5 votes away from total ban on guns.
Party bosses say they have scrutinised how every MP will vote, and believe if a handful of waverers join the crusade, John Major's cop-out gun laws could be defeated on Monday night.
They have launched a last-ditch offensive this weekend to persuade dithering Tories to back an amendment calling for a total handgun ban.
A Labour spokesman warned: "Without this small number of votes, we will almost certainly be staring at one of the saddest days Parliament has ever seen."
Four Tory rebels - David Mellor, Hugh Dykes, Robert Hughes and Terry Dicks, who was sacked by Major this week - have also vowed to use their influence and plead with Conservative colleagues to support a ban.
The 11th-hour bid comes despite John Major's refusal to allow a free vote.
The Ulster Unionists made it clear they will not support Labour's amendment calling for a total prohibition.
But anti-gun MPs, plus the Dunblane parents and Snowdrop campaigners, were encouraged when Labour shooter Frank Cook said he'd miss the vote.
And Hughes claims two Tories - Den Dover and Sir Gerard Vaughan - could back a full ban. They were not available for comment.
Labour chiefs admit that, if they fail to rally more Tories, Major's proposal to allow 40,000 .22 guns to remain in circulation will become law.
The Labour aide added: "We reckon we need five votes to win.
"We've greatly increased our effort to convince wavering Tories that outlawing all handguns is the only way to secure public safety and ensure a tragedy like Dunblane never happens again."