LONDON (Dow Jones)--Sportswear retailer JJB Sports PLC (JJB.LN) Thursday said sales at its stores open more than a year rose 22.3% in the six weeks to July 4, adding a trial format store it opened in May has outperformed the average sales performance across the group. JJB said since its last update at the end of May sales have remained in line with its expectations, despite what it called England's "premature" exit from the soccer World Cup. Replica soccer shirts are a big sales driver for the company. Comparable sterling gross margin climbed 54.5% in the same six weeks, giving an overall comparable gross margin over the same period of 43.9%. JJB's sale started July 1, which is 10 days later than last year. The firm closed and refurbished its Slough, Berkshire, store in April and re-opened it a month later as a trial format. JJB said since its reopening, sales in that store are up 9% on the company average, while margins have improved 17%, which is consistent with expectations. A further four stores will be refitted before the autumn, to "test the learnings from Slough in different store environments," JJB said. -By Hannah Benjamin, Dow Jones Newswires; 44-20-7842-9298; hannah.benjamin@dowjones.com (END) Dow Jones Newswires July 08, 2010 02:25 ET (06:25 GMT)