Stoney Point OAL gauge

[brselman]

I would be interested in knowing if anyone has used the Stoney Point OAL gauges for determining bullet seating depth, and, if so, if you think this is a reasonable investment? brselman

[Unclenick]

I have and use them. A couple of limitations need to be understood:

It takes practice to get a consistent result. Averaging ten readings is a common strategy for the gauge itself.

If you also buy the Stoney Point or any other caliper-based comparator, you need to understand they measure from the bullet ogive to the back of the case head. Given how inconsistent bullet noses can be, this is a superior method of determining over-all seating length, once you have determined what that length should be. It is not, however, an exact representation of seating depth of the bullet off the rifling if you are full-length resizing. To know that, you have to measure from the ogive to whatever determines headspace for the cartridge you are reloading. This is because full-length resized cases don't always wind up with the same relative headspace determinant location. I doubt that belted cases see much movement, but a full-length die will not push the shoulder back the same amount on cases of different makes or with different reloading histories. It is common to see some resizing variation even in cases that are matched in these regards. For cases that headspace off the shoulder, this adds a variable the standard comparator doesn't concern itself with.

Redding makes a gauge to replace the comparator that does measure from bullet ogive to headspace determinant. They call it the Instant Indicator. At $135 a pop, it isn't cheap. I have also come up with a poor man's workaround using the less expensive RCBS Precision Mic in conjunction with the Stoney Point Gauge and comparator. Keep in mind that if you neck-size only, the shoulder setback problem described below goes away and the regular comparator method works fine.

To illustrate the problem I have three drawings below:

The first shows how a body-resized bottle-neck case (one resized any further than just the case neck) normally fires in a gun and how the headspace slack comes out when it is headspacing on the shoulder.

The second shows what a standard comparator measures with an exaggerated shoulder setback difference in the two cases to make the difference obvious. In real cases this is likely to be within 0.005" or so.

The third illustration shows, like the first, what happens when the firing pin first strikes, so you can see why ignoring the shoulder setback difference affects how far the bullet is off the lands?







The poor man's workaround for bottleneck cases that are resized below the neck and that headspace off the shoulder is to use the case measuring feature of the RCBS Precision Mic to first measure the Stoney Point gauge's threaded case that you used with your bullet, then all the cases you intend to reload (after they are sized). For each case, if your case measures bigger than the Stoney Point case, add the difference to the comparator reading you got with the bullet in the Stoney Point gauge. If your cases measure smaller, subtract the difference from the comparator reading you got with the bullet in the Stoney Point gauge. This new reading is what you will need to see for the bullet to actually have the same distance from the lands on firing as it did in the Stoney Point gauge.

Nick

[brselman]

Unclenick:

That was extremely helpful to the naive loader such as myself. I fireform my cartridges, neck size only, and then trimm (to the same size as nearly as I can with my crude equipment) before charging, etc. It seems from reading the Stoney Point literature [propaganda as the case (no pun intended) may be] that I may be able to improve my accuracy (which most probably suffers more from my inadequacy than anything else) by seating all of my bullets to the same and "proper" depth. I wonder if it will really help.

[amamnn]

You might want to look into the RCBS precision mic kit. It can be used to set bullet runout and the shoulder length as well. As opposed to caliper type devices, there is no guesswork or interpetation involved. They are made for specific calibers, so keep in mind that one kit will only do one caliber.
Through the use of this kit, you can set your full length sizer to size the shoulder very lightly or not at all, as you choose. This method is superior to neck sizing only, as it helps retain the inside concentricity of the neck, which when added to improved bullet runout will add to accuracy.
Once you know your necks are concentric inside, then any variations outside can be checked and corrected by neck turning.

[Ausserordeutlich]

The Stoney Point tool works fine. Just buy the tool and the dummy case that comes with it. After you're a few thousand rounds into the game, you might want to make this a lot more complicated than it needs to be for you now.

[Leftoverdj]

It's the latest fad. They come and go, and I have better uses for the money.

[Harry Bonar]

Dear Nick:
Best explanation and illustration I've ever seen!
Harry B.

[Bullet94]

brselman Quote – “I would be interested in knowing if anyone has used the Stoney Point OAL gauges for determining bullet seating depth, and, if so, if you think this is a reasonable investment?”

I use my rifle and a comparator to set OAL, but I only neck size.

Here are a couple links you might find interesting -

http://www.benchrest.com/forums/showthread.php?t=28867

http://www.benchrest.com/forums/show...=seating+depth

[kingudaroad]

I have the guage and the comperator that attaches to my calipers. What it does for me is determines the max length I can make the cartridge from the case head to where the ogive touches the lands.

Now I can make a few cartridges that are just short of the lands and then make a few more a little shorter and then a few more a little shorter in small increments.

Now that I have several different lengths I can see which one shoots the most accurately the same way you experiment with powder charges.

I usually do this length experimentation after I have decided on a powder charge.

The way I understand this is I'm trying to time the bullets exit from the muzzle with the most optimum timing of the barrel harmonics, resulting in the most consistent groups.

Although I believe it does make a more accurate round, it's probably not neccessary to be that accurate for hunting applications.

I just enjoy the process of the quest for the elusive one hole group.

Edited after rereading Nicks post...
I can see the problem if using inconsistent cases,but wouldn't this not be a problem if all the cases were uniform? (ie. all new unfired and flr, or all fired once and neck resized only etc.)

[Unclenick]

Harry,

Thanks. Glad you liked it. I've tried verbal descriptions, but they seem to fall flat. It's hard enough to see it even with the pictures.


Kingudaroad,

The consistent case problem is real. It usually adds no more than a couple or three thousandths in a batch loads with same-history cases. But if you start mixing your brass or it doesn't all have the same load history, differences in material distribution or in work hardening will result in differences in spring-back of the cases coming out of the sizing die. I would speculate that if you don't have a rigid press or you don't have every case lubricated identically, those factors will add variation as well, but I haven't done any experiments to validate that. If your sizing die isn't in exactly the same position in the press threads from one reloading session to the next, it will obviously shift the effective seating depth off the throat. Obviously a die that gets loose during resizing could cause a serious variation.

I think the RCBS Precision Mic is a worthwhile investment to check on case shoulder position or to sort brass after sizing so that you only take identical stuff to a match. I don't use its bullet seating depth feature because I find it tricky to their cartridge-shaped gauge without incurring position shift, plus the contour of their "bullet" doesn't exactly match the contours of my actual bullets, so the Stoney Point get the nod for that part of the job. I've considered grinding open the hole in the base of the Precision Mic to let it slide over the Stoney Point tool, but the latter is too large for that to work with caseheads much smaller than the .308's.

However, if you are benchrest shooting all with one lot of brass with identical histories to all cases, the problem goes away if you neck size only. Then the headspace is locked-in to your rifle and the standard gauge is fine.


Brselman,

How much accuracy effect you see depends on the individual gun. Seating depth seems to be yet another item that some guns are affected by significantly and that others seem indifferent to. Most prefer a bullet closer to the lands, but not all. The only way you will find out is to try it. Try giving this link a read for an interesting tale about an old Mauser with a worn-out throat shooting one-holers.

Nick

[Bullet94]

Unclenick

I use the RCBS Precision Mic to check headspace for my semi-autos (223) and when setting up my sizing die. Works real good, but just like you I find their bullet seating depth feature to be lacking (bullet not same shape as mine).

[raktrak]

I always use it to get a starting point to set up my Dies. I have found that case prep is the most important thing I do . I have a ritual that I go through.First I run the cases through a case trim die by RCBS. That tells me how many need trimmiming and it sets the shoulders and case neck in line. Then I run all cases needing to be trimmed through my Lyman case trimmer. I then proceed with preparation of the cases through the RCBS case prep machine to champher the necks inside and out and clean the primmer pockets. From there its to an Expander die by wilson that trues all the neck to a perfect size and makes them round. I follow up with redding case neck sizing dies. All thats left is to prime, put in powder and seat a bullet that barely kisses the lands. My best performance in powder charges are 2-3 grains below absolute MAX usually. I also choose the powder that has the lowest PSI at the exiting of the muzzel, so turbulance behind the bullet is as low as possible. My NECO SOFTWARE gives that info to me. I prefer to not weigh any closer than a Tenth grain on hunting loads but I do on benchrest loads. I also use the bullet with the longest bearing surface , like the Sierra Pro hunter. Works great for me and it all starts with a STONEY POINT.

[Yuriens]

I would speculate that if you don't have a rigid press or you don't have every case lubricated identically, those factors will add variation as well, but I haven't done any experiments to validate that.

Nick,

The non-rigid press is a real issue. Having used a Turret press for bottle neck rifle case sizing it can be a real pain getting it to size consistently. For my accuracy critical rifle reloading I use the full D ring Rockchucker for consistency in full length sizing. I also use the Stoney Point headspace gauge to set my FL size to bump the shoulder back only .002" from my fired cases out of the specific rifles chamber. In the turret it can be off either way by 6 thousandths.

I always use my Stoney Point gauges for reloading. A buddy had a problem where his full length resized 30-06 reloads would occasionally fail to fire in his ruger. Certain reloads would fail to fire multiple times. I threw one in my remington and touched it off one day. It fired and produced partial case head separation. Taking his FL sized reloads home and micing them against fired brass from his chamber showed a major difference in headspace of the fired vs. unfired brass (some 20 thousandths if i recall). The Ruger's firing pin was too short to set off his reloads as they were so short they could move far enough forward in his chamber to absorb the impact without detonating. He had been adjusting his die by turning it down to contact an elevated ram on the press and then a quarter turn farther, per manufacturer instructions (Lee die). Now he has a set of stoney point gauges and mics everything too.

FWIW,

Mike

[Unclenick]

20 mils is quite a stretch. If you look at Lee's current instructions, they say that extra third of a turn applies only to their aluminum presses, but not to their new cast steel press. If I recall correctly from school, aluminum's modulus is about three times what steel's is, so for equal size parts under a given force, the aluminum will deform three times further. The cast steel press is not only made from a stiffer material, it is thicker, so there will be more than three times less stretch.

Thanks for your tale about the brass variance from the turret press. It validates my concern that bullet seating depth needs either to be measured with respect to the headspace determinant or else that brass headspace uniformity must be measured and added to a conventional comparator reading.

Nick

[ConRich]

Unclenick,

Your diagram and explanation were very enlightening, thak you.

Rich

[raktrak]

UNCLENICK, every once and a while you check my old grey matter out. I think your explanation was awesome. Now give us some discourse on why certain calibers are so inclined to need the shoulders set back every so often and others just keep on trucking.My most accurate 270, built by P.O.ACKLEY RIFLE CO. SLC UTAH needs the brass full length sized or run through a trim die to set the shoulder back after every 4-5 reloads. I have loaded some of my 6.5-06 hulls 10-12 times and only neck sized. WHY?

[sdtuna]

What a crew here!

Thanks for the explanations that make perfect sense once I engage my gry matter. i appreciate the willingness you all share your expertise.