I'm new to reloading and have a question about COAL. I am reloading .284 Win with 7mm Hornady SST 139gr bullets with 50gr IMR4350. When I checked the Factory Ammo its 2.784, my Reloading Manual says Maximum COAL 2,800. So if I reloaded a bullet at 2,783 is this fine to shoot? I LGS guy said go 2.784 to 2.781 would be ok? Any advise would be greatly appreciated. I'd like to start off on the right track.
Bullet Seating depth Question
- Thread starter JoeP
- Start date
jepp2
Gold $$ Contributor
I will give a more complicated answer to your simple straightforward question.
3 things can dictate the maximum OAL for a given bullet for your rifle:
3 things can dictate the maximum OAL for a given bullet for your rifle:
- Does it need to feed through a magazine? This can limit the maximum length
- What is the OAL where the bullet will contact the lands when you chamber the round. This is really the maximum OAL and is actually measured from the ogive, not the tip of the bullet. But you probably aren't set up to determine this.
- The bullet design may be such that to have "enough" bullet in the case, you have to seat to a shorter OAL than what you would like to used based on measuring 2. And the boat tail portion of your bullet doesn't give grip to the bullet in the case neck.
FeMan
Gold $$ Contributor
COAL as a true measurement is most relevant to magazine length; i.e. will the loaded round still fit. When you start talking about COAL with respect to being safe, it is a whole different world. Assuming you are using a load from a reputable manufacturer you can assume the powder charge and case capacity will yield a load that is within safe pressure limits. If you are concerned about staying off the lands and not jamming the bullet, one can't really say by comparing COAL of two different bullets. No two bullet manufacturers are likely to have the exact same nose profile, so one brand of 139 gr bullet at the COAL you state may be jumping and another may be jammed at the same COAL. To make sure you are ok, I would suggest you load a dummy round (no power) at the COAL you want, take out your firing pin, and see if the bolt closes without any resistance. That should help you determine whether or not you are into the lands. If not and you are within the load bracket recommended in a manual, you should be fine. HTH.
Your maximum COL is what will function in your magazine, if the ogive of the bullet does not touch the lands at that point. COL is a driver in your data but if you are staying under max loads you can make it shorter or even to the lands. Be careful if you are touching the lands as pressure spikes are common. I bet your mag max will not be close to the lands in a factory gun.
If you are not concerned about extracting the last little bit of accuracy out of your gun, then 2.800" is fine, and it should feed fine from your magazine.
If you want to advance further in reloading techniques and extract a little more accuracy, then you should be setting your bullet seating depth based on how far it is from contacting the lands. A 0.005" jump to the lands for example may be a good position to seat to. However, that length, depending on your bullet, and where the lands are in your gun, may be too long to let you feed from the magazine.
There are more complex ways of doing it but what I do is sacrifice a case by cutting a slot in the neck and shoulder. See photo below. Adjust the tension with your fingers so the you can seat the bullet and pull it back out with a little firmness. Seat it quite long. Next chamber the cartridge and close the bolt carefully. Then open the bolt carefully and hold the cartridge so it does not pop out. Measure the cartridge OAL with a vernier gauge. Do it a few times to get a consistent reading. That is your overall length for that particular bullet to touch the lands. Mark it with a felt marker. If you wanted to load to 0.005" off the lands you would subtract that amount from the measured OAL. Now load a round for real using that marked bullet starting real long. Then adjust your seater die down until you get that OAL calculated above. That sets your die to seat all bullet to the ogive the same as your first one. The actual OAL may vary a bit from bullet to bullet, but to the ogive they should be very similar. The starting point of course is determining if you magazine can handle bullets seated out close to contacting the ogive.
Factory chamber I assume? If yes then you should be around 3K below pmax and should be ok. I doubt that you could jam a 139 SST even with a short freebore.
The reason for 2.784 is used not all have Have a guns magazine lingth that 2.800 will work with. The manual that are using is the pressure when you're reloading. That is the reason they say start low and work up .
Larry
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