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Reloading / Re: Do I need a Comparator?
« on: March 13, 2014, 05:31:21 PM »used to check if you are bumping the shoulder back enough when you are full length resizing
The OAL gauge is to check if your cases need to be trimmed
That is incorrect.
The comparator is used to get an accurate measurement of the cartridge length by measuring from the ogive (ohh jive) of the bullet to the case head (primer end). Example: If make one round on your press and measure from the tip to case head you will have one measurement A. You've locked your press down and the bullet OAL (over all length) matches what is published in your preferred manual. You then make 19 more and measure your last case just to confirm everything is still A OK, you get a measurement .005" shorter than case number one. Trying to find when your press went out of calibration you check bullet number 10 and find it is .003" longer than spec per you manual. Now you start thinking something is all wacked out with your press and start contemplating pulling everything back apart and redoing and measuring each case as it is done, (because we know that changes in the length will cause us an issue with consistency and that will be seen at the range). But then your buddy stops by with his comparator and caliper and tells you not to fret, he will save the day. Your savior then puts measures bullets 1, 10, and 20 and they all measure the same. How, is this possible? Right...because the comparator measures off the ogive it is measuring from a spot that is made to be consistent during the manufacturing process. You then look at each bullets meplat and notice that some are really pointy and some are a bit jagged or banged up.
Next up...your OAL gauge. It is not used to determine if your cases need trimming (that would be the job of a case length gauge). The OAL is used in conjunction with the comparator. You use the gauge to determine the chamber size of your rifle from ogive to case head. You place your chosen bullet into the modified case that is attached to the gauge and insert it into the rifle with the bolt removed. With the case all the way in, you push the grey rod in and slowly begin pushing the bullet out of the case. When the bullet stops moving the slightest, you stop. Remove the gauge and bullet from the rifle and put the bullet back into the case if it got stuck. Then measure the ogive to case head length with the comparator and caliper. You then repeat the process a few times and verify your measurement average. These measurements are now the dimensions of the rifle. When you start making your ammo you can use this measurement (minus .015"-.020" length because most bullets are more accurate with a small jump from to the bore and you want enough room for manufacture error that the cartridges chamber and de-chamber easily) to build for that rifle. This will not work for you if you like to load the magazine with your ammo as the measurement may be too long for the bullets to fit. This also will not work if you are loading for several rifles in the same caliber i.e. .223 Remington that you want to shoot from an AR and a bolt action and mini-14 as they will all have different size chambers and you want to be able to just grab a box of ammo to go to the range. Overall, if you are using it to make ammo for one gun at a time (Barrett 98B) and you only have one rifle in that caliber, it makes sense to do this as it will help you tune your loads to vastly improve accuracy and consistency. I would however recommend not buying the modified case and instead sending a once fired case from your rifle in to Hornady for modification. P.S. You will have to take the measurement for every bullet you use as they will all be different (175gr Sierra MK vs. 168gr Hornady BTHP Match)
Is all of this needed? No, but it will help as consistency is key to accurate shooting.
If you have multiple rifles in one caliber, I would avoid all this mess as you will have a lot more work to keep everything separate during the reloading process. Just full length resize and load to specs. You could still use a comparator to help some with reloading consistency.
