1st shot chrono discrepancy on Sig MPX

[2scoops]

On my Gen 1, Gen II and my shooting buds, Gen 2 and Gen "3" Sig MPX we always have a huge (80fps on 900fps avg) velocity variance on the 1st shot over the chrono. The next shots are always with acceptable variation (15fps to 20fps). I can understand a  lower velocity from a cold barrel (often i've chrono'd after a practice session), but not to this extent.  Any ideas what could be causing this ?

[nso123]

Handloads or factory ammo?

[stick]

Handloads can be caused by powder fluctuations, OAL issues and a variance in case size by different manufacturers.  If it's factory ammo, well...that's another issue.  

[Hi-Power Jack]

Which chrono are you using ?

 

Distance from muzzle ?

[Acer2428]

Did you try a control of a different platform with the same ammo? Or even just a different setup to eliminate chrono issues?

[2scoops]

hand loads with Labradar. This is not only mine it's with buddies (2 other buddies - 6 guns between us) gun and his hand loads as well as factory ammo. SD is running low after the 1st round. Its not an ammo issue. 

[dauntedfuture]

oil in chamber or bore would do this too

[RaylanGivens]

On 11/4/2019 at 9:10 PM, 2scoops said:

hand loads with Labradar. This is not only mine it's with buddies (2 other buddies - 6 guns between us) gun and his hand loads as well as factory ammo. SD is running low after the 1st round. Its not an ammo issue. 

 

If the SD was always low on the first round...  and on the first round only...  that would seem to rule out the ammo being the issue.

 

Try another chrono.