‘Shot’ my chrono

[mwf008]

Had a new experience today... Was messing around with the 6.5 guys 10 round ladder/ chrono test to try and find a little more velocity. The 2 highest loaded rounds did something I’ve not seen- after the shot (2’d last of the 10) I noticed the chrono ever so slightly rocking. When I looked at the face to see the velocity I noticed it was ‘peppered’. It looked kinda like a paper target would if you were patterning bird shot. It didn’t damage the function, but it permanently damaged the cosmetics of the chrono. I saw no pressure signs on the brass or hard bolt lift, so I shot the 10th shot. I can’t be sure, but I believe it MAY have happened again on that last shot. Again, no pressure signs. Was this unburned powder impacting the face of the chrono? Is that a pressure sign in itself? I’m pretty sure those last 2 rounds were compressed- does that make a difference with this scenario? My most accurate load while doing development was only getting me 2800 FPS, so I was trying to get nearer to 3000 FPS. These last two shots were just under 3000 and just over. This is for 7mm RM, 168 Berger’s, IMR 7977.

Sorry if this is a newb question- I’m a little out of my element doing single stage ‘precision’ loading for hunting rounds. All my previous experience is loading bulk pistol and 223 on my Dillon 650. Thanks for any comments or advise.

 

[thinhorn_AK]

Did you happen to pull the bolt and see if there was I burned powder in the barrel?

 

[mwf008]

Did you happen to pull the bolt and see if there was I burned powder in the barrel?

I did. And no, not that I could tell.

 

[fraz01]

Are you setting the chrono 10 feet or so in front of the muzzle ?

 

[mwf008]

Are you setting the chrono 10 feet or so in front of the muzzle ?

It wasn't quite that far. I did some more research on that and I did learn I need to place the chrono farther away and more consistently every time. Still, many rounds through this thing and this is first time this has happened.

 

[rayporter]

did you look close at the target to see if both shots made nice round holes? any comet trail on the paper?

 

[mwf008]

did you look close at the target to see if both shots made nice round holes? any comet trail on the paper?

I was focused more on the chrono readings than the paper, but all the holes were normally round. That does remind me that I remember only seeing 8 holes. I assumed I had a pair of doubles but maybe there is more to that...

 

[rayporter]

sounds like you had some not reach the target.

 

[mwf008]

sounds like you had some not reach the target.

What would cause that to happen??

 

[MeatBuck]

Scope your bore and find out

 

[Laelkhunter]

I think your chrono should be 15 feet from the rifle muzzle, 10 feet for a pistol.

 

[rayporter]

usually bullets disintegrate about 50yds out but they can come out of the rifle in pieces. my stepson blew up a brake on a new barrel when the 25th shot blew up in the brake.

i have had it happen on old barrels with a lot of rounds on it -especially if the barrel is hot.

sometimes you can see tell tale signs on the target as the holes will have a shadow swirled out to one side. but dont count on that.

3000fps may exceed what that barrel will allow. just a guess until you can confirm more shots not reaching paper.

 

[mwf008]

I bought a bore scope and took a look today. I can’t see anything in there that looks like damage, but honestly I can’t say I know what I’m looking for. Any tips on things to look for with a borescope ?

 

[fraz01]

Check for carbon buildup in the chamber neck and throat area. You can also see if you have copper and carbon buildup in the barrel. Check the barrel crown for burrs and if you have a brake you can check for fowling and possible bullet strikes. Assuming you bought Teslong Scope, they are money well spent. You can also check for sharp edges on the lands and pitting & rough spots. Lilja barrels had some good videos of scoping barrels on their web site for reference.

 

[mwf008]

Check for carbon buildup in the camber neck and throat area. You can also see if you have copper and carbon buildup in the barrel. Check the barrel crown for burrs and if you have a brake you can check for fowling and possible bullet strikes. Assuming you bought Teslong Scope, they are money well spent. You can also check for sharp edges on the lands and pitting & rough spots. Lilja barrels had some good videos of scoping barrels on their web site for reference.

Thank you!