300BlkTalk

So, I am new to loading. I have gotten the required tools/press, etc.

However, in learning the setup I have tried loading one to get my dies setup, etc without powder. I see alot of peoples post on OAL length for 300 blackout that is right around 2" for a 125 gr. sierra bullet.

How are you guys measuring OAL? Is it using a tool such as this with a 308 insert:
http://www.midwayusa.com/product/709931 ... roductDesc

I also see some load data with OAL length around 2.2". Im assuming that is from tip to tip. Which way is better?

Also, do you guys use an overall length gauge to measure your gun to get the optimum length?

Just looking for a little insight on this process. Thanks in advance.

We use a Caliper.

They are digital or use a dial indicator.

You must get one.

Try your local Lowes or Home Depot. I got one at Harbor Freight Tools. They can cost from $18.00 to $30.00. Any amount over that and you are paying to much.

Twistomatic wrote:We use a Caliper.

They are digital or use a dial indicator.

You must get one.

Try your local Lowes or Home Depot. I got one at Harbor Freight Tools. They can cost from $18.00 to $30.00. Any amount over that and you are paying to much.

Thanks for the response.

I do have a caliper though. Just trying to figure out the best way to measure the OAL. I loaded one as a test using someones guide for 2.040" for OAL with the sierra 125 gr bullet. Me being new, assumed this measurement meant tip to tip. Im pretty sure this is incorrect because the bullet looks way to far down in the brass...

I am also fairly new to reloading myself.

Maximum length for the round is 2.26" OAL so that it is able to fit in and feed from a standard AR-15 magazine from tip to tip.

I use the comparator you listed with the .30 cal insert to measure consistency between my reloads, as it is MUCH more accurate to measure from the ogive of the bullet rather than the tip.

Basically, the comp is great for checking your consistency. You can load a round and ensure that it is 2.26" or less for function, and measure that same round with the comp. The rest of the rounds can then be measured with the comp also. Some bullets within the same batch are slightly longer or shorter than another and your measured OAL without the comp will vary.

As a side note, I have been playing with the 125gr sierra OTM for a few weeks now. If what you are reading is listed as 2.040" and it looks too far down in the brass, then i am guessing the measurement is in fact tip to tip. I noticed the same thing at 2.085".

BradV wrote:I am also fairly new to reloading myself.

Maximum length for the round is 2.26" OAL so that it is able to fit in and feed from a standard AR-15 magazine from tip to tip.

I use the comparator you listed with the .30 cal insert to measure consistency between my reloads, as it is MUCH more accurate to measure from the ogive of the bullet rather than the tip.

Basically, the comp is great for checking your consistency. You can load a round and ensure that it is 2.26" or less for function, and measure that same round with the comp. The rest of the rounds can then be measured with the comp also. Some bullets within the same batch are slightly longer or shorter than another and your measured OAL without the comp will vary.

As a side note, I have been playing with the 125gr sierra OTM for a few weeks now. If what you are reading is listed as 2.040" and it looks too far down in the brass, then i am guessing the measurement is in fact tip to tip. I noticed the same thing at 2.085".

Thanks for the help!

What do your sierra rounds measure from the ogive on average?

You may want to seat your bullet a little further out of the case.

You do not want it to deep or to long.

If its to deep the pressure will go up and flatten primers.
If its to far out then it may not feed well from a magazine as the bullet tip is dragging on the magazine end wall. Or it may feed well but jam into the rifling and again pressures shoot sky high.
A happy medium is what you are looking for.

I hope this helps.

Ideally you want your bullet to be inside the case at least 0.25", or so the base of the bullet will be even with the base of the neck (where the shoulder's angle starts). This ensures the neck has complete contact with the bullet and can apply an even tension to hold it.

You can determine this by measuring the length of your bullet with your calipers, then adjusting your seating die so that it barely pushes the bullet into the case. Once this is done, you can slowly adjust the die to push the bullet further while using your caliper to see when the base of the bullet is flush or just past the base of the neck.
As long as you are under 2.260" OAL, and the bullet is seated deep enough to ensure complete contact with the neck, you should not need to push it any deeper.

The Sierra 125 MatchKing should be loaded no longer than 2.245 and no shorter than 2.230.

The Spitzer should be loaded shorter though. Really the Spitzer is not a good bullet to use in the AR, even though it performs well in gel.

BradV wrote:I use the comparator you listed with the .30 cal insert to measure consistency between my reloads, as it is MUCH more accurate to measure from the ogive of the bullet rather than the tip.

+1 on comparator usage. Measuring from the tip is not accurate. I've always used the Sinclair "Nut", which has a slight learning curve to it.
But is handy if you're measuring different bullets/items in one sitting.

Sinclair Nut

I have not read too much about it lately, but there is this internal ridge inside the magazine at approx: 1.70" forward of the rear of the magazine. This internal ridge helps keep the .223 round stable in the mag. At the 1.7" length up from the base of the brass is the neck area of the .223 round and it is about .250" dia. at this point. At one time, and maybe still, alot of these .308 bullets are being loaded so the bullet diameter is close to .250" at this 1.7" length. So, you might see some of these bullet designs loaded very deep. This is to help with reliability, from what I understand. But, not the 125 OTM.

Some, folks don't bother with it and they load the bullets to whatever OAL that they like or that will fit in the mag. Some, modify the magazines to remove the upper ridge or lower the ridge to open up the size. Some, like Wilson, will take a Lancer magazine and sell it already modified. This of course means that you will need to use different mags in your 300 Blk. I use modified mags. I have different mags for all the other firearms, its just no big deal for me to use slighty different mags for my 300 Blk. That just me.

If you are loading for standard mags, here is a little trick. That drilled nut type caliber gage you speak of is really handy for helping one find this .250" point on the bullet. Just put the .308 diameter bullet into the .277" hole and spin it around a couple of times to mark it. ( the gage will leave a small ring around the jacket of the bullet) You can now seat this bullet into a test brass and keep adjusting the seating die a little at a time until this mark is a little bit below the 1.70" length.( base to this mark say 1.675") This will put you real close to having the .250" point at the ridge area. The mark also lets you see the bullets placement when you place the round into a mag. It, of course, would be better if your Cal Gage had a .256" hole. Mine don't.

If it helps, here are the measurements from my 125 OTM loads. They are rounded off for clarity. You loaded rounds should measure somewhere close to these measurements.

The Sierra 125 OTM bullets that I have loaded are currently set to an OAL of 2.235" (tip to tip). With the .30 Cal Gage on the bullet, I measure the orgive to the base of the brass at approx: 1.50". ( Measured from the outside edge of the cal gage to the base of the brass and then subtract the gage size off your total reading. ( my gage is 1.0" dia. yours may be different ) In my case, I read 2.50" overall with the cal gage, but the orgive is 1.50" from the head of the brass.) And just for fun here, the .277" point is 1.680" above the base of the brass and I will say that the .250" point is real close to the 1.70" inch mark. Wow, that is so cool. I bet the engineers at AAC and Sierra designed it that way.
I hope this helps.