I'm posting here in competitive shooting in hopes someone will have an idea as I'm stumped. Problem is snug chambering closing bolt.

Reloading 264 Win Mag with Redding FL bump die and bushing dies. Cases are all trimmed to 0.005 -0.007" under specified case length. When sizing, up to +0.008" shellholder, it has no change in bolt closing pressure.

Marking case with Sharpie on belt area shows no interference. Case neck angle may show some contact but no change in pattern or pressure despite 0.000 to 0.008" shellholder.

Have never had a situation where bolt was really tight, but I'd like to remedy the pressure to protect the bolt lugs and believe it could be affecting accuracy. Gun is Sendero and shoots under 1 MOA.

Any ideas?

Should have mentioned that factory new brass chambers effortlessly. Unfortunately don't one a regular FL sizing die. Could it be Redding FL die is just too large?

Those Redding shell holder sets are in increments of less sizing, not more.

Normal Dies (FL included) do a poor job of squeezing down a belted mag case in the web area. If you're shooting load hot enough to expand the area above the belt you have a couple of options that I know of;
1) Reduce your load so they don't expand.
2) Buy one of Larry Willis' collet dies. http://larrywillis.com/

Watching this thread to see if the ingenious folk on the fire have different or better ways to manage the expansion on belted mags.

I managed a workaround when I loaded for a buddy's 257 Weatherby with the just above the belt tightness issue. I wound up running his cases through a 300 Weatherby die that happened to be tighter in the critical region. Then I did the usual loading with the 257 set.

A Redding body die for .264 Win Mag Redding #75127 may help. Redding will also make you a custom sizing or body die by sending in 5 fired cases to them.

Thanks for responding guys. My first inclination was that the area above the belt was what was causing the interference, but as stated above, when I marked it up with a Sharpie, there's no sign of contact at all. If I measure with calipers just above the belt, there is a difference of 0.005" between New unfired cases and mine. These brass had several reloading on them and have grown increasingly tighter. Primers show normal pressure and pockets are still tight. All loads have been under max data by at least 1.0gr or in many instances more.

Might just be time to cycle the grass out but I'd like to know why. I plan to blue up the entire case and look closer.

You`re bumping the shoulder back, but doing nothing to the case body..resizing it..You stated the fired cases were becoming progressively harder to chamber after each firing, resize the entire case. Pee on the shoulder bump only...I tried that with my 7 Wby mag...after a few firing, had the same problem as you. FL sizing did not change the accuracy of my load..but it sure fed smoother. You can still set up the FL sizing die to head space off the shoulder, if you want.
If your running that case to full bore, remember the pressure your dealing with.

CGPAUL, thanks for your take.
The body die according to Redding, sizes both the body taper and shoulder. I see witness on the brass that the body above the belt and just below the shoulder are being sized. It could be that the Redding die is simply too big for my chamber. Sounds like i need to get a regular sizer die and try it.

I plan to Dykem blue up a case fully and look closer, will report out.

All primers appear slightly flattened as normal, but no dimple nibs from firing pin hole and O/D of primers still have a generous radius.

Small base dies? Might cure the problem

It isn't possible to size right down to the belt (or the belt itself) with a regular FL Die. You need the collet die mentioned above. Only have to use it when they get tight in the chamber.

How many loads on the brass that is tight?

The Redding body die sizes right down to the belt, and brass measures under the SAAM dimensions listed in a Hornady manual for both belt area (-0.001 under) and body near shoulder (-0.003). I'd estimate brass have 5-6 reloading on them, Winchester, not lost a single case to neck splits and I turn/ream necks. Have annealed only 1 firing ago.

The easiest thing would be to try a different full length die. Otherwise id sent the fired cases and the die to Redding.
Annealing dosent matter as your not annealing that part of the case anyway.
Also remember that only fools dont full length resize cases on rounds used for hunting.

Read your Reading fl die instructions, the answer is printed there .