.0 grns Varget and seating 107 moly coated SMK's .030 in the lands! The gun wouldn't shoot on the lands, a little off the lands or just .010 in the lands. The gun wanted them well in the lands!!!!! Go Figure!

I have heard this several times with 6br's! I even thought about trying it in my 6.0x47Lapua!

 

[lpreddick]

tried 87 berger vlds into lands repeatedly in one of my 6x47 lapuas and they would not group, same in the 6 br. after seeing sam hall jump vlds i tried same and BINGO! one hole with 25 thou jump. the bullet is exiting the muzzel when the shock wave is at the breech. i am a firm advocate of chris long's shock wave theory explaining what makes a gun shoot a specific bullet/powder accurately. [/quote] if i can see you, i can touch you.BANG!

 

[bozo699]

One thought...
Often I read where a shooter posts about trying loading "jammed" with nothing further explained. I makes me wonder if he knows the degree of subtlety involved in finding the correct seating depth when seating into the lands. To do it correctly, a definite procedure should be followed and differences of as little a .002 can be significant. simply loading the bullet so that it is marked somewhat will not get you there. Also, jam, was I think originally used by short range benchresters to mean the farthest that a bullet can be loaded into the rifling (with the neck tension that is used for actual loading) without it being pushed back into the case. Anything less than that was/is described as so many thousandths off (shorter than) jam. From there shooters who were not aware of this meaning, and how it is used to indicate a more precise location have picked up, and used the term to mean anything that is longer than touch. This does not convey any real detail about what has been, or should be done, and I think that it would be better to say with the bullet seated so much longer than touching (or off jam, working from another reference) instead if jammed. In short, I think that we would do a better job of communicating what we have done, with a different choice of words.

Boyd,
This is very interesting I would like to learn more about it, I will try to p.m you with some semi intelligent questions tomorrow.
Wayne.

 

[jhord]

I've done a lot of bullet seating depth trials particularly with Berger VLD bullets, in .223, 6BR and now 6.5x47. I won't bore anyone with details (ravings of an uninformed idiot) but it seems to me, if you are going to see if a bullet will shoot better jammed vs. jump, then you really have to jam it or jump it. None of this playing around .010" in or out of the lands as your range of adjustment. I started to see results in my 6BR when I got more like .030-.050" off the lands. And I'm seeing the same thing in my 6.5x47. I went to a 100 yd bench match last weekend with my 6.5x47 just to test seating depths. 5 shots each at 5 different depths. The results backed up what I saw on my home shooting range, with a big jump it shot well, and as things got closer to or in the lands the groups opened up significantly. I have a theory that what is being played with here is not so much bullet vs. alignment with the lands, rather the "compression ratio" of the cartridge and what the powder likes. One could then say that the powder charge therefore needs adjusting... round and round we go and where does it stop, then?

 

[UltraBR30]

I find seating depths on, in, or near the lands to be greatly effected by as little as .003".
When backed off the lands by say .050" I don't see much effects with changes of less then .020".
More times then not, benchrest shooters are in or near the lands (both short & long range) which says a lot by itself.

 

[BoydAllen]

A very knowledgeable short range benchrest shooter once told me that, in a similar fashion to powder charge sweet spots or nodes, seating depth settings run in a cycle of good and bad, along the range of possibilities. This can cause shooters who do not make a careful study, to reach a premature conclusion that their rifle, or a particular bullet won't shoot into or out of the lands, simply because they did not do enough testing, and/or that testing was done with increments of change that were so large that the good spots were unknowingly skipped over. Another issue in all of this is the number of shots per test group. When I am looking for a sweet spot, I shoot two shot groups, until I find something worth investigating. (Loading at the range makes all of this so much easier.) If it is ugly with two, more isn't going to make it smaller. The classic short range benchrest test would start at jam, which, used properly, is the longest seating depth that a bullet can be seated to, that will not result in the bullet not being pushed into the case as the round is chambered, at the neck tension that will actually be used for shooting. This is only one way to approach the problem, but it has the advantage of starting at a point that is quick to find, and only requiring one to work in one direction when trying different settings. I find it interesting that some long range shooters have found their best accuracy with VLD bullets with relatively long jumps. In the past, my theory on accurate bullet loads that had a lot of jump was that the bullet was somehow centered by the gas flow around it, and sort of "weather vaned" into pointing down the center of the bore, and that too short of a jump did not leave enough time and space for this to happen. Of course, this was pure speculation, nothing more, and subsequent testing has shown something that was more in agreement with the thought that it is more about the timing of when the bullet reaches the muzzle, as was mentioned in an earlier post, although it is possible that both mechanisms are at work. As a practical matter, it would seem that we are reduced to trial and error.

 

[queen_stick]

Boyd,

I agree 100% with your posts here. Bill Goad and Harley Baker (Both are well respected short range BR shooters) practice shooting at my local range. (I consider myself lucky in that regard). In fact, the main reason I'm shooting BR is because Harley Baker let me shoot is BR rig one day... That had me hooked! Anyway, both of those guys stress bullet seating depth more than any other aspect in load development. Every barrel that Bill goad owns has the bullet seating depth written in black sharpie right on the shank.

That reminds me... I need to call Bill Goad. He offered to go out for a range session to show me everything I'm doing wrong, and what I need to do to fix it. He said we'll start with bullet seating....

Walt

 

[BoydAllen]

Thanks for the pics. Do you plan on fiddling a little with powder charge at that seating depth? Tell us a little about the rifle.
Boyd