About Gas Guns, Mag Length, CBTO, and Jump

[hhudson]

I’m trying to decide on the best practice to load and test some 6 ARC 95 grain SMKs for my precision AR/DMR.

Bullet OALs vary up to .010” and this seems to be normal for hollow point rifle bullets, but bullet base to ogive is very consistent. Sierra’s data recommends loading them to max AR mag length of 2.26”. The longest bullet loaded to 2.26” does not contact the lands.

I don’t have the tool to measure where the bullet contacts the lands, but I’m not sure it matters much here because I’m limited by mag length.

Is the best practice to load the longest bullet to 2.26” COAL to ensure they all fit in the magazine and cycle reliably, take the CBTO measurement, and then start loading at that CBTO -.003”, -.006”, -.009”, etc?

That seems like it will give a more consistent jump distance than the traditional COAL -.003” increments due to the bullet lengths, right? Or am I overthinking it?

 

[Cfshooter]

Since the OAL varies so much, I like to start at 2.250 on a 2.260 max mag length magazine, then take that BTO measurement. Then i work deeper in .010 increments for gas guns now, I found .005 wasn’t enough to see much with all the other variables the gas guns throw at you.

 

[bun_groker]

If you want to seat them longer, the stainless ASC magazines (Ammunition Storage Components - ammosc.com) will allow up to 2.290" or so

 

[jelenko]

Is the best practice to load the longest bullet to 2.26” COAL to ensure they all fit in the magazine and cycle reliabl

Assuming you're going to feed from a mag, almost. The issue is 'what is the longest bullet in a box of 100? In two boxes of 100? etc.

I think it's best to provide a margin of safety in case I hadn't found the longest bullet by loading the longest bullet you've found to something less than 2.260. From my experience, I've been using 2.257.

As mentioned, ASC and PRI mag's allow for an OAL around 2.3. With ASC mags, some of them are constrained to ~ 2.9 due to the way they were welded together.

 

[Sniper338]

I got a AR bob sled and single shot everything in my AR while doing load development to just not mess with a mag and to find out what it really likes and where. Makes a big difference taking the mag out of the equation to find a bullet and load. Id try doing that and see what it likes first before you fool with a mag length.

Turns out the load I found fits perfect in a mag...