new Nosler 260 Rem brass, Federal large rifle match primers seated using primer arm in ram of Lee Breechlock press - lots of leverage. Same primers seated fine in older Rem 260 cases. After first 2 failed to seat flush I used a Sinclair primer pocket uniformer on the rest. It took of very little brass and really didn't make much difference. The rest of the 50 lot had substantial and only slightly varying degrees of protrusion. I fired 16 of them anyway in Ruger #1 - chambered with difficulty but no appreciable difference in accuracy compared to same loads in the older brass. Primers were quite flattened and flush after firing. I haven't prepped the fired cases yet but am hoping that one firing will rectify the problem.

Any comments? I was rather dissapointed that the Sinclair tool didn't make a difference. Has anyone else experienced this problem with Nosler brass?

Something related, I use the Sinclair primer tool on my large rifle primers. I noticed a certain batch of brass the primers didn't seat perfectly, they didn't stick out, but the brass would rock ever so slightly when set down. Other brass didn't have this problem. I took the Sinclair priming tool apart and turned the shaft about 1/3 turn which seats the primers just maybe .015-.020 further in, problem solved. I should have checked that before but never adjusted tool cause it was ok on other brass.

Never had any problems firing either way the primers were seated.

Have you used that same lot of primers successfully in other cases? Could it be a bad box of primers?

You answered your own question; if they fit fine in older Rem brass and you changed brass to Nosler; then the Nosler brass has tight pockets. So ream them out to spec. Or try another primer brand.

Zhurh thanks will try that

You can easily tell whether your primers are too "tall" or your primer pockets too "shallow" using a decent caliper to measure one against the other, and each against other brands. Measuring the depth of a recess is what the little thingy that sticks out the back of your caliper is made for.

Obviously, there is a mismatch between primer and pocket. The easiest solution would be to find a shorter brand/lot of primers; however if none are short enough, then the only other solution would be to make the primer pockets deeper.

Shooting the loaded brass won't do anything to deepen the primer pockets; excessive pressure will only make them larger in diameter.

I had this same exact problem a few years back but with Remington primers going into Winchester brass. As I recall the Remmy primers were on the outer fringes of maufacturing specs and the Winchester primer pockets were on the lower/shallow side of specs. I remember trying the Remington primers in Remington brass and they were all below the case face iow; they were fine. Likewise tried Winchester primers in th Winchester brass and "ditto", the primers were below the face also.
I think the componant manufacturers play the spec. Numbers to their advantage when possible, in an effort to keep things as proprietary as they can. Just my opinion.

Get this Lee tool. Or RCBS