Case length for gas guns

[Ape_Factory]

I know this'll raise the ire of a few but I purchased a Giraud case trimmer last year, received it in December and I'm just getting around to using it (I know, I know!). Had to build a 300 blackout rifle and scrounge up enough loading supplies to actually produce cartridges. Normally that'd take a week but in today's climate it definitely takes a bit longer.

This'll be the first time I've had control over case length and I'm wondering what to consider when reloading for AR-type gas guns knowing that I use a very light crimp (separate Redding taper die). Logic dictates testing so I'm looking for a good starting point of say keeping the neck longer vs. shorter with AR loads, practical accuracy, without "wasting" an inordinate amount of supplies in the process.

Is it best to keep them as long as possible, taking conformity into account or should I be towards the shorter end of specification?

Does that change when talking about subs vs supers? I already load for 5.56 and .308 and am adding 300 blackout to the mix, both supers and subs. Supers will be 110gr. Hornady V-Max and subs will be the Hornady 190gr. Sub-X. I have the factory rounds for both bullets to compare. I do have a bunch of Berry's 220gr subs for fun/training as well.

So far I've prepped my first 250 cases with trimming being the next step. Advice on where to start?

 

[r.tenorio671]

....it would be worthwhile (and inexpensive) to do a cerro cast of your CLEAN chambers to get the actual measurement of the max allowable case length of the particular chamber. Otherwise, keeping within the SAAMI spec will serve your purposes....

 

[Ape_Factory]

I'll look into that. Right now I'm keeping it within SAAMI specifications (always have) and monitoring growth with my particular loads and brass manufacturer. After experimenting, I'm taking neck tension and bullet dimensions into account as well. I can see the cerro cast helping me determine headspace for sure.

 

[smoothy8500]

I've used the chamber neck gauge that fits in a short-trimmed case to measure length.

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[918v]

My 556 chamber accepts cases as long as 1.795” and I like longer necks. They hold on to the bullet better. You should determine how long your chambers are. 300 BO is easy as you‘re starting off with longer cases. The others will stretch themselves to length within a few loadings so just be patient.

 

[Molon]

Keep in mind that case length and case-neck length are not synonymous. You can have variations in each depending upon how well you control head-space during resizing and upon the method in which your trimmer references adjustments. That being said, the Sinclair gauge is a good starting point for such examinations.

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