Case set back for semi auto rifle

[merbeau]

Hi

My competitive shooting is with bolt action rifles and routinely set the case shoulder back to match my chamber. I have used a Sinclair Bump Gauge and also the feel method by removing the firing pin from the bolt and lower the fl die until the bolt closes freely.

My son has a 308 semi auto competition rifle. We are starting to build a competitive load for it. I have seen references when using for example, Sinclair Bump Gauge set back anywhere from 0.002 to 0.004 inches. Is there a way like the feel method for a semi auto; or is it not critical on a semi auto; or use 0.004 inches.

Thanks

Robert

 

[mtwarych]

I have a DPMS GII Hunter I reload for but not for competition. I set the shoulders back .004 inches and have no problem with function. I need to FL size every 3 loads because the brass is being extracted under some pressure and will swell enough to impede chambering and the bolt lock. My hunting rounds need FL sizing on every reload due to increased pressure of higher velocity round. (~75fps)

Your sons rifle being an accuracy type rifle probably has a tight chamber and MAY need FL resizing on every reload.

I would try making a couple dummy rounds to see if they will feed and chamber without FL sizing.

 

[merbeau]

Thanks for replying. Yes, the chamber is match. I may just experiment a little by setting back 0.002, then 0.003 up to 0.005 to see if there is any difference in groups or if any clambering problems occur.

 

[SealT5]

I would say .004"-.006" would be fine. I've found that .002" still provides resistance in my bolt rifles. .003"-.004" is where I start seeing minimal or no contact

Joe

 

[just country]

morning, quality FL sizer. trim brass depending on
hot loads. justme gbot tum

 

[cohunt]

I fl all my semi auto rifles, I bump them all .003 also

 

[merbeau]

Many thanks to all that replied. At least I have a starting point.