An interesting experiment (bullet consistency)

A

AmbulanceDriver

Inactive
So, admittedly, my methods were slightly crude in this experiment, but I wanted to share what I discovered today.

First, the backstory - I have two rifles chambered in .30-06. One is an M1 Garand I obtained from the CMP, the other is a Marlin XL-7.

After doing some load development for the Garand, I found a combination that it *really* liked. Sierra MatchKing 168gr HPBT, HXP brass, Winchester standard primers (what I could find at the time - prefer CCI, but whatever) and 45.5 grains of H4895. Sub 1.5MOA group at 100 yards off the bench, better than I have a right to ask of a 60+ year old rifle with iron sights :D

So I thought I would try the same cartridge in the Marlin..... Funny, the rounds won't chamber properly. Have to really reef on the bolt to get it to close... Well there's no way I'm pulling the trigger on that round, extracted just fine, no obvious scratches or anything that would make me think there's a burr in the chamber. Feeds factory ammo just fine, and getting 1 MOA groups at 100 yards with factory ammo - sweet. Long story short, the chamber on the Marlin is a little shorter than the Garand. No biggie, just means working up a different load entirely, but figured that would be the case anyways.

So I decided to make a poor man's OAL gauge by following the instructions here: http://www.larrywillis.com/OAL.html

The methodology:

After making the gauge from a sized .30-06 case, I randomly selected 3 bullets from each box of bullets, and measured each bullet 3 times. To attempt to maintain consistency, I squeezed the case mouth until the cut slits were touching (closed) between each measurement. I inserted the case/bullet into the chamber, then slowly closed the bolt by pushing it forward until I could just use the locking lugs to finish pushing the bolt forward as I levered the bolt down. Left the bolt closed for 1 second, then slowly opened the bolt and extracted the cartridge. I then measured it with a Lyman 6" dial caliper. The two data points I failed to obtain that I should have - bullet diameter, and bullet weight.

The results:

Sierra MatchKing 168gr HPBT (#2200)
Bullet 1) 3.247" 3.247" 3.246"
Bullet 2) 3.249" 3.249" 3.249"
Bullet 3) 3.260" 3.261" 3.261"

Hornady Match 168gr BTHP (#30501)
Bullet 1) 3.243" 3.244" 3.243"
Bullet 2) 3.240" 3.242" 3.241"
Bullet 3) 3.236" 3.236" 3.236"

Hornady 150gr FMJ/BT (#3037)
Bullet 1) 3.232" 3.233" 3.234"
Bullet 2) 3.236" 3.237" 3.235"
Bullet 3) 3.239" 3.237" 3.234"


The question:

I've heard for accuracy, you should seat the bullet (x) thousandths of an inch back from the rifling. With measurements like the above, how would you go about determining how far back you should set your bullet? Because as an example, even with the SMK's, the shortest measurement was 3.246", and the longest 3.261" - that's a difference of 15 thousandths of an inch. If I'm supposed to seat them 10 thousands off the rifling, as an example - well, how would I do that? If I go with 3.246", so I seat them at 3.236" - well the one that measured at 3.261" is gonna be jammed into the rifling. And if the distance from the rifling is so critical - well then if we go the other way, that means that instead of a 10 thousandths jump to the rifling, we're now at 25 thousandths - and from a non-benchrest rifle - is that difference *that* critical?



Oh, and just for reference, the Garand loads were set at 3.330 - 10 thousandths short of SAAMI Max OAL
 
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I've heard for accuracy, you should seat the bullet (x) thousandths of an inch back from the rifling. With measurements like the above, how would you go about determining how far back you should set your bullet? Because as an example, even with the SMK's, the shortest measurement was 3.246", and the longest 3.261" - that's a difference of 15 thousandths of an inch. If I'm supposed to seat them 10 thousands off the rifling, as an example - well, how would I do that? If I go with 3.246", so I seat them at 3.236" - well the one that measured at 3.261" is gonna be jammed into the rifling. And if the distance from the rifling is so critical - well then if we go the other way, that means that instead of a 10 thousandths jump to the rifling, we're now at 25 thousandths - and from a non-benchrest rifle - is that difference *that* critical?
Click to expand...

Bullet jump isn't an exact science. If bullet jump were necessary then Federal Gold Medal Match ammunition must have some mystical voodoo to shoot well through all those different chambers with all those different jumps to the lands.

The reason why the benchrest crowd is concerned with the jump to lands is because it helps with a consistent pressure curve. As the throat wears, they'll add a touch more length to keep the pressure curve consistent across the life of the barrel, generally this lengthening needs to happen in as few as 100 rounds from some of the BR rounds.

Your 30-06 is not a BR round. Don't worry about the jump to the lands at the beginning of load workup, just find a distance that allows you to close the bolt easily and do the load workup there. If you don't find acceptable accuracy at that seating depth, then start changing the seating depth ever so slightly to see what happens.

Good luck on your load workup!

Jimro
 
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How do you know the oval was causing the bolt to close hard in the Marlin ? It very possibly could have been the case size too. Are you full length sizing?

If it was oval and not case size, what was the oval of the cartridge you used in the garand? You likely won't know if the oval is too long ,how do you know the bolt was not forcing the cartridge into the rifling on the garand?

This is very important as with a semi auto you won't feel the bolt close like you do a bolt and if it does touch the rifling you could get a slamfire.

Bullets by different manufacturers , regardless of weight, will have slightly different tapers on them. It's not so much the oval by measuring to the tip that matters. It measuring to the point that touches the rifling that matters and that isn't the tip of the bullet. That's what your experiment proved.
 
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In reading through your readings it does appear that your measuring from the base of the case to the tips of the bulets. If this is the case your never going to nail down anything exact as this distance varies from bullet to bullet even from the same box.

To get a closer measurment you will need a comparator which enables you to set the overall length based upon the ogive at the diameter of the lands and not the tips of the bulets. That is the critical length your looking for. Even with that if you REALLY want to narrow it down then you will need to also measure the bullets before you load them to make sure you have a batch which are all within a couple of thousands of the same deminsion.

To be honest this is a good measurement to have, but more or less a needless excersise with the rifles your looking to work up loads with. Once you do know the max OAL for the particular bullet and rifles your working with this can be good as you can then seat the bulets roughly to .010" - .025" off the lands and work your loads up.

Personally I load everything to a functioning magazine length then start working my loads up. Some bullets will feed seated right at the magazine length some won't so I try them with dummy rounds first. Once they feed properly with no hang ups I go from there. When I get to the velocity range I'm looking for, with the powder I am working with, I will then start to seat the bullets in deeper by .005" at a time. I do 5 rounds at a time and look for the best groups. Sometimes I have found that it doesn't come into it's own until I have gone .050" or even more in some cases, but when it does, there is no doubt about it.

My close friend and hunting bud worked on a load for his 300 RUM for a couple of months and was just about to sell the rifle. He was setting things up close tot he lands and not getting anything good. Then he set the OAL to the book listing, and it all came together. This listing had his bullet sitting back at .110" off the lands. It shoots wonderfully now and he hasn't changed anything with it in a couple of years now.

So don't get hung up sitting up close, sometimes things just don't want to work that way.
 
You need to measure the length of the cartage from the ogive
( there are a lot of companies that make this tool )
( usually it fastens onto your calipers with a set screw )

You can measure the length of the cartage from ogive to base
of the cartage
( this is the measurement you need to to maintain a consistent
jump to the lands )( not the OAL )( the only time I worry about
OAL or COAL is to make sure the cartage fits into the magazine )

All of that goes out the window if you have not sized your cases
with the use of a tool measuring from the datum line on the case
shoulder to the base of the case giving you a consistent case
length
( I size my cases 2 to 3 thou. shorter than the chamber of the rifle )

I have found that both Sierra and Hornady bullets work best with
a jump between 10 to 15 thou. off the lands
 
What you should have also measured was the length of each bullet. They can vary that much.

Did you get a round that would chamber in the Marlin?
 
So when I repeated this experiment (just using the SMK's, since that's what I worked my load up with) on the Garand, the COAL jumped up to 3.370, so my starting point of 3.330 for those loads worked well on the Garand - and my accuracy out of a Field Grade CMP rifle bore that out - slightly better than a 1.5" group at 100 yards.

Now, based on the length of my loaded rounds for the Garand, and the measurements that I took for the Marlin, to me, that gives me at least an idea of why those rounds wouldn't chamber in the Marlin when factory ammo would. The cartridge was about a tenth of an inch too long for the chamber in the Marlin.

And yes, an empty (full length sized) case chambers easily in the Marlin.

My plan is to buy a comparator to get a more consistent measurement next. But I just found it very interesting that the total bullet length would vary that much even in "match" grade bullets
 
I've heard for accuracy, you should seat the bullet (x) thousandths of an inch back from the rifling. With measurements like the above, how would you go about determining how far back you should set your bullet? Because as an example, even with the SMK's, the shortest measurement was 3.246", and the longest 3.261" - that's a difference of 15 thousandths of an inch. If I'm supposed to seat them 10 thousands off the rifling, as an example - well, how would I do that? If I go with 3.246", so I seat them at 3.236" - well the one that measured at 3.261" is gonna be jammed into the rifling. And if the distance from the rifling is so critical - well then if we go the other way, that means that instead of a 10 thousandths jump to the rifling, we're now at 25 thousandths - and from a non-benchrest rifle - is that difference *that* critical?
Click to expand...

I have heard for accuracy?
Click to expand...
is that difference *that* critical?
Click to expand...

I can not help you if you are shredding the case neck, I call that squidling the case. I make transfers, I transfer the dimensions from the chamber to the seating die. I could surround myself with expensive tools and drop names but I do not find it necessary.

And then there is that part about bullet jump, I want bullet jump, I want my bullets to have that running start. To accomplish that I have to know the distance from the rifling to the bolt face.

F. Guffey
 
For me, and my Garand and Ruger bolt gun, bullet seating depth/OAL is way down on the list for "accuracy methods/techniques". I Played around with it a bit for my Garand with new Criterion barrel, but found very little, if any, difference than just using the bullet manufacturer's recommended seating depth/OAL...
 
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"...shortest measurement was 3.246", and the longest 3.261"..." Both of which are way below Max OAL. for .30-06. 3.340" is max. Never had any issues with M1 Rifle ammo loaded to 3.340" OAL regardless of the bullet weight(or shape) I've used.
The whole off-the-lands thing is a load tweaking technique you really don't need to bother with a) if you don't want to or b) until you've worked up the load.
As mentioned, it's also a trail and error thing. Every chamber is slightly different and the so-called 'sweet spot' is different for every one of 'em.
Mind you, if you're getting a 1.5" group at 100 out of a FG M1, quit fixing it. That's outstanding. An XL is a hunting rifle anyway. Doesn't need 1.5" groups.
Your issue is far more likely a sizing related thing than OAL. To use the same brass in two rifles(been doing it for eons myself with an M1 and an '03A4.) you must FL resize. A semi requires that anyway, but if your loaded ammo won't chamber in both rifles look at the sizing first.
 
I think once I have the comparator, I'll have to repeat this experiment with the Marlin to see a true apples to apples comparison. Methinks that will yield a much more workable result.
 
AD,

There are a couple of faults in your approach. First, bullets in one box generally are the combined output of several tooling sets. Exact length of the tip from the bullet base and exact location of the point where a comparator encounters the ogive with respect to the bullet base vary as a result of the different forming tools, each of which is hand made and surface finished and polished, introducing that variation.

Below is the result of measuring 15 randomly selected .30 caliber 150 grain Match Kings. Note about 0.015" of bullet base-to-tip variation and about 0.008" of base to ogive contact point variation is measured.

150%20gr%20SMK%202015-04-16b_zpssosy8kqw.gif


This is one reason I'm convinced that folks trying to tune seating depth to the closest 0.005" are likely wasting their time.

The second thing thing you are doing that will throw actual distance off is using your gauge by closing the bolt on it. When the bullet meets the throat, it starts pushing back on the case via the split neck friction. This holds the case head against the bolt face. That's not normally what happens during firing. What normally happens is the case tends to be pushed forward by the firing pin impact, followed by primer ignition pushing the primer back like a little piston. That all gets reversed when pressure expands the case and pushes the head back, but until that point, the case shoulder is against the chamber shoulder or close to it. Therefore, it is the distance from the shoulder contact point to the bullet ogive that actually determines how close the bullet ogive is to the throat; not the distance to the case head.

Fortunately, if you size all your cases for one rifle to the same length from head to shoulder, since your seating die most likely pushes down on the bullet ogive, that difference will come out pretty consistent. I typically get plus or minus a couple of thousandths when measuring from case shoulder to the bullet ogive throat contact point, though I had to make a special gauge to do that.

To measure a seating depth with your improvised gauge, rather than closing the bolt on it, remove the bolt and press the gauge into the chamber until it stops. Usually your pinky finger can do this. Then, to remove the case, gently push the bullet out from the muzzle end with a cleaning rod. That will overcome any degree to which the bullet is stuck in the throat without changing its position in the case, as extracting it normally can do.

As to your jammed up cases, it is likely just due to your Garand chamber being longer than the XL-7 chamber. Brass has some spring to it. My first Garand had a chamber +0.007 over minimum, and the brass just didn't resize back to minimum in the standard sizing die I had at the time. You may find you need to segregate your brass by the rifle it's used in. Otherwise you have to over-resize it for one of them, and that wears it out faster by encouraging earlier incipient head separation in the longer chamber.
 
Unclenick, thanks for the in depth response there. My plan is already to have brass that is FL sized for the Garand, and brass that is neck sized for the Marlin. The cartridge OAL for the rounds I loaded for the Garand were definitely too long for the Marlin. An empty, sized case dropped into the chamber and the bolt closed on it with absolutely minimal effort. So I know the case/chamber are properly sized. That was part of what was throwing me off when I was trying to figure out what was wrong with my reloads for the Garand that they wouldn't fit the Marlin. It wasn't until I took these measurements that I was able to put all the pieces together.

A Hornady comparator is next on my purchase list for the reloading bench. I know that will give me a much better apples to apples comparison of my OAL for the Marlin.

A follow up question would be what is peoples experience with the Lee Collet Neck sizing die? I have seen a couple of videos of people neck sizing cases with this die and showing absolutely minimal runout, nearly perfectly concentric cases. Based on those videos, it seems like this die is a really good choice, but are there any reasons to avoid it? Something better that isn't going to cost 3 times as much?
 
In my table you see I used a comparator with inserts both from Hornady and Sinclair. The latter come closer to touching the ogive where the throat of your rifling will, so if you are going this route, I suggest you get one of those stainless steel inserts in 30 cal (#749-000-931WS). They fit in the Hornady comparator adapter or you can buy Sinclair's adapter. The difference is the Sinclair comparator adapter is centered in the caliper jaw while the Hornady has an offset to make it work together with their OAL comparator.

Also, you can buy Hornady's case comparator inserts or the Sinclair case bump inserts. This will give you a means of finding case head to shoulder measurement that you can subtract from the case head to bullet ogive measurement to find how far off the lands you will be, if that interests you.

I use the Lee Collet Die. I usually lap them to smooth their operation, but they do as the videos showed. I then use a Redding Body die to size the rest of the case if I need the case shoulder set back any. I normally set it back at least 0.001" each firing cycle as neck sizing gradually grows the case.

Suggest you read this article on bullet jump, if you haven't already.
 
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