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Forum Index > Rifles general discussion > Bullet Comparators and Results

Bullet Comparators and Results

14 Jan 2017
@ 09:45 pm (GMT)

Paul Leverman

Never having had any kind of comparator, I usually just used my calipers and went with bottom to tip measurements. Now I have a comparator, so I randomly selected some previously made up loads and ran them through. In each of the separate lots, there was always a length difference. Roughly speaking, the difference between longest and shortest was 0.003". (One of the bunch was .005" so I'll fix it later.)

In the Reloading book, the guru says "We want to see something measurable as far as barrel harmonics go, so there is not much point in adjusting the jump by a very small fraction." He goes on to describe different jump lengths. So is the 0 -.003" that I'm seeing in my lengths critical? Where would the difference show up? Would it be in long range group size, as a result of different pressure resulting in different velocity? Or is it a small enough difference that it would not be a concern?

These loads were all with the A-MAX/ELDM bullets, and I'm thinking that's why they were so even across the board. Better bullet, better tip. But that's my usual guess.

Replies

15 Jan 2017
@ 08:13 pm (GMT)

jason

Re: Bullet Comparators and Results

My guess is the difference is in the bullets. I haven't used the eld, but have amax etc, and it's fairly typical.
It could possibly be in the seating operation.
Does it matter.... If your load is 3 thou from the lands it could, giving you jump and jam in the same load.
But only the target really knows.I try to eliminate the difference between rounds.
a fresh developed load probably won't as it was developed that way. But I would say yes, jump changes things and if loads vary it will fall out of spec before loads that don't vary.
As an example iv had a magnum load that was fine, start to open up, I used my comparator and the same projectile to find the lands again after so many rounds fired. The best I could make out was it had worn 3 thou. I seated back out to where it was supposed to be and added .1 grain of powder and the groups came back.
15 Jan 2017
@ 08:49 pm (GMT)

Paul Leverman

Re: Bullet Comparators and Results
Thanks, Jason. I was more concerned about the differences between rounds in a given load. The loads I have built are .010" off the lands, so from long to short they will be somewhere between .008" and .012", roughly. I see what you are saying about the short jump, it's just too close and would probably count as a jam. I'll try some different numbers and see what happens.
15 Jan 2017
@ 10:24 pm (GMT)

mark whiteley

Re: Bullet Comparators and Results
Hi Paul
my answer to what you ask would be that if you have found the true sweet spot for your barrel IMO a 3 thou difference would not give to much of a change
but
saying that I have found that using a comparator to length sort and batch projectiles before you seat them helps with not having a difference at the ogive for coal and in my mind helps to keep groups smaller,
of coarse there are other things that come into play as well eg.. neck tension, a square case mouth and concentricity
trying to duplicate one round many times can be a chore
most people cant be bothered
best regards Mark

15 Jan 2017
@ 10:36 pm (GMT)

Bob Mavin

Re: Bullet Comparators and Results
I never measure OA length of a loaded round to the tip of the point, the very tip could have been bumped. My gunsmith gives me a 1" piece of barrel with the lead in to measure with, if I want to. Once your sweet spot ,,,distance off the lands is found, your bullet seater will set the projectile the same distance off the lands, it doesn't touch the tip.

I might measure OA to tip to make sure it fits the magazine :)
Bob
15 Jan 2017
@ 10:46 pm (GMT)

jason

Re: Bullet Comparators and Results
Well it all really depends on the pet load you have chosen.
Let's say I work up a load and at ten thou jump I get .25 inch groups, if at 15 thou jump my groups are .5 inch groups. Using the same powder charge.
You therefore know that as the barrel wears or if your jump is more you know your heading towards that .5 inch group. It's why when developing you don't want to be right on the edge, or bottom edge of a node.
But if we are being practical, strive for the same jump every time. And if it's not quite there you just live with what you have. A few thou probably won't make too much difference unless your on the bottom edge of that node. But it also won't help things like es.
Often it's thought that if you can get away with slight variations in powder weight or oal that is a good load as it's not fussy.
When developing a load if I seat something a little too deep I will mark that round as such, but I will fire it to see how it reacts with the rest of the group. Definitely at 100 for me it usually doesn't matter much. Maybe out further but by the end of developing my dies are haven't usually changed and are spot on.
If it suits you and your in n.z try the targex bullets, similar to a berger, compared to hornady they weigh and measure as close as exact every time for me. They have deffinatly helped my seating measurements.
Also a real heavy neck tention won't help.

These are just things I have noticed and may help you.
15 Jan 2017
@ 11:37 pm (GMT)

Paul Leverman

Re: Bullet Comparators and Results
My thanks to all of you. That is a lot of really good information to work with. It all helps when we are striving for that last little bit. Each step towards consistency must add in it's own benefit, and I think the sum of the parts is the real goal. Who wouldn't want to shoot .2 and .3? Thanks again guys, you've been a big help.
16 Jan 2017
@ 03:59 am (GMT)

Martin Taylor

Re: Bullet Comparators and Results
I jump all my loads .030" minimum but often larger though here's my 2 bobs worth.

If .003" is affecting your groups you have a damn finicky rifle (see a smith and check lead angles & throat) or you have developed your pet load on the knife edge of a bloody small node as already said.
Remember your seater contacts toward the tip often in a very small (most) contact patch (often leaving a ring mark on the pill) and projectile forming variations will always cause small changes in final seating depth.

We operate many sub .5moa rifles shooting multiple projectiles types & weights so the seaters are adjusted constantly. The seater die is set off a dummy round, first couple checked with comparator and batch loaded, done..... (some even loaded with an average coal, oh the shame).

I loaded rounds for Nathan whilst l was over and all where tested inside .2 moa then shot out past 1km and we didn't check them with a comparator.

But as stated at the start we jump all the rifles we load for, from 223 all the way through to the magnums as l don't want to be anywhere near the lands in these hunting rigs.
16 Jan 2017
@ 09:09 am (GMT)

Paul Leverman

Re: Bullet Comparators and Results
This is my first comparator, Martin. Previously, like yourself, depths were set off of a dummy and adjusted inwards. All those loads seemed to work just fine. Now that I can see what is happening with the comparator, maybe I'll just put it back in the drawer. After all, it's not the number that counts, it's the shot.
16 Jan 2017
@ 11:18 am (GMT)

mark whiteley

Re: Bullet Comparators and Results
Paul
I really don't think Martin was suggesting that a comparator is unnecessary,
he did say he use's one himself
anyway if your happy I am
best regards mark

16 Jan 2017
@ 03:30 pm (GMT)

Paul Leverman

Re: Bullet Comparators and Results
Hi Mark - sometimes thoughts don't translate to posts. It wasn't that I would never use the comparator, I was thinking that maybe it wasn't as necessary as I was led to believe (listening to range talk again). It definitely has a purpose, such as Jason mentioned, as an indicator of throat wear. I can also see it as a useful reference tool used in combination with the seater die.

I had been using a split case and whatever bullet I was loading for decades, and never had any issues. But these were mainly short range hunting rounds, and differ vastly from what I am trying to learn here. This extreme accuracy game is totally new to me. While both disciplines share the same basic procedures, the methods and tools used are somewhat different.

I think what triggered the original question was the idea that if one or two thou of runout could affect accuracy, would the same measurement in seating depth have an effect as well.

And to tell the truth, it is a pain in the ass to use. Maybe because it's a new tool, or a gimmick, or whatever, but it is awkward to use and it took me about two seconds to find the first design flaw.

And it was only $10, so not a huge deal.

16 Jan 2017
@ 04:09 pm (GMT)

Nathan Foster

Re: Bullet Comparators and Results
These are the sort of romantic discussions Steph and I have of an evening. And the conversations pretty much play out and go around in the same circle as here. A comparator can only measure case head to leade. A dummy round measures bolt face to lead. A dummy round plus partial use of the comparator measures bolt face to lead with an accurate ref point on the ogive.

Certainly some good common sense posts here and I think everyone is on the same page.
16 Jan 2017
@ 06:46 pm (GMT)

Bob Mavin

Re: Bullet Comparators and Results
A little trick my gunsmith mate taught me long ago.

Seat a projectile into the mouth of the case, chamber it and force the bolt shut. Put that round in your press, lower the handle then adjust your seater down to press on the projectile. Now, take your seater out of the press and measure the overall length of the seater accurately. Write that measurement down as touching the lands for that projectile, then shorten the die (screw the top in) reduce the OA length by the amount you want off the lands.

Bob
16 Jan 2017
@ 07:10 pm (GMT)

Bryan Webster

Re: Bullet Comparators and Results
I have all the neat tools, comparators and loads more, but normally what Bob Mavin has stated is how I do it. Works well, is simple too.
16 Jan 2017
@ 08:42 pm (GMT)

Martin Taylor

Re: Bullet Comparators and Results
For the new players!
Just be mindful with the above method when setting up long, high BC VLD style pills as they can wedge into the lands a long way giving false readings. This can be felt with the comparator when measuring by hand though its also dependant on lead angles etc.

Paul, I use my home made comparator extensively with fire formed shells when setting up for a new pill. The dummy round is made up and sat in the box with the pills and used as a guide to re-set my seating die for that load.

With your load development, treat the seating depth like a powder charge and check either side of your "good load". If unstable one way move it slightly to the stable length which gives a margin for era. With a possible powder tweak if it's a real tight node (ie, going for the highest velocity node rather than a wide, slower more stable one).

I always load on a stable node so the PIO isn't drastically changed by temp variations, like loading a round into a hot chamber and waiting for an animal to settle. Winter to summer temps that sort of thing.

17 Jan 2017
@ 05:23 am (GMT)

mark whiteley

Re: Bullet Comparators and Results
no worries Paul,
a comparator does have it's place for checking meaningful measurement's for coal when setting up your die, using a dummy or not
if the 3 thou bothers you or you are anal about wanting consistency in your reloaded ammo (like me) sorting projectiles with the comparator does fix the inconsistency as long as your neck tension is comparable
and it takes minutes to do
if like Martin you get ring marks on your projectiles after seating I would be looking at heavy or inconsistent neck tension and polishing the seater stem,
but as I said most people cant be bothered and good for them,
I've got my own cats to skin

best regards Mark
17 Jan 2017
@ 12:01 pm (GMT)

Paul Leverman

Re: Bullet Comparators and Results
Thanks again, guys. I have copied and filed this thread to have it as a quick reference for later. This is good stuff.

Because it's winter and I'm bored silly, I took an unopened box of 208gr ELD-Ms and put each bullet through the comparator. Interesting results. Of course, we will never know why this is, but there were two distinct bullet groups. In each of these groups, the differences between bullets was less than one thou. The difference between the two groups was four thou. Twenty-five per cent of the bullets were .004" shorter from the ogive to the base.

I separated these two lots into their own boxes, so now when I do my loads I will be able to see if this will affect velocities, etc.
18 Jan 2017
@ 05:05 am (GMT)

Ronald Le May

Re: Bullet Comparators and Results
Martins on the train as a variation of .003 thou is not going to affect your rifle to a great degree unless your doing jams.
I have tried jams up to 10thou and whilst it may work for the likes of Shehane it did not for me besides I believe in trying to keep pressures down.
Unless you are going to measure and adjust every time you seat a projectile you have to say there will be variations in the loads small they maybe but definately there.
If your using a normal linkage press not an arbour type like a Wilson then you have wear & tear to contend with as well.

The secret to re loading is consistency but there will always be a +- somewhere along the line.
Bullet variation, primer variation, powder batch variations case to case small they maybe but they will still be there.
I have 4 rifles that do sub .5's one does .3's all day every day built by APRS its just me that mucks the equation?
I have gone down the road of weighing each bullet, case, each bullet ogive, depth of primer hole reamed, inside flash hole de-burred till I discovered I had a house to live in and not a shed.
Now I just use loads that I know work from experience I have recently put my 3rd barrel into my 6.5 x 284 and it shoots very well using previous load data. My last barrel had 2 recrowns a re chamber as well losing 2" of barrel at the chamber end from fire cracking barrel count was 1434 shot out.
All I did was to make a dummy up for the new chamber and that's it as you cannot go on from worked for the other barrel.
With a +- .003 as I am using VLD Bergers 140's I will be either .013 or .00 7 from the lands.

What I have learned hit the books I have oodles of them Lee, Hornady, Speer, all of Nathans books, Nick Harvey, ADI to name but a few.
Digest what is said set it all up in a safe zone as only the very intrepid would go out and use max loads right off the bat.
Then as you play only change one thing at a time to see what affect it has on the groups or pressure.
I had one chap trying new loads at the club the other day at 600M there is no way you can expect to get validation at that range he should have done it at 300M.
Anyway all the best to you all by the way Nathan my wife still beats me hands down with that dam F class Moogun of hers!
Ron Le May & Co.
 

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