load development with magazine fed rifles?

[Hollywood]

Looking for some input on what is seen in mag fed rifles for base to ogive length compared to what fits in the magazine. I am loading for a RRA LAR-8 .308. I have been loading to a reliable feed length of 2.227 with 175gr smk. Using Hornaday OAL gauge and comparator, chamber measures 2.332 oal. .105 difference, Seems like alot of extra room knowing it oal is limited by the mag length.

Your thoughts
Thanks

 

['Freak]

Start seated out to the longest OAL that’ll still run from the magazine and then test to find where it’ll shoot its best. But there on ignore OAL, instead go by ogive contact with the lands backing further away from the lands adjusting to seat deeper into the case in increments of .003” or so.

 

[Hollywood]

Made correction in first post. Measurements are base to ogive not oal.

 

['Freak]

When you have no choice but to jump to the lands then dinking with the distance jumped making it ever longer in .003” increments can still work to your advantage. If a jump of .105” is best you can do and still have the thing run from a magazine then that’s the point where you begin the testing.

If you want for ogive to the lands numbers other folk read from their measuring contraptions then something maybe somewhat close is the best they’ll be able to offer, yours would return a different number.

 

[watercam]

In addition, you can play with powder charges. Shoot your ladder test with the longest OAL that will feed. Somewhere in there is your best option. Keep your bullet tension in the .003" range if you have bushing dies.
If you really want to shorten your jump have a gunsmith pull the barrel, turn the shoulder and breech face back the amount you need (if your lugs are not lapped this is the time to do it) and reinstall. I have shortened my shoulders as much as .100" without mishap, still plenty of thread there to secure the barrel. Plus you may get a cleaner chamber to boot.

 

[Hollywood]

Never checked it until recently. Just trying to step up to 175gr from 168gr smk and was gathering all the info I can. Was going to try Erik Cortina tunning method. Why would a company build that much jump into a rifle. Is it just to make sure most all ammo will function.

 

[Hollywood]

In addition, you can play with powder charges. Shoot your ladder test with the longest OAL that will feed. Somewhere in there is your best option. Keep your bullet tension in the .003" range if you have bushing dies.
If you really want to shorten your jump have a gunsmith pull the barrel, turn the shoulder and breech face back the amount you need (if your lugs are not lapped this is the time to do it) and reinstall. I have shortened my shoulders as much as .100" without mishap, still plenty of thread there to secure the barrel. Plus you may get a cleaner chamber to boot.

you mean trimming at A or B?

 

['Freak]

He’s talking “setback and re-chamber” where gunsmith guy will ‘trim’ at (A) and (B) moving both forward by the same amount so shortening the existing chamber making room to come back in with a different chamber reamer ground to different dimensions allowing gunsmith guy to cut a new business end with those different dimensions into the frontend of what’s left of the original chamber.

 

[Brians356]

Was going to try Erik Cortina tunning method. Why would a company build that much jump into a rifle. Is it just to make sure most all ammo will function.

Functionality, reliability, and safety are the primary concerns for AR designers. Yet, guaranteed bolt gun accuracy is quite common nowadays. It serves to point out that seating bullets out near the lands is not the overarching factor I myself, and many others, once assumed it was.

 

[Hollywood]

Most of what I've read is the sweet spot is jammed or relatively close. Mine in comparison is jumping the grand Canyon. I'm able to get pretty good Acura with 168 gr but I just stumbled onto the load and I will get flyers. Switching to 175 is just to be able to have the possibility to reach 1k if the oprotunity ever comes around. These methods on this site are more precise than just load some up and get the best group and be done. This way you can know for sure and actually know why. I like knowing why things do what they do.

 

[Brians356]

Most of what I've read is the sweet spot is jammed or relatively close.

The context of that common maxim is bolt-action accuracy. Once you switch context to ARs you are in another universe. Is it even possible to feed rounds from an AR magazine which will place the bullet touching, or even within 0.020", of the lands? I honestly don't know, but that strikes me as very unlikely.