pierced primers


Well-Known Member
Dec 6, 2008
Question - Can a muzzle break cause changes in chamber pressures?

I went to the range the other day and shot my Rem 700 P chambered in 300 Win Mag. The rifle has a 25" barrel thats threaded 5/8-28 with thread a protector. I picked up a used muzzle break that a guy had on a different 30 cal 700P. So I figured I'd give it a try.

300 Win Mag
210 Berger VLD
CCI 250
80gr H1000
COL 3.612"

I'm shooting the above load and with the thread protector I'm getting about 2960fps. It's a little hot but no sticky bolt lift or super flat primers. I then tried the same load with the muzle break screwed on. WOW! I got some powder blast back in my face and eyes, and velocity shot up to over 3100FPS (that's 300RUM velocities)! I had to try one more round to make sure it wasn't just some lazy reloading (this time I stood back and shot from the hip). It did it again. The primers on both rounds were pierced.

So, I took off the muzzle break and put the thread protector back and shot a couple more. Everything was fine.

Anyone every have this happen? I always assumed what was safe without a break, would also be safe with one......


Is the bore of the brake aligned with the bore of the rifle? From the picture it almost looks like the bullet was scraping the brake on one side hard to tell.
The other thing to check besides alignment is the bore diameter of the break.

It should be a minimum of .020 larger than the bullet dia. (.308 + .020 =.328)

I like .025 larger myself .

Find a drill bit that will measure .328 and insert the shank of the bit into the break.and
if it will not go in freely that may be your problem.

Make sure it goes "all" the way through the break. (I recently purchased a high end break
and the exit hole was right but the baffled holes were less than .277 and the break was for
a .308) and it could have caused major problems if I had not checked it first.

I agree w/Robster. It looks like some scraping going on inside the brake. Let us know if you have .020 minimum end to end.
I have two 300 win's and have worked up several loads for others using H-1000 and 210 Bergers. IMHO, 80 gr of H-1000 is a stout load. I have not been much over 77 gr. I had a Sendero that started showin pressure signs at 75 gr.

Hope this helps.

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