Typical round count for barrel speed-up

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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Odysseus
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Joined: Sat Jun 06, 2020 10:02 am

Typical round count for barrel speed-up

Post by Odysseus »

A commonly-reported phenomenon in centerfire rifles is that new barrels "speed up". In other words, velocity with a given load tends to increase over the first 100-200 rounds in a new barrel (the velocity increase seems to be either negligible or not commonly reported in chrome-lined or melonited barrels). While the barrel steel, type of rifling, and cartridge are all variables, the reported velocity increase is generally in the 50-150 fps range.

I worked up to a load of 19.3 grains of H110 with Speer TNT 125s, CCI BR-4 primers, and brand new Starline brass. I'm only getting an average 2003 fps from an 8", 1:8 twist, stainless Bartlein barrel -which seems slow. The barrel has about 200 rounds through it, but I thought it would have sped up by now.
As the velocity of supersonic 300blk (2000-2300) is much lower than most supersonic rifle chamberings (2600-3200), how many rounds do you find it takes for your barrel to speed up?
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