[mccurter]

I recently had the barrel on my xs7 .308 cut to 18''. I chronographed Rem factory loads @ 2738 fps in the 22'' barrel before I had it cut off. On Friday I shot a 5 shot group of these same shells, they averaged 3111 fps. I was amazed. I was hoping to not lose more than 200 fps but I gained 373 fps. Has anyone else had this happen when shortening a barrel?

 

[Ridgerunner665]

Something went wrong somewhere...what you say happened is not possible within safe pressure limits.

Chrono error I suspect...low battery?

 

[mccurter]

I thought the same thing,so I checked the battery. It was ok. Then I fired a few rounds out of my 10/22 they came in around 1200fps just like normal.

 

[mccurter]

I just chrono'ed 4 rem factory loads, they averaged 2802 fps. It is still a velocity increase of 64 fps. The first 5 were some kind of fluke it was April Fools Day. I also chrono'ed the last 2 win power max that I had they showed 2780 fps.

 

[Click Click Boom]

My money is on chrono error.

The only other thing that I can think of is a temperature induced pressure difference in the rounds, i.e. ammo left in the sun in a hot vehicle or on a heater vent on the dash of a truck are going to run higher pressure then they would at normal room temp or an outdoor winter temp.

 

[donut slayer]

there are a lot of things that will cause errors in a chrono. too close to the muzzle will cause the chrono to read the muzzle blast instead of the bullet shadow. also just the distance from the muzzle will make a difference.

 

[Click Click Boom]

there are a lot of things that will cause errors in a chrono. too close to the muzzle will cause the chrono to read the muzzle blast instead of the bullet shadow. also just the distance from the muzzle will make a difference.

^^^You're probably getting a bigger muzzle blast from the 18" barrel then you do with the 22".

 

[dmsbandit]

In my 308 carbine, I get about 2650fps with a 150gr Hornady SP handload. This weekend I shot another 308 "X" gun with the same load and got about 2725 with the same load. So, my gun lost about 75fps with 4" less barrel.

I would say temp, or bullet placement over the chrony "eyes" had something to do with your curious results.