Dollar Shave Club claims it passed Schick to become the No. 2 razor cartridge brand by volume in July, a little more than three years after the online shaving brand hit the market.

While that isn't independently confirmed, the company's claim is largely consistent with available third-party data. If true, it still leaves the upstart well behind Procter & Gamble Co.'s market-leader Gillette, and behind Schick in dollar sales.

Dollar Shave Club has doubled its subscriber count to 2.2 million in less than 10 months since launching a major national TV ad push in November, according to founder and CEO Michael Dubin. Flush with venture capital, the brand founded on a viral video has been the biggest-spending razor brand on TV since November, even edging out Gillette by $64.5 million to $43.4 million, according to iSpot.tv.

Though Dollar Shave Club isn't yet profitable, the $75 million venture-capital round it closed in June will help fund more TV ads, nine months after a $50 million round that helped fund its initial TV push.

"I can't talk about budgeting, but TV has been a winner for us and a space we're going to stay in," Mr. Dubin said. A new round of ads breaking this month aim to drive home the value of using fresh blades.

"It feels great to shave with a fresh blade," Mr. Dubin said. "And we feel there are millions more guys out there that have that perception and would enjoy that experience. This campaign is about finding those guys."

Cartridges are the biggest and, at least for the established players, most profitable segment of shaving, and indeed one of the highest-margin categories in packaged goods. Dollar Shave Club said it had a 16% volume share of cartridges for July, based on its own sales data, compared to scanner data from Nielsen indicating a 15% volume share for Schick on an annual basis (if online sales are added in). Nielsen data from Deutsche Bank, however, show Schick's cartridge volume share for the four weeks ended Aug. 8 about a point ahead of its annual share – which would leave the two brands roughly tied.

Chris Gough, VP-investor relations of Edgewell, Schick's owner, declined to comment on Mr. Dubin's share claim, saying Dollar Shave Club is a private company without publicly audited financials and operating in an online marketplace without widely available third-party sales data. Even Nielsen doesn't cover the entire shaving market, he said.

But third-party data from Slice Intelligence, which mines electronic receipts of online purchases from a panel of 2 million, suggests that if it hasn't already happened, it may only be a short time before DSC becomes the No. 2 U.S. razor cartridge brand, even by dollars.

Slice data jibes with Dollar Shave Club's growth tally, showing the club had online sales of $16.3 million in July. That's more than double the $7.7 million recorded in October, before its in-house-created TV campaign started, and nearly triple the club's sales rate a year ago.

By contrast, Schick's offline unit sales were down 6.8% from a year ago for the four weeks ended Aug. 8, according to Nielsen, and its dollar sales fell 5.5%, both numbers somewhat better than results for the full year.

Dollar Shave Club, which focuses on cheaper blades that men change weekly, still trails Schick in cartridge dollar share by a 9% to 16% margin by its own Nielsen-aided estimate. And Schick remains ahead on volume and dollars counting broader razor products, including disposables and razor handles.

Even so, it's a remarkable run for a three-year-old razor upstart nipping at an 89-year-old incumbent. If Dollar Shave Club maintained its current monthly sales level, it would have nearly $200 million in sales the next 12 months, per Slice data. Even if its current growth pace of the past year were cut in half, Dollar Shave Club would pass Schick in cartridge dollar sales within a year. And were the club to somehow triple its sales again – certainly a stretch – it could pass Schick in total dollar sales.

Schick has had $222 million in cartridge sales the past year, per Nielsen, and as much as $235 million adding in Slice's estimate of its online sales. Schick also has another $115 million in sales of razor handles and $239 million in sales of disposables, the latter a segment where Dollar Shave Club doesn't compete.

The online shaving business is still relatively small but growing explosively. All brands included, Slice pegs it at $271 million for the 12 months ended in July, with Dollar Shave Club alone at $132 million during that period. While online shaving sales have grown 70% the past year, Dollar Shave Club has grown almost three times as fast – 192%.

The offline razor business is much bigger, but shrinking. Nielsen pegs offline razor cartridge sales at $1.3 billion, razor handles at $427 million, and disposable razors at $1.2 billion – totaling nearly $3 billion. While disposables grew 1.8% the past year, sales of blades and handles each fell more than 4%.

Mr. Dubin's success hasn't gone unnoticed by competitors. Gillette began advertising the latest incarnation of its online sales effort – the Gillette Shave Club – in June with ads claiming its blades are 50% cheaper than the "other shave club," based on using Fusion blades for a month vs. changing Dollar blades weekly.

Nielsen shows Gillette's offline sales and share continuing to dip in recent months, and Mr. Dubin said the ads have had no noticeable impact on his business. But Slice does show Gillette's online share rebounding more than 4 points to 18.6% from June to July while Dollar Shave Club's share has slipped more than 4 points since March from a high of nearly 54%. Not coincidentally, the new Dollar Shave Club ads poke fun at shaving with old, dirty blades to save money.

Gillette is also preparing to launch an improved men's cartridge early next year and new theft-resistant packaging designed to get blades out from behind locked cases in stores – a practice that has provided fodder for Dollar Shave Club ads.

Dollar Shave Club also faces stiffer competition in cheap blades, including possibly friendly fire. Dorco, the South Korean manufacturer believed by other industry players to make the club's blades (which Dollar Shave Club won't confirm) has been more aggressively marketing its own brand online, capturing an 8.5% share of U.S. online sales last month, according to Slice. Dorco also makes value-priced Swipe blades launched at Costco earlier this year.