Need for a comparator when mag length is the limiter???

[rjacobs]

I am loading 308, 300blk and .223. All guns are magazine fed so real OAL is the limiter. I dont believe on any of my guns I can get close the lands and still stay inside of the mag limitations. Loading for both AR15's using P-Mags(2.255ish), an LMT MWS using LR-Pmags(2.820ish), and a Rem 700 AAC-SD 308 which generally has a very generous chamber(hard to get to the lands anyway) and will be shortly fed by AI mags(I believe is about 2.850 with the spacer) once I get my Rock Solid chassis.

I loaded up 50ish rounds of .308 the other night with varying(obviously) OAL's from 2.795(I think that was the lowest I saw) to 2.815(I believe was the highest). Was loading both 175g SMK's and 185g Berger LRBT's.

From what my mind is thinking I am just going to have to live with the slight variation and make sure that the rounds I load fit in my magazines on the long end and just deal with the short ones. I run Forster Ultra micrometer dies so in theory I could just dial down a little on the long ones, but that doesnt seem like a great idea to me because then I have some bullets seated slightly deeper than others and the varying pressures associated with that could lead to worse accuracy(or at least varying accuracy).

I will be dealing with jump no matter what I do so I am trying to find bullets that deal with jump better. The Berger 185's are supposed to be very jump tolerant, not sure on the 175g SMK's. I have a 155g Nosler load that has been shooting great in the LMT, but its not really optimized for the gun except through pure dumb luck by my old man.

So in my situation, would having, and using a comparator even do anything for me? I am thinking the answer is no.

 

[milo 2.0]

I'm thinking you're right.

 

[unoboats]

I use a comparator and then on my bergers if they are tight in the mag, I just sand down the tips to the same oal. Make sure all are sanded to the same length and your accuracy will not be hurt. I'm shooting these out to 1000 yds in matches and it works every time.

 

[thrusty]

The comparator is going to be the best option for you in making consistent ammo, as they take measurements from the ogive of the bullet and not the tip....as you have noticed, the tips aren't always uniform. The uniformity of the tips also do not effect performance/accuracy.

Lets say you want to load to mag length and you want all your ammo to be consistent:

Seat a round that is what you consider the OAL you're looking for...let's say 2.84" for your .308 AAC-SD bolt gun. You took the measurement from the bullet tip to the bottom of the case with a caliper.
Next, put on your .30 cal comparator and take a measurement from the bottom of the case to the ogive.
The number you come up with will be around 2.25" for a 175SMK 30cal using Hornady match brass.
That number is the number you want all your other rounds to be loaded at....this means the ogive to the lands of your rifle will be the same distance for all the ammo you produce for that gun.

This is how I load for my AAC-SD....so the numbers are real. I run them at just under mag length to keep me from having feeding issues.

To answer your question simply - a comparator is a tool necessary to load consistent ammo...it will make a difference.

 

[rjacobs]

Thrusty:
I understand what a comparator does, not asking that question which it seems is what you are trying to explain. I am also NOT dialing anything to get my OAL's consistent because I KNOW they will not be with the true OAL measurement method. If I did dial I would have very inconsistent ogive to ogive measurements. Every round I load IS consistent from an ogive to ogive standpoint(or at least should be) because I am not changing my seating die at all(which seats at the ogive).

So it seems that with your method you are using a comparator to make sure you're seating to the same ogive measurement each time AND THEN measuring OAL to also make sure they fit in your mags and just dealing with the ones that the base to tip are a little short. I guess I dont necessarily understand WHY the ogive measurement means ANYTHING unless you are able to load to approach the lands.

I am thinking I can simply leave the ogive measurement out of it since as long as I dont change my seater die depth they will all be the same if measured base to ogive. Now if I come across a round where the true OAL is to long for a mag, I will have to dial down and in that case I would probably run every round back through the seater die to get them all seated uniformly base to ogive.

 

[Deadshot2]

Bullets can vary in several ways. Different OAL's due to irregular meplats, varying BT dimensions, varying base to ogive measurements, etc.

A comparator has many uses besides measuring seating depth to ogive. It can be useful in sorting out a group of consistent bullets. If you're looking to make the ammo as consistent as possible then you need the same amount of bullet inserted in the case, every time. Comparing base to ogive measurements and sorting can insure this.

Use two comparators on you caliper and you can get a feel for uniform bearing surfaces as well.

It just depends on how much "fly crap you want to pick out of the pepper".

 

[thrusty]

rjacobs....it seems you already knew the answer to your question before you asked it.

I do not check every loaded round...however, I do check every 10th one or so just to see if there's runout...it's not a bad habit really.

What I explained was how to initially determine the length to set your seating die to. I have a single stage press...I take my seater die in and out of it. In order for me to get the correct seating depth every time, I need to first check with the comparator...if it's off, I adjust the micrometer on top the die + or -...then I recheck with the comparator. I only do this for one loaded round until I get it just to where I want the seating depth on the ogive. I then load the rest of my ammo without making any adjustments to the die or press.

If you NEVER EVER change your seating die depth and you NEVER EVER take it out of your press or tighten or loosen it in the press...then you're correct, you wouldn't need a comparator..

INITIALLY - If you want the COL measurement...I find a bullet out of a pack of 100 or 500 that looks like it has a nice and uniform tip. I seat it and measure from base to tip...If that measures 2.84" that is my standard for all my loaded rounds from that point forward for that particular bullet. I then take a measurement of the ogive of that same round - this measurement is what I now seat ALL of my loads with that bullet to. I do not measure COL ever again...Only once; any reload thereafter is to the ogive.

 

[Deadshot2]

I guess I dont necessarily understand WHY the ogive measurement means ANYTHING unless you are able to load to approach the lands.

Having a uniform case head to ogive measurement can give the bullet the SAME amount of jump with each shot.


Bullets can vary in several ways. Different OAL's due to irregular meplats, varying BT dimensions, varying base to ogive measurements, etc.

A comparator has many uses besides measuring seating depth to ogive. It can be useful in sorting out a group of consistent bullets. If you're looking to make the ammo as consistent as possible then you need the same amount of bullet inserted in the case, every time. Comparing base to ogive measurements and sorting can insure this.

Use two comparators on you caliper and you can get a feel for uniform bearing surfaces as well.

It just depends on how much "fly crap you want to pick out of the pepper"

 

[rjacobs]

I thought I had a grasp on why or why not to use a comparator before asking the question, just wanted to make sure. Im still not 100% sure it wouldnt be something for me to have, but since I am not going to be able to get close to the lands(the real purpose of the comparator IMO) and I am ok with dealing with the differences in OAL as long as all the rounds fit in my magazines, I think it would just be a $40 tool sitting on my bench not receiving any use.

I have a Forster Coax so no I dont change my seating die depth very often. I set it and leave it unless I am changing projectiles and I try to settle on a bullet and leave it set. Like you I use one bullet and set up the seating depth. I have a collet puller so I can pull said bullet. I have a few bullets so far that their only purpose is to set seating depth and I have them labeled and saved off to the side.

 

[rjacobs]

Having a uniform case head to ogive measurement can give the bullet the SAME amount of jump with each shot.

I understand that. And how I am loading they SHOULD have the same jump every time. I am not dialing every round to have the same OAL. I am accepting the tolerances as what they are and dealing with them. Every bullet is seated the same amount. I am confident that if I had a comparator and measured all of my rounds they would all be pretty damn close in the base to ogive measurement.

I guess I am just trying to wrap my head around, in my circumstance, where the real OAL(or should I say the MAX OAL of a batch of loaded ammo) has to fit into a magazine, I am accepting of the shorter base to tip OAL rounds and not trying to dial the long ones down to the short ones, I am accepting of the fact that I will have to jump and not have any real say over how much, etc... why a base to ogive measurement really means anything to me accept another number to write down or compare to?

 

[P7id10t]

RJ, seems to me too much thought. If the 155s shoot well out of your LMT, stay with 'em and do the same thing over and over. Do something similar for all your others and be done with it. Use your B to O and OAL as QA/QC metrics.

FWIW, I have found on 175SMKs I shoot, using an RCBS Micrometer seater, Base to Ogive variation can be 0.004 and OAL by as much as 0.015. In shooting the different bullets I've tried, like you I have found that some group nicely, others don't. I've chalked it up to powders, not considering the effect of jump.