Factory 250 FTX bullets jumping forward when chambered

[Texican Hairless]

Today I was reloading some 200gr FTXs. I seated all the rounds and then made up a dummy round with no powder to work on my crimp. Using the Hornady taper crimp I crimped all the way down to .470 and was still having the bullet jump forward in the case around .01" when I chambered the round. I inspected a factory 250 FTX and noticed that the case mouth is .479" which is what my reloads were measuring before I crimped them. It got me wondering if the factory rounds jump forward in the case when they are chambered as well. Sure enough! I chambered a factory round three times and each time the bullet jumped forward in the case as the bolt closed. Here are the measurements after each time the round was chambered:

unchambered: 2.241"
first time: 2.262"
second time: 2.277"
third time: 2.295"

So, after chambering the round three times, the OAL increased by .054"! I tried another round from the same lot and got similar results. I'm quite concerned by this. Has anyone else noticed this????

[Colohunter]

Yes, this has been noted a few times before. You can try the LeGendre crimp, or just try not to rechamber your rounds too many times. Most of us see excellent accuracy with factory ammo, I'm personally not too worried about the movement as long as the same round isn't chambered over and over.

[Texas Sheepdawg]

Here's a play by play on the mod.
viewtopic.php?f=5&t=685
Plus more info...
viewtopic.php?f=5&t=95

[Siringo]

Bullet jump is normal. Repeatedly chambering the same round time and time again will continually move the bullet forward as you found out. Slamming the cartridge home is not any different than using a bullet puller.

While hunting and using the same cartridge day in and day out, I soft seat the round using the forward assist or insert the round in the chamber and slowly release the bolt so it does not have its full force.

Some time ago I did a test using different carrier weights. The forward jump was worse using a carbine stock with a lite buffer (3.0 oz.). Changing to a heavy buffer (H3) and a Tubbs Carrier Weight System, I reduce the bullet jump down to .002 to .003 inches. Something to consider. Slow the carrier down.

If you read the Sierra Manual about reloading for Automatics, they mention that even with the 5.56, bullet jump was as great as .007 inches.

[Hoot]

...snip...
While hunting and using the same cartridge day in and day out, I soft seat the round using the forward assist or insert the round in the chamber and slowly release the bolt so it does not have its full force....snip...

That's what I do as well, or else cycle the removed round to the bottom of the stack of rounds. But, I prefer easing it in and using the FA to set it home.

Hoot

[Texican Hairless]

I'll try easing the bolt closed the next time i'm at the range and see if my group improves. Thanks for the tip guys. I'm still suprised that after chambering a round four times the bullet had jumped enough that the OAL was too long to fit in the magazine any longer but oh well. I'll just re-seat them in the press.