Interesting concentricity results

[jetinteriorguy]

I’ve been working up a load for my AR in 7.62x39 and have hopefully found a nice 1.25-1.5 MOA load using H335. I loaded up 20 rounds to test my potential load and have been putting a light crimp on them. Just for S&G’s I also loaded up 20 rounds with no crimp. I’m not worried about trying to make this rifle a 1/2 MOA shooter so haven’t bothered checking concentricity. Just messing around this morning thought I’d check concentricity and was pleasantly surprised. Of the crimped rounds all but two of them were less than .001” off and the other two were just slightly over .001”. Considering these aren’t some high quality match Bullet and they were seated with just a regular Lee seating die and crimped with a Lee collet die I was pretty impressed. Then I checked the 20 rounds that I didn’t crimp and found the more typical runout of .002-.004” runout I typically get from a Lee seating die, which is still more than acceptable in this instance considering my expectations for this ammo. I haven’t had a chance to test these yet to see if there’s any difference on paper. Wondering if anyone else has ever noticed this. Of course I do realize this is a pretty small sampling and not a particularly scientific test, but just has me curious.

 

[hounddawg]

I would not worry about the brand seating die Jet. As long as the cone in the stem is deep enough so that the stem hits the ogive before the meplat you are good to go.

But thanks for the post. I am on a similar mission with my 6.5 Grendel and check the concentricity and may crimping some today

 

[lugerstew]

Now you got me curious, I think for a while, I will check concentricity of a seated round, before using the Lee factory crimp die, and then check it after to see if the crimp die actually does improve concentricity and if so, by how much.

 

[lugerstew]

Just got done loading 10 rounds of 308win, 168g Hornady HPBT, seated to coal of 2.800. I measured all 10 rounds before and after a Lee factory crimp.
I had about .001 to .002 runout before the crimp and it stayed the same after the crimp, so this crimp didn't help me in this instance to improve concentricity.

 

[hounddawg]

Just checked the last 10 rounds of that 6.5 grendel I loaded yesterday. All runouts between .0005 and .0025. I never bothered crimping any to see if it changed since even in my bolt guns I figure anything less than .003 is not worth he bother

 

[Nathan]

Good results! I find anything under 0.005” TIR to be best quality ammo.

 

[jetinteriorguy]

Now you got me curious, I think for a while, I will check concentricity of a seated round, before using the Lee factory crimp die, and then check it after to see if the crimp die actually does improve concentricity and if so, by how much.

That’s what I was thinking of trying next. Personally I have no issue using my Lee seating die. For my intended purpose with this rifle it produces ammo that has exceeded my expectations. I just happen to notice this difference while trying to see if the crimp is necessary or if I get better accuracy without it.

 

[lugerstew]

jetinteriorguy: Ya I was loading these 308 rounds for my AR-10, so I wanted to end up crimping them anyway, so it was easy enough to do the test with my Hornady concentricity checker.

 

[Unclenick]

Lee collet die I was pretty impressed. Then I checked the 20 rounds that I didn’t crimp and found the more typical runout of .002-.004” runout I typically get from a Lee seating die, which is still more than acceptable in this instance considering my expectations for this ammo. I haven’t had a chance to test these yet to see if there’s any difference on paper. Wondering if anyone else has ever noticed this.

I've never noticed that occurring, but I rarely crimp. I'm not surprised Lugerstew got no change, as he started out already as good as the improvement you got. 0.002" is a pretty common level of neck wall thickness runout, and I would not expect crimping could fix runout due to that, so it sets a lower limit (assuming that's the amount of neck wall runout your brass has).

Now you've got me wondering, is Lee's claim that their Factory Crimp Die improves accuracy based on a tendency it has to correct some degree of runout? Some experiments are in order.

As to how much bullet-tilt matters, it depends on how far forward of the geometric center of the bullet design's bearing surface its center of mass is. A. A. Abbatiello showed back in the '60s that 0.004" of tip-tilt (0.008" total indicated runout) would open groups by an average of 1 moa shooting the M1 Type military match bullet from Springfield '03 match accurized rifles. When the late Harold Vaughn did the same test on some 6 mm benchrest type bullets from a one-holer machine rest rifle, it only opened about 2/5 of that.

 

[Bart B.]

Unclenick,

Please post your pictures showing how a given crooked cartridge will have different runout numbers depending on how it's positioned and measured in the gauge. There's no universal standard.

Lugerstew,

I don't think any crimped in bullets are needed. The most accurate 308 match ammo used in semiautomatic rifles doesn't have crimped in bullets.

 

[jetinteriorguy]

Definitely more experimenting is in order. Funny thing is, I normally don’t crimp either and have never had any issues in any of my AR’s. Usually when seating bullets you kind of get a feel that your getting good neck tension, but with these I wasn’t quite getting that feeling. Since I wasn’t overly concerned with getting any kind of match grade accuracy and felt anything under 2 MOA would be fine, I just felt a little crimp wouldn’t be a big deal. Then just for the sake of testing I loaded some uncrimped to see if there is any noticeable change in accuracy. I may also test some using the .308 expander ball vs. the .310 expander ball to see what happens. Funny thing is, this rifle isn’t anything special, just an AR Stoner upper I got on sale cheap from Midway a few years ago on an Anderson lower. These bullets aren’t anything special either, just some PPU’s from Grafs they had on sale a while back, and it’s all mixed brass with no special prepping. But I’m getting much better results than expected so feel it’s worth exploring any improvements.

 

[Unclenick]

The attached PDF is the file Bart was referring to.

I also have an Excel file that is a radial drift calculator that can be downloaded here.

 

[lugerstew]

I agree, different methods of measuring can for sure give different results,
Myself, I only use the Hornady tool, I always use it the same way, I do agree, the further out you measure, the more the runout will be, but if you stick to consistency with this tool, I am comfortable with the results.

 

[Unclenick]

Note that zero is zero, regardless of the measuring method you use to sort. I included bullet tilt calculations taken from each measurement method. That provides a consistent method of determining runout. You can plug twice that tilt into the total indicated runout cell in the above Excel worksheet. Be aware that tilts in excess of about 0.004-0.005" (0.008"-0.010" TIR by the Sinclair style tool and indicated at the tip method) are usually straightened out by the bore, so additional drift does not occur as bullet tilt gets greater than that.

I will rework the calculator so it stops adding drift as a bullet tilt exceeds the above limit and to accept bullet tilt as an argument directly instead of doubling TIR. I can include the calculations from the drawing in the PDF file as well. That would make it more useful.

 

[hounddawg]

I also use the Hornady tool. As of late I have been debating getting on of the units such as a Sinclair, Redding, or 21st century. The reason being is that the Hornady uses the case rim and the bullet ogive as pivot points where the other three show the deflection between the case body and the bullets ogive. That has caused me to wonder if the Hornady could actually be more an indicator of case heads being out of perpendicular than the bullets being cocked.

Just something to think about. So far in my shooting at least I am not finding the concentricity to make any differences in the grouping either good or bad

 

[Unclenick]

Try Harold Vaughn's experiment. Find 8 rounds with about 0.008" TIR and use a magic marker to mark the high side. Fire them by locating the high spot at 12:00, then 3:00, then 6:00, then 9:00 for chambering and firing, and then repeat with the next four rounds. See if you get 4 distinct pairs making a sort of four-leaf clover pattern.

 

[hounddawg]

I am not sure how I would get .008 runout and also not sure I would want to take a chance on tweaking the necks on my cases that far out of kilter. I think I have gotten my reloading to the point where I need to have it and for the next season at least I am concentrating more on my fine tuning my wind reading, and strategy.

 

[Unclenick]

You could certainly do it with less. It just gets harder to see the effects. Also, the gun Vaughn used was a one-holer integral machine rest rifle. If you're not shooting bugholes, it gets hard to see, too.

 

[hounddawg]

My 30 Grendel gets consistent five round groups in the low .3's and high .2's, the problem would be getting runout. I firmly believe runout occurs in the way you size the cases and using one piece dies with no expanders followed up with expander mandrels gives me very low runouts. At the moment Grendel brass is pricy and scarce so I sure am not going to chuck some up in a vise and bend the necks on purpose.

At any rate I would wager that wind mirage reading comes into play a heck of a lot more when it comes to misses and bad groups than runout for 99.99% of shooters. Even among those who compete on a regular basis the wind reading skills are what separate the tier one shooters from the rest of the pack

 

[Unclenick]

...And bending necks on purpose might not match the result of it being done by basic reloading tools. A lot of folks have tried straightening bullets by bending them and found it changed the neck's hold on the bullet enough to stop its performance from matching the rest.