-
Be sure to read this post! Beware of scammers. https://www.indianagunowners.com/threads/classifieds-new-online-payment-guidelines-rules-paypal-venmo-zelle-etc.511734/
How accurate do I need to be with OAL?
- Thread starter bw8755
- Start date
The #1 community for Gun Owners in Indiana
Member Benefits:
Fewer Ads! Discuss all aspects of firearm ownership Discuss anti-gun legislation Buy, sell, and trade in the classified section Chat with Local gun shops, ranges, trainers & other businesses Discover free outdoor shooting areas View up to date on firearm-related events Share photos & video with other members ...and so much more!
Member Benefits:
The question I have always had is: what do you do to tighten up the COL. It depends on the bullet nose and ogive uniformity (which often is NOT uniform) and any play in the press. The seating stem/die are locked down, so they are not a variable.
However, your COL variance is rather extreme.
However, your COL variance is rather extreme.
Keep in mind that most bullets do not have exactly the same profile. While the seating die presses the bullet into the case, it does not do it from the tip. It presses the bullet into the case somewhere along the ogive of the bullet. Minor differences in the bullet forming dies create small differences in where that happens on the bullet, leading to small variations in cartridge length. I know I'm not explaining this very well, but a difference of +/- .005" is not going to make a lot of diffence in your cartridges accuracy. Unless you're loading for benchrest shooting at which point your doing a lot of measuring of the bullet before it even gets to the point of loading it in the case.
I definitely think the calipers are inconsistent as I can get several readings from one cartridge. However, I can get the same reading on some cartridges too, but I might get a consistent 1.1255 on a couple and then 1.1285 on a few, which makes me think that my finished product has a variance.....maybe.
Depends on the cartridge, bullet seating depth, and powder.
A good answer is that it can.
It's probably most important to ask you where in the load range are you working? If you are at or near your max powder charge in a high CUP cartridge, with a fast powder and you are measuring 1.1210 against a specified OAL of 1.1250 then those 4 thousandths might be cause for some concern. That same 4 thousandths wouldn't give me near as much pause, if I'm loading .45ACP to 1.255 using Win231, I'm making 750 FPS range loads, and I'm seeing an OAL of 1.251. Same variance, but perhaps completely different result.
If the long cases aren't into the lands of your rifling, then those are not a problem. The rounds that are .004" too short "might" be a problem, but that isn't too likely, either.
The concern I have, based on your postings, is that you say you can get different readings from the same round. That suggests a couple of possible problems. You might be pretty new to measuring things with calipers, making it something you're not very confident in doing correctly. I would also ask you to look at your primers and make SURE they all sit flush or slightly below flush. (Run your thumb across the case head and you can feel this.)
Also, you said you're using Harbor Freight calipers and you haven't mentioned what make of bullets you're loading. Either one of those could be the entire explanation for the variance you're seeing. With quality tools and bullets, I expect no more than +/- .003" on my loaded 9mm cases. When you are more experienced at measuring, and get better tools to measure with, you might find you're not as far off as you think you are.
One final thought: Make sure you are exercising the same positive stops on your reloading press each and every time. Timid use of a press by newbies has often caused the issue you're seeing.
The concern I have, based on your postings, is that you say you can get different readings from the same round. That suggests a couple of possible problems. You might be pretty new to measuring things with calipers, making it something you're not very confident in doing correctly. I would also ask you to look at your primers and make SURE they all sit flush or slightly below flush. (Run your thumb across the case head and you can feel this.)
Also, you said you're using Harbor Freight calipers and you haven't mentioned what make of bullets you're loading. Either one of those could be the entire explanation for the variance you're seeing. With quality tools and bullets, I expect no more than +/- .003" on my loaded 9mm cases. When you are more experienced at measuring, and get better tools to measure with, you might find you're not as far off as you think you are.
One final thought: Make sure you are exercising the same positive stops on your reloading press each and every time. Timid use of a press by newbies has often caused the issue you're seeing.
I am fairly new to using calipers on any regular basis as I've never really had a need until now. So, I am a little unsure if I am measuring it correctly, consistently. I am checking the primers so I don't think that's the issue, but I'll double check.
The bullets are a mixed bag of copper plated 180gr that I got from Profire. They were just bringing them in when I was at the counter and I asked for the whole bag. We sorted out the most obviously different ones (JHP, lead, flat nose as well as about a few dozen defective ones that had deformities/damage). I imagine Profire would have sorted these out to smaller quantities had we not asked for the whole bag, but we needed projectiles. I have a box of Rainier 135gr that I haven't loaded yet, and using as a comparison, these 180gr copper plated flat nose are visibly not as nicely made as the Rainier's. So, I have been wondering if some of these inconsistent numbers aren't caused by the differences in bullets. If I had to guess, there's probably three different copper plated flat nose 180gr bullets in the mix (some have one or two grooves, some have smaller flat nose tips, etc.
I kind of planned on finishing these to get my feet wet and hope to have more consistent results when I switch to the Rainier's.
Also, I am using once-fired brass.
The bullets are a mixed bag of copper plated 180gr that I got from Profire. They were just bringing them in when I was at the counter and I asked for the whole bag. We sorted out the most obviously different ones (JHP, lead, flat nose as well as about a few dozen defective ones that had deformities/damage). I imagine Profire would have sorted these out to smaller quantities had we not asked for the whole bag, but we needed projectiles. I have a box of Rainier 135gr that I haven't loaded yet, and using as a comparison, these 180gr copper plated flat nose are visibly not as nicely made as the Rainier's. So, I have been wondering if some of these inconsistent numbers aren't caused by the differences in bullets. If I had to guess, there's probably three different copper plated flat nose 180gr bullets in the mix (some have one or two grooves, some have smaller flat nose tips, etc.
I kind of planned on finishing these to get my feet wet and hope to have more consistent results when I switch to the Rainier's.
Also, I am using once-fired brass.
I've done some tests with overall length with the .45 acp. These were Berry 230 gr. plated RN, Winchester large pistol primers, assorted brass and Titegroup. Velocities are the averages of 10 shots through a Kimber Tactical Custom II (5 in barrel):
Grains ... OAL ... velocity (f/s)
4.2 ....... 1.20 ..... 780
4.2 ....... 1.23 ..... 720
4.2 ....... 1.26 ..... 680
4.6 ....... 1.20 ..... 815
4.6 ....... 1.23 ..... 765
Thus I expect less than +/- 10 f/s change in velocity for a +/- 0.005 cm change in overall length for my conditions. Note, these are all within the range of loading data I could find and are specific for the powder I am using. The results will be different if you are making really hot loads.
I haven't done enough tests (yet) to get the powder equivalent change for a given change in length ... my guess is that a +0.03 cm change in length is like a - 0.2 reduction in charge for Titegroup in a .45 acp.
Grains ... OAL ... velocity (f/s)
4.2 ....... 1.20 ..... 780
4.2 ....... 1.23 ..... 720
4.2 ....... 1.26 ..... 680
4.6 ....... 1.20 ..... 815
4.6 ....... 1.23 ..... 765
Thus I expect less than +/- 10 f/s change in velocity for a +/- 0.005 cm change in overall length for my conditions. Note, these are all within the range of loading data I could find and are specific for the powder I am using. The results will be different if you are making really hot loads.
I haven't done enough tests (yet) to get the powder equivalent change for a given change in length ... my guess is that a +0.03 cm change in length is like a - 0.2 reduction in charge for Titegroup in a .45 acp.
In one sentence you speak of cartridge OAL. In another sentence you speak of case OAL.
1. Which are you asking about? Case? or Cartridge?
2. What caliper are you asking about.
3. If you are asking about loaded cartridge OAL, do you have a bullet comparater? Using one of these is the only way to get accurate OAL measurements as the ogive differs from one bullet to another, not much but slightly to make a difference.
1. Which are you asking about? Case? or Cartridge?
2. What caliper are you asking about.
3. If you are asking about loaded cartridge OAL, do you have a bullet comparater? Using one of these is the only way to get accurate OAL measurements as the ogive differs from one bullet to another, not much but slightly to make a difference.
Sorry for any confusion. I am referring to a loaded cartridge (.40 S&W).
This is the caliper 6" Digital Caliper with Metric and SAE Fractional Readings
No, I don't have a bullet comparator. I'll have to look into one. Thanks!
This is the caliper 6" Digital Caliper with Metric and SAE Fractional Readings
No, I don't have a bullet comparator. I'll have to look into one. Thanks!
Exactly.
What really matters is the change in case volume behind the bullet. OAL itself is somewhat irrelevant, but it's the best proxy you can usually measure.
.010 setback on a .40SW might be a big darn deal. On a 30-06, pretty much no risk at all. Why? Because that % change in volume on the much larger rifle case is so small at the same amount of setback.
I'd think that COL acceptable tolerance is largely a function of case capacity and max pressure for a given powder.
Careful when buying a cheapo caliper like that. They eat batteries like you wouldn't believe. Over the course of a year or two, you'll buy enough batteries to replace it.
Or you could buy one that is the world standard for excellence, never needs batteries and is waterproof. Buy it once and it will last forever:
Super Caliper-Solar Powered- Series 500-No battery or origin reset needed for IP67 Digital Caliper
Yes, you are worrying about nothing significant. I do commend you for having a penchant for detail. Sloppy reloaders usually end up hurting themselves, guns, or both.
Ya right, we all need to rush out and buy a $2/3 hundred dollar caliper.
Better yet take a small SHARP knife and carve the foam on the lid of the case away where it could contact the ON/OFF button on the caliper. Solves the above problem.
If in fact the H/F calipers were so bad/defective they would have gone the way of the YUGO years ago.
Being as a standard sheet of paper ie; magazine page, is .003, 3 of them would come very close to the difference the OP is experiencing. Not enough to be really concerned about unless the OP is already at or past max load, which then there are other concerns anway.
NO, it doesn't. The display is the only thing turned off on a cheap caliper. The actual measurement mechanism is ALWAYS on and cannot be turned off.
I only mention this because I also have cheap calipers, but get to use the nice ones at work. Now I know why the nice ones are worth the $$.
I am not saying the cheap ones don't work. Just that the nice ones work better, for longer.
I own cheap guitar and very nice guitars. Both are worth every penny of their respective prices. But I much prefer to play the nice ones, and in 40 years they will still be worth something, while the cheap ones will be burned as kindling most likely.
Anyway, sorry to derail the thread.
H
