300blk reload data confusion

[DngBat7]

So just starting to reload for pistol length, 1:8 300 blkout. I have Sierra 220 smk and h110 powder. Question is if you look at the 2 uploaded images, one is Hodgdon’s, and one is Sierra. H says 9.2gr is the max load, while Sierra says 10.1-12.2. So I cannot say I’m not confused.

 

[Sniper338]

Start with the lowest one and work up.

 

[DngBat7]

Start with the lowest one and work up.

I understand that, But who’s correct? Ones says max is 9.2, Sierra does not even start at that. They start at 10.1, thanks again

 

[Sniper338]

I dont know, but you will find out when you work up. Reloading manuels are just a source, they arent "right". Each gun is different.

 

[nso123]

Looks like you are looking at subsonic loads on the Hodgdon page and the ones in the Sierra manual include supersonic.

 

[Gabe22BR]

If your running a suppressor, you want to start low, chrono them, & see if it’ll cycle the bolt & see if it’ll hold the bolt open..(AR platform)
so it doesn’t matter who’s right- it’s what works in Your gun, and you have somewhere to start that’s written in black &white.

 

[DngBat7]

Thanks!

 

[AJC]

Look to the coal. Different lengths

 

[DngBat7]

Look to the coal. Different lengths

So, interesting you should say that. I did notice the difference in coal on those attachments. So I checked with my Hornady bullet depth gauge, and realized I can get nowhere near what the data says which is 2.230. Pushing into the lands, the best I could get is 2.091. The 220smk has a fat ogive. Which I would think I’m better off measuring of Cbto instead of coal? Maybe the data is referring to a bolt gun with more freebore?? So my last question here is because of that, so I start with a much less powder charge because the bullet is in the case much more and there will be more pressure I’m assuming? A little confused.

 

[dellet]

They both are correct, but providing different information. The Sierra data is more complete.

The Hodgdon load data, max load is based on velocity, note the pressure calculated.

The Sierra data is max pressure.

Use the Sierra data like any other data, starting below max. Near the middle.

Use the Hodgdon or any other data based on subsonic velocity, the opposite. Start high and work down to your desired velocity. The reason for this is to keep from having a squib load.

Using the Hodgdon data as an example, pressure is half of max. 28,000. No real danger of pressure.

For the most part the dangers of sub loads are a stuck bullet and firing a second round.

Always a good practice to work the load and check for stability without a suppressor, it’s a good way to prevent baffle strikes. This is also a good reason to start at the higher end of the load range.

Use a chronograph, it saves headaches of guessing if the load is subsonic or not an also confirms the bullet has left the barrel. Not uncommon to have an 800 fps load and not know it.

It is quite possible that powder and bullet combination will not properly cycle an AR without a suppressor attached. It may not lock back on empty. If it at least cycles and the bullets are stable around 1000fps, the can will ad enough pressure to lock the bolt. H110 is not the easiest choice to work with for subs, but it will work. Not always without the suppressor.

 

[dellet]

So, interesting you should say that. I did notice the difference in coal on those attachments. So I checked with my Hornady bullet depth gauge, and realized I can get nowhere near what the data says which is 2.230. Pushing into the lands, the best I could get is 2.091. The 220smk has a fat ogive. Which I would think I’m better off measuring of Cbto instead of coal? Maybe the data is referring to a bolt gun with more freebore?? So my last question here is because of that, so I start with a much less powder charge because the bullet is in the case much more and there will be more pressure I’m assuming? A little confused.

This is a big red flag, and you need to sort it out. The chamber was designed around a 220 SMK. At max length of 2.260”, the bullet should be .010” off the lands.

 

[AJC]

This might be a good thing to work out on that fancy load data program that I have yet to buy. Seems like a logical choice for safety. Every detail matters in this game, and having a problem could be more than a bad day.

 

[DngBat7]

I actually think I’m gonna give Sierra technical support a call today. See what they say

 

[dellet]

I actually think I’m gonna give Sierra technical support a call today. See what they say

Either you do not have a 220/240 SMK, there is a problem in your chamber, or you're checking it wrong. All of the SMK line can be loaded to at least 2.260".

Only the 220 round nose needs to be loaded short.

 

[Zero333]

Sierra shows max load...

Hodgdon shows subsonic load.

Big difference between the 2.

If you want max velocity then use Sierras data.

If you want Subsonic, use Hodgdon's data and a chrono.