Off topic:Gene variation study with number of genomes

Question

[Eva_Maria]

I tired to find a gene variation with in 400 genome by flowing steps

bwa index 400genome.fasta

bwa mem 400genome.fasta gene.fasta >out.sam

samtools view -bt 400genome.fasta  out.sam >out.bam

samtools index out.bam

samtools mpileup -u -f 400genome.fasta out.bam>out.vcf

bcftools call  -m -v out.vcf >aa.txt

I did not get any variation form bcftool out. But when i tried with one genome as reference, bcftool shows some variation. Is there any problem in my steps?