Slow proof prefit?

[Rosebud]

Find another chrono to shoot thru. This may be very inlighting.

 

[clark33]

Find another chrono to shoot thru. This may be very inlighting.

Thought about that, but it has been accurate on 2 other rifles that had MV's verified earlier with magnetospeed. Too be clear I have used this chrono on 3 rifles, the only rifle that is giving odd numbers is this new prc with new proof prefit. I'm going to give it 50 more rounds or so and see where the MV is.

Was mainly curious if others have seen slower than average proof barrels, or possibly slower than avg lots of Berger ammo. That is the one that is really throwing me off.

 

[clark33]

Went out again today, the berger ammo with 140s avg 2830fps over 10, I tried some berger loaded 156s and that avg'd 2850 over 10 shots. Wonder if I got a bad/ or very mild lot of the 140 ammo from berger.

 

[HandgunHTR]

I was going to add that I would suspect the numbers on the box before anything else.

The test barrels that most factories use for velocity numbers are 26 or 28 inches and are fired under near perfect conditions.

 

[Duffman]

I've had proof prefits that have(had) notably undersized chambers showing pressure signs early on brass. One was a prc, others 65 and 6mm creeds. I have some jgs saami reamers on hand, and cleaned them up. After reaming them, I had adequate neck clearance on the 2x 6cm blanks, and proper body dimensions on the 65cm. The prc was opened with AW2 reamer at 0.200 line. All was better after the clean up, running as expected velocity without any psi signs.

Proof runs their prefit reamers way too long wearing them down, or they buy in bulk off PTG's ebay page, possible combo of both.

Great info here appreciate it! I have exactly 1 proof prefit: 22" 6.5 prc and it is slow. Pressure started at 2810 fps (right before pressure) with 143 eld now at 2875. Stupid slow with 147 eld-m which is the bullet I wanted to use. I am way under book max charge weights. However it was effortless to get an accurate load for this barrel so I'm not complaining!

I'm trying again this spring with same setup and .300 prc might run the aw reamer through it first!

 

[clark33]

I was going to add that I would suspect the numbers on the box before anything else.

The test barrels that most factories use for velocity numbers are 26 or 28 inches and are fired under near perfect conditions.

I believe most are 24" unless otherwise stated/indicated on the box of ammo.

 

[sierracharlie338]

Went out again today, the berger ammo with 140s avg 2830fps over 10, I tried some berger loaded 156s and that avg'd 2850 over 10 shots. Wonder if I got a bad/ or very mild lot of the 140 ammo from berger.

In my experience, I've never had factory ammo run at the advertised speed on the box but I've also never had one 300fps slower unless it was a super short barrel.